Revolutionizing Electrochemical Sensing with Nanomaterial-Modified Boron-Doped Diamond Electrodes

Abstract

Nanomaterial advancements have heralded a new era in electrochemical sensing by enabling the precise modification of boron-doped diamond (BDD) electrodes. This review investigates recent remarkable advances, challenges, and potential future directions of nanomaterial-modified BDD electrodes for biosensing applications, emphasizing their game-changing potential. This review begins by investigating the intrinsic properties of boron-doped diamond electrodes, emphasizing their inherent advantages in electrochemical biosensing. Following that, it embarks on an illuminating journey through the spectrum of nanomaterials that have revolutionized these electrodes. These materials include carbon-based nanomaterials, metal and metal oxide nanostructures, their combinations, patterned nanostructures on BDDs, and other nanomaterials, each with unique properties that can be used to tailor BDD electrodes to specific applications. Throughout this article, we explain how these nanomaterials improve BDD electrodes, from accelerated electron transfer kinetics to increased surface area and sensitivity, promising unprecedented performance. Beyond experimentation, it investigates the challenges—stability, reproducibility, and scalability—associated with the use of nanomaterials in BDD electrode modifications, as well as the ecological and economic implications. Furthermore, the future prospects of nanomaterial-modified BDD electrodes hold the key to addressing pressing contemporary research challenges.

1. Introduction

1.1. Boron-Doped Diamond (BDD) Electrodes

Carbon materials have been extensively explored and used in a variety of disciplines due to their excellent features such as strong thermal conductivity, chemical inertness, and electrical conductivity [1,2,3,4]. These characteristics make carbon-based materials ideal for use in electronics, energy storage, and catalysis [3,5,6,7]. Diamond, a three-dimensional lattice of sp³–hybridized carbon atoms, is one of the most intriguing forms of carbon material [8,9]. Diamond has extraordinary physical qualities, such as great hardness and strong thermal conductivity [10]. However, natural diamond is an electrical insulator due to its carbon atoms being fully bonded, leaving no free charge carriers [11]. To overcome this constraint and unlock diamond’s electrical conductivity, researchers developed synthetic diamond materials with controlled impurities known as dopants [12]. Boron is one such dopant, and, when it is incorporated into diamond during the growth process, it produces boron-doped diamond (BDD). Proferl et al. reported in 1973 that the growth of BDD crystals led to the production of p-type diamond, which demonstrated a high level of electrical conductivity [13]. This breakthrough was significant because it revealed that diamond, an excellent electrical insulator, could be converted into a conducting substance. BDD is a one-of-a-kind substance that combines the exceptional characteristics of diamond with the electrical conductivity generated from boron impurities [14,15]. The unique combination of diamond durability and boron-induced conductivity has established BDD electrodes as indispensable tools in electrochemistry and electroanalysis.

1.2. Significance of BDD Electrodes in Electrochemical Applications

BDD electrodes hold a unique and pivotal role in various electrochemical applications, distinguishing themselves from other existing electrodes in fundamental ways [1,2,16,17,18,19]. In comparison to other electrode materials, such as glassy carbon (GC), platinum, gold, and carbon paste electrodes, BDD has exceptional chemical stability and corrosion resistance. This fundamental property is due to diamond’s remarkable stability, which makes BDD electrodes suitable for electrochemical applications in harsh and corrosive environments containing strong acids or bases, where conventional electrodes would degrade rapidly [20,21,22]. Aside from that, BDD electrodes are suitable for long-term electrochemical applications, such as implantable medical devices that require long-term performance [23,24,25]. Additionally, the high bandgap of diamond contributes to a distinctive characteristic of BDD electrodes, resulting in low background currents by reducing thermally generated charge carriers [26,27]. This low background current is especially beneficial in electrochemical sensing applications, allowing for the detection of small variations in electrochemical signals while maintaining high signal-to-noise ratios and resolution. The suitability of BDD electrodes for such applications is further emphasized by their ability to detect small variations with precision, making them useful in situations where precise and sensitive measurements are critical. Another distinguishing feature of BDD electrodes is their exceptional electrical conductivity, which can be significantly tuned by boron doping [28,29]. This increased electrical conductivity promotes efficient electron transfer at the electrode surface, resulting in improved electrochemical performance and faster reaction kinetics. In practice, BDD conductivity translates to faster and more responsive electrochemical processes, which contribute to the overall efficiency of BDD electrodes in a variety of applications. Another distinguishing feature of BDD electrodes is the wide potential window they exhibit. This wide potential window allows these electrodes to operate across a wide range of potentials without undergoing irreversible chemical reactions [18,29,30]. This versatility enables the oxidation or reduction in a wide range of compounds, broadening the applicability of BDD electrodes across a wide range of electrochemical processes. Biocompatibility is an important aspect of BDD electrodes, as evidenced by their ability to stimulate brain tissue and record neural activity [23,24,25]. Because of their biocompatibility, they are suitable for applications in neurological stimulation, biosensing, and implantable devices. Because BDD electrodes are non-toxic, they cause minimal inflammatory and immune reactions, making them ideal for interfacing with biological materials. Moreover, BDD electrodes have a high degree of selectivity for a variety of analytes, including heavy metals and organic pollutants [31,32]. This selectivity is important in many electrochemical sensing applications where the ability to differentiate between different species is required. In essence, the exceptional selectivity of BDD electrodes contributes to their effectiveness in addressing specific analytical requirements. Considering the above, BDD electrodes stand out as a remarkable technology in the field of electrochemistry.

1.3. Tunability and Structural Considerations

Achieving optimal BDD electrode performance relies on three crucial factors: boron doping level, surface orientation, and surface termination (Figure 1a) [14]. Boron doping concentration, typically expressed in parts per million (ppm), has a significant impact on the characteristics of BDD electrodes [33]. Variable boron levels cause variable conductivity, and the interaction of boron and sp² (graphitic) carbon influences their electrochemical properties. The optimal composition of boron and sp² (non-diamond) to sp³ (diamond-like) carbon is application-specific, making the design of BDD electrodes highly versatile [34]. Yasuaki [14] investigated the influence of surface orientation, specifically (100) and (111) facets, on BDD electrode performance (Figure 1b–d) [35]. It is found that (100)-oriented BDD exhibits a slower response compared to (111)-oriented BDD. The presence of different facets within the same BDD grain contributes to the heterogeneity of boron concentration and electrochemical activity. Moreover, surface termination (hydrogen or oxygen) is also an important factor in determining the electrochemical properties of BDD electrodes. Different surface terminations lead to varying electrochemical behaviors, affecting the sensitivity and reactivity of the electrodes. Recently, Gong et al. [29] prepared high-quality BDD electrodes with varying boron doping levels (B/C ratios ranging from 1000 to 5000 ppm) using a self-designed microwave plasma chemical vapor deposition (MPCVD) reactor. The results reveal that increasing boron doping from 1000 to 5000 ppm reduced BDD grain size, enhanced conductivity, and improved electrode reversibility. Yet, the potential window slightly narrowed. Another recent study by Long et al. [36] investigated the impact of BDD film thickness on electrochemical properties. Using the hot filament chemical vapor deposition (HFCVD) method, BDD films of varying thickness are deposited on silicon wafers. Thicker films are found to have larger grain sizes, reduced grain boundaries, and higher boron doping levels. Electrochemical assessments show that thicker films exhibit improved performance, with smaller peak potential differences, lower charge transfer resistance, and higher electron transfer rates. These enhancements are attributed to the columnar growth mode of polycrystalline diamond film, suggesting potential applications in various fields.

1.4. Synthesis Techniques and Versatility in Applications

Synthesis conditions, temperature, growth parameters, impurities, and boron incorporation all influence the generation of sp² carbon within BDD electrodes, resulting in regions with varying carbon bonding characteristics [37,38,39,40]. The presence of sp² carbon regions has an effect on electron-transfer kinetics, potential window, and adsorption properties (Figure 1e,f). Understanding and controlling sp² carbon generation is critical for tailoring the BDD electrodes electrochemical behavior and optimizing performance across applications. Previous investigations have provided insights into the complex relationship between sp² and sp³ carbon and how this dynamic interaction influences electrochemical processes. Furthermore, the discovery of new synthesis procedures for BDD electrodes resulted in significant sector breakthroughs. BDD electrodes were discovered to be synthesized utilizing a variety of processes, including high-pressure high-temperature (HPHT) synthesis, MPCVD, and HFCVD [14,16,41,42].

Figure 1. (a) The performance of BDD electrodes is determined by three critical factors: boron doping level, surface orientation, and surface termination. Reproduced from Ref. [14]. Cyclic voltammograms recorded using (b) (100) and (c) (111) single-crystal BDD electrodes, and (d) polycrystalline BDD, in a buffer solution containing 1.0 mM K₄[Fe(CN)₆] and 1.0 M KCl. Photographs for (b,c) and a SEM image for (d) are shown at the right. Reproduced from Ref. [35]. Potential windows of (e) 0.1% BDDs and (f) 1% BDDs in 0.1 M of H₂SO₄ at a scan rate of 0.1 V s⁻¹. Reproduced from Ref. [39].

Figure 1. (a) The performance of BDD electrodes is determined by three critical factors: boron doping level, surface orientation, and surface termination. Reproduced from Ref. [14]. Cyclic voltammograms recorded using (b) (100) and (c) (111) single-crystal BDD electrodes, and (d) polycrystalline BDD, in a buffer solution containing 1.0 mM K₄[Fe(CN)₆] and 1.0 M KCl. Photographs for (b,c) and a SEM image for (d) are shown at the right. Reproduced from Ref. [35]. Potential windows of (e) 0.1% BDDs and (f) 1% BDDs in 0.1 M of H₂SO₄ at a scan rate of 0.1 V s⁻¹. Reproduced from Ref. [39].

These synthesis techniques made it possible to develop BDD electrodes with various qualities and features depending on the application. Since then, there has been an increase in research groups’ interest in BDD electrodes, and they are working to enhance their characteristics and look into potential applications. Currently, BDD electrodes are widely used in several applications, such as energy conversion, electroanalysis, biomedical applications, and environmental monitoring [43]. Their success in electrochemical research has established them as vital tools, contributing significantly to the advancement of several fields of study.

1.5. Motivation for Nanomaterial-Modifying BDD Electrodes

The modification of boron-doped diamond (BDD) electrodes with nanomaterials enhances their electrochemical properties, including improved sensitivity, selectivity, and stability [18]. Due to their distinct characteristics like high surface area, enhanced reactivity, and quantum size effects, nanomaterials significantly differ from bulk materials [44]. When applied to BDD electrodes, nanomaterials enhance their capabilities across diverse applications, such as detecting heavy metals, organic pollutants, biosensing, and catalyzing reactions, including oxygen reduction and hydrogen evolution [18,20,45,46,47]. Such improvements occur through increased electrode surface area, providing additional active reaction sites and thus boosting sensitivity. Nanomaterial coatings also enhance electrocatalytic activity, accelerating reactions beneficial for water treatment and energy conversion. These coatings facilitate better electron transfer kinetics, reducing resistance and improving conductivity. Additionally, choosing specific nanomaterial coatings allows the customization of electrode selectivity towards particular analytes or reactions. Nanocoatings also protect BDD electrodes, prolonging their lifespan under harsh conditions. Combining BDD electrodes’ inherent advantages, such as chemical inertness and wide electrochemical windows, with catalytic nanomaterials leads to synergistic improvements in overall performance. Furthermore, nanomaterials introduce functional groups onto typically inert BDD surfaces, enabling the attachment of biomolecules for advanced biosensor applications.

1.6. Objectives of This Review Article

This comprehensive review aims to provide an up-to-date and insightful exploration of recent advances, current challenges, and future opportunities in nanomaterial-enhanced boron-doped diamond (BDD) electrodes for biosensing applications. While several previous reviews have discussed aspects of nanomaterial modifications to BDD electrodes [14,48,49,50,51], this article focuses on recent developments, emphasizing new breakthroughs, emerging nanomaterials, and significant improvements in electrochemical performance.

We discuss recent advances in the synthesis and characterization of nanomaterial-modified BDD electrodes, including graphene, carbon nanotubes, metal nanoparticles, metal oxide nanostructures, composites, and patterned nanostructures. We discuss their unique properties and how these nanomaterials improve electron transfer kinetics, electrode surface area, and biosensing sensitivity. Furthermore, this review critically assesses ongoing challenges in stability, reproducibility, scalability, and environmental and economic impacts, offering a balanced and practical viewpoint. Finally, we identify future directions and potential research areas, emphasizing promising nanomaterials and biosensing strategies that can drive innovation while addressing current challenges in healthcare diagnostics and environmental monitoring.

1.7. Overview of Nanomaterials and Their Role in BDD Electrode Enhancement

As the name suggests, “nanomaterials” operate on a scale where dimensions are measured in nanometers, or one billionth of a meter [52]. At this astonishingly small scale, materials exhibit unique properties, behaviors, and capabilities that distinguish them from their bulk counterparts [53,54]. This section provides a fundamental understanding of nanomaterials by emphasizing their nanoscale dimensions and exploring their significance across various scientific disciplines. These properties lay the groundwork for understanding their transformative role in modifying BDD electrodes. The nanoscale dimensions of nanomaterials produce quantum confinement effects, increased surface area-to-volume ratios, and novel optical, electronic, and chemical properties [53,54]. Nanoscience and nanotechnology advancements enable precise control over material properties, enabling tailored designs for specific applications [55,56,57]. Although nanoparticles are often only tens or hundreds of nanometers in size, their high surface area allows for efficient catalysis, making them indispensable in a variety of chemical processes [44,53]. Nanomaterials have an impact on fields as diverse as physics, chemistry, materials science, biology, and engineering. In the context of electrochemistry, nanomaterials have emerged as innovation catalysts, improving the performance of various electrode materials [58,59,60,61,62]. They have rewritten the rules of electrochemical processes, allowing for faster electron transfer, increased active surface area, and the precise control of chemical reactions [63,64,65,66,67]. Among the many applications of nanomaterials in electrochemistry, their role in modifying BDD electrodes stands out [18,68,69,70]. Nanomaterials’ extraordinary properties make them ideal candidates for improving the performance of BDD electrodes. BDD electrodes are already advantageous due to their high chemical inertness and broad electrochemical potential window. However, nanomaterial modifications add a new dimension to BDD electrodes, improving their electrochemical and biosensing capabilities. The combination of nanomaterials and BDD electrodes has the potential to enable innovative solutions in a wide range of fields, from environmental monitoring to biomedical diagnostics.

In the following sections, we will explore how various nanomaterials, such as carbon, graphene, carbon nanotubes, metal/metal oxide nanoparticles, metallic alloys, hybrids, nanocomposites, and emerging nanomaterials, have improved BDD electrodes, enhancing their electrochemical and biosensing capabilities. We will also address challenges, future prospects, and transformative possibilities in this field, providing insight into nanomaterial-enhanced BDD electrode technology.

1.8. Methods Used to Fabricate Nanomaterial-Modified BDD Electrodes

Several factors have an impact on the synthesis process used to create nanomaterial-modified BDD electrodes. These factors include the specific qualities desired in the nanoparticles, the specific requirements of the intended application, and the resources available. The selection of an appropriate synthesis method is critical in tailoring nanomaterials to meet the specific characteristics required for optimal performance in a wide range of electrochemical applications. Considerations such as particle size, morphology, and surface chemistry are critical in determining the best synthesis route. Furthermore, the scalability and reproducibility of the chosen method are critical factors in ensuring the practical applicability of the nanomaterial-modified BDD electrodes in various settings. Finally, the synthesis process evolves into a strategic decision-making process that integrates scientific objectives, application-specific demands, and practical constraints to produce nanomaterials that improve the electrochemical properties of BDD electrodes. Some of the most commonly used synthesis strategies for nanomaterial-modified BDD electrodes are as follows:

Electrodeposition: Electrodeposition or electrochemical deposition is a frequently used technique to create nanomaterial-modified BDD electrodes [71,72]. This technique dissolves a nanomaterial precursor in a suitable electrolyte solution, and the BDD electrode serves as the working electrode. When the appropriate voltage is applied, targeted ions are reduced and deposited on the surface of the BDD electrode. In recent years, a range of nanomaterials including Au [73,74], Pt [75,76], Ag [77], Pd [75], Ir [78] nanoparticles, bimetallic Cu-Pt [79], molybdenum [80], and Prussian blue (PB) [81] have been electrodeposited on BDD electrodes.

Drop casting: This technique is relatively simple and is frequently used to modify BDD electrodes with specific nanomaterials, including nanoparticles, nanosheets, and nanocomposites [82,83,84,85,86,87]. In this method, a solution containing the nanomaterial of interest is prepared, and a small volume of this solution is then “dropped” or placed onto the BDD electrode, typically with a pipette or micropipette. The droplet containing the nanomaterial is allowed to spread and adhere to the BDD electrode surface naturally. After a certain time, the solvent in the droplet evaporates, leaving behind a layer of nanomaterials firmly attached to the BDD electrode. Depending on the material and solvent used, it is possible to improve the process by gently heating the deposited BDD electrode. Heating helps evaporate the solvent quickly, remove any side products, and strongly adhere the nanomaterials to the BDD surface.

Electrophoretic deposition (EPD): The EPD technique has been used to deposit nanomaterials such as MWCNTs [88,89] and nickel-nanodiamond [90] on BDD electrodes. In this procedure, a DC voltage is applied between the BDD electrode and a counter-electrode in a suspension containing nanomaterials. Nanomaterials migrate toward and deposit on the surface of the BDD electrode as a result of the applied electric field [91]. This technology allows for fine control over nanomaterial deposition, allowing for the modification of BDD electrodes with a range of nanoscale materials such as nanoparticles, nanowires, nanosheets, and nanocomposites [92]. Electrophoretic deposition has advantages in terms of uniformity, thickness control, and the ability to adapt the electrode’s characteristics for specific applications in electrochemical sensing and biosensing.

Vapor deposition techniques: The vapor deposition technology uses a vapor phase process to deposit nanomaterials onto a BDD electrode. This approach enables the precise control of nanomaterial deposition, resulting in homogeneity and customizable features [93]. It also allows for the deposition of thin nanoscale coatings, which can have a substantial impact on the surface properties of BDDs. Chemical vapor deposition and physical vapor deposition are two of the most prevalent vapor deposition processes.

• Chemical vapor deposition (CVD): In the context of CVD, nanomaterial-containing precursor gases are introduced into a reactor. Within the reactor, these gases undergo a reaction process, resulting in the deposition of a thin film onto the surface of the BDD electrode [94,95].
• Physical vapor deposition (PVD): In PVD, nanomaterials are vaporized through physical means, such as evaporation or sputtering, and then condensed onto the BDD electrode. These techniques enable the modification of BDD electrodes with nanomaterials to enhance their performance in various applications. The sputtering method is a versatile technique for depositing nanomaterials onto BDD electrodes [96,97,98,99,100,101,102,103,104]. In this technique, nanomaterials are employed as a target material, and high-energy ions are used to dislodge and deposit atoms or molecules onto the BDD surface. Sputtering has advantages such as great adhesion, minimal contamination, and the ability to deal with a wide range of materials such as metals, metal oxides, and ceramics.

Each method has advantages and disadvantages over other methods.

Table 1. Comparative summary of nanomaterial modification strategies for BDD electrodes.

Modification Strategy	Advantages	Disadvantages
Electrodeposition	- Precise control over deposition parameters, such as voltage and time - High adhesion of nanomaterials - Suitable for a wide range of nanomaterials, including metals and bimetallics	- Needs conductive substrate - Can result in uneven distribution if not optimized - May require a complex electrochemical setup
Drop Casting	- Simple, low-cost, and easy to perform - No special equipment required; applicable to various nanomaterial types	- Inadequate control over film thickness and uniformity - Weak adhesion without proper treatment - Less consistent results
Electrophoretic Deposition (EPD)	- Excellent control over film thickness and uniformity - Suitable for a diverse range of nanomaterials - Allows for tailored surface characteristics	- Requires a stable colloidal suspension - Particles may aggregate - High voltage may cause damage to some substrates
Chemical Vapor Deposition (CVD)	- Creates high-quality, uniform, and conformal coatings - Strong chemical bond with the surface - - Suitable for thin film applications	- Requires high temperatures and a complex setup - Limited to materials with volatile precursors - High cost and limited scalability
Physical Vapor Deposition (PVD)	- Versatile and clean procedure - Creates films with strong adhesion and minimal contamination - Compatible with metals, oxides, and ceramics	- Requires high vacuum and advanced equipment - Limited stoichiometry control for complex materials - Reduced throughput compared to other methods

compares the various nanomaterial modification strategies for BDD electrodes, including electrodeposition, drop casting, EPD, CVD, and PVD. It highlights the benefits of each method, such as control, simplicity, or coating quality, as well as the disadvantages, such as complexity, poor uniformity, or the need for equipment.

1.9. Factors Affecting Properties of Nanomaterial-Modified BDD Electrodes

The physicochemical properties of nanomaterial-modified BDD electrodes can be altered by a variety of factors. These factors include the type of nanomaterial, its morphology, deposition process, thickness, doping, alloying, functionalization, BDD quality, electrochemical and ambient conditions. The effect of each of these factors is detailed below.

BDD Electrode Quality: The quality of the underlying BDD electrode is undeniably important in different electrochemical applications [16,26]. When assessing the effectiveness of the BDD substrate, several crucial characteristics come into play. For starters, the level of boron doping in the diamond structure has a substantial impact on its electrochemical behavior, affecting its ability to enable certain processes [14,105,106]. Furthermore, the smoothness of the BDD electrode’s surface is important, since a rough surface might hinder uniform electron transport and severely affect performance [107]. Additionally, the electrical conductivity of the BDD substrate is an important concern since it directly affects the electrode’s capacity to conduct and transfer charge efficiently, consequently impacting the overall performance of the modified electrode in electrochemical operations.

Dimension and Morphology: Each nanomaterial has various electrical, catalytic, and structural properties, delivering a distinct fingerprint to the modified electrode and so impacting its overall performance [44,53,108]. The dimension and morphology of nanomaterials have a major impact on their performance when utilized to modify BDD electrodes [109,110,111]. Nanostructures with a high surface area-to-volume ratio, such as nanowires or nanoparticles, provide more electrochemically active sites for reactions, increasing the electrode’s sensitivity and reactivity. Furthermore, their compact size provides for improved dispersion and uniform coverage on the BDD surface, ensuring effective electron transport. Specific morphologies, such as nanorods or nanosheets, can also provide increased charge transport routes, allowing for faster electron mobility. For example, nanoparticles, with their high surface area to volume ratio, may boost catalytic reactivity [112], whereas nanowires, with their elongated morphology, may improve charge transport characteristics [113]. Nanosheets, with their two-dimensional structure, may encourage a high degree of surface exposure [63]. Finally, modifying the dimensions and shape of nanomaterials allows for fine control over the electrocatalytic capabilities, making them perfect candidates for increasing the performance of BDD electrodes in a variety of applications, including electrochemical biosensing applications.

Quantity: The assessment of nanomaterial concentration is critical in assessing the efficacy of a modified electrode. The degree of nanomaterial integration has a significant impact on the performance characteristics and functionalities of the BDD electrode. Increasing nanomaterial concentrations can result in more significant and transformative benefits, increasing the electrode’s overall utility. Nonetheless, extreme concentrations can have negative consequences [114,115]. These downsides could include the unfavorable effect of nanomaterial aggregation, which can reduce the electrode’s effectiveness, or a decrease in electrical conductivity, which can impair its usefulness [116]. Thus, achieving an optimal nanomaterial concentration balance is critical for realizing the full potential of the electrode while avoiding negative consequences.

Deposition Technique: The method employed for depositing nanomaterials onto the surface of a BDD electrode can significantly influence the resulting properties and performance [73,117]. Several techniques are commonly utilized for deposition, and each of the below methods present unique advantages and characteristics for distinct research or application needs. For example, the CVD technique allows for precise control over the deposition process, enabling the uniform and controlled growth of nanomaterials on the BDD electrode. Electrodeposition, on the other hand, is an electrochemical technique that can provide good coverage and may be preferred when fine-tuning material properties is essential. The PVD technique offers a different approach, relying on physical processes like sputtering or evaporation to deposit nanomaterials, which can be advantageous in specific scenarios. The choice among these deposition techniques should be made carefully, as it can significantly impact the quality, uniformity, and performance of the nanomaterial-modified BDD electrode in various applications.

Surface Functionalization: Surface functionalization of nanomaterials has been shown to have a considerable impact on the characteristics and performance of nanomaterial-modified BDD electrodes. Attaching functional groups or molecules to the nanomaterial surface can change the surface chemistry of the electrode, improving its catalytic activity and selectivity [118,119]. This alteration improves the electrode’s capacity to support diverse electrochemical reactions, making it more useful for immobilizing biomolecules for biosensing applications. Functionalization can also improve the stability and dispersibility of nanomaterials on the BDD electrode surface, ensuring long-term performance.

Electrochemical Conditions: The electrochemical environment, which includes variables such as pH levels, temperature changes, and the applied potential, has a significant impact on the electrochemical performance and long-term stability of the modified BDD electrode [120,121,122]. These critical characteristics influence the behavior of the electrode in a variety of ways, including its ability to catalyze certain reactions, the rate of electron transfer, and the overall efficacy of electrochemical processes. pH levels, for example, can have a considerable impact on the surface charge and reactivity of the BDD electrode, whilst temperature changes can affect reaction kinetics. Furthermore, the direction and magnitude of electrochemical reactions are determined by applied potential. Understanding and managing these environmental parameters is crucial for improving the performance and longevity of BDD-based electrochemical systems.

Post-treatment Processes: Post-synthesis treatments are critical in fine tuning and enhancing nanomaterial-modified BDD electrodes [30]. These treatments have a major impact on many elements of the electrode’s properties. Annealing, in particular, can modulate nanomaterial concentration while altering the structure, crystallinity, and chemical composition of the electrode [123,124]. This precise control enables the optimization of BDD electrode performance, allowing it to be tailored to specific applications in domains as diverse as electrochemistry, catalysis, and sensing. As a result, post-synthesis treatments allow for the precise manipulation of nanomaterial properties, opening up a new world of possibilities for the creation of revolutionary materials science and technology.

Environmental Factors: Environmental factors have a significant impact on the long-term durability and effectiveness of modified BDD electrodes. Variations in humidity, exposure to potentially corrosive pollutants, and temperature fluctuations can all have a substantial impact on the performance of these electrodes. Water adsorption, for example, can change the surface characteristics of an electrode and potentially modify its conductivity. Contaminant exposure, on the other hand, may cause chemical reactions that damage the electrode’s surface or active sites. Temperature changes can cause physical changes like expansion and contraction, which can jeopardize the structural integrity of the electrode material. Understanding and managing these environmental conditions is therefore critical for ensuring the reliability of modified electrodes in a variety of applications.

Overall, understanding and optimizing these factors are crucial for tailoring nanomaterial-modified BDD electrodes to specific applications, including electrocatalysis, sensing, energy storage, and electrochemical biosensing. Proper control and manipulation of these parameters can lead to improved electrode performance and enhanced functionality.

1.10. Biosensors Based on Carbon Nanomaterial-Modified BDD Electrodes

Carbon nanomaterials have emerged as effective modifiers for BDD electrodes in biosensing applications [125,126]. The incorporation of carbon nanotubes, graphene, and similar nanomaterials into BDD electrodes improves their electrochemical performance and sensitivity, making them suited for a variety of biosensing activities. These changes increase the surface area, which improves the immobilization of biomolecules such as enzymes or antibodies for selective target detection. Furthermore, the superior electrical conductivity of carbon nanomaterials enhances electron transfer kinetics, resulting in reduced detection limits and increased sensitivity. Furthermore, the intrinsic biocompatibility and durability of BDD electrodes, along with the unique features of carbon nanomaterials, make them appropriate for implantable biosensors and in vivo monitoring applications. A millimeter-scale carbon nanorod array was directly (template-free) synthesized on a BDD substrate through thermal catalysis in a CVD chamber at 700 °C using nickel (Ni) as the catalyst [127]. Each carbon nanorod comprised of an amorphous carbon core and a layered graphite outer structure. This carbon nanorod array/BDD electrode exhibited exceptional glucose sensing capabilities, detecting concentrations as low as 0.5 μM with a high sensitivity of 1740.1 μA mM⁻¹ cm⁻², surpassing other reported BDD-based electrodes. The superior performance was attributed to the synergy between nickel nanoparticles’ catalytic activity and the three-dimensional carbon nanorod structure, enhancing the electroactive surface area and mass transfer rate. Li et al. [128] introduced a novel modification technique for BDD electrodes, involving the immobilization of nanoparticles within nanopores on the BDD surface. The porous BDD with an average pore size of 73.9 nm was obtained through thermal catalytic etching (Figure 2). This prevents nanoparticle aggregation and enhances stability through an anchoring effect. Carbon black, a highly conductive carbonaceous nanomaterial, exhibits excellent electrical properties. The fabricated carbon black/Nafion-modified porous diamond electrode exhibits improved electrochemical performance, the selective detection of dopamine, and resistance to interference from ascorbic acid and uric acid. The method’s effectiveness is confirmed in real sample tests, demonstrating promise for practical biosensing applications.

Porous nanostructured carbon materials have significant advantages over solid carbon materials for electrochemical biosensing applications [129,130]. Their large surface area provides an abundance of binding sites for biomolecules, increasing sensitivity. Their porous network is interconnected, allowing for efficient mass transport and electron transfer, resulting in quick response times. Furthermore, the tunable porosity and large specific surface area facilitate enzyme and biomolecule immobilization, improving selectivity. Wei et al. [83] reported an amperometric biosensor for detecting organophosphate pesticides (OPs) by inhibiting acetylcholinesterase (AChE). Nitrogen-doped porous carbon was synthesized by using SiO₂ spheres as a template and the ionic liquid 1-butyl-3-methylimidazolium dicyanamide as precursors. AChE was immobilized on this porous carbon material and placed on a BDD electrode. The biosensor exhibited a strong enzymatic activity and affinity due to the nitrogen-doped porous carbon. It was highly sensitive, with a low detection limit of 1.50 pg·L⁻¹ for dichlorvos and 4.40 pg·L⁻¹ for fenitrothion. The inhibition mechanism is broad-spectrum, making it suitable for various OPs.

Despite the use of amorphous carbon nanostructures, other carbon species, such as graphite and graphene, were also used to modify BDD electrodes [94,131]. Graphite is a layered carbon allotrope composed of stacked graphene sheets. Graphene, on the other hand, consists of a single layer of carbon atoms arranged in a hexagonal lattice. Graphite, although less conductive than graphene, is still suitable for biosensing due to its conductivity and cost-effectiveness. A novel electrode, combining nanometer-sized graphite (NG) with BDD, was synthesized through chemical vapor deposition [94]. NG was formed on the (111) facet of BDD by converting the sp³ diamond structure to an sp² graphitic phase in a boron-rich environment at high temperatures. The NG-BDD electrode was used for electrochemical biosensing, accurately detecting trace acetaminophen. It exhibited a linear electrochemical response to acetaminophen within a concentration range of 0.02–50 μM, with a low detection limit of 5 nM. This research offers a reusable NG-BDD sensor for stable acetaminophen detection and potential for broader applications. The advantages of graphene for electrochemical biosensing include its high electrical conductivity, large surface area, and excellent biocompatibility [132]. These properties improve electron transfer and provide a large number of binding sites for biomolecules, resulting in increased sensitivity. Rezaei et al. [131] developed a biosensor using a thick-film BDD electrode sequentially modified with graphene, cobalt NPs, horseradish peroxidase, and DNA. The biosensor, assisted by multivariate curve resolution-alternating least squares (MCR-ALS), simultaneously determined rates of DNA damage induced by benzo(a)pyrene (BP), dibenzo(a,e)pyrene (DBP), and indeno(1,2,3-cd)pyrene (IP). Mimicking the enzymatic effects of cytochrome P450, the biosensor used chemometric methods to estimate DNA damage rates. It was also expanded to the simultaneous detection of BP, DBP, and IP. This work lays the foundation for intelligent procedures in DNA damage detection and analytical applications.

Carbon nanotubes (CNTs) are in high demand due to their exceptional structural, electronic, and mechanical properties, which make them a promising candidate for electrochemical biosensing [133]. These nanotubes are made up of seamless hexagonal honeycomb patterns of sp² carbon units with nanometer-scale diameters and micron-scale lengths (Figure 3a–d) [134]. They are divided into two types: MWCNTs and single-walled (SWCNTs), each with its own set of characteristics. This inherent electrocatalytic activity has practical applications in the field of electrochemical sensors. MWCNTs were utilized in the modification of a diazonium-functionalized BDD electrode, creating a highly sensitive electrochemical biosensor for the detection of Bisphenol A (BPA) in water [84]. The immobilization of tyrosinase onto this modified electrode enhanced its sensitivity for BPA detection. As shown in Figure 3e, the electrode fabrication involved electrografting amino groups on the BDD surface using in situ generated diazonium cations. Then, carboxyl-functionalized multi-walled carbon nanotubes (MWCNTs) and tyrosinase were homogenized and deposited onto the modified BDD surface. The electrode was exposed to glutaraldehyde vapor for cross-linking, facilitating enzyme immobilization. This process created a robust BDD-based biosensor for BPA detection, combining electrochemical modification, carboxyl-functionalized MWCNTs, and enzyme immobilization to enhance sensitivity and selectivity in detecting the target analyte. The biosensor displayed excellent electroactivity towards the enzymatic reaction of BPA oxidation catalyzed by tyrosinase, with a broad linear range (0.01 nM to 100 nM) and a low detection limit (10 pM) (Figure 3f,g). This biosensor holds promise for the on-site monitoring of BPA in wastewater due to its remarkable sensitivity and reliability.

Lee et al. reported a novel method for the precise growth of MWCNTs on BDD using electrostatic self-assembly of stainless steel 316L nanoparticles as catalysts via photolithography [135]. This approach led to an improved MWCNT/BDD electrode with enhanced electrochemical properties, including a larger surface area and lower electron transfer resistance compared to the BDD electrode. Glucose sensing was employed as a test, revealing a higher sensitivity (7.2 μA mM⁻¹ cm⁻²) and a broader linear range, thanks to the synergistic effect between MWCNTs and BDD. In another study, Chang et al. [89] investigated three types of microelectrodes, including boron-doped ultrananocrystalline diamond (BDUNCD), Nafion-modified BDUNCD, and Nafion–MWCNT–modified BDUNCD microelectrodes, for long-term neurochemical detection. The Nafion–MWCNT–modified BDUNCD microelectrode demonstrated excellent sensitivity and selectivity for dopamine and serotonin detection, even in the presence of interfering substances. The sensitivity for dopamine (DA) was reported as 6.75 μA μM⁻¹ cm⁻², and, for serotonin (5-HT), it was 4.55 μA μM⁻¹ cm⁻². These modified electrodes exhibited rapid response times (less than 2 s), low detection limits, and enhanced stability during long-term measurements.

In summary, carbon nanomaterials improve BDD electrode conductivity, surface area, and biomolecule immobilization, allowing for sensitive, selective biosensing. CVD, nanopore anchoring, and CNT/graphene integration are techniques that improve electrochemical performance across a wide range of targets. Enzyme-functionalized electrodes, porous architectures, and in vivo sensors with low detection limits allow for the real-time monitoring of analytes such as glucose, dopamine, pesticides, and BPA.

1.11. Biosensors Based on Metallic Nanostructure-Modified BDD Electrodes

BDD electrodes modified with metal nanostructures such as gold (Au), silver (Ag), and platinum (Pt) NPs offer significant advantages for electrochemical biosensing applications. First of all, these NPs enhance the surface area of the electrode, allowing for higher biomolecule loading and improved sensitivity. Second, they promote efficient electron transfer, lowering reaction overpotential and improving the electrochemical signal. Moreover, they are highly biocompatible, resulting in minimal interference with biological samples and promoting stable and reliable biosensing. Furthermore, nanoparticle-modified BDD electrodes exhibit exceptional stability and durability, making them appropriate for long-term biosensing applications. As displayed in Figure 4, a hierarchical dendritic gold microstructure was created on a BDD electrode through a double-template method [136]. The dendritic Au/BDD electrode is fabricated through chemical and electrochemical oxidation of the BDD surface, followed by a double template method. Zn particles are dispersed on the BDD surface using hydrogen bubbles as the first template, and dendritic Au growth is guided by the Zn particles as the second template. This unique electrode construction method is essential for the subsequent development of a 17β-estradiol (E2) aptasensor. E2-specific aptamers were immobilized on the dendritic Au/BDD electrode through Au-S interaction, resulting in a highly sensitive E2 aptasensor. The developed impedimetric E2 sensor exhibits exceptional sensitivity, with a detection limit of 5.0 × 10⁻¹⁵ mol/L and a wide linear range (1.0 × 10⁻¹⁴ to 1.0 × 10⁻⁹ mol L⁻¹). The aptasensor demonstrated excellent specificity, even in the presence of interference materials. An electrochemical impedance aptasensor for bisphenol A (BPA) detection was designed using aptamers and 6-mercapto-1-hexanol (MCH) on Au NP-coated BDD electrodes [137]. Au-NPs were coated on BDD by sputtering, and aptamers were grafted onto the Au-NPs/BDD substrate through Au-S bonds, followed by MCH absorption to create the aptasensor. The synergy of BDD, Au-NPs, aptamers, and MCH contributed to its high sensitivity, specificity, and stability. The aptasensor displayed excellent linearity (1.0 × 10⁻¹⁴ to 1.0 × 10⁻⁹ mol L⁻¹) and a low detection limit (7.2 × 10⁻¹⁵ mol L⁻¹) for BPA detection.

In the context of developing a BDD electrode-based biosensor for the detection of acrylamide, a carcinogenic and neurotoxic substance, Uman et al. [74] electrodeposited Au NPs on the BDD surface to enhance its affinity for hemoglobin. Then, the resulting Au NPs modified BDD electrodes were immersed in a hemoglobin solution at pH 5. The biosensor exhibited a linear response to acrylamide concentrations ranging from 5 to 50 μM, with a detection limit of 5.14 μM. A similar architecture of an acrylamide biosensor was reported by Annisa et al. [138], where BDD electrodes were modified with Au NPs and hemoglobin (Hb) through nitrogen groups on the BDD surface. Initially, BDD was transformed into nitrogen-terminated BDD (N-BDD) through allylamine treatment under UV light, and AuNPs were deposited onto it using a procedure involving heating a HAuCl₄ solution and trisodium citrate. The biosensor displayed a linear response to acrylamide concentrations in the range of 0–30 µM, with a limit of detection (LOD) of 13.10 µM, surpassing the performance of the Hb-Au electrode with an LOD of 38.15 µM. This modification process significantly improved the acrylamide-sensing capabilities of BDD electrodes. Anggraini et al. [73] also focus on developing a biosensor for the detection of acrylamide. BDD electrodes were modified with gold and hemoglobin (Hb) to create a sensitive detection platform. The modification process involved wet chemical seeding and electrochemical overgrowth of gold on the BDD, resulting in stable and homogeneous particles. Hb was then immobilized on the gold-modified BDD surface. The resulting sensor demonstrated excellent performance, with a linear detection range of 0.6 to 6 μM for acrylamide, a high linearity (R² = 0.9901), and a low estimated limit of detection (0.845 μM).0020In another work, BDD electrodes coated with Au NPs and aptamers to develop a highly sensitive electrochemical aptasensor for detecting trace aflatoxin B1 (AFB1) [99]. The synthesis involved depositing BDD films on silicon substrates, sputtering a thin Au layer, and thermally treating it to form Au nanoparticles. The aptamer was modified with a mercapto group and bonded to Au-NPs on the BDD electrode. The sensor exhibited a wide linear range (1.0 × 10⁻¹³ to 1.0 × 10⁻⁸ mol L⁻¹) and an impressively low detection limit (5.5 × 10⁻¹⁴ mol L⁻¹). The aptasensor’s synergy of BDDs, Au NPs, aptamers, and MCH contributed to its superior performance. The potential of this novel diamond-based sensor is demonstrated by its detection of trace AFB1 in peanut samples. Yuan and colleagues [102] reported a highly sensitive electronic biosensor for detecting toxic PCB-77 by depositing dense Au NPs on a BDD substrate through a process involving sputtering and annealing (Figure 5). This biosensor, using aptamers for PCB-77, exhibited an impressive detection range from femtomolar to micromolar concentrations and an ultra-low detection limit of 0.32 femtomolar. The combination of the BDD substrate, Au NPs, and aptamers resulted in outstanding sensor performance, offering great potential for the trace detection of PCB-77 and other low-concentration substances in various applications.

A non-enzymatic electrochemical lactate sensor was developed by modifying a BDD electrode with ZnAl layered double hydroxide (LDH) nanosheets and AuNPs [82]. These nanomaterials were synthesized separately using wet chemical co-precipitation and citrate reduction methods. They were then alternately assembled on the BDD surface, resulting in LDH_Au NP nanomaterial assembly. This modification enhanced the electrode’s surface area, electrocatalytic activity, and electron-transfer rate. The sensor exhibited excellent selectivity, repeatability, reproducibility, and operational stability, making it a promising tool for diagnosing small metabolites in human body fluids. A Pt-deposited BDD (Pt-BDD) electrode, prepared using cyclic voltammetry, effectively detects hydrogen peroxide in the 0.05–20 mM range [139]. The same electrode was applied for horseradish peroxidase (HRP) detection in the 5–600 mU range. Additionally, it proved useful for selective and quantitative melamine detection in the range of 5–100 μg ml⁻¹, with a 0.51 μg ml⁻¹ detection limit, offering potential for melamine detection in strip tests. In another study, BDD electrodes were modified with Pt and hemoglobin (Hb) for use as highly stable and sensitive acrylamide biosensors [140]. The Pt modification involved the wet chemical seeding of Pt particles on the BDD surface, electrochemical Pt seed overgrowth, thermal annealing at 700 °C in an N₂ atmosphere, and CV for refresh and activation. Characterization confirmed homogeneous Pt deposition with 200 nm average particle size and preservation of the BDD’s sp³ carbon structure. The fabricated Hb-Pt-BDD biosensor exhibited excellent sensitivity, with a linear response to acrylamide concentrations from 0.01 to 1 nM, and a detection limit of 0.0085 nM. Recently, Henderson et al. [141] also modified BDD electrodes with Pt NPs and utilized them for in vitro nitric oxide (NO) detection in the mouse colon. The Pt NPs were potentiodynamically deposited on the BDD electrode, followed by the application of a Nafion overlayer. The optimized electrode conditions were determined to ensure efficient NO oxidation and the rejection of nitrite interference. Using this electrode, neurogenic NO release from myenteric ganglia in the mouse colon was successfully measured, revealing gender differences in NO release patterns.

A recent study by Garcia et al. [75] focused on enhancing the detection of hydrogen peroxide (H₂O₂) using Pt and palladium (Pd)-modified BDD electrodes. A two-step modification process involving wet chemical seeding and electrochemical deposition was optimized. Pd-modified BDD electrodes exhibited sharper H₂O₂ oxidation peaks than Pt-modified ones, significantly improving sensitivity (150–200×) compared to bare BDD. The lowest limit of detection achieved was 50 nM on BDD-PdNPs electrodes. This research highlights the applicability of metal NP-modified BDD for highly sensitive and selective H₂O₂ detection, with potential applications in biological and biochemical research, especially at the microscale. Another study on H₂O₂ detection using Prussian Blue modified BDD electrodes demonstrated highly sensitive H₂O₂ sensors with up to ten times increased signal-to-background ratios compared to conventional graphite electrodes [81]. BDD electrodes were modified with Prussian Blue (PB) through electrochemical synthesis and open-circuit deposition, followed by immobilizing PB-based nanozymes. The modified BDD electrode exhibited high sensitivity (0.14 A M⁻¹ cm⁻²) for detecting sub-micromolar H₂O₂ concentrations. The transparent BDD electrodes also enable spectro-electrochemical studies, enhancing their versatility in biosensing applications. A novel paper-based analytical device (PAD) with a silver NP-modified BDD (AgNPs/BDD) electrode was developed as a cholesterol sensor [77]. The AgNP/BDD electrode was created via electrodeposition, while wax printing defined the hydrophilic and hydrophobic regions on filter paper (Figure 6). Counter and reference electrodes were screen-printed on the hydrophilic region. Cholesterol and cholesterol oxidase (ChOx) were drop-cast onto the hydrophilic area for amperometric detection, yielding a sensitive biosensor with a broad linear range, low detection limit, high sensitivity, good selectivity, and excellent recovery for cholesterol detection in bovine serum.

Nickel (Ni)-based catalysts are undergoing extensive research for non-enzymatic glucose-sensing electrodes [142]. They excel in glucose electrooxidation and resist chloride poisoning, making them ideal for cost-effective and stable glucose sensors. Nickel’s potential in glucose sensing is showcased in various forms, including pure Ni, compounds, and conductive metal–organic frameworks. Its effectiveness is attributed to the potent Ni(II)/Ni(III) couple’s oxidation ability and innate resistance to halogen poisoning. Its affordability, being 2500x cheaper than gold, drives its increasing use as a support or catalyst in diverse applications. Dai et al. [143] introduced an amperometric biosensor for detecting L-alanine using a nanoporous Ni-modified BDD electrode. The nanoporous Ni/BDD electrode, created through ultrasound-assisted electrodeposition, enhances electron transport and sensing performance due to increased redox moiety concentration. The biosensor exhibited a linear detection range of 0.5 to 4.5 μM, a detection limit of 0.01 μM, and excellent anti-interference ability, stability, and reproducibility, making it promising for L-alanine detection. Metal oxide nanomaterials offer significant advantages in electrochemical biosensing over metal nanoparticles. They are cost-effective and improve selectivity when combined with biorecognition molecules. These nanomaterials can have diverse morphologies, displaying unique electrical and photochemical properties due to their size and high surface area [144]. Their biocompatibility makes them suitable for immobilizing biomolecules in various sensors, facilitating rapid electron transfer and functioning as “electronic wires” and “electrocatalysts” [145]. However, metal oxide nanomaterials may have wide band gaps, poor ion transport kinetics, and electrode film pulverization issues, which can be mitigated by hybridization with carbon materials, other metal nanoparticles, or polymers [63,146,147]. A novel synthesis method involving electrochemical imprinting was employed to fabricate half-nanotubes (HNTs) made of polycrystalline nickel and nickel (II) oxide (Ni–NiO) on BDD film [148]. Ni–NiO HNTs were fabricated using pulsed electrodeposition. Initially, a Ni layer was deposited onto a porous polytetrafluoroethylene template using radio frequency magnetron sputtering (Figure 7). This template was then attached to the BDD electrode surface. Electrochemical imprinting was conducted in an electrolyte containing NiSO₄, resulting in the formation of Ni–NiO HNTs on the BDD electrode. The HNTs exhibited semicircular profiles, with outer diameters ranging from 50 to 120 nm and inner diameters from 20 to 50 nm. The resulting Ni–NiO HNTs/BDD electrode was utilized to construct a biosensor for L-serine detection, displaying excellent analytical performance with high sensitivity (0.33 μA μM⁻¹) and a low detection limit (0.1 μM). This achievement was attributed to the unique properties of the Ni–NiO HNTs and the BDD, including a large surface area, efficient electron transport, and electrocatalytic activity. Long et al. [101] achieved varying thicknesses of Ni layers on BDD through different sputtering times (30 s, 1 min, 2 min) and demonstrated the effect of Ni layer thickness on thermal catalytic etching and electrochemical performance for glucose oxidation. Three distinct surface structures emerged with increasing thickness: one with Ni nanoparticles embedded in the BDD film, another with Ni microparticles on the BDD surface, and the last with residual lamellar Ni. Electrochemical results were correlated with these surface structures, and it was discovered that the Ni/BDD electrode that Ni sputtered for 1 min had the best performance due to the abundance of agglomerated Ni nano- and microparticles on its roughened surface. In summary, metal nanostructure-modified BDD electrodes, such as Au, Ag, Pt, and Ni, provide more surface area, electron transfer, and biocompatibility, allowing for ultrasensitive, stable biosensors. These modifications enable aptamer and enzyme immobilization for the detection of analytes such as hormones, toxins, neurotransmitters, and metabolites. Advanced fabrication techniques and hybrid nanostructures enhance detection limits, specificity, and long-term performance in biosensing applications.

1.12. Biosensors Utilizing Alloy, Composite, and Hybrid Nanomaterial-Modified BDD Electrodes

The utilization of alloy, composite, and hybrid nanomaterial modifications for BDD electrodes in electrochemical biosensing has brought about significant advantages. These modifications offer tunable electrocatalytic properties, improved mechanical stability, and enhanced sensitivity. They also facilitate rapid electron transfer, biocompatibility, and multifunctionality [149,150,151]. As a result, these modified BDD electrodes are poised to play a pivotal role in the development of highly sensitive and selective electrochemical biosensors for a wide range of applications, from healthcare diagnostics to environmental monitoring. Alloy nanomaterials, composed of two or more metals, offer improved electrical conductivity and mechanical stability, making them ideal for electrode materials in biosensors [152]. Their tunable composition allows for tailored electronic properties, enabling the design of biosensors with enhanced sensitivity. Moreover, alloy-based electrodes can resist corrosion, ensuring the longevity of the biosensing platform. A Ni-Cu alloy nanomaterial-modified BDD complex electrode for non-enzymatic glucose detection was formed through a two-step heat treatment process [96]. Ni and Cu were integrated onto the BDD surface, forming a porous structure under high-temperature catalytic conditions. The Ni/Cu/BDD electrode displayed remarkable catalytic activity for glucose detection, offering an extensive detection range (0.022–18.3 mM) and high sensitivity (1007.68 μAmM⁻¹ cm⁻², 1.28 times higher than Ni/BDD). It also exhibited selectivity and excellent long-term stability (93.3% after one month), thanks to the synergistic effect between Ni and Cu. This composite electrode holds significant potential as a non-enzymatic glucose sensor, providing superior catalytic performance, selectivity, and stability. A non-equilibrium thermodynamic coupling model and optical emission spectroscopic analysis were employed by Yao et al. [100] to explain the mechanism of using solid boron as a dopant in low-temperature, low-pressure conditions. The BDD films were used in a non-enzymatic glucose sensor, with a porous Au/Ni layer enhancing sensitivity. The modified electrode demonstrated rapid response to glucose, featuring two linear ranges (0.02–2 mM and 2–9 mM) with a detection limit of 2.6 μM and excellent sensitivity (157.5 μAmM⁻¹ cm⁻²). The solid amorphous boron-doped BDD electrode shows promise for efficient non-enzymatic glucose detection, with future work exploring the effects of Au and Ni proportions and real-world applications.

Core–shell nanomaterials consist of a central core surrounded by a distinct shell, offering unique properties and versatile applications across various fields. Core–shell nanomaterials have unique properties that can improve the performance of Boron-Doped Diamond (BDD) electrodes. Because of their ability to provide tailored functionalities, improve stability, and enhance electrochemical properties, these materials with a well-defined core–shell structure are increasingly used to modify BDD electrodes. Incorporating core–shell nanomaterials onto BDD surfaces contributes to advanced electrode designs, allowing for increased sensitivity and selectivity in a variety of electrochemical applications. Core–shell copper-gold (Cu@Au) nanoparticles were synthesized and used to modify BDD electrodes [97]. These nanoparticles were successfully attached to the BDD surface, resulting in approximately three times higher gold coverage compared to normal gold nanoparticles. The use of allylamine as a bridge proved effective for attaching more gold than copper nanoparticles. The modified Cu@Au BDD electrodes exhibited about two times higher current responses for the oxygen reduction reaction, demonstrating improved electrochemical performance. The modified electrodes also showed good sensitivity and stability in detecting glucose and biochemical oxygen demand (BOD).

Nanocomposites combine different nanomaterials, such as nanoparticles or graphene, with polymers or other materials to create structures with synergistic properties [153]. One key benefit of nanocomposite-modified electrodes is the increased surface area, which provides an enlarged surface area for efficient biomolecule immobilization and facilitates rapid electron transfer during the sensing process [154,155]. Moreover, nanocomposite-modified BDD electrodes can be tailored to enhance biocompatibility. Surface functionalization with biocompatible polymers or biomolecules enables the selective and stable immobilization of biological recognition elements, such as enzymes or antibodies, on the electrode’s surface. This ensures high specificity when detecting target analytes in complex biological samples. Recently, Berna et al. [156] developed a novel electrochemical sensor, the glutaraldehyde–zinc oxide nanocomposite-modified BDD electrode (GA₂–ZnO/BDD), for the rapid and sensitive detection of metoprolol (MTP), a hypertension drug and doping agent. To fabricate GA₂–ZnO/BDD electrodes, GA₂–ZnO suspension was carefully deposited onto the BDD electrode surface and allowed to dry under ambient conditions. Various modified electrodes were compared for MTP electroanalysis, with the GA₂–ZnO/BDD electrode demonstrating the highest peak current in CV. The sensor exhibited a linear working range of 9.99 × 10⁻⁷ to 3.85 × 10⁻⁵ mol L⁻¹ and a low limit of detection (LOD) of 7.53 × 10⁻⁸ mol L⁻¹ in pH 7 Britton–Robinson buffer solution. Excellent reproducibility and applicability were confirmed, with a mean recovery rate of 95.6% ± 1.7% for commercial MTP-containing drug tablets. This sensor holds promise for pharmaceutical quality control and doping agent monitoring. A biosensor for detecting organophosphate pesticides (OPs) was developed using a BDD electrode modified with a nanocomposite of carbon spheres (CSs) and Au NPs [85]. The fabrication involved synthesizing CSs, coating them with AuNPs, and preparing the AChE/AuNPs-CSs/BDD biosensor. This modification improved electron transfer resistance and increased the surface area for acetylcholinesterase (AChE) immobilization. The biosensor exhibited enhanced sensitivity, lower detection limits (1.3 × 10⁻¹³ M for chlorpyrifos and 4.9 × 10⁻¹³ M for methyl parathion), good precision, and stability. A novel biosensor for detecting organophosphate pesticides (OPs) was developed using a honeycomb-like hierarchically porous carbon material modified with ionic liquids ([BSmim]HSO₄) and Au NPs, deposited onto a BDD electrode [86]. The biosensor exhibited high sensitivity and stability for acetylcholinesterase (AChE) immobilization and organophosphate detection. The inhibition of dichlorvos was linearly proportional to its concentration in the range of 10⁻¹⁰–10⁻⁶ g L⁻¹, with a detection limit of 6.61 × 10⁻¹¹ g L⁻¹. This platform offers improved AChE adsorption, biocompatibility, and conductivity, making it a promising biosensor for organophosphate detection. Liu and Wei [87] developed a sensitive biosensor for OP detection using a Pt–carbon aerogel (CA) composite on a BDD electrode. Pt–CAs were synthesized via sol–gel polymerization and liquid-phase reduction methods. The modified BDD electrode exhibiting high surface area and high conductivity demonstrated excellent sensitivity, with detection limits of 3.1 × 10⁻¹³ M for methamidophos and 2.7 × 10⁻¹² M for monocrotophos, along with good reproducibility and stability. Carbon-coated nickel nanoparticle-modified BDD composite (C@Ni-BDD) electrodes were synthesized through a multistep process [98]. First, BDD electrodes were grown on silicon films using hot filament chemical vapor deposition. Next, a layer of nickel (Ni) was sputtered onto the BDD surface. The Ni-BDD sample underwent high-temperature heat treatment in a mixture of H₂ and CH₄ gases, resulting in the transformation of Ni into nanoparticles, while carbon atoms from BDD formed a graphite carbon layer on the Ni nanoparticles. Longer heat treatment times led to increased carbon coating. These electrodes exhibited high sensitivity, selectivity, and long-term stability for glucose detection, particularly the 60 min Ni(C)-BDD electrode.

Hybrid nanomaterial-modified BDD electrodes are a novel approach in electrochemical biosensing. These nanohybrids combine distinct nanomaterials, often carbon-based substances like nanotubes or graphene, with metallic nanomaterials, leveraging complementary properties for superior electrocatalytic performance and efficient charge transfer. While nanocomposites improve specific aspects of BDD electrodes, nanohybrids use multiple nanomaterials to improve overall electrochemical performance. Hybrid nanomaterial-modified BDD electrodes combine the advantages of various nanomaterials to create multifunctional platforms for electrochemical biosensing. Researchers can design biosensors tailored to specific applications, such as the detection of toxins, pathogens, or environmental pollutants, by strategically selecting nanomaterial components and surface functionalization. A Ni-Microcrystalline graphite-BDD complex electrode was developed by thermally catalytic etching the BDD film with a nickel layer [103]. The Ni particles embedded into the BDD film increased surface area and electrochemical stability while catalyzing the conversion of sp³-bonded diamond to sp²-bonded microcrystalline graphitic carbon. This modification improved electrode conductivity and resulted in excellent electrochemical performance for glucose detection, with wide linear ranges, high sensitivities, low detection limit, selectivity, reproducibility, and long-term stability, making it promising for non-enzymatic glucose sensors. A stable and sensitive non-enzymatic glucose sensor was created by modifying the BDD electrode with Ni nanosheets and nanodiamonds (NDs) through electrophoretic deposition [90]. The Ni nanosheet-NDs/BDD electrode displayed enhanced electrochemical performance, extending the potential window and improving conductivity. It exhibited excellent current response to glucose oxidation in alkaline conditions, with a linear range of 0.2–1055.4 μM and a low detection limit of 0.05 μM. The sensor demonstrated high selectivity, reproducibility, and stability, making it a promising, cost-effective, and easily prepared non-enzymatic glucose sensor. In summary, modified BDD electrodes containing alloy, composite, and hybrid nanomaterials have better electrocatalytic properties, sensitivity, stability, and biocompatibility. These advancements enable the high-performance biosensing of glucose, drugs, and pesticides. Core–shell nanoparticles, carbon composites, and hybrid materials are examples of innovations that enable tailored functionality and widespread application in healthcare and environmental monitoring with superior detection limits, reproducibility, and long-term stability.

1.13. Other Nano-Material/-Structure Innovations for Modified BDD-Based Biosensors

Nanocrystalline BDD (NBDD) is a boron-doped diamond material made up of nanoscale diamond grains that have a high surface area, improved electron transfer, and are better suited for biosensing. Rather than modifying BDD with nanomaterials, NBDD was modified with polyclonal anti-M1 antibodies (aM1) to develop a novel biosensor for the early diagnosis of influenza virus (M1 protein) (Figure 8) [157]. The approach achieves an impressive limit of detection (LOD) of 5 × 10⁻¹⁴ g mL⁻¹ in saliva buffer. The NBDD-aM1 electrode demonstrates high stability, low background current, biocompatibility, and a large potential window. This label-free biosensor holds promise for rapid and sensitive influenza virus detection, showing specificity and reliability in detecting viral particles as low as 50 fg mL⁻¹ concentration levels.

Another study for detecting human influenza viruses (Figure 9) using a modified BDD electrode was reported by Matsubara et al. [158] where the BDD electrode was terminated with a receptor-mimic peptide nanomaterial [159].

The fabrication of the biosensor involves modifying the BDD electrode with peptides and dendrimers, altering the efficiency of viral binding, and enhancing charge-transfer resistance. This modification results in an excellent detection limit for seasonal H1N1 and H3N2 viruses, as well as avian viruses (H5N3, H7N1, H9N2). The peptide density and dendrimer generation on the electrode surface significantly enhanced viral binding and charge-transfer resistance. These peptide-terminated electrodes exhibited an excellent detection limit of less than one plaque-forming unit for seasonal H1N1 and H3N2 viruses. They were also effective in detecting avian viruses like H5N3, H7N1, and H9N2, showing potential for detecting all influenza A virus subtypes, including new ones. A free-standing BDD hollow nanorod (BDD HR) electrode was synthesized for glucose detection [95]. Tungsten oxide nanorods (WOx NRs) were used as a removable framework to create the BDD HRs. The WOx NRs’ morphology was optimized through a two-step growth process. A BDD layer was deposited on the WOx NRs to form BDD-WOx core–shell nanostructures. An electrochemical oxidation process completely dissolved the WOx NRs’ core, resulting in the BDD HR structure. These improvements were attributed to the unique properties of the BDD HRs, such as a large surface area and efficient direct electron transfer. Electrochemical analysis showed that, compared to a planar BDD electrode, the BDD HR electrodes exhibited enhanced sensing performance, including higher sensitivity, lower detection limit, faster response time, and a wider linear range.

Chang et al. [88] improved the performance of Boron-doped ultra-nanocrystalline diamond (BDUNCD) microelectrodes for dopamine (DA) sensing using a droplet-based microfluidic setup. They modified these microelectrodes with MWCNT thin films and Nafion coatings via the EPD technique. Various coating parameters were studied, revealing that a 50 nm Nafion coating led to a 3-fold increase in DA detection signal, while combining MWCNT films and Nafion coatings resulted in an impressive 10-fold sensitivity boost. In contrast, the unmodified surface showed poor sensitivity and fouling. This modification holds promise for sensitive and stable DA detection in diverse biosensing applications. An electrochemical platform based on an array of nanoelectrodes (NEAs) was fabricated for the detection of specific antigens [160]. NEAs were created by forming arrays of nanoholes on a thin polycarbonate film deposited on BDD macroelectrodes using thermal nanoimprint lithography (TNIL) (Figure 10). Gliadin was detected using NEAs through an immuno-indirect assay. The NEAs showed the efficient immobilization of biomolecules and demonstrated the ability to detect gliadin in the concentration range of 0.5–10 μg mL⁻¹. The TNIL technology allowed for the fabrication of high-resolution nanostructures, offering potential for scalable electrochemical sensing platforms in both food and biomedical applications.

In the realm of nanotechnology research, DNA is regarded not merely as a biological entity but also as a nanomaterial [161]. This unique perspective enables the utilization of DNA as a nanomaterial for the modification of BDD electrodes, particularly in biosensing applications. Niedzialkowski et al. [162] reported a novel method for detecting the presence of the DEFB1 gene unique to humans in saliva samples. The approach utilizes multisine impedance spectroscopy during the potentiodynamic polarization of BDD electrodes. The BDD electrodes undergo a series of modifications, including electropolymerization with carboxylic groups, functionalization with ssDNA probes, and incubation with the target DNA sample. The presence of the DEFB1 gene is detected through changes in electron transfer kinetics, observed as an increase in charge transfer resistance. This technique offers a rapid and specific way to distinguish human DNA from other sources, making it a promising alternative for DNA testing without amplification methods. The entire process takes less than two hours, making it suitable for various applications in DNA testing.

Table 2. Modification of BDD electrodes by various nanomaterials and their electrochemical biosensing applications.

	Nanomaterial Morphology	Modification Method	Enhanced Properties	Technique	Analyte	Linear Detection Range	Sensitivity	LOD	Ref.
Carbon	Carbon Black	Drop casting	Sensitivity, Selectivity, Resistance to Interference	Electrochemical	Dopamine	1 to 100 μM	0.305 μA μM−1	54 nM	[128]
	NG Nanoparticles	CVD	Surface Area, Electron Transfer	DPV	Acetaminophen	0.02–50 μM	--	5 nM	[94]
	MWCNTs	EPD	Surface Area, Electron Transfer	FSCV	Dopamine	1 nM to 100 μM	0.15 μA μM−1	1.78 nM	[88]
	MWCNTs	EPD	Sensitivity, Selectivity	DPV	Dopamine and serotonin	1 nM to 100 μM	6.75 µA µM−1 cm−2	5.4 nM	[89]
	MWCNT	Drop casting and then exposure to glutaraldehyde vapor (as a cross-linker)	Surface Area, Catalytic Activity	CV	BPA	0.01 nM to 100 nM	1.81 µA µM−1 cm−2	0.01 nM	[84]
	MWCNT	Patterned for selective growth on BDD	Surface Area, Electron Transfer	Amperometric	Glucose	0.006–1.16 mM	7.2 μA mM−1 cm−2	0.07 μM	[135]
	Porous N-doped carbon	Template-assisted synthesis, followed by drop casting on BDD	Conductivity, Catalytic Activity	Chronoamperometric	OPs	100 pg·L−1 to 10.0 μg·L−1	--	1.50 pg·L−1	[83]
Metal and metal oxide nanomaterials	Au Nps	Electrodeposition and wet chemical seeding	--	Electrochemical	Acrylamide	0.6 to 6 μM	0.035 µA µM−1 cm−2	0.84 μM	[73]
	Au NPs	In situ synthesis of Au NPs	Electron Transfer, Sensitivity	CV	Acrylamide	0–30 µM	--	13.10 µM	[138]
	Au NPs	Sputtering	Sensitivity, Selectivity	EIS	Aflatoxin B1	1.0 × 10−13 to 1.0 × 10−8 mol L−1	--	5.5 × 10−14 mol L−1	[99]
	Au NPs	Sputtering	Electron Transfer, Sensitivity, Immobilization	EIS	PCB-77	1.0 × 10−15 to 1.0 × 10−11 M	--	0.32 fM	[102]
	Au NPs	Electrodeposition	Electron Transport, Immobilization	CV	Arylamide	5–50 μM	--	5.14 μM	[74]
	Au Hierarchical dendritic microstructure	Double-template method	Surface Area, Electron Transfer	EIS	17β-estradiol (E2)	1.0 × 10−14 to 1.0 × 10−9 mol L−1	--	5.0 × 10−15 mol L−1	[136]
	Ag NPs	Electrodeposition	Electron Transfer	Amperometric	Cholesterol	0.39 to 270.69 mg dL−1	49.61 µA µM−1 cm−2	0.25 mg dL−1	[77]
	Pt NPs	CV	Electron Transfer, Selectivity	CV	H2O2 and melamine	0.05–20 mM and 5–100 μg mL−1	--	100 nM and 0.51 μg mL−1	[139]
	Pt NPs	Wet chemical seeding followed by thermal annealing	Sensitivity, Selectivity	CV	Acrylamide	0.01 to 0.1 nM	--	0.008 nM	[140]
	Ni nanoporous	Ultrasound-assisted electrodeposition	Electron Transport	Amperometric	L-alanine	0.5 to 4.5 μM	0.05 μA μM−1 cm−2	0.01 μM	[143]
	Pt NPs	Electrochemical deposition	Surface Area, Electron Transfer, Sensitivity	Amperometric	Glucose	1.98 μM to 1.95 mM	17.1 μA mM−1	0.14 μM	[163]
	Ni NPs	Sputtering	Surface Area, Sensitivity	Amperometric	Glucose	9.9 μM to 5.64 mM	839.30 μA mM−1 cm−2	1.23 μM	[101]
	PB NPs	Electrodeposition	Sensitivity, Selectivity	Electrochemical	H2O2	0.1 µM to 1 mM	~0.14 A M−1 cm−2	100 nM	[81]
	Ni–NiO half-nanotube	Electrochemical imprinting	Surface Area, Electron Transport, Electrocatalytic Activity	Amperometric	L-serine	0.2 to 6.54 μM	0.33 μA μM−1	0.1 μM	[148]
Nanocomposites, alloys, nanohybrids	Pt NPs	Wet chemical seeding followed by electrodeposition	Sensitivity, Selectivity	CV and chronoamperometry	H2O2	0.1 to 1.0 mM	40.1 μA mM−1 cm−2	1.7 μM	[75]
	Pd NPs	Wet chemical seeding followed by electrodeposition	Sensitivity, Selectivity	CV and chronoamperometry	H2O2	0.1 to 1.0 mM	80.8 μA mM−1 cm−2	0.7 μM	[75]
	Au NP-embedded carbon sphere nanocomposite	Nanocomposite synthesized via the Stöber method and drop-cast on BDD	Surface Area, Electron Transfer	Electrochemical	Organophosphate pesticides (OPs)	10−11 to 10−7 M and 10−12 to 10−6 M	--	1.29 × 10−13 M and 4.9 × 10−13 M	[85]
	Porous carbon _ Au NP nanocomposite	Drop casting followed by drying	Biocompatibility, Conductivity	Electrochemical	Organophosphate pesticides	4.5 × 10−13 –4.5 × 10−9 M	--	2.99 × 10−13 M	[86]
	Platinum–carbon aerogel (Pt–CAs) Composite	Drop casting followed by drying	Surface Area, Conductivity, Sensitivity	Electrochemical	Organophosphorus pesticides	10−11 to 10−6 M	--	3.1 × 10−13 M	[87]
	ZnAl nanosheets and Au NP assembly	Drop casting	Surface Area, Electrocatalytic Activity, Electron-Transfer Rate	SWV	Lactate	0.1 to 30 μM	13.9 μA mM−1 cm−2	0.1 μM	[82]
	GA2–ZnO nanocomposite	Drop casting—drying		Electrochemical	Metoprolol	9.99 × 10−7 to 3.85 × 10−5 mol·L−1	--	7.53 × 10−8 mol·L−1	[156]
	Cu@Au Core–shell	Allylamine as a binder		Electrochemical	Glucose and BOD	0.1 to 0.5 mM	0.017 mA mM−1	--	[97]
	Cu@Au Core–shell	Allylamine as a binder		Electrochemical	Glucose and BOD	1.9–50.0 mg L−1	17.4 μA mg−1 L	1.9 mg L−1	[97]
	Au/Ni porous	Sputtering followed by heat treatment	Surface Area, Sensitivity	Amperometric	Glucose	0.02—2.0 mM, and 2–9 mM	157.5 μA mM−1 cm−2	2.60 μM	[100]
	C@Ni NPs	Sputtering	Electroactive Surface Area, Mass Transfer Rate	Amperometric	Glucose	1.0 × 10−3–4.0 mM; and 4.0–10.0 mM	1130, and 420 μA mM−1 cm−2	0.69 μM	[98]
	Ni + Nanodiamond NPs	EPD	Conductivity, Electron Transfer, Potential Window	Amperometric	Glucose	0.2–12; 31.3–1055.4 μM	120; 35.6 μA mM−1 cm−2	0.05 μM	[90]
	Graphene + cobalt NPs Nanostructures	Drop cast + drying	Surface Area, Immobilization, Electron Transfer	Electrochemical	Benzo(a)pyrene (BP)	0.05–5.4 pM	--	0.01 pM	[131]
	Graphene + Cobalt NP nanostructures	Drop cast + drying	Surface Area, Immobilization, Electron Transfer	Electrochemical	dibenzo(a,e)pyrene (DBP)	0.5–6.8 pM	--	0.12 pM	[131]
	Graphene + cobalt NPs nanostructures	Drop cast + drying	Surface Area, Immobilization, Electron Transfer	Electrochemical	indeno(1,2,3-cd)pyrene (IP)	0.1–8 pM	--	0.23 pM	[131]
	Ni-microcrystalline graphite nano	Ni by sputtering, followed by thermally catalytic etching for MG	Surface Area, Electrochemical Stability, Electron Transfer	Amperometric	Glucose	2.0 μM–0.5 mM; and 0.5–1 5.0 mM	1010.8; and 660.8 μA mM−1 cm−2	0.24 μM	[103]
	Ni-Cu Alloy NPs	Sputtering		Electrochemical	Glucose	0.022–18.3 mM	1007.7 μA mM−1 cm−2	5.7 μM	[96]
Other nano-materials/-structures	Peptide	Click chemistry	Viral Binding and Charge-Transfer Resistance	EIS	Influenza viruses	3 to 400 pfu	--	0.33 pfu	[158]
	BDD nanorods	HF-CVD followed by Electrochemical oxidation	Surface Area, Electron Transfer	Amperometric	Glucose	1.12 μM to 0.067 mM	349.7 μA mM−1 cm−2	0.066 μM	[95]
	BDD nanocrystalline	Chemical vapor deposition	Electron Transfer, Surface Area, Sensitivity	EIS	Influenza	50.0 to 650.0 fg mL−1	--	5 × 10−14 g/mL	[157]
	DNA	Click chemistry	Selectivity,	EIS	DEFB1 gene	--	--	--	[162]
	BDD nanohole arrays	Thermal nanoimprint lithography	Surface Area, Immobilization	CV	Gliadin	0.1 to 0.5 μg mL−1	--	0.1 μg mL−1	[160]

provides a detailed overview of BDD electrodes modified with various nanomaterials, highlighting their morphologies, modification methods, and the resulting enhancements in electrochemical properties. It summarizes the analytical techniques used, target analytes, and key performance metrics, including linear detection range, sensitivity, and limit of detection (LOD). This comparison underscores the impact of nanomaterial selection and electrode design on biosensing efficiency and application specificity.

2. Current Challenges and Limitations

Nanomaterial-modified BDD electrodes have attracted a lot of attention in recent years because of their unique features and prospective uses in electrochemical sensing, energy conversion, and environmental remediation. However, despite their potential, various hurdles must be overcome before these materials may be efficiently utilized in actual applications. Some of the current issues in this sector include the following:

Fabrication and Reproducibility Challenges: One of the most challenging things in the field of nanomaterial-modified BDD electrodes is reproducibility of the fabrication process. The production of high-quality nanostructures with controlled size, shape, and distribution is crucial for achieving the appropriate electrochemical characteristics. However, the fabrication process is frequently complex and comprises numerous processes, including nucleation, growth, and surface modification, which can result in variances in the final product. As a result, there is a need to create dependable and scalable fabrication processes capable of producing uniform nanostructures with predictable electrochemical characteristics. Furthermore, modern analytical techniques are required for the characterization of the resultant materials in order to establish the presence and characteristics of the nanoparticles, as well as their interactions with the BDD surface.

Stability and Durability Concerns: Another issue in the field is the stability and durability of the modified BDD electrodes. Many metals and metal oxide nanoparticles are prone to aggregation and dissolution under electrochemical circumstances, which can result in a loss of catalytic activity and stability over time. Furthermore, the intense electrochemical conditions might cause degradation of the BDD substrate itself, resulting in a loss of electrode performance. As a result, it is critical to build robust and persistent nanostructures that can endure harsh electrochemical conditions while maintaining catalytic activity over time.

Comprehending the electrochemical mechanism: The fundamental understanding of the electrochemical mechanism behind the performance of the improved BDD electrode is still lacking. The interactions between nanomaterials and the BDD surface are complicated, and the specific mechanisms behind catalytic activity are still unknown. A deeper understanding of the electrochemical mechanism can help to build better-performing modified BDD electrodes.

Scale-up and Commercialization Hurdles: While various research investigations have proved the promise of nanomaterial-modified BDD electrodes, scale-up and commercialization remain difficult. The manufacturing cost and scalability of the fabrication process can be substantial barriers to commercialization. Furthermore, variances in the final result can occur due to a lack of standardization in the fabrication process, making it difficult to mass-produce dependable and consistent electrodes. The transition from benchtop experimentation to scalable manufacturing requires innovative approaches to maintain the quality and performance of nanomaterial-modified electrodes at a larger scale. Cost-effective and environmentally sustainable manufacturing processes are areas that demand particular attention.

Incorporating into Real-World Applications: Finally, the incorporation of nanomaterial-modified BDD electrodes into practical devices necessitates careful consideration of aspects such as device design, fabrication methods, and compatibility with other components. Furthermore, factors such as stability and durability must be carefully addressed to ensure the long-term performance and reliability of these devices.

Implications on the Environment and Economics: The integration of nanomaterials into BDD electrodes presents both promising advancements and considerations. On one hand, these modifications can contribute to more efficient and sensitive electrochemical sensors, aiding in the monitoring and mitigation of environmental pollutants. However, it is crucial to acknowledge the environmental and economic dimensions. The production and disposal of certain nanomaterials may raise concerns related to environmental sustainability. Additionally, the cost associated with the synthesis and implementation of nanomaterials can be a factor. Striking a balance between the benefits and the environmental and economic implications is vital in ensuring the responsible and practical use of nanomaterial-modified BDD electrodes in environmental applications. Careful consideration of these factors is essential for realizing the full potential of these innovative technologies while minimizing their ecological and economic footprint.

3. Potential Future Directions and Areas of Development

To overcome the challenges and limitations discussed previously and realize the full potential of nanomaterial-modified BDD electrodes, future research efforts should prioritize several strategic areas. While previous sections highlighted the challenges that researchers are currently facing, this section outlines innovative, practical, and interdisciplinary paths forward, emphasizing the advancements required to bridge the gap between laboratory research and practical applications. Given the identified fabrication and reproducibility issues, advanced synthesis techniques will be essential. Template-assisted synthesis, self-assembly, atomic-layer deposition, and bottom-up approaches all promise greater precision, reproducibility, and scalability. These techniques could make it easier to mass-produce uniform, high-quality nanostructures, which are required for dependable and cost-effective commercial applications. Another area of promise is the development of multifunctional nanomaterials. Future BDD electrodes could serve multiple purposes at the same time by combining multiple functionalities, such as catalytic activity, sensing capability, and energy conversion, into a single nanomaterial. This multifunctionality has the potential to significantly reduce the complexity, size, and cost of electrochemical devices, increasing their commercial attractiveness and usability. Environmental remediation is a particularly appealing application for nanomaterial-enhanced BDD electrodes. Future research should broaden applications for the effective removal of hazardous pollutants from water sources, such as heavy metals and persistent organic contaminants. Targeted studies aimed at improving electrode performance, durability, and cost-effectiveness in real-world settings will hasten the use of these electrodes in environmental cleanup processes. Further miniaturization and integration into wearable technologies offer exciting opportunities in healthcare. Real-time health monitoring, personalized diagnostics, and early disease detection will all benefit from advances in flexible, portable, and biocompatible nanomaterial-BDD systems. Future research should focus on integrating these electrodes with flexible substrates and durable biocompatible coatings to enable continuous physiological monitoring outside of clinical settings. Nanomaterial-modified BDD electrodes have the potential to revolutionize biomedical applications significantly. Advanced interfaces for neural stimulation, drug delivery systems, and cellular-level biosensors could revolutionize biomedical technology. Future research should focus on biocompatibility, long-term stability, and increased sensitivity to enable more precise interaction with biological systems and expand their utility in medical diagnostics and therapeutics. The standardization of fabrication protocols and characterization techniques will also be increasingly important. Establishing widely accepted guidelines can help to improve reproducibility, streamline research efforts, and promote industry adoption of nanomaterial-modified electrodes. Collaborative efforts among academia, industry, and standardization bodies will be critical in achieving these standards, allowing for scalable and reliable commercialization. Evaluating and mitigating environmental and economic impacts will be critical for sustainable innovation. Comprehensive life-cycle assessments, which focus on the production, use, and disposal of nanomaterials, should guide future development pathways and ensure responsible and sustainable practices. Efforts to develop environmentally friendly synthesis methods and recyclable or biodegradable electrode components could significantly improve the sustainability of these technologies. Cross-disciplinary collaborations among materials scientists, electrochemists, biologists, engineers, and industry stakeholders will drive innovation in this area. Interdisciplinary collaborations can better address complex challenges, allowing for breakthroughs at the intersections of these various fields. Encouraging collaborative research initiatives and fostering interdisciplinary networks will speed up progress and innovation. Another promising area of research is the integration of nanomaterials with emerging materials such as conductive polymers, graphene, MXenes, and other two-dimensional materials. Combining these materials could result in electrodes with better electrical conductivity, catalytic efficiency, and flexibility. Investigating synergistic interactions between these materials will improve electrode performance and versatility. Finally, translating laboratory-scale discoveries into commercially viable products will necessitate concerted efforts in commercialization and industrial partnerships. Collaboration between academic research teams and industry players will speed up technology transfer and scaling, allowing for the wider adoption of these advanced electrochemical technologies in healthcare, energy production, environmental monitoring, and other areas. By pursuing these forward-looking strategies, future research in nanomaterial-modified BDD electrodes will move beyond current limitations, unlocking their substantial potential for transformative impacts across diverse scientific and technological domains.

4. Conclusions

Recent advances in the field of nanomaterial-modified BDD electrodes have ushered in a new era of possibilities for electrochemical biosensing applications. These breakthroughs represent a significant advancement in biosensor technology, providing improved performance and versatility for the detection of a wide range of biomolecules and analytes. One of the most notable advancements is the development of nanotechnology/fabrication technologies that provide precise control over the size, shape, and distribution of nanomaterials on the BDD surface. Electrochemical deposition, electrophoretic deposition, chemical reduction, physical vapor deposition, and other techniques have enabled researchers to create nanostructures with enhanced catalytic properties, resulting in increased biosensor sensitivity and selectivity. Stability and resilience have also been key areas of progress. Researchers have successfully engineered stable nanostructures that can withstand harsh electrochemical conditions while retaining catalytic activity over long periods of time. Protective layers and nanomaterial encapsulation have been instrumental in achieving this durability, ensuring reliable and long-lasting biosensor performance. Moreover, a deeper understanding of the electrochemical principles governing modified BDD electrodes has led to the development of more efficient and selective sensors for specific biomolecules. This knowledge has paved the way for tailored biosensors capable of precise and rapid biomarker detection. The potential impact of these advances on electrochemical biosensing applications is profound. With improved fabrication techniques and stability, biosensors can offer enhanced accuracy and reliability in detecting critical biomarkers. This holds significant promise for early disease diagnosis, personalized medicine, and point-of-care testing, where rapid and accurate results are paramount. In summary, nanomaterial modifications offer various advantages, including increased surface area, improved catalytic activity, enhanced conductivity, tailored selectivity, stability, and synergistic effects, ultimately enhancing the electroanalytical performance of BDD electrodes. The recent strides in nanomaterial-modified BDD electrodes have positioned them as powerful tools in the realm of electrochemical biosensing. These advances, marked by improved fabrication, stability, and a deeper understanding of electrochemical principles, offer the potential to revolutionize healthcare, environmental monitoring, and various other biosensing applications. As research continues to push the boundaries of what is achievable, we can anticipate the emergence of biosensors that are more accurate, durable, and adaptable, ultimately improving our ability to detect and respond to critical biomarkers and environmental threats.