Diatomaceous Biosilica: A Multifunctional Resource for Biomedicine and Sustainable Applications

Abstract

Diatomaceous biosilica has emerged as a functional material with unique properties, driving innovations in energy storage, therapeutic systems, and environmental catalysis. This article critically reviews recent advances in using natural biosilica in lithium-ion battery anodes, emphasizing how its hierarchical morphology and high porosity contribute to ion insertion and transport efficiency. Its surface chemistry enables controlled drug release and tissue regeneration in biomedical applications. Its synergy with metal catalysts enhances pollutant degradation in photocatalytic systems, especially via surface biofunctionalization. By linking these areas, this review highlights the potential of diatom biosilica as a viable and sustainable alternative to synthetic materials, promoting technological solutions aligned with circular economy and materials engineering.

1. Introduction

The structural properties and chemical stability of silica make it stand out as one of the most studied and widely used inorganic polymeric materials in various industries. It occurs in different forms, including ordered mesoporous silica, amorphous silica, pyrogenic silica, and silica gels, all with the same stoichiometric composition of SiO₂. Its three-dimensional structure consists of a network of SiO₄ tetrahedra, which confers high thermal and chemical stability to the material [1].

On the other hand, diatomaceous biosilica (DB) refers to the porous, amorphous silica (SiO₂) derived from the cell walls of diatoms, a group of microalgae belonging to the class Bacillariophyceae. Diatoms are unicellular microalgae ubiquitous in aquatic environments that efficiently utilize solar energy in photosynthetic processes. This performance can be attributed to their intricate structure and the patterns of their silica-based exoskeleton [2], as illustrated in Figure 1.

DB is formed through a biofabrication process, which involves the synthesis of silica through biological silicification. This process converts soluble silicate into amorphous silica, forming diatom cell walls with complex, highly ordered structures [3]. The biosilica is composed not only of amorphous silica but also of organic components, such as proteins and carbohydrates, which are responsible for the formation of the nano- and microporous architecture of the frustules [3]. These biopolymers’ templating and scaffolding activities are essential for creating the unique, highly organized pore structures found in diatom frustules (Figure 1). Figure 1 schematically illustrates the hierarchical porosity of diatom biosilica and highlights the potential strategies for surface functionalization, which further modulate the dynamic interactions with target molecules.

Furthermore, biosilicification in diatoms reveals an impressive diversity of environmental conditions under which these organisms have evolved to form their intricate silica frustules. Traditionally associated with temperate marine environments, diatoms also thrive in extremes of temperature and pH, demonstrating the remarkable plasticity of life. Antarctic species, such as Fragilariopsis cylindrus, can depose biosilica at temperatures as low as −1.9 °C and pH around 8.2, characteristic of the icy waters of the Antarctic Ocean [4]. In contrast, thermophilic diatom species, such as those isolated from hot springs, can synthesize their siliceous structures at an impressive 98 °C and in highly acidic conditions, with pH as low as 1.5 [5]. This versatility highlights the biochemical robustness of silicification mechanisms and inspires the vision of new biomaterials adaptable to extreme conditions. This age-old lesson reinforces the need to value the study of natural processes as an eternal source of innovation.

The intricate and highly porous structure of DB (Figure 2) offers unique optical and mechanical properties, contributing to the diatom’s efficiency in photosynthesis and its resistance to predators [3]. The layered, porous structure of DB also plays a critical role in nutrient separation, filtration, and the elimination of harmful microorganisms. The structural complexity of DB, which cannot currently be replicated by artificial synthesis, further highlights its potential applications in a variety of fields (see Figure 3). Its biocompatibility, tunable surface chemistry, and cost-effective production make it an attractive alternative to synthetic silica in various high-tech applications [6] and, thus, has great potential in biotechnology applications.

Regarding environmental applications, diatomaceous biosilica stands out as a naturally abundant and environmentally friendly material with significant potential for application as a cleaner energy resource [8]. Its intrinsic porous structure and high surface area offer a unique advantage for ion transport and structural stability during cycling [9]. Moreover, its affordability and natural abundance further enhance its appeal as a sustainable material for developing environmentally friendly technologies focused on pollution control and ecological preservation.

Regarding applications in the biotechnology field, diatom-derived biosilica has been widely explored as a platform for immobilizing biomolecules such as antibodies, enzymes, and DNA aptamers in biosensor development. Among detection techniques, fluorescence and surface-enhanced Raman scattering (SERS) are the most employed. Fluorescence-based biosensing has been extensively studied due to its reliability and versatility. A common strategy involves functionalizing diatom biosilica surfaces via silanization to anchor antibodies for immunoassays [10].

In the biomedical field, diatomaceous biosilica shows great potential as a matrix for controlled drug release and the development of advanced biomaterials. Its porosity allows the incorporation of therapeutic agents that can be released gradually and locally, increasing treatment efficacy and reducing adverse effects [11].

This study aims to explore diatomaceous biosilica as a multifaceted resource with versatile applications in advanced materials. The work highlights the most innovative and current uses of this promising material, with a focus on nanotechnology, biotechnology, and sustainable processes.

2. Physical and Chemical Properties of Diatom-Derived Silica

Diatom-derived silica, originating from the unique microshells of diatoms, presents an impressive array of physical and chemical properties that make it a formidable candidate for various applications, particularly in drug delivery and nanotechnology [12]. Diatom frustules exhibit intricate pill-box microstructures characterized by highly porous architectures at the micro- and nanoscale, providing a significant surface area that can reach up to 200 m²/g, which enhances their capacity for adsorption and interaction with other substances [13]. Compared to conventional synthetic silica particles, which often require harsh synthesis conditions and surfactant templates to achieve comparable textural properties, diatom biosilica offers a low-cost and environmentally friendly alternative, with the added benefit of inherent morphological complexity [1].

Although it is composed of amorphous silica, diatom-derived biosilica displays several hallmark characteristics of ceramic materials [14]. Ceramics and bioceramics are generally defined as inorganic, non-metallic solids that exhibit high thermal resistance, mechanical strength, and chemical durability, properties that diatom biosilica inherently possesses [15,16]. It is thermally stable up to approximately 1000 °C, resistant to chemical degradation across a broad pH range, and mechanically rigid due to its dense, silicified structure [1,17,18]. These traits allow biosilica to retain structural integrity under harsh environmental conditions, similar to sintered ceramic components [18]. Furthermore, its electrical insulation capacity and low thermal conductivity reinforce its classification within the broader family of ceramic materials, particularly in the context of functional ceramics used in filtration, catalysis, and biomedical applications [1,19].

One important distinction is that these ceramic-like properties are achieved without the need for high-temperature processing or synthetic doping. The biosilica is naturally fabricated by diatoms at ambient temperature and pressure yet results in a material that behaves comparably to engineered silica-based ceramics [14]. In addition, compositional analyses have shown that certain non-silicon elements, such as Al, Fe, Ca, K, and Mg, can be present in diatom frustules at concentrations exceeding 500 ppm and are thus classified as impurities, while others like Ba, Sr, Rb, Mn, and Ti are typically found below this threshold and are considered trace elements Ref. [14]. These elements can modulate surface reactivity, electronic behavior, or catalytic potential in a way that parallels the doping strategies commonly employed in advanced ceramics to tailor their properties for specific applications.

Furthermore, it is crucial to reframe discussions around biosilica ceramic-like attributes to strengthen its relevance in advanced material science. Beyond its intrinsic robustness, diatom biosilica represents an untapped platform for the bioprospecting of advanced ceramics [20]. The immense biodiversity of diatom species offers a natural repository of silica architectures with tunable porosity, surface area, and morphology, traits that are otherwise challenging and costly to reproduce via synthetic means [21]. This biological diversity can be leveraged to generate pre-designed ceramic microstructures suitable for use in areas such as energy storage, optical coatings, and structural composites. The notion of using diatom frustules as bio-derived templates or active components in composite ceramics introduces new possibilities for sustainable design, minimizing the reliance on synthetic processes and reducing environmental impact.

Diatomaceous biosilica displays the characteristic physical and chemical resilience of engineered ceramics, supporting its integration into high-performance material systems. These features endow diatom biosilica with the potential to complement or even replace conventional ceramic materials in applications such as thermal insulation, catalysis, biomedical implants, and filtration technologies [13,22,23,24]. Compared to synthetic silica produced via sol-gel or pyrolytic routes, diatomaceous silica offers key advantages: its hierarchical architecture enhances capillary-driven transport, mechanical interlocking, and molecular accessibility, while its natural biocompatibility enables safe application in biological systems [21,25,26]. When incorporated into hybrid ceramic materials or biocomposites, biosilica can improve stiffness, surface functionality, and thermal resistance without compromising weight or processability.

Diatom-derived silica fulfills the structural, chemical, and thermal criteria to be considered a functional bioceramic. It offers a unique blend of ceramic-like performance, natural complexity, and ecological sustainability, positioning it at the frontier of modern material research. Its study and application reflect a growing shift toward integrating biological inspiration into the development of advanced ceramic technologies.

Table 1. Highlighting differences between diatom-derived silica and commercial or synthetic porous silica sources.

Fundamental Aspects of Materials	Diatom-Derived Silica	Commercial/Synthetic Porous Silica
Origin and Structure	Rigid cell walls of diatoms, composed mainly of silica (SiO2), with intricate, ordered nanostructures and unique species-specific designs [27]	Produced through chemical processes (e.g., sol-gel, pyrolysis), the structure can be tailored but typically lacks complex morphology [28]
Porosity and Surface Area	Naturally high surface area and porosity with varied pore sizes and shapes based on species, providing unique adsorption properties [14]	Engineered for high surface areas and porosity; more uniform and less complex pore size distribution compared to diatoms [29]
Biocompatibility and Environmental Impact	Generally, more biocompatible and environmentally friendly, suitable for food, cosmetics, and pharmaceuticals, with fewer environmental concerns [14]	Some can be biocompatible, but manufacturing may involve harmful chemicals and a larger environmental footprint [30]
Mechanical Properties	Unique combination of strength and lightweight characteristics, suitable for applications like filtration and lightweight fillers [31,32]	Mechanical properties vary widely; they may lack the structural uniqueness and strength of diatom frustules [33]
Functionality and Application	Provides functional benefits in bio-sensing, drug delivery, and catalyst carriers, leveraging natural properties [12]	Tailored for specific functionalities but may lack the biological interactions or specific surface functionalities of diatoms [34]
Cost and Availability	Availability and cost are influenced by diatom species abundance and harvesting methods, often more costly due to extraction and processing [35,36]	Produced at larger scales, often more cost-effective depending on production processes [37]

summarizes the differences between diatom frustules and commercial/synthetic porous silica sources. Thus, diatom-derived silica offers unique structural, environmental, and functional advantages compared to commercial or synthetic porous silica. Their natural origin, intricate designs, and biocompatibility make them suitable for various niche applications, while synthetic silicas provide versatility and uniformity for broader industrial uses.

3. The Application of Diatomaceous Biosilica in Cement

The search for sustainable alternatives to reduce the environmental impact of the cement industry has driven significant interest in the use of supplementary cementitious materials (SCMs). Diatomaceous biosilica, derived either from fossilized diatoms (diatomaceous earth, DE) or freshly cultured diatom frustules, has emerged as a promising SCM owing to its high silica content, inherent porosity, and pozzolanic reactivity [38,39].

Recent research highlights that biosilica obtained from living diatoms such as Thalassiosira pseudonana and Phaeodactylum tricornutum can be purpose-grown and processed to yield highly reactive pozzolanic materials [39]. This research showed that T. pseudonana biosilica exhibited a chemical reactivity higher than blast furnace slag, though lower than metakaolin, while P. tricornutum biosilica displayed reactivity comparable to Class F fly ash. These results underscore the potential of engineered diatom biosilica to serve as a sustainable, tunable SCM for the construction industry.

Traditional diatomaceous earth (DE), formed by fossilized diatom frustules, has also been extensively investigated as a cement replacement or geopolymer precursor. DE is characterized by a high amorphous SiO₂ content (60% to over 90%) and a highly porous microstructure [38]. Its incorporation into cementitious systems, at replacement rates varying from 10% to 40%, has been shown to improve mechanical strength, enhance chemical durability, reduce permeability, and lower the overall carbon footprint of concrete [38].

Additionally, using diatomaceous biosilica contributes to the densification of the cement matrix by forming secondary calcium silicate hydrate (C-S-H), refining pore structure, and reducing porosity [39]. This densification is essential for improving resistance to deleterious agents such as chlorides and sulfates, thus extending the lifespan of concrete infrastructures.

From an environmental perspective, biosilica and DE offer a compelling route to decarbonization. Cultivating diatoms for biosilica production inherently captures CO₂ through photosynthesis, potentially offsetting part of the emissions associated with cement manufacturing. Furthermore, valorizing industrial waste streams, such as spent diatomaceous earth from filtration processes, provides an additional avenue for sustainable material recovery.

4. Diatomaceous Biosilica Applications in Batteries and Catalytic Reactions: Environmental Positive Impacts

Diatomaceous silica is gaining increasing attention as a natural, sustainable material with valuable environmental applications. Due to its remarkable surface area, porous architecture, and chemical resilience, diatomaceous silica has found diverse applications in water purification, air filtration, soil decontamination, and catalytic support material [1]. Moreover, its affordability and natural abundance further enhance its appeal as a sustainable material for developing environmentally friendly technologies focused on pollution control and ecological preservation.

Diatomaceous biosilica stands out as a naturally abundant and environmentally friendly material with significant potential for application as an anode in lithium-ion batteries [8]. Its intrinsic porous structure and high surface area offer a unique advantage for ion transport and structural stability during cycling [9]. A comparative analysis between species like Nitzschia sp. and Craspedostauros sp. further showed that surface area and pore morphology strongly influence performance, with specific capacities reaching over 800 mAh·g⁻¹ and retention above 95% after 200 cycles [40]. These results highlight the relevance of species selection and post-treatment design in tailoring diatom-based anodes. Still, issues such as coulombic efficiency and the scalability of cultivation remain to be addressed before broader application is possible.

Purified frustules from species such as Chaetoceros, Navicula, and Stephanodiscus have been used as carbon-coated templates, leading to stable discharge capacities above 900 mAh·g⁻¹ [41]. Combining biological porosity and in situ carbon generation helps buffer structural changes during cycling and improves charge transport. In another study, silica extracted from Coscinodiscus diatoms was coated with carbon using glucose pyrolysis and subjected to electrochemical activation [42]. The final material showed reversible capacities near 800 mAh·g⁻¹ at low current and maintained over 450 mAh·g⁻¹ under fast cycling, while full-cell tests with commercial cathodes confirmed energy densities approaching 390 mWh·g⁻¹. Blanco et al. [43] observed that when particles from diatomaceous earth were reduced to submicron size and coated with a carbon layer, they reached stable discharge capacities of 840 mAh·g⁻¹ after 100 cycles. The coated particles also performed significantly better at high currents, with double the capacity compared to uncoated samples. Structural analysis confirmed the complete transformation of crystalline silica into amorphous phases after activation, which was key to lithium insertion. In a different approach, Norberg et al. [44] preserve the natural architecture of diatom frustules with minimal processing. Cleaned and milled frustules, combined with conductive additives such as carbon black, showed capacities of up to 723 mAh·g⁻¹, increasing over repeated cycles. Carbon-coated frustules offered a more stable profile around 600 mAh·g⁻¹. Additives in the electrolyte, such as fluoroethylene carbonate, improved coulombic efficiency and reduced decomposition, pointing to the importance of interface control in these materials.

Biosilica obtained from Pseudostaurosira trainorii, composed of amorphous silica with a porous three-dimensional frustule structure, was combined with carbon black to improve conductivity [45]; according to the authors, the 1:1 weight ratio between the two components delivered the most balanced performance, reaching around 409 mAh·g⁻¹ after 90 cycles at 20 mA·g⁻¹. Despite reduced capacity under high current, the electrodes maintained good structural integrity. These results point to the potential of diatom-derived silica for stationary energy storage, where stability and sustainability are valued over power density. In another work, Pseudostaurosira trainorii biomass was directly employed as a dual source of silica and carbon for anode production [46]. The material pyrolyzed at 600 °C delivered the best electrochemical performance, reaching 460 mAh·g⁻¹ after 70 cycles at a current density of 40 mA·g⁻¹. While calcium compounds in the biomass reduced the amount of electroactive silica at higher temperatures, the authors affirmed that adjusting cultivation conditions will probably improve its efficiency.

In recent work, Chen et al. [47] have explored the chemical modification of frustules from Navicula sp. to improve electrochemical performance. The study focused on incorporating functional groups (-SH) into the biosilica surface, modifying its cultivation using tetramethoxysilane (TMOS) and (3-mercaptopropyl)trimethoxysilane (MPTMS). The results showed that the modification led to Ag nanoparticle anchoring, improving the material’s conductivity. Temperature-dependent studies showed that structural integrity played a more critical role at elevated temperatures, whereas electrical conductivity was the key factor at lower temperatures. Incorporating other transition metals, such as Co, onto the frustule surface resulted in hybrid structures with improved cycling stability and capacities exceeding 600 mAh·g⁻¹ [48].

Beyond functionalization, other strategies have involved integrating the diatom silica into composite architectures to address the typical limitations of pure silica, such as poor electrical conductivity and structural degradation due to volume changes. In the work of Sun et al. [49], a hydrothermal method was used to coat the biosilica from Navicula sp. with manganese orthosilicate (Mn₂SiO₄) nanoclusters, followed by a conformal carbon layer. This “sandwich” structure, where Mn₂SiO₄ and carbon encapsulate the silica, effectively buffered volume expansion and promoted charge transport. The resulting material showed a specific discharge capacity of approximately 1112 mAh·g⁻¹ after 100 cycles at 100 mA·g⁻¹, which represents a significant enhancement over uncoated silica structures.

An alternative route has been converting the diatomaceous earth into nanosilicon. Campbell et al. [50] could preserve the diatomaceous earth’s original architecture using a magnesium thermic reduction process while producing a highly porous silicon material. This approach dramatically increased surface area from 7.3 to 162.6 m²·g⁻¹ and enabled high-capacity cycling. When tested under practical conditions, this nanosilicon anode delivered 1102 mAh·g⁻¹ after 50 cycles at 0.7 A·g⁻¹ and still maintained a capacity of 654 mAh·g⁻¹ under a fast charge/discharge regime of 14.3 A·g⁻¹. These values are significantly higher than the theoretical limit of commercial graphite, which stands at 372 mAh·g⁻¹. The same approach was used by Le et al. [51] by converting silica from diatoms into silicon using a magnesiothermic process and coating the surface with manganese dioxide (MnO₂) nanosheets. This three-dimensional hybrid electrode achieves high specific capacitance and excellent cycling stability. The final device achieved a power density of 2.22 kW·kg⁻¹ and an energy density of 23.2 Wh·kg⁻¹, suggesting broad applicability in low-cost and high-performance energy storage.

In addition to energy storage, diatom-derived structures have shown remarkable potential in solar energy conversion and water purification technologies [52]. Taking inspiration from the hierarchical light-harvesting architecture of diatom frustules, recent approaches have employed these biosilica as functional scaffolds for advanced photothermal and photocatalytic systems. Pan et al. [53] use the fabrication of a bilayer foam composed of polyaniline and titanium dioxide (TiO₂) coated onto melamine, forming a diatom-like structure capable of achieving high solar steam generation efficiency (88.9%) and a water evaporation rate exceeding 2 kg·m⁻² h⁻¹ under standard solar irradiation while also enabling dye degradation via photocatalysis. In another study, mesoporous carbon frameworks templated from diatoms were combined with reduced tungsten oxide (WO₃) to produce a nitrogen-doped composite with enhanced photocatalytic performance [54]. This system exhibited visible-light-driven hydrogen generation rates up to 2765 μmol·g⁻¹ h⁻¹ and efficiently degraded various β-lactam antibiotics, highlighting its dual role in energy production and water remediation. Chandrasekaran et al. [55] developed boron-doped diatom silica from Aulacoseira sp. into nanostructured silicon photocathodes, preserving the original biological morphology. When modified with indium phosphide (InP) nanocrystals and an iron–sulfur catalyst (Fe₂S₂(CO)₆), these materials enabled hydrogen evolution with measurable photocurrent and faradaic efficiency, confirming their viability as bio-derived semiconductors for solar-driven water splitting.

Diatom-based materials have shown significant promise in the photocatalytic degradation of hazardous organic compounds thanks to their porous structure, high surface area, and compatibility with metal/semiconductor loading. Metal-based systems have demonstrated high reactivity. A PdCl₂-loaded biosilica from Pseudostaurosira trainorii composite exhibited rapid degradation of methyl orange, achieving 85% removal in just one minute and over 98% within 75 min under UV light [56]. The efficiency was attributed to a synergistic photonic scattering effect between palladium nanoparticles and the diatom matrix.

TiO₂-based composites are the most explored class. In one example, TiO₂ vesicles inspired by the shell deposition of diatoms with an anatase shell (3–5 nm) showed enhanced charge transfer and a smaller band gap (3.16 eV) compared to traditional nanoparticles (3.20 eV), improving methylene blue degradation under UV light [57]. Another study introduced TiO₂ inside diatom pores using sonochemistry, producing hierarchical macro/mesoporous structures with 30 wt% TiO₂ loading that outperformed commercial P25 [58]. A carbon self-doped TiO₂/SiO₂ composite inspired by Cocconeis placentula frustules exhibited enhanced visible-light absorption and Rhodamine B degradation thanks to its preserved biotemplated structure and broad spectral absorption [59].

Biogenic TiO₂ deposited on biosilica frustule of Caloneis schroederi showed Congo red degradation of 27.8% and chloroform removal up to 91% under UV light, comparable to chemically synthesized TiO₂ [60]. In terms of pollutant-specific removal, TiO₂-incorporated Stephanodiscus hantzschii degraded up to 93% of N,N-diethyl-meta-toluamide (DEET) and bisphenol A (BPA) under UV light, with removal rate constants increasing from 0.376 to 0.683 h⁻¹ as hydraulic retention time (HRT) was reduced from 24 to 6 h [61]. When applied to real wastewater (palm oil mill effluent), a 54% TiO₂-loaded Cyclotella striata biosilica reduced the chemical oxygen demand by 47% and exhibited good photostability over multiple cycles [62]. Further development using a TiO₂/diatomite system calcined at 750 °C (anatase/rutile ratio of 90/10) achieved optimal degradation of Rhodamine B under UV light, following pseudo-first-order kinetics [63]. In a more applied context, titanium-silica frustules maintained photocatalytic efficiency for PPCP degradation in the presence of natural organic matter, showing 3–4 times higher normalized removal rates than P25 [64].

Zinc-oxide-based composites have also been explored. A biosilica@ZnO hybrid synthesized using functionalized diatoms showed complete Congo red degradation under visible light [65]. The chitosan-functionalized version showed superior performance due to higher ZnO loading and a reduced band gap, making it effective for multiple azo dye types. Other oxides and semiconductors like cadmium sulfide (CdS) have shown complementary roles. CdS-coated diatomite achieved efficient methylene blue degradation in both flow and suspension under solar light, with degradation half-time around 46 min [65]. Similarly, Cu_2-xS nanoparticles uniformly anchored on diatomite allowed for 99.1% methylene blue and 96.9% methyl orange degradation in only 40 min, supported by hydroxyl and superoxide radical generation under UV–vis light [66].

Diatom-based photocatalysts have also shown considerable potential in air purification, particularly for the degradation of airborne pollutants like nitrogen oxides and volatile organic compounds. Van Eynde et al. [67] used biosilica frustules from Pinnularia sp. as biotemplates for TiO₂ immobilization via a sol-gel process. The resulting silica–TiO₂ composites, containing up to 75 wt% TiO₂, exhibited high photocatalytic activity for NO_x removal under UV irradiation, with the highest TiO₂-loaded samples outperforming even commercial 100% TiO₂ catalysts [67]. The hierarchical porosity and high surface area of the frustules contributed to better dispersion and stability of the TiO₂ phase, highlighting the material suitability for sustainable air purification technologies. Complementarily, frustules from Thalassiosira pseudonana were functionalized with TiO₂ nanoparticles using an aqueous, environmentally friendly method, achieving a material that was 2.5 times more active than the commercial P25 photocatalyst for acetaldehyde degradation [29]. Notably, the performance remained stable even at 50% relative humidity, conditions representative of an indoor environment, demonstrating long-term efficiency and resilience, which makes this system highly suitable for integration into photocatalytic air filtration devices.

Finally, beyond their recognized photocatalytic capabilities, diatom-derived materials have emerged as highly efficient adsorbents for both organic compounds and metal ions in aqueous environments. Their intrinsic high surface area and tunable surface chemistry suit them for environmental remediation. For instance, biosilica obtained from three marine Nanofrustulum strains demonstrated remarkable efficiency in removing methylene blue from water, achieving up to 98.1% removal at pH 7 with adsorption capacities reaching 19.02 mg·g⁻¹. Under alkaline conditions (pH 11), the removal efficiency increased to 99.08% [68].

In the context of metal recovery, diatomaceous earth functionalized with thiol groups successfully adsorbed Au (III) ions, showing high affinity at acidic pH and achieving recovery rates above 95% using acidified thiourea, with adsorption following a Langmuir isotherm model [69]. For arsenic removal, frustules from Melosira sp. modified with both thiol and amino groups showed a maximum As (III) adsorption capacity of 10.99 mg·g⁻¹ at pH 4, with adsorption kinetics governed by both film and pore diffusion mechanisms. The process followed Langmuir–Freundlich isotherms and occurred through chemisorption, as confirmed by FTIR and XPS analyses [70]. In the case of mercury, silica microparticles functionalized with mercapto and amino groups demonstrated rapid and efficient Hg (II) adsorption, with maximum capacities of up to 185.2 mg·g⁻¹ and equilibrium reached within 60 min. The adsorption process followed a pseudo-second-order kinetic model and a Langmuir isotherm [71].

5. Industrial Applications: Healthcare, Biotechnology, and Food Industry Applications

Diatoms are ubiquitous photosynthetic microalgae with species-specific porous silica frustules, offering unique structural, optical, and mechanical properties that enable cost-effective, eco-friendly applications in biomedicine, sensing, energy, and nanotechnology through tailored surface modifications and structural mimicry.

In biotechnology, diatom-derived biosilica has been widely explored as a platform for immobilizing biomolecules such as antibodies, enzymes, and DNA aptamers in biosensor development. Among detection techniques, fluorescence and surface-enhanced Raman scattering (SERS) are the most employed. Fluorescence-based biosensing has been extensively studied due to its reliability and versatility. A common strategy involves functionalizing diatom biosilica surfaces via silanization to anchor antibodies for immunoassays. For example, Rea et al. transformed Aulacoseira sp. diatomite into silicon replicas using magnesia thermic reduction, then immobilized His-tagged p53 protein probes on the surface. The semiconductor properties of the modified diatoms enabled photoluminescence-based detection, with signal amplification upon target binding [10].

Photonic crystal structures derived from diatoms have demonstrated exceptional fluorescence enhancement. Squire et al. [72] utilized Pinnularia sp. frustules to develop an immunoassay for mouse IgG, achieving a 100-fold improvement in detection sensitivity (LOD: 14 fg/mL) compared to conventional methods. The same group later applied this platform to detect cardiovascular biomarkers, specifically NT-proBNP, in human plasma with high specificity (93%) and sensitivity (65%). The periodic nanopores of diatom biosilica were found to enhance both excitation and emission via electromagnetic field amplification and the Purcell effect, doubling fluorescence intensity compared to flat substrates [12].

Further applications include pathogen detection, such as Selvaraj et al.’s [73] work on Amphora sp. diatoms functionalized with Salmonella typhi antibodies. The biosensor exhibited high specificity for S. typhi antigens, with a detection limit of 10 pg, attributed to the material’s large surface area and photoluminescent properties.

Diatoms have also been adapted for cancer diagnostics. Esfandyari et al. [74] developed magnetic Chaetoceros sp. frustules coated with iron oxide nanoparticles and conjugated with Trastuzumab antibodies. These constructs enabled the selective capture of HER2-positive breast cancer cells (SKBR3) from blood under a magnetic field while exhibiting strong fluorescence emission at 493 and 650 nm. The chemotherapeutic effect against RAW 264.7 macrophages and MDA-MB 231-TXA breast cancer cells was investigated by using silicon nanoparticles (SiNP) from diatom silica, and it was observed that besides the cell viability of 53 and 73%, respectively, the particles tend to settle down due to gravity, either directly on the cells or nearby. Thus, SiNP might act as drug-delivering reservoirs at the cell’s surface [75]. The sustained and controlled release kinetics of curcumin-loaded frustules of T. weissflogii with a diatom pore size of 143.12 ± 48.29 nm had anticancer activity against the ACHN cell line compared to the HEK-293 cell line [76].

Surface-enhanced Raman scattering (SERS) leverages the inelastic scattering of photons upon interaction with matter amplified by nanostructured substrates. With its photonic crystal-like porous architecture, diatom biosilica enhances localized surface plasmon resonance (LSPR), creating an electromagnetic hot spot that significantly boosts SERS signals. This unique property has enabled diverse applications in biochemical sensing, diagnostics, and therapeutics.

Kong et al. [77] utilized Pinnularia sp. diatoms to create nano-plasmonic sensors by the in situ growth of silver (Ag) or the self-assembly of gold (Au) nanoparticles (NPs) on frustules. The large surface area of diatoms concentrates analytes, enabling the ultrasensitive detection of biomolecules or the controlled release of target molecules with good adhesion to lipid matrices by functionalization of hydrophobic aliphatic portions [78], tunable for hydrophobic or hydrophilic drugs (i.e., indomethacin and gentamicin, respectively) [79].

Other delivery systems, such as antigen and/or adjuvant transportation for vaccines, were suggested by Reichinger et al. [80] through R5 and RRIL peptides from silaffin—a protein linked to mineralization of C. fusiformis—coupled with peptide antigens, which led to IL-6 and TNF-α secretion in murine bone-marrow immune system cells.

Innovatively, a gelatin-based diatom-silica composite (GDA) for sponge applications after extraction of a tooth, in a way to prevent bleeding, showed biocompatibility, hemostatic effects, and sustained antibiotic release, maintaining a steady 5% release rate over 64 h. GDA was a carrier for doxycycline and demonstrated a high adsorption rate (90%) and loading efficiency (21%), effectively inhibiting LPS-induced inflammation in macrophages by over 50% and protecting osteoblasts from inflammatory damage. These properties highlight GDA’s potential in wound healing and periodontal treatments. However, further research is needed to address purification, immune responses, and biocompatibility challenges before clinical application [81].

Sun et al. [82] developed a composite combining alkylated chitosan and diatom biosilica for hemostatic purposes, demonstrating effective hemorrhage control and making it highly suitable for military trauma and traffic accident applications. Its procoagulant structure significantly reduced clotting time by 78% in vitro while maintaining excellent biocompatibility (hemolysis ratio < 5% with no cytotoxicity). The intense interaction between the sponge and blood activated platelets and erythrocytes, accelerating coagulation. Regarding in vivo essays, it achieved the shortest clotting time (106.2 s) and low blood loss (328.5 mg), highlighting its potential as a safe and efficient hemostatic material.

On the other hand, Yang et al. [83] further enhanced SERS sensitivity by immobilizing antibody-functionalized Pinnularia sp. frustules on glass slides, achieving a detection limit of 10 pg/mL for mouse IgG—100× better than conventional flat substrates. Kamińska et al. [84] developed an anti-IL-8 antibody-conjugated diatom biosensor with AuNP Raman reporters, detecting interleukin-8 in blood plasma at 6.2 pg/mL, which is clinically relevant for inflammatory diagnostics. Korkmaz et al. [85] demonstrated a low-cost SERS platform by depositing diatom-AgNP composites on adhesive tape, identifying bacterial strains (S. aureus, E. coli) with an enhancement factor of 10⁵.

Considering the research in intracellular tracking and fluidic systems, Raman imaging was already employed to monitor siRNA-conjugated diatomite uptake in cancer cells, revealing time-dependent intracellular distribution and membrane interaction dynamics. Optofluidic-SERS microcapsules with Pinnularia sp. diatoms and AgNPs detected Rhodamine 6G at 0.1 pM (single-molecule level) and environmental pollutants in water. Diatom–AgNP hybrids were integrated into microfluidic devices for accelerated DNA capture, achieving four-fold enhancement via mechanical rotation [12].

Lab-on-a-chip applications have been a hot topic in biotechnology areas. In this line of work, Kong et al. [86] engineered diatomite “chips” with AuNPs for chromatographic SERS, enabling the label-free detection of toxins (e.g., phenethylamine at 10 ppm) and miRNAs in human plasma.

Diatom biosilica’s innate photonic properties and compatibility with plasmonic nanomaterials make it a powerful platform for SERS-based sensing. Recent advances highlight its potential for point-of-care diagnostics, environmental monitoring, and single-molecule detection, driven by innovations in hybrid material design and microfluidic integration.

Due to its unique structural, chemical, and functional properties, the food industry has increased attention to diatomaceous biosilica, derived from the porous frustules of diatoms. Scientific research highlights its potential in food safety, preservation, nutrient delivery, and packaging.

Regarding food safety, recent studies have focused on antimicrobial activity and mycotoxin adsorption. Diatomaceous earth (DE) functionalized with silver (Ag) or zinc oxide (ZnO) nanoparticles exhibits strong antibacterial effects against foodborne pathogens, E. coli and Salmonella. The high surface area of biosilica enhances nanoparticle dispersion, improving contact-based microbial inactivation [87]. Raw and modified DE effectively adsorbed aflatoxins and ochratoxins from contaminated grains and liquids. Studies show that amine-functionalized DE binds > 90% of aflatoxin B1 in maize, offering a low-cost detoxification method [88]. Porous diatom biosilica extends shelf life by absorbing oxygen and moisture when incorporated into biopolymers (e.g., chitosan, PLA). Research demonstrates a 50% reduction in O2 permeability in DE-reinforced films [89].

Regarding food conservation, DE loaded with essential oils (e.g., thymol and carvacrol) shows sustained release, inhibiting mold growth in bread and cheese. This approach reduces the need for synthetic preservatives [90].

The encapsulation of bioactives to be applied in food has also been studied and reported recently in the literature. During processing, diatom frustules protect heat-sensitive compounds (e.g., omega-3s, probiotics) [91].

Scientific evidence underscores diatomaceous biosilica as a versatile, eco-friendly material for enhancing food safety, packaging, and nutrition. Ongoing research aims to refine functionalization techniques and secure regulatory endorsements for broader industrial adoption.

6. Nanotechnology and Advanced Materials

Nanotechnology is the branch of science that focuses on studies at the nanometric scale, as exemplified by biosilica derived from diatoms, an increasingly relevant material due to its origin from a natural source of porous silica. Its unique structural and physicochemical properties enable innovative applications across various scientific domains. Composed primarily of nanoporous silica with ordered, nanopatterned three-dimensional structures known as frustules, this material offers high surface area, thermal stability, biocompatibility, and significant potential for chemical functionalization. These attributes make diatom-derived biosilica a versatile and promising resource for chemistry, materials engineering, and biomedicine applications. Its use has been extensively investigated in high-value-added fields, including developing biomedical and regenerative therapies [8,11,22]. It has become a raw material with economic specifications for industrial use in the medical field.

In the biomedical field, diatomaceous biosilica shows great potential as a matrix for controlled drug release and the development of advanced biomaterials. Its porosity allows the incorporation of therapeutic agents that can be released gradually and locally, increasing treatment efficacy and reducing adverse effects; Figure 4. Aw et al. [92] used porous silica microparticles derived from fossilized diatoms, known as diatomaceous earth (DE), which have been investigated as natural carriers for controlled drug release. Indomethacin, a model drug with low water-soluble content, was used to evaluate the incorporation and release capacity. The results demonstrated a loading capacity of 22% by weight and sustained release for up to two weeks. The profile presented two phases: a rapid initial release (up to 6 h) and a slow and continuous release associated with the internal porous structure of the frustules.

In regenerative therapies, biomaterials based on diatomaceous biosilica have been used as a promising natural biomaterial in tissue engineering, especially in therapies aimed at bone regeneration. Their porous structure, high surface area, and biocompatibility confer significant advantages in the fabrication of bioactive scaffolds. Cicco et al. [93] demonstrated in an experimental study the in vivo functionalization of biosilica with sodium alendronate, evidencing its ability to activate osteogenic cells and favor the formation of mineralized matrix, suggesting its potential as a functionalizable osteoinductive material.

Beyond biomedical and industrial applications, diatomaceous biosilica has also emerged as a sustainable solution for water purification and treating contaminated effluents. Its ability to adsorb heavy metals and remove toxic organic compounds makes it an excellent material for selective filtration systems.

Patent US11066306B2 [94] describes using diatomaceous biosilica in energy storage devices such as printed batteries and supercapacitors. The frustules are used for their porous structure, high surface area, and biocompatibility, and they act as functional supports in electrodes and separators. After treatment and functionalization with metals or conductive nanomaterials, they are incorporated into inks for printing lightweight, flexible, and sustainable devices. The proposal highlights the potential of biosilica as a natural and efficient material in manufacturing low-cost energy technologies.

The growing number of scientific studies and patent registrations reinforces its relevance in interdisciplinary research and innovation projects. It highlights its role as a promising resource for developing advanced health, environment, engineering, and clean technology solutions.

7. Challenges, Limitations, and Future Directions and Research Opportunities

Diatomaceous silica stands out as a compelling, sustainable alternative to synthetic silica, primarily due to its natural origin, minimal processing requirements, and ecological compatibility. Derived either from fossilized deposits known as diatomaceous earth (DE) or cultivated diatom microalgae, this biomaterial represents a renewable resource that can be obtained with reduced environmental burden. This contrasts with conventional silica production, which is often reliant on energy-intensive processes and hazardous chemicals such as strong acids, bases, and high-temperature calcination. Utilizing diatom-derived silica in nanobiotechnology presents several challenges, particularly concerning the action of current extraction methods, which frequently involve chemical treatments that risk compromising the structural integrity and purity of the silica. There remains a significant challenge in optimizing these extraction techniques to enhance yield while maintaining the unique properties inherent to diatom silica. Additionally, harvesting from natural ecosystems can disrupt ecological balances, making it imperative to establish sustainable harvesting practices that minimize environmental impact, thereby ensuring the long-term viability of biosilica as a resource [89].

Another critical challenge lies in the standardization of characterization protocols and quality assessment for diatom-derived silica since there are several diatom species and distinct ways to process them, causing a high range of products. These differences probably affect the properties and their functions and efficiency. Scalability can also be a challenge, especially considering the differences among the obtention protocols, as well as the technological availability, method of cultivation, and separation needed to obtain biosilica.

From the data evaluated, it is very clear that future research should prioritize the development of greener and more efficient extraction methods, such as enzymatic or biotechnological processes, to enhance yield while preserving the quality of diatom-derived silica. The potential applications of diatom-derived silica in biotechnology and nanotechnology—such as drug delivery systems, biosensors, tissue engineering, and energy storage devices—offer exciting opportunities for innovation. Investigating the compatibility of diatom-derived silica with biological systems may yield novel biomedical applications. Additionally, integrating this biosilica into nanocomposites for use in material science, including construction, packaging, and electronics, represents a promising avenue for research. Understanding how diatom-derived silica can augment the properties of other materials will be critical in this regard.