Recent Progress in Photoelectrochemical Sensing of Pesticides in Food and Environmental Samples: Photoactive Materials and Signaling Mechanisms

Pesticides have become an integral part of modern agricultural practices, but their widespread use poses a significant threat to human health. As such, there is a pressing need to develop effective methods for detecting pesticides in food and environmental samples. Traditional chromatography methods and common rapid detection methods cannot satisfy accuracy, portability, long storage time, and solution stability at the same time. In recent years, photoelectrochemical (PEC) sensing technology has gained attention as a promising approach for detecting various pesticides due to its salient advantages, including high sensitivity, low cost, simple operation, fast response, and easy miniaturization, thus becoming a competitive candidate for real-time and on-site monitoring of pesticide levels. This review provides an overview of the recent advancements in PEC methods for pesticide detection and their applications in ensuring food and environmental safety, with a focus on the categories of photoactive materials, from single semiconductor to semiconductor-semiconductor heterojunction, and signaling mechanisms of PEC sensing platforms, including oxidation of pesticides, steric hindrance, generation/decrease in sacrificial agents, and introduction/release of photoactive materials. Additionally, this review will offer insights into future prospects and confrontations, thereby contributing novel perspectives to this evolving domain.

Unveiling the Latest Developments in Molecularly Imprinted Photocatalysts: A State-of-the-Art Review

Responding to the growing concerns about environmental pollutants, scientists are increasingly turning to innovative solutions rooted in the field of environmental science. One such promising avenue combines the robustness of traditional photocatalysis with the precision of molecular imprinting, leading to the proposition of molecularly imprinted photocatalysts (MIPCs). These MIPCs hold the potential to specifically target and eliminate environmental pollutants, marking them as a promising tool in modern environmental remediation. As researchers delve deeper into this field, the design and optimization of MIPCs have become hotbeds for scientific inquiry. This comprehensive overview delves into the multifaceted approaches to MIPC design, elucidating on aspects like the selection of appropriate photocatalytic bases, the pivotal role of templates, the choice of monomeric building blocks, and the integration of effective cross-linking agents. However, as with all burgeoning technologies, the development of MIPCs is not without its challenges. These potential impediments to the successful innovation and implementation of MIPCs are also explored.

Precisely Navigated Biobot Swarms of Bacteria Magnetospirillum magneticum for Water Decontamination

Hybrid biological robots (biobots) prepared from living cells are at the forefront of micro-/nanomotor research due to their biocompatibility and versatility toward multiple applications. However, their precise maneuverability is essential for practical applications. Magnetotactic bacteria are hybrid biobots that produce magnetosome magnetite crystals, which are more stable than synthesized magnetite and can orient along the direction of earth's magnetic field. Herein, we used Magnetospirillum magneticum strain AMB-1 (M. magneticum AMB-1) for the effective removal of chlorpyrifos (an organophosphate pesticide) in various aqueous solutions by naturally binding with organic matter. Precision control of M. magneticum AMB-1 was achieved by applying a magnetic field. Under a programed clockwise magnetic field, M. magneticum AMB-1 exhibit swarm behavior and move in a circular direction. Consequently, we foresee that M. magneticum AMB-1 can be applied in various environments to remove and retrieve pollutants by directional control magnetic actuation.

Recent advances in electrochemical and optical sensing of the organophosphate chlorpyrifos: a review

Chlorpyrifos (CP) is one of the most popular organophosphorus pesticides that is commonly used in agricultural and nonagricultural environments to combat pests. However, several concerns regarding contamination due to the unmitigated use of chlorpyrifos have come up over recent years. This has popularized research on various techniques for chlorpyrifos detection. Since conventional methods do not enable smooth detection, the recent trends of chlorpyrifos detection have shifted toward electrochemical and optical sensing techniques that offer higher sensitivity and selectivity. The objective of this review is to provide a brief overview of some of the important and innovative contributions in the field of electrochemical and optical sensing of chlorpyrifos with a primary focus on the comparative advantages and shortcomings of these techniques. This review paper will help to offer better perspectives for research in organophosphorus pesticide detection in the future.

Thioglycolic acid-modified AuNPs as a colorimetric sensor for the rapid determination of the pesticide chlorpyrifos

Herein, we report the preparation of a gold nanoparticle-thioglycolic acid (TGA@AuNP) suspension for the label-free colorimetric detection of the organophosphorus pesticide chlorpyrifos. This colorimetric sensor was synthesized by a one-pot method, providing thioglycolic acid (TGA)-modified gold nanoparticles with a negatively charged surface. The formation of TGA@AuNPs was confirmed by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and dynamic light scattering (DLS). In addition, chlorpyrifos was quantitatively determined by UV-vis spectrophotometry. The modification time, TGA concentration, pH, incubation time, temperature, ionic strength, and interference of other pesticides were also investigated. The synthesized TGA@AuNP colorimetric sensor possesses a detection limit as low as 20 μg L^-1 and a selective sensing response, and the detection time is less than 2 minutes. In addition, this method can also be applied to detect various practical samples in life, such as environmental water samples and tea.

Molecularly Imprinted Polymers (MIPs) in Sensors for Environmental and Biomedical Applications: A Review

Molecular imprinted polymers are custom made materials with specific recognition sites for a target molecule. Their specificity and the variety of materials and physical shapes in which they can be fabricated make them ideal components for sensing platforms. Despite their excellent properties, MIP-based sensors have rarely left the academic laboratory environment. This work presents a comprehensive review of recent reports in the environmental and biomedical fields, with a focus on electrochemical and optical signaling mechanisms. The discussion aims to identify knowledge gaps that hinder the translation of MIP-based technology from research laboratories to commercialization.

Highly Sensitive and Selective Photoelectrochemical Aptasensors for Cancer Biomarkers Based on MoS2/Au/GaN Photoelectrodes

An Au/GaN photoelectrode was prepared by sputtering 30 nm thick Au film on the surface of n-type gallium nitride (GaN). When the electrode contacts with multilayered molybdenum disulfide (MoS₂), photogenerated electrons and photogenerated holes transfer to MoS₂ because of the band gap matching of MoS₂ and GaN. The presence of Au promotes charge transfer and results in a greater recombination of electrons and holes; by this means, a more significant suppression of photocurrent can be detected. This characteristic has been coupled with the high selectivity of an aptamer and applied to develop a novel photoelectrochemical aptasensor for cancer biomarkers (alpha-fetoprotein (AFP) as a model). The aptamer of AFP was modified on the surface of the Au/GaN photoelectrode by Au-S bonds, which can bind to the target protein with high selectivity. Then, the transfer process of the charge carriers of GaN to MoS₂ can be blocked by the target protein so that the suppression of photocurrent is reduced. The difference of the photocurrent in the presence and absence of AFP (ΔI) showed a linear relationship with AFP concentration that ranged from 1.0-150 ng/mL (R² = 0.9995), and the detection limit was 0.3 ng/mL. The standard addition recovery rates ranged from 85.2 to 91.7%. The method possessed good sensitivity and high selectivity for AFP detection. The developed biosensor can be modified to detect other cancer biomarkers by simply replacing the aptamer used.

Electrochemical aptasensor based on Mo2C/Mo2N and gold nanoparticles for determination of chlorpyrifos

Two-dimensional Mo₂C/Mo₂N composites were synthesized by high temperature ball milling and used as support materials for fabricating a chlorpyrifos (CPF) aptasensor. Gold nanoparticles (Au NPs) were electrodeposited on the surface of a Mo₂C/Mo₂N-modified electrode to connect with the ferrocene (Fc) probe via Au-S bonds. The Fc probe can hybridize with the aptamer probe to form a double-stranded structure. The addition of CPF made the double strands melt and the Fc probe approached the surface of the electrode, thereby resulting in amplification of the electrochemical response. The current response of the aptasensor for detecting CPF in solutions linearly varied from 0 to 400 ng mL^-1 (with a maximum at 0.98 V vs. Ag/AgCl). The Au NPs/Mo₂C/Mo₂N composites exhibited satisfactory electrochemical behavior due to their excellent electrical conductivity and large surface area. This ultrasensitive aptasensor showed a low limit of detection of 0.036 ng mL^-1. It was applied to determine CPF in real samples with acceptable recoveries from 94.7 to 116.7%, and the relative standard deviation was from 2.57 to 7.08%.Graphical abstract Schematic diagram of the manufacturing process of the aptasensor. Electrochemical aptasensor based on Mo₂C/Mo₂N/Au NP composites show excellent performance in detecting CPF.

Mesoporous MIP-capped luminescent MOF as specific and sensitive analytical probe: application for chlorpyrifos

Specific recognition of organophosphate pesticides (OPs) is a significant challenge for analytical researchers. Herein, surface imprinted terbium-based luminescent metal-organic framework (MOF-76) are presented as a highly specific probe for the measurement of chlorpyrifos (CP). A mesoporous molecular imprinted polymer (mMIP) layer was generated on the surface of nano-sized MOF-76 using CP, as template. The resulting mMIP-capped MOF-76 (mMIP@MOF-76) contained specific sites for adsorption of CP molecules, guaranteeing the selectivity of the designed probe. The high porosity of rod-shape MOF-76, as well as the mesoporous structure of the MIP layer improved the diffusion process and caused the high sensitivity of the probe. The detection process is based on the remarkable quenching effect of CP on the fluorescence emission of mMIP@MOF-76. Plotting the CP concentration against the fluorescence intensity (λ_ex = 285 nm and λ_em = 544 nm) gave a linear curve in the concentration range 10-1000 ng mL^-1 CP, with 3.41 ng mL^-1 limit of detection. The designed probe was utilized for CP determination in fruit juice and environmental samples. The combination of the stable MOF-based support, as well as its remarkable fluorescence features and specific MIP sites, led to a highly selective and ultrasensitive detection system.Graphical abstract.

Highly Sensitive and Selective Photoelectrochemical Aptasensor for Cancer Biomarker CA125 Based on AuNPs/GaN Schottky Junction

A gold nanoparticle (AuNPs)/gallium nitride (GaN) Schottky junction was fabricated by growing AuNPs in situ on the surface of GaN and then etched by H₂O₂ to appropriate diameter. The photogenerated electrons of GaN can be captured and transferred by the AuNPs to increase the migration efficiency, and the electron-hole pairs were separated, which results in the enhancement of the photoelectric performance of the system. The Fermi energy level of AuNPs and the charge transfer efficiency of the AuNPs/GaN can be adjusted by controlling the size of the AuNPs. Then the AuNPs/GaN Schottky photoelectrode had been applied to develop a novel photoelectrochemical (PEC) aptasensor for the epithelial ovarian cancer marker-CA125 detection. The DNA aptamer of CA125 was modified on the surface of the AuNPs via Au-S bonds. The aptamer can bind with the target with high selectivity, and the photoelectron transfer process of the system can be blocked by the protein, which results in the decrease of the photocurrent of the system. The ratio of photocurrent before and after incubation with CA125 (I₁/I₀) has a linear with the concentration of CA125 in the range of 1-100 U/mL with a detection limit of 0.3 U/mL. The standard addition recovery rates were between 86.01% and 90.09%. This method showed good sensitivity, selectivity, and reliability in detecting CA125 in serum.

Functional polymers in photoelectrochemical biosensing

Photoelectrochemical (PEC) analysis is a detection technique that has gained a wide attention in sensing applications. PEC presents the advantages of high sensitivity, low background signal, simple equipment and easy miniaturization. In PEC detection, light is used as an excitation source while current or voltage is measured as the output detection signal. The ability to couple the PEC process with specific bioreceptors gives PEC biosensing a unique advantage of being both selective and sensitive. The growing interest in PEC bioanalysis has resulted in essential progress in its analytical performance and biodetection applications. Functional polymers have different applications in the development of novel PEC biosensing platforms. Recently, the interest in polymer-based photoactive materials has emerged as they are efficient and less toxic alternatives to certain kinds of inorganic semiconductors and sensitizers. Moreover, molecularly imprinted polymers are a class of synthetic bioreceptors that are increasingly used in PEC bioanalytics. In this review, we will provide an overview on functional polymer-based PEC biosensing approaches. Novel classes of polymers as photoactive materials are reviewed and selected applications are described. Furthermore, molecularly imprinted polymers in the development of smart and sensitive PEC bioanalytical strategies are discussed.

A visible-light-driven photoelectrochemical molecularly imprinted sensor based on titanium dioxide nanotube arrays loaded with silver iodide nanoparticles for the sensitive detection of benzoyl peroxide

A novel ultrasensitive photoelectrochemical sensor for benzoyl peroxide (BPO) was constructed under visible light irradiation.

Ultrasensitive label- and amplification-free photoelectric protocols based on sandwiched layer-by-layer plasmonic nanocomposite films for the detection of alpha-fetoprotein

A label- and amplification-free photoelectric immunosensor based on well-defined layer-by-layer sandwich-structured AuNP/TNW/AuNP composite is proposed for direct and ultrasensitive detection of α-fetoprotein (AFP). The AuNP/TNW/AuNP composite is produced by assembling an Au nanoparticle underlayer and anatase TiO₂ nanowires (TNW) onto the FTO substrate, followed by decorating Au nanoparticles onto the TNW surface, through a simple sputtering and hydrothermal process. The resulting AuNP/TNW/AuNP electrode exhibits a 14-fold and 2-fold enhancement in photocurrent density under simulated sunlight compared with that of bare TNW and AuNP/TNW, respectively, which benefits from the SPR-induced photoabsorption increment and charge separation improvement in Au nanoparticle and interfacial charge transfer promotion at the TiO₂/substrate interface in the Au underlayer. As a proof of concept, the AFP antigen can be quantitatively detected by the proposed AuNP/TNW/AuNP coupled with anti-AFP through the analysis of the photocurrent change. This novel AFP photoelectric immunosensor exhibited sensitive detection of AFP with an ultrahigh sensitivity of 0.001 ng mL^-1 and good specific selectivity. Moreover, the practical determination of AFP in human serum is also investigated, demonstrating its applicability and potential attraction for clinical tests and disease diagnosis.

Synthesis and Applications of Molecularly Imprinted Polymers Modified TiO₂ Nanomaterials: A Review

Titanium dioxide (TiO₂) nanomaterials have caused a widespread concern in the past several decades for their bulk characteristics and potential applications in many different areas. Lately, the combination between molecularly imprinted polymers (MIPs) and TiO₂ nanomaterials have been proven to improve the relative adsorption capacity, selectivity and accelerate the rate of mass transfer of analyte which is not possible using TiO₂ alone. Considering the unique performance of the MIPs modified TiO₂ nanomaterials, this review intends to give an overview of the recent progresses in the development of MIPs modified TiO₂ nanomaterials, the potential applications of their tailor-made characteristics. The limitations and challenges in this practically promising nanomaterials have also been raised and summarized. By means of the points raised in this article, we would like to provide some assistance for further development of preparation methodologies and the expansion of some potential applications in the field of MIPs modified TiO₂ nanomaterials.

Current Progress of Nanomaterials in Molecularly Imprinted Electrochemical Sensing

Nanomaterials have received much attention during the past decade because of their excellent optical, electronic, and catalytic properties. Nanomaterials possess high chemical reactivity, also high surface energy. Thus, provide a stable immobilization platform for biomolecules, while preserving their reactivity. Due to the conductive and catalytic properties, nanomaterials can also enhance the sensitivity of molecularly imprinted electrochemical sensors by amplifying the electrode surface, increasing the electron transfer, and catalyzing the electrochemical reactions. Molecularly imprinted polymers that contain specific molecular recognition sites can be designed for a particular target analyte. Incorporating nanomaterials into molecularly imprinted polymers is important because nanomaterials can improve the response signal, increase the sensitivity, and decrease the detection limit of the sensors. This study describes the classification of nanomaterials in molecularly imprinted polymers, their analytical properties, and their applications in the electrochemical sensors. The progress of the research on nanomaterials in molecularly imprinted polymers and the application of nanomaterials in molecularly imprinted polymers is also reviewed.

Near-Infrared Light-Driven Photoelectrochemical Aptasensor Based on the Upconversion Nanoparticles and TiO2/CdTe Heterostructure for Detection of Cancer Cells

A near-infrared-driven photoelectrochemical aptasensor was developed as a new method for the detection of the breast cancer cell MCF-7. The upconversion nanoparticles and TiO₂/CdTe heterostructure were combined to prepare the film electrode, and the high-affinity aptamer AS1411 was conjugated to the electrode to recognize MCF-7 cells. In this fabrication, the upconversion nanoparticles transferred the near-infrared light to visible light, which could excite the semiconductor to enhance the current response. As a result, the aptasensor revealed good sensitivity and specificity with MCF-7 cell concentrations ranging from 1 × 10³ to 1 × 10⁵ cells/mL. The results presented a favorable determination of MCF-7 cells, which was achieved with the help of the upconversion nanoparticles and the photoelectrochemical interface.

Cadmium Sulphide-Reduced Graphene Oxide-Modified Photoelectrode-Based Photoelectrochemical Sensing Platform for Copper(II) Ions

A photoelectrochemical (PEC) sensor with excellent sensitivity and detection toward copper (II) ions (Cu²⁺) was developed using a cadmium sulphide-reduced graphene oxide (CdS-rGO) nanocomposite on an indium tin oxide (ITO) surface, with triethanolamine (TEA) used as the sacrificial electron donor. The CdS nanoparticles were initially synthesized via the aerosol-assisted chemical vapor deposition (AACVD) method using cadmium acetate and thiourea as the precursors to Cd²⁺ and S^2-, respectively. Graphene oxide (GO) was then dip-coated onto the CdS electrode and sintered under an argon gas flow (50 mL/min) for the reduction process. The nanostructured CdS was adhered securely to the ITO by a continuous network of rGO that also acted as an avenue to intensify the transfer of electrons from the conduction band of CdS. The photoelectrochemical results indicated that the ITO/CdS-rGO photoelectrode could facilitate broad UV-visible light absorption, which would lead to a higher and steady-state photocurrent response in the presence of TEA in 0.1 M KCl. The photocurrent decreased with an increase in the concentration of Cu²⁺ ions. The photoelectrode response for Cu²⁺ ion detection had a linear range of 0.5–120 μM, with a limit of detection (LoD) of 16 nM. The proposed PEC sensor displayed ultra-sensitivity and good selectivity toward Cu²⁺ ion detection.

Localized-surface-plasmon-enhanced multifunction silicon nanomembrane Schottky diodes based on Au nanoparticles

Au nanoparticle (NP)-modified Si nanomembrane (Si NM) Schottky barrier diodes (SBDs) were fabricated by using a transfer-printing method to create pedestals using only one photomask on a flexible substrate. The transfer using the pedestals afforded a yield of >95% with no significant cracks. The plasmonic Au NPs can facilitate the improvement of the incident optical absorption. The Au NP-modified Si NM SBD exhibited enhanced photoresponse characteristics with an external quantum efficiency (η(EQE)) of 34%, a photosensitivity (P) of 27 at a voltage bias of -5 V, a light intensity of 1.2 W cm(-2), and a responsivity (R(ph)) of 0.21 A W(-1). Additionally, the mechanical bending characteristics of the device were observed while a compressive strain up to 0.62% was applied to the diode. The results suggest that the Au NP-modified Si NM SBD has great potential for use in multifunction devices as a strain sensor and photosensor.

"Signal-on" photoelectrochemical biosensor for sensitive detection of human T-Cell lymphotropic virus type II DNA: dual signal amplification strategy integrating enzymatic amplification with terminal deoxynucleotidyl transferase-mediated extension

A novel "signal-on" photoelectrochemical (PEC) biosensor for sensitive detection of human T-cell lymphotropic virus type II (HTLV-II) DNA was developed on the basis of enzymatic amplification coupled with terminal deoxynucleotidyl transferase (TdT)-mediated extension strategy. The intensity of the photocurrent signal was proportional to the concentration of the HTLV-II DNA-target DNA (tDNA) by dual signal amplification. In this protocol, GR-CdS:Mn/ZnS nanocomposites were used as photoelectric conversion material, while pDNA was used as the tDNA recognizing unit. Moreover, the TdT-mediated extension and the enzymatic signal amplification technique were used to enhance the sensitivity of detection. Using this novel dual signal amplification strategy, the prototype of PEC DNA sensor can detect as low as ∼0.033 fM of HTLV-II DNA with a linear range of 0.1-5000 fM, with excellent differentiation ability even for single-base mismatches. This PEC DNA assay opens a promising platform to detect various DNA targets at ultralow levels for early diagnoses of different diseases.

N-doped TiO2 based visible light activated label-free photoelectrochemical biosensor for detection of Hg(2+) through quenching of photogenerated electrons

A novel photoelectrochemical (PEC) biosensor was fabricated based on N-doped TiO2 for the detection of Hg(2+) through the quenching of photogenerated electrons. The N-doped TiO2 was synthesized by a sol-gel method with urea and tetrabutyl titanate as the N and Ti sources. Compared with the undoped TiO2, the N-doped TiO2 showed an enhanced photocurrent response under visible light (λ > 420 nm). The sensing surface was functionalized with 5'-amino-modified T-rich oligonucleotides. The photoelectrochemical biosensor bound Hg(2+) on the surface by a highly specific T-Hg(2+)-T recognition. Hg(2+) on the surface of the N-doped TiO2 film withdrew the photogenerated electrons and decreased the recorded current signal. The dynamic linear range for Hg(2+) has been determined to be as low as 2-6 μM.

Simple synthesis and photoelectrochemical characterizations of polythiophene/Pd/TiO2 composite microspheres

We report here a simple, effective, and low cost method to synthesize polythiophene/Pd/TiO2 (PTh/Pd/TiO2) ternary composite microspheres and apply such a composite to photoelectrochemical (PEC) sensing. TiO2 spherical aggregates of 200 nm diameter, consisting of nanoscale building blocks of TiO2, have been prepared by hydrolysis of tetrabutyl titanate in a water-in-oil emulsion system (Vwater/Vacetone=1/100). Pd species and PTh layer were decorated onto TiO2 microspherical substrates by reduction of Pd salts and polymerization of thiophene, respectively. The high surface area, effective charge transfer, and enhanced light absorption of the ternary composite could improve PEC performance under simulated sunlight. The sensitivity, selectivity, and stability of PEC sensor for detecting l-cysteine were much higher than those of the traditional electrochemical sensor. The detection limit of l-cysteine was 9.24 μM in the linear range of 0.31-5.30 mM. Moreover, the results also indicated a good anti-interference and acceptable accuracy in practical application, providing a rapid and sensitive detection method.

Metal/Semiconductor hybrid nanostructures for plasmon-enhanced applications

Hybrid nanostructures composed of semiconductor and plasmonic metal components are receiving extensive attention. They display extraordinary optical characteristics that are derived from the simultaneous existence and close conjunction of localized surface plasmon resonance and semiconduction, as well as the synergistic interactions between the two components. They have been widely studied for photocatalysis, plasmon-enhanced spectroscopy, biotechnology, and solar cells. In this review, the developments in the field of (plasmonic metal)/semiconductor hybrid nanostructures are comprehensively described. The preparation of the hybrid nanostructures is first presented according to the semiconductor type, as well as the nanostructure morphology. The plasmonic properties and the enabled applications of the hybrid nanostructures are then elucidated. Lastly, possible future research in this burgeoning field is discussed.

Nanostructured photoelectrochemical biosensor for highly sensitive detection of organophosphorous pesticides

A sensitive photoelectrochemical (PEC) biosensor for detection of organophosphorus pesticides (OPs) using the nanocomposite of CdSe@ZnS quantum dots (QDs) and graphene deposited on the ITO coated glass electrode as a photoactive electrode is presented. The integration of CdSe@ZnS/graphene nanocomposite with biomolecules acetylcholinesterase (AChE) as a biorecognition element yields a novel biosensing platform. Under visible light irradiation, the AChE-CdSe@ZnS/graphene nanocomposite can generate a stable photocurrent and the photocurrent is found to be inversely dependent on the concentration of OPs. Under the optimal experimental conditions, the photocurrents were proportional to the logarithm of paraoxon and dichlorvos within the concentration range of 10(-12)-10(-6) M. The detection limits (LOD) of the proposed biosensor for paraoxon and dichlorvos are as low as 10(-14) M and 10(-12) M. The photoelectrochemical biosensor shows good sensitivity, reproducibility, stability, and could be successfully applied to detection of OPs in real fruit samples.

Highly photoactive heterojunction based on g-C3N4 nanosheets decorated with dendritic zinc(ii) phthalocyanine through axial coordination and its ultrasensitive enzyme-free sensing of choline

A highly photoactive heterojunction based on g-C₃N₄ and dendritic zinc(ii) phthalocyanine was proposed for the ultrasensitive detection of choline.