Laser-Induced Graphene Electrochemical Sensors: An Emerging Platform for Agri-Food and Environmental Detection

Abstract

Harmful substances in food and agricultural environments pose significant risks to human health, necessitating the development of sensitive detection technologies. Electrochemical sensors are ideal for rapid monitoring because of their low cost, high efficiency, and portability. Recently developed laser-induced graphene (LIG)-based electrochemical sensors have demonstrated exceptional potential owing to the unique structural properties and outstanding electrochemical performance of LIG. In this review, the key factors influencing the LIG material characteristics during fabrication are discussed. Then, LIG-based electrochemical sensors are systematically categorized as pristine LIG and nanomaterial-functionalized, biomaterial-modified, and polymer-functionalized electrochemical sensors, and their application in the detection of functional components, additives, and agrochemicals in food products, and the detection of environmental pollutants, is comprehensively analyzed. Finally, the current challenges and the directions for future development are discussed.

1. Introduction

The assurance of food quality and safety has long been and still remains a vital concern of global importance for governments, industry, and academic research [1]. Food quality plays a key role in the nutritional value, energy content, and functionality of food products. While the extensive use of agrochemicals and food additives has resulted in substantial enhancements in agricultural productivity, enhanced food quality and appearance, and prolonged shelf life, it has also given rise to significant concerns with regard to food safety and environmental impact [2]. For example, excessive food additive residues pose a direct risk to human health while agrochemicals such as pesticides and antibiotics, which are utilized to protect and promote plant growth, can potentially contaminate the soil and irrigation water sources [3,4]. Furthermore, the presence of toxic chemicals, including heavy metal ions and toxins, in agricultural environments (soil and water) poses a significant threat to human health through the consumption of contaminated produce [5,6]. Therefore, the rapid and sensitive detection of key functional components in food, residues of agrochemicals and food additives in food products, and harmful chemicals in agricultural environments is vital for ensuring food quality and safety.

Conventional techniques for food analysis and agricultural environmental detection, including high-performance liquid chromatography (HPLC) [7], Raman spectroscopy [8], mass spectrometry [9], and their combinations [10], typically offer significant advantages in terms of high sensitivity and selectivity [11]. However, these techniques also have disadvantages, such as the use of complex operational procedures, substantial financial costs, and extended response times, which decrease their effectiveness in the detection of target analytes. These methods adapt to high-precision detection in the laboratory rather than on-site testing of plants and food [12]. Electrochemical detection methods have recently attracted significant attention owing to their low cost, high efficiency, and wide range of possible applications, particularly in flexible and convenient electrochemical sensors [13,14]. Electrochemical sensors, which generally comprise three electrodes (a working electrode, counter electrode, and reference electrode), are highly promising for applications in the rapid detection of substances encountered in daily life [15]. The working electrode is considered to be the core component of an electrochemical sensor, and the selection of electrode materials has a significant impact on the sensor detection performance [16]. Nanomaterials have been demonstrated to be effective working electrodes in electrochemical sensors [17,18]. In particular, the use of carbon nanomaterials as electrodes or modifiers has been widely reported to improve the performance characteristics of electrochemical sensors, including their sensitivity, selectivity, and limit of detection (LOD), owing to their large specific surface areas [19]. In particular, due to its excellent electrical conductivity, large specific surface area, fast electron transfer kinetics, and mechanical flexibility, graphene is often used in electronic components [20]. Synthetic techniques for graphene preparation include mechanical exfoliation [21], chemical vapor deposition [22], and the derivatization of graphene oxide [23]. Unfortunately, these methods are usually carried out under harsh conditions and involve complex preparation processes [24].

In 2014, Tour et al. first reported laser-induced graphene (LIG) produced from commercial polyimide (PI) sheets via simple laser scribing (Figure 1A) [25]. The instantly generated energy at the localized area of the PI during laser patterning destroys the chemical bonds and induces the rearrangement of the carbon atoms, leading to the graphitization of the substrate material to form the 3D structure of the LIG [25,26]. As laser power rises, the morphology of LIG undergoes changes until it is eventually cut. (Figure 1B) [27]. Although the production of reduced graphene oxide from graphene oxide through laser scribing has been reported in an earlier study [28], Tour’s work paved the way for its use in the convenient preparation of graphene. As a novel three-dimensional nanomaterial with a porous structure, LIG possesses good electrical conductivity and meets the conditions required for use as an electrode for electrochemical sensors. For example, flexible LIG is an ideal electrode that meets the requirements of practical use as a working electrode in a typical three-electrode system [29] and in an integrated three-electrode array [30,31,32]. LIG avoids the complex production and functionalization methods involved in the production of glassy carbon and screen-printed electrodes [33,34,35]. In addition, the abundant porous concave structures on the LIG surface provide space and attachment sites for biomolecules, which can facilitate heterogeneous interfacial electron transfer [36,37], thereby enhancing the detection performance of LIG-based electrochemical sensors in terms of high sensitivity, low detection limit, and strong anti-interference capability [38]. For example, a recent study demonstrated that an LIG-based electrochemical sensor exhibited a wider detection range and a lower LOD than the LC method for detecting benomyl in food samples [12]. Taken together, LIG-based electrochemical sensors offer advantages such as simple fabrication, ease of integration, and high detection performance, making them highly suitable for on-site and sensitive detection in agri-food and environmental analysis (Table S1).

In this minireview, we provide a brief overview of the effects of various preparation parameters, including substrate materials, laser illumination parameters, and atmospheres, on the properties of LIG. Subsequently, four types of LIG-based electrochemical sensors fabricated by functionalizing the prepared LIG electrode are discussed, and the application of LIG electrochemical sensors in food analysis and agri-environmental detection is reviewed. Finally, we present a critical outlook and perspective on the future development of LIG-based electrochemical sensors.

2. Factors Affecting Characteristics of LIG

As a novel carbon nanomaterial, LIG, with a 3D porous structure, high specific surface area, and high electrical conductivity, is expected to be widely applied in various fields such as flexible electronics, chemical sensors, energy storage devices, water treatment, and smart agriculture [39,40,41]. However, the formation of LIG is a relatively complex process that involves photothermal/photochemical effects [26]; therefore, it can be affected by various factors. In this section, the effects of precursor materials, laser-scribing parameters, and atmosphere on LIG characteristics are summarized (Figure 2).

2.1. Precursor Materials

PI film was the first carbon precursor substrate used for LIG production in the pioneering study by Tour et al. [25]. Only two polymers, namely PI and poly(etherimide) (PEI) [42,43], both of which contain aromatic and imide repeat units, were reported to produce LIG in the early work. Subsequently, the range of polymer precursor materials for LIG production was expanded to a variety of polymers, such as polyetheretherketone (PEEK) [44], poly(ether sulfone) (PES) [45], Kevlar [46], and phenolic resin (PR) [25,47,48]. Various polymeric materials have been considered as substrates, owing to their different advantages. Thakur et al. compared the LIG obtained from polymeric materials such as Kevlar fabric, with a low cost and high mechanical performance; the widely used PI; and PES films that show excellent solubility (Figure 3A). Among these three films, PI film was found to be most easily graphitized, so PI-LIG showed the highest degree of graphitization and conductivity among the studied films. LIG obtained from Kevlar fabric was limited by the material structure, and its performance was inferior to that of PI-LIG and PES-LIG [49]. For electrochemical applications, the use of such polymers as precursors has the advantages of ease of acquisition, due to their commercial production, and ease of integration for electrochemical chips, due to their good mechanical performance. For example, highly integrated LIG electrochemical chips produced by commercial PI and PEEK sheet have been reported for the detection of bioflavonoids in citric products [44,50].

In addition to using polymers, researchers have successfully fabricated LIG on the surfaces of foods (e.g., coconut, potato, bread) [51,52], and other natural materials such as wood [53], filter paper [54,55], cork [56,57], chitosan [58], and lignin [59] (Figure 3B). For example, Kulyk et al. reported a filter-paper-based LIG produced on common filter paper using a CO₂ laser. Filter paper is significantly less expensive than commercial polymers such as PI and PES, making it well-suited for large-scale single-use applications [60]. However, it must be noted that for the preparation of LIG from thermally sensitive materials, such as paper, the addition of a flame retardant (e.g., sodium tetraborate decahydrate [61]) that inhibits ablation and volatilization in ambient air is necessary. These natural substrates are attractive mainly because they are both environmentally benign and inexpensive. Vaughan et al. reported an eco- and cost-friendly natural cork–LIG electrochemical sensor for the detection of tyrosine, with its precursor material sourced from the bark of Quercus suber L. tree [56]. Furthermore, abundant in crab and shrimp shell waste, chitosan is biodegradable and widely applied in sensor technology [58]. Hamidi et al. cast chitosan-based formulations on glass slides and wrote LIG features using a laser after biofilm curing. Compared to paper, chitosan films are more flexible, and their thickness can be controlled more precisely (approximately 120 μm) [58].

Figure 3. (A) LIG was generated on Kevlar, PES, and PI films using an 8 W CO₂ laser (a), and SEM images of Kevlar–LIG (b), PES-LIG (c), and PI-LIG (d). Reprinted from [49] Copyright (2022) with permission from American Chemical Society; (B) LIG was produced on coconut and bread (a), wood (b), paper (c), and cork (d). (a) reprinted from [51] Copyright (2018) with permission from American Chemical Society. (b) reprinted from [53] Copyright (2017) with permission from WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (c) reprinted from [55] Copyright (2022) with permission from MDPI. (d) reprinted from [56] Copyright (2023) with permission from Wiley-VCH GmbH (B).

Figure 3. (A) LIG was generated on Kevlar, PES, and PI films using an 8 W CO₂ laser (a), and SEM images of Kevlar–LIG (b), PES-LIG (c), and PI-LIG (d). Reprinted from [49] Copyright (2022) with permission from American Chemical Society; (B) LIG was produced on coconut and bread (a), wood (b), paper (c), and cork (d). (a) reprinted from [51] Copyright (2018) with permission from American Chemical Society. (b) reprinted from [53] Copyright (2017) with permission from WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (c) reprinted from [55] Copyright (2022) with permission from MDPI. (d) reprinted from [56] Copyright (2023) with permission from Wiley-VCH GmbH (B).

2.2. Laser-Scribing Parameters

A carbon dioxide infrared (IR) laser was utilized in the initial work on LIG and continues to be employed for LIG fabrication [25]. In addition to IR lasers, near-IR [62,63,64], visible [33,65], and ultraviolet (UV) [59,66] lasers can be used for LIG fabrication. The type of laser used can affect the morphological and structural properties of LIG. Santos et al. compared LIG produced on PI using UV and IR lasers (Figure 4A). Their results showed that LIG produced by a UV-laser exhibits lower spacing (≈20 µm vs. ≈75 µm of IR-LIG), a higher nitrogen content, and a lower degree of oxidation (C:O ≈ 5.2 vs. 8.1 of IR-LIG), than that produced by an IR laser, while LIG produced by an IR-laser shows a higher density of graphene edges and larger electrochemically active area provided by the abundant pores (Figure 4B), and thus shows a superior sensitivity and lower detection limit in dopamine detection than LIG produced using a UV laser [67]. Similar results were also reported by Wang et al., who found that LIG produced on PI by a CO₂ IR laser was characterized by micron-sized pores, while that produced using a UV laser displayed micron-and nano-sized pores [68]. Furthermore, under the same laser fluence, a much lower sheet resistance was observed for the LIG fabricated using the CO₂ IR laser than for the LIG obtained using the UV laser.

In addition to the laser source, the impact of the laser power and speed on the LIG should also be considered [69,70]. It has been reported that the use of lasers with insufficient power output results in the formation of amorphous carbon on the substrate or fails to form carbon owing to a lack of energy, whereas excessively high laser power may lead to the over-carbonization of the substrate and increase the risk of LIG detachment (Figure 4C) [69,71,72]. Similar to laser power, laser speed also has a significant effect on the morphology and properties of LIG. Low laser speeds may lead to high cumulative energy deposition at each spot and further carbonization of the substrate, eventually causing it to melt into droplets, while with high laser speeds, the limited exposure time of the polymer to the laser is insufficient to induce an adequate quantity of graphene (Figure 4D) [42,73,74,75]. It should be noted here that both the laser power and speed should often be optimized at the same time [76]. For example, Diédhiou et al. reported an LIG-based electrochemical sensor for the detection of heavy metal ions. They found the optimal parameters of LIG preparation, with a laser power and speed of 6.4 W and 30 cm⁻² exhibiting the highest response to Pb²⁺ [77].

Figure 4. The effect of laser parameters. (A) The fabrication of LIG used by an IR (a) and UV (b) laser with same d on PI film (c), (B) SEM image of UV-LIG (a,c) and IR-LIG (b,d) on PI film. Reprinted from [67] Copyright (2021) with permission from Wiley-VCH GmbH. (C) The morphology and SEM of LIG of laser power from 1.2 W to 1.5 W on chitosan film. Reprinted from [72] Copyright (2024) with permission from MDPI. (D) Photographs, sheet resistance values, and SEM images of the samples formed under different scan speeds on filter paper, for laser powers of ≈700 mW. Reprinted from [75] Copyright (2021) with permission from American Chemical Society.

Figure 4. The effect of laser parameters. (A) The fabrication of LIG used by an IR (a) and UV (b) laser with same d on PI film (c), (B) SEM image of UV-LIG (a,c) and IR-LIG (b,d) on PI film. Reprinted from [67] Copyright (2021) with permission from Wiley-VCH GmbH. (C) The morphology and SEM of LIG of laser power from 1.2 W to 1.5 W on chitosan film. Reprinted from [72] Copyright (2024) with permission from MDPI. (D) Photographs, sheet resistance values, and SEM images of the samples formed under different scan speeds on filter paper, for laser powers of ≈700 mW. Reprinted from [75] Copyright (2021) with permission from American Chemical Society.

2.3. Gas Atmosphere

In addition to the precursor materials and laser-scribing parameters, the gas atmosphere during laser writing affects the surface characteristics of LIG. Li et al. reported that LIG surfaces prepared in oxidizing gases (i.e., oxygen) or oxygen-containing gases (i.e., air) have abundant oxygen-containing functional groups and exhibit superhydrophilicity (water contact angle ≈ 0°). By contrast, LIG prepared in reducing (i.e., hydrogen) or inert (i.e., argon) environments are superhydrophobic (water contact angle > 150°) [78]. Dallinger et al. achieved continuous modulation of LIG from hydrophilic to superhydrophobic (water contact angle of 160°) by modulating the localized inert atmosphere used in LIG fabrication. Atmospheric oxygen depletion effectively suppresses the generation of oxygen-containing surface functionalities on LIG, decreasing its surface energy and consequently reducing its hydrophilicity (Figure 5). Based on these findings, they developed a device for the efficient collection of water droplets in mist using superhydrophobic LIG materials [79]. The hydrophilic/hydrophobic properties of the electrode surfaces play a critical role in the performance of electrochemical sensing interfaces. A hydrophilic surface facilitates the penetration of sample solutions into the electrode’s internal structure, thereby enhancing the enrichment of target analytes and improving detection sensitivity [56]. In contrast, a hydrophobic surface helps to minimize nonspecific adsorption from complex matrices—such as those encountered in agri-food and environmental samples—thereby enhancing anti-interference capability and sensor selectivity [80]. Although the direct regulation of LIG-based electrochemical sensors via a gas atmosphere remains scarcely explored, and most LIG sensors are still fabricated in air for convenience, this strategy represents a novel and viable route for tailoring electrode surface properties.

3. LIG-Based Electrochemical Sensors

LIG is considered to be an ideal electrode for constructing electrochemical sensors, owing to its good electrical conductivity and electrochemical activity. First, as a carbon nanomaterial, LIG can be directly utilized as a catalyst for the detection of electrochemically active species. Furthermore, the modification of LIG with functionalized materials can extend the range of target analytes of LIG-based electrochemical sensors based on either the enhanced conductivity [81,82], increased electrocatalytic area [83], improved electrocatalytic activity [84,85], or the recognition behavior of functionalized materials, which enable LIG electrodes to detect one or more substances [86,87]. In the discussion below, LIG sensors are classified according to their functionalization as bare LIG electrochemical sensors, nanomaterial-functionalized LIG electrochemical sensors, biofunctionalized LIG electrochemical sensors, and polymer-functionalized LIG sensors (Figure 6).

3.1. Electrochemical Sensors Based on Pristine LIG

LIG materials with high defect density and porous nanostructures exhibit a substantial number of adsorbable active sites, making them suitable for direct utilization in the electrochemical detection of a wide range of electroactive substances [33,88,89]. For example, our group reported the electro-oxidation of several typical flavonoids in citrus fruits using LIG produced from both PI and PEEK (Figure 7). Consequently, LIG produced from PI and PEEK was used directly as the working electrode in electrochemical sensors for the simultaneous detection of citrus flavonoids, such as hesperidin, naringin, and nobiletin, and showed high sensitivity and reproducibility [50]. Liu et al. reported an electrochemical sensor based on unfunctionalized LIG for the detection of Pb²⁺ in natural aquatic environments. The LIG used in this work was obtained using an infrared laser on a PI film and detected Pb²⁺ in solution when used as the working electrode under a constant potential, and exhibited anti-interference capability in a solution in which the concentration of other ions was 200 times higher than that of Pb²⁺. The large specific surface area of the hierarchically porous structure provides abundant active binding sites for lead ions (Pb²⁺), while the oxygen-containing groups (e.g., −OH) on the LIG surface further facilitate the adsorption of Pb²⁺ [90]. Sain et al. reported a flexible electrochemical sensor based on LIG for on-site detection of paraquat in water. The LIG electrode was treated with phosphate-buffered solution (PBS) to increase the porosity of the structure and the electrochemically active surface area and exhibited mechanical flexibility up to 180°, reproducibility within 10.12%, and stability for over one month, demonstrating its potential for real-time environmental monitoring [91].

3.2. Nanomaterials Functionalized LIG Electrochemical Sensors

Nanomaterials, characterized by a large specific surface area, high surface energy, enhanced electron transfer capability, and strong adsorption capacity, are commonly employed in the fabrication of electrochemical sensors with improved detection performance [92]. Among these, metal-based nanomaterials and carbon nanomaterials are widely utilized due to their excellent electrical and electrochemical properties [93]. Typical strategies for functionalizing laser-induced graphene (LIG) electrodes with metal nanomaterials include electrodeposition [94], drop coating [35], and doping [95]. In particular, the in situ doping of homogeneous metal nanomaterials onto the LIG surface via laser induction provides a rapid approach for electrode modification [96]. Liu et al. reported a flexible plant-wearable sensor based on Fe-doped LIG for the rapid in situ quantification of salicylic acid (SA) in plants under salt stress. To fabricate the Fe-LIG electrode, a two-step laser scribing process was adopted: after initially creating an LIG layer on a PI substrate, a 0.1 M FeCl₂ solution (6 µL) was drop-cast onto the working area, followed by a second laser treatment under the same conditions to incorporate Fe atoms into the graphene lattice via the formation of Fe–O bonds. A much higher electrochemical response to SA was found on the Fe-LIG electrode than that on the bare LIG electrode. The enhancement was contributed to by both the improved electrochemical properties of Fe-LIG electrode and the high affinity between the Fe atom and SA molecule. The Fe-LIG electrode delivered an LOD of 0.27 µM for SA in 0.2 M PB buffer (pH 7) via differential pulse voltammetry (DPV), maintained >96% recovery in plant extracts, and enabled smartphone-controlled monitoring of SA levels on living cucumber leaves [96].

The use of carbon nanomaterials as functional materials for electrochemical detection has been demonstrated to yield several advantages [97,98]. Examples of such materials include multiwalled carbon nanotubes (MWCNTs), reduced graphene oxide, and graphene conductive inks, which enhance the mechanical properties and electrical conductivity of electrodes and sensor sensitivity. Furthermore, the stability of carbon nanomaterials renders them less susceptible to corrosion in complex environments [29,98,99]. Nasraoui et al. reported a flexible voltammetric sensor for 4-aminophenol (4-AP) based on LIG electrodes functionalized in situ with an MWCNT-polyaniline (MWCNT-PANI) nanocomposite. The sensitivity of the PANI/LIG electrode was increased by modification with MWCNTs, surpassing that achieved when using electrodes based on either MWCNT or PANI alone [100]. Wang et al. reported a TiO₂@Enteromorpha-derived carbon (EDC)/LIG electrochemical sensor to monitor potential pesticide in food matrices [101]. EDC, which is prepared by carbonizing fresh Enteromorpha at 900 °C under an inert atmosphere for 2 h, enhances the adsorption of diuron due to its mesoporous structure. In addition, the TiO₂ nanomaterial significantly enhances the catalytic activity of the TiO₂@EDC/LIG electrode toward diuron in vegetable matrices (Figure 8) [101].

3.3. Biomolecule-Functionalized LIG Electrochemical Sensors

LIG electrochemical biosensors utilize biomolecules (e.g., enzymes, antibodies, antigens, nucleic acids, and aptamers) as recognition sites for the specific detection of the object to be tested. The high specificity of the enzyme for a particular substrate facilitates the detection of the target substance using an LIG enzyme sensor [6,102]. For example, Settu et al. reported a glucose oxidase (GOx)-modified LIG electrochemical sensor for glucose detection with a sensitivity of 43.15 µA mM⁻¹ cm⁻² and a detection limit of 43.15 μM [103]. The glucose was detected based on the electro-oxidation of H₂O₂, which is generated during the glucose oxidation catalyzed by GOx on the LIG at an applied potential of 0.8 V. Such a system is dependent on O₂ and frequently suffers from low selectivity due to a high applied potential. An enzymatic electrochemical sensor that tackled this issue by immobilizing GOx and aminoferrocene (AFc) at the LIG produced on filter paper (GOx/AFc/LIG) was reported by Gao et al. [55]. AFc was used here as an electron acceptor instead of oxygen. As a result, the glucose was detected by the GOx/AFc/LIG at an applied potential of −90 mV, at which potential interfering species did not have a noticeable effect on the detection of glucose (Figure 9).

LIG electrochemical immunosensors have been shown to exhibit higher specificity for target biomarkers than for similar structural markers or in the presence of nonspecific binding. For example, Soares et al. introduced an LIG immunosensor that enables the 22 min, label-free quantification of Salmonella Typhimurium in complex food matrices (e.g., chicken broth) [104]. To fabricate the immunosensor, the LIG electrodes were sequentially exposed to EDC/NHS (3:1, 1 h), and then 1.0 µM anti-Salmonella polyclonal antibody (4 °C, overnight), followed by ethanolamine quenching and Super Block blocking. The sensor exhibited a linear response in the range of 25–10⁵ CFU mL⁻¹, a limit of detection of 13 ± 7 CFU mL⁻¹, and a total assay time of 22 min. These results demonstrate the feasibility of LIG electrodes for sensitive, low-cost food safety monitoring.

3.4. Polymer-Functionalized LIG Electrochemical Sensors

The electropolymerization of functional materials on the surface of LIG electrodes is a controllable process that can be used to obtain polymer-modified LIG electrodes that achieve enhanced biocompatibility and reduced interference [105]. For example, Barber et al. reported a polymer-modified LIG electrochemical sensor for the detection of H₂O₂ [106]. A one-step anodic electrodeposition from a mixed precursor solution containing 2.5 mM FeCl₃, 2.5 mM K₃[Fe(CN)₆], 0.1 M KCl, 0.01 M HCl, and 0.01% chitosan in 1% acetic acid was performed at +0.4 V (vs. Ag/AgCl) for 300 s, leading to the simultaneous deposition of a Prussian blue–chitosan (PB–CS) nanocomposite film. Then, post-treatment steps including cyclic voltametric activation (scanned from −0.25 to +0.65 V at 0.05 V s⁻¹) and thermal curing at 100 °C for 1 h were performed to crystallize and anchor the PB–CS layer. The resulting LIG/PB–CS electrode exhibited a detection limit of 6.31 µM for H₂O₂ at −0.036 V (vs. Ag/AgCl) in real samples, demonstrating the viability of laser-patterned, polymer-stabilized redox coatings for wearable electrochemical biosensing applications.

Ding et al. developed a polymer-modified LIG sensor for the sensitive detection of the atenolol pharmaceutical molecule [107]. A polydopamine (PDA) film was electrochemically polymerized onto the LIG working electrode via 15 cyclic voltammetry (CV) cycles (scanned from −0.5 to +0.5 V vs. Ag/AgCl at 50 mV s⁻¹) in a 5 mM dopamine solution prepared in 0.1 M PBS, pH 7.2. This process increases the electroactive surface area of the LIG surface by 3.4 times (from 0.067 to 0.225 cm²) by forming a superhydrophilic amine-rich film. Furthermore, the NH₂ groups on the surface of the LIG electrode from PDA could enhance the adsorption of atenolol by π-π interactions and hydrogen bonds. Consequently, the optimized LIG-PDA-15 electrode exhibited a sensitivity of 0.020 ± 0.004 µA µM⁻¹ and an LOD of 80 µM for atenolol in a pH 10 Britton–Robinson buffer. These results confirm that the controlled electropolymerization of PDA on laser-induced graphene provides a low-cost and scalable strategy for the development of sensing platforms.

Molecular imprinting uses an eluent to remove template molecules, forming a cavity structure in which the target can be specifically adsorbed [108]. For example, Zheng et al. developed an LIG electrochemical sensor for 3-nitrotyrosine (3-NT) using molecularly imprinted polymers [109]. Zeolitic imidazolate framework-67 (ZIF-67) was potentiostatically electrodeposited (−0.8 V, 300 s) from Co(NO₃)₂·6H₂O/2-methylimidazole/tetrabutylammonium tetrafluoroborate in methanol onto the LIG surface. Subsequently, 13 mM dopamine and 5 mM l-tyrosine (as a dummy template) were co-electropolymerized via 15 CV scans (ranging from −0.5 to +0.9 V at 50 mV s⁻¹) in the presence of 100 mM LiClO₄, forming a molecularly imprinted polydopamine (MIPDA) film with the dummy template encapsulated. After eluting l-tyrosine in a methanol/acetic acid mixture (7:3, v/v) for 1 h to create specific recognition cavities, the resulting MIPDA/ZIF-67/LIG electrode achieved an LOD of 6.71 nM for 3-NT with a linear range from 0.04 μM to 100 μM. The LIG sensor facilitates the precise, portable electrochemical detection of 3-NT, obviating the need for the pretreatment of biological samples. Marques et al. developed a dual-molecule detection platform based on LIG and MIP technologies, which is intended for the simultaneous detection of ascorbic acid (AA) and amoxicillin (AMOX) in water. Dual-LIG platforms, which are highly reproducible, low-cost, flexible, and made via high-resolution, design-flexible technology, match commercial screen-printed electrodes in features. However, the removal of AMOX templates necessitates incubation in acetonitrile (ACN) followed by 40 cyclic voltammetry scans (+0.5 to +0.8 V, 0.1 V/s), a process that is not only reliant on the strictly controlled use of the hazardous solvent ACN but also increases fabrication cost and time due to the requisite residue verification (Figure 10) [110].

We simply classified LIG-based electrochemical sensors into four categories based on the primary elements in the detection. However, it should be noted here that, in the current research, “multi-component synergistic modification” is a key trend for enhancing the comprehensive performance of sensors. Johnson et al. reported an enzymatic electrochemical biosensor, in which glycine oxidase (GlyOx) is immobilized on platinum (Pt) nanoparticle-decorated LIG, for glyphosate detection (Figure 11) [111]. In such a system, the LIG circuit is decorated with Pt nanoparticles to further improve its electrochemical reactivity and is further biofunctionalized with GlyOx to permit the selective monitoring of glyphosate. Zhang et al. developed a portable electrochemical biosensor based on an LIG composite electrode, which was prepared by the immobilization of GOx on a poly(3,4-ethylenedioxythiophene (PEDOT) and Au nanoparticle (AuNPs)-functionalized LIG surface (LIG/PEDOT/Au/GOx) [65]. As a result, the electrochemical sensors showed a higher sensitivity of 341.67 µA mM⁻¹ cm⁻² and a lower detection limit of 2 µA, compared to that reported in the GOx/LIG electrode.

4. LIG-Based Electrochemical Sensors for Food Analysis and Agricultural Environmental Detection

4.1. Detection of Functional Components in Agricultural Product

The accurate and stable detection of constituent functional groups is pivotal for the quality assurance of agricultural products and provides the basis for the optimization of food-processing protocols and development of precision agriculture toward sustainable production systems [112,113]. For example, glucose significantly influences the nutrition value, texture, and flavor of foods, necessitating the use of reliable glucose detection methods for analyses of food and agricultural products. Huang et al. developed a hierarchical NiCo-layered double-hydroxide-modified LIG electrode (NiCo-LDH/LIG) for glucose detection [83]. Under optimized conditions, this electrode achieved a detection limit of 0.05 μM with sensitivities of 9.75 μA cm⁻² μM⁻¹ (0.5–270 μM) and 3.76 μA cm⁻² μM⁻¹ (270–3600 μM). The sensor exhibited excellent anti-interference properties for citric acid (CA), lactose (Lac), uric acid (UA), sucrose (Suc), AA, fructose (Fru), NaCl, dopamine (DA), and Na₂CO₃ in 0.1 M NaOH solution. Recovery tests on coffee drinks, milk, milk tea, cola, orange juice, and honey yielded rates of 96.3–102%. AA, a potent antioxidant involved in numerous biochemical processes, occurs naturally in fresh fruits and vegetables and is added as a nutrient to food products. Kongkaew et al. fabricated a gold-nanoparticle-functionalized LIG electrochemical sensor for AA detection in orange juice [114]. The sensor was prepared by the laser ablation of a PI film coated with a co-polymer solution containing HAuCl₄, pyrrole, and chitosan, and exhibited sensitivities of 27.8 μA mm⁻² mM⁻¹ (0.25–5 mM) and 4.6 μA mm⁻² mM⁻¹ (5–25 mM), with a detection limit of 0.22 mM. The sensor exhibited an excellent anti-interference capability, as the current response of 10.0 mmol L⁻¹ AA remained nearly unchanged (RSD 2.4%) in the presence of CA, glucose, Suc, Fru, CaCO₃, and KCl. The sensor detected AA in six commercial orange juices, with recoveries of 97–109.1%. In addition to nutritional compounds, such as glucose and AA, certain functional components serve as key indicators in agricultural products with dual food and medicinal efficacy (e.g., food medicine homology). Xia et al. reported a sensor based on unmodified LIG obtained from a PEEK film for the simultaneous detection of polymethoxylated flavones (PMFs) and hesperidin in Citri Reticulatae Pericarpium (CRP), a renowned traditional Chinese medicine that is consumed as a health food, condiment, and dietary supplement [44]. The sensor demonstrated effective electrocatalytic performance for both analytes with high detection efficiency, good reproducibility, and reliability (Figure 12). PMFs and hesperidin were detected within 5–100 μM, with LODs of 0.1 μM and 1.7 μM, respectively. Recovery tests in real CRP extracts showed 90–107% recovery, confirming the practical reliability of the sensor.

4.2. Detection of Additives in Food

Food additives are substances that are added to preserve flavor, enhance appearance, and improve product quality [115]. While food additives play an essential role in modern food production (particularly of packaged goods), their improper use may cause contamination and health risks. For example, synthetic colorants improve food appeal but pose health hazards under certain conditions. Kondusamy et al. reported an LIG-based sensor functionalized with Ag-doped La(OH)₃@Dy₂O₃ nanoparticles for the detection of tartrazine (TRZ) [87]. The sensor showed a sensitivity of 3.99 × 10⁻⁴ A μM⁻¹ cm⁻² with an LOD of 0.96 nM for TRZ. The modified LIG demonstrated high selectivity, with <5% error in TRZ detection despite the presence of various electroactive, pharmaceutical, food-related, and nitro compounds. Recovery tests in river water, isotonic drinks, milk, and snacks yielded recoveries of 96–104% (RSD < 5%). Thiocyanate, which is added to dairy products because of its bacteriostatic effects, may cause iodine deficiency, hypothyroidism, or acute poisoning upon excessive exposure. Yuan et al. developed a PEDOT-functionalized LIG electrochemical sensor for thiocyanate detection, achieving a sensitivity of 3.06 μA cm⁻² μM⁻¹ and LOD of 0.52 μM under optimized conditions [116]. Even with 10-fold levels of common ions and organic species—and 4-fold uric acid—the SCN⁻ signal varied by <5%, confirming the sensor’s excellent selectivity. Testing in pretreated milk yielded recoveries of 96.2–103.4% (benchtop workstation) and 94.6–97.2% (smartphone-based analyzer). Clenbuterol hydrochloride (CLB), an adrenal nerve stimulant, can increase the proportion of lean meat in animals when illegally added to animal feed or veterinary drugs. CLB may accumulate and reside in animal tissues, posing risks to human health. Tang et al. proposed an LIG electrochemical sensor based on LIG modification with Pt nanoparticles for CLB detection [117]. This sensor showed a sensitivity of 0.2383 μA μM⁻¹ and LOD of 0.072 μM, which was attributed to the modification with Pt nanoparticles. Using the standard addition method, the recovery rates of CLB in real beef samples were determined to be between 90% and 110%. Formaldehyde (HCHO), an organic compound misused in food to inhibit spoilage, presents significant health risks. Owing to its potential toxicity and carcinogenicity, this substance may induce irreversible damage to the human body. Chen et al. designed an LIG@Ag microscale electrochemical sensor device (LIG@Ag ECSD) for HCHO detection [118]. The LOD of LIG@Ag ECSD is only 0.275 μM, and the sensitivity is 0.363 μA μM⁻¹ cm⁻². Testing with 5 μg/mL HCHO shows a rapid, stable response, while 50 μg/mL CH₃OH, C₂H₂OH, and HCOOH cause no obvious current interference. The recovery rate ranges from 92.9% to 103.5% in NH₃·H₂O solution, indicating that the LIG@Ag ECSD exhibits good accuracy and precision for HCHO detection (Figure 13).

4.3. Detection of Agrochemicals

Agrochemicals protect crops from pests and weeds and enhance yield and quality [119]. However, pesticide and veterinary drug residues in agricultural products pose significant health threats, necessitating their reliable detection. Salicylic acid, which is a phenolic phytohormone used in agriculture, irritates the respiratory and gastrointestinal tracts, skin, and eyes. Chronic exposure to salicylic acid may harm the kidneys, lungs, and skin, whereas environmental contamination affects water, soil, and air. Li et al. developed a disposable LIG-based electrochemical sensor for salicylic acid detection, achieving a sensitivity of 10.99 μA μM⁻¹ and LOD of 0.16 μM [120]. The LIG electrode maintained a stable SA signal even in the presence of higher-concentration interferents, demonstrating robust anti-interference performance. Recovery tests in lettuce and watermelon extracts showed 97.07–100.80% recovery, confirming the practical utility of the sensor. Glyphosate is a widely used herbicide, and its extensive use has resulted in the presence of its residues in the environment and food products. Notably, (aminomethyl)phosphonic acid (AMPA), which is the primary metabolite of glyphosate, is associated with oxidative stress and genotoxicity, and thus is potentially harmful to humans. Zribi et al. immobilized glycine oxidase on transition metal dichalcogenide (MoX₂: MoS₂ or MoSe₂)-functionalized LIG electrodes to create an electrochemical biosensor for glyphosate. Detection at low or negative potentials was found to minimize the interference from endogenous electroactive substances, and sensitivities of 47 nA μM⁻¹ (MoS₂) and 22.8 nA μM⁻¹ (MoSe₂) were achieved within 10–90 μM, with LODs of 4.0 μM and 6.1 μM, respectively. The biosensor retained its response in the mixed presence of 50 μM glyphosate and equal levels of various pesticides plus AMPA, confirming outstanding specificity. Testing in soybeans and pinto beans yielded 81.3–120% recovery compared to the LC-MS results (Figure 14). After five consecutive uses, the sensor signal decays to 81.3–84.2% of its initial value, and electrode cleaning is required to restore performance—this limitation restricts its capability for continuous monitoring [121]. Zhao et al. developed a plant-wearable electrochemical biosensor by functionalizing organophosphorus hydrolase (OPH) on Au nanoparticle-modified flexible LIG/PDMS electrodes and achieved a sensitivity of 2.13 μA (lgμM)⁻¹ and LOD of 0.01 μM for parathion. The lower peak currents observed on spinach leaves and apple surfaces compared to PET film can be attributed to the complex surface composition of agricultural products and the limited penetration of pesticide residues; nevertheless, distinct peak currents are still detectable on both crop surfaces. The validation of this sensor for parathion detection in spinach leaves and apples demonstrated its practical applicability for pesticide residue monitoring. During the detection on real crop surfaces, the signal intensity is significantly lower than that on PET films under ideal conditions. This is due to the complex surface structure of crops and limited pesticide penetration, which affects the quantitative accuracy [122].

4.4. For Agri-Environmental Detection

Soil and irrigation water quality critically affect plant growth [123]. In particular, the accumulation of metal (e.g., Al³⁺ in acidic soils, pH < 5) induces plant stress and inhibits development, necessitating the development of methods for rapid and accurate metal detection. Reyes-Loaiza et al. developed a bismuth-modified LIG electrochemical sensor for Al³⁺ detection using square wave anodic stripping voltammetry. A linear range of 1.07–300 ppm was achieved even in the presence of coexisting Pb²⁺, Cd²⁺, and Cu²⁺. The results obtained from the soil extracts using the electrochemical sensor were in agreement with results obtained by potentiometric titration, ICP-OES, and flame AAS analyses. However, variations in bismuth deposition kinetics may affect the reproducibility of detection results [124]. Additionally, the levels of nitrogen, which is essential for plant growth, are a key indicator of soil fertility. Garland et al. created a flexible LIG-based electrochemical sensor with ion-selective membranes for NH₄⁺ and NO₃⁻ detection, achieving LODs of 28.2 ± 25.0 μM (NH₄⁺) and 20.6 ± 14.8 μM (NO₃⁻) within 10⁻⁵–10⁻¹ M (Figure 15) [125]. Furthermore, testing in a complex sensing matrix (soil) yielded recoveries of 96% for NH₄⁺ and 95% for NO₃⁻, showing performance comparable to that of commercial electrodes by comparing the average baseline, peak, and flush for two cycles, but at a lower cost. Compared with similar devices, the LIG sensor is comparable to or slightly lower than previously reported. Although the electrode meets the requirements for soil detection, it has not yet achieved the highest performance level among similar ion-selective electrodes [125].

Listeria monocytogenes is an important contaminant in hydroponic systems for crops, has been proven to persist for a long time, and causes foodborne illnesses in humans. Cavallaro et al. reported a multi-aptamer biosensor with both aptamer A8 [126] and aptamer LMCA2 [127], which shows superior sensitivity (154 mF log CFU⁻¹ mL), accuracy (lettuce hydroponic water, 86%), and LOD (16 CFU 10 mL⁻¹) compared to the state-of-the-art impedimetric biosensors reported in the literature [128]. The LIG aptasensor for Listeria monocytogenes detection in lettuce hydroponic water exhibits good anti-interference ability in complex samples. However, within the low-concentration range near the LOD, the sensor exhibits limited ability to discriminate between the target bacterium (Listeria monocytogenes) and non-target bacterium (Escherichia coli). In practical complex sample matrices, the reliability of detection results at low concentrations is insufficient, prone to false positive or false negative determinations [128]. Furthermore, the integration of sensors with machine learning enables the analysis of complex impedimetric data, performance optimization, and reduction in interference from hydroponic matrix components. This integration improves identification accuracy, enables real-time interpretation and predictive monitoring, and facilitates the development of intelligent and automated early warning systems for food safety in hydroponics.

5. Conclusions and Perspective

LIG is a novel and simple approach for the rapid preparation of graphene materials as well as three-dimensional structured electrodes. The wide range of possible precursors, moderate preparation conditions, and tunable properties obtained by optimization of the laser scribing parameters have attracted an intense interest in the use of LIG in electrochemical applications. Electrochemical detection using LIG-based sensors facilitates field-deployable, real-time monitoring, thereby addressing the critical needs of chemical detection for food safety and sustainable agriculture. LIG-based electrochemical sensors offer compelling advantages such as low manufacturing costs, operational simplicity, and scalability for miniaturized devices. An increasing number of electrochemical sensors have been reported for various applications, including in the food industry and agriculture. However, the sensors reported in the studies carried out to date show several limitations that must be addressed in future work. Firstly, although several precursors have been explored, most sensors still rely on commercial polymer, particularly polyimide (PI, Table S1). Expanding the repertoire of precursors with diverse chemical compositions and structures is therefore necessary. In particular, heteroatom-doped precursors may offer unique advantages in electrocatalytic applications. In addition, while several factors influencing LIG formation have been identified, the precise control over its structural and functional properties remains unclear. A deeper mechanistic understanding of how laser parameters govern the formation process is essential to achieve tailored performance. Furthermore, although the flexibility of LIG substrates holds promise for wearable devices—as extensively demonstrated in biomedical research [129]—reports on wearable LIG electrochemical sensors for food and agricultural applications remain limited. Other key challenges include improving sensor selectivity and stability in complex matrices, reducing false positives/negatives, and scaling up production without compromising performance. Thus, future efforts, including exploring a wider range of eco-friendly and low-cost precursors, elucidating the detailed formation mechanisms of LIG, and advancing applied sensor development for specific use cases (including wearable formats) with high performance, will be critical for progressing LIG-based electrochemical sensors toward practical, real-world applications.

As a forward-looking perspective, interdisciplinary research that integrates laser-induced graphene (LIG) with microfluidics, artificial intelligence (AI), and machine learning offers a promising pathway to achieve advanced system functionalities such as real-time data interpretation and predictive analytics. Microfluidics—characterized by device miniaturization, low sample consumption, and high throughput—can be seamlessly combined with LIG-based electrochemical sensors, which benefit from in situ fabrication, low cost, and high sensing performance. This synergy provides a powerful platform for the on-site, rapid, and multiplexed detection of analytes in agri-food and environmental monitoring. AI has emerged as a transformative tool in scientific research, with particular relevance to electrochemical analysis due to its ability to process large datasets rapidly and identify subtle patterns in complex systems. These capabilities are crucial for improving detection limits and accuracy, especially in agri-food and environmental applications where samples often exhibit complex matrices and variable composition [130]. Furthermore, as a subset of AI, machine learning leverages computational algorithms to continuously learn and optimize performance. It has been increasingly applied across all stages of electrochemical sensing—from sensor design and fabrication to signal processing, data modeling, and the interpretation of results [131]. Taken together, the amalgamation of LIG-based sensors, microfluidics, AI, and machine learning is poised to drive significant progress in the development of intelligent, sensitive, and field-deployable detection systems for sustainable agri-food and environmental monitoring.