Construction of an impedimetric immunosensor for label-free detecting carbofuran residual in agricultural and environmental samples

Enhancing Sensitivity and Selectivity: Current Trends in Electrochemical Immunosensors for Organophosphate Analysis

This review examines recent advancements in electrochemical immunosensors for the detection of organophosphate pesticides, focusing on strategies to enhance sensitivity and selectivity. The widespread use of these pesticides has necessitated the development of rapid, accurate, and field-deployable detection methods. We discuss the fundamental principles of electrochemical immunosensors and explore innovative approaches to improve their performance. These include the utilization of nanomaterials such as metal nanoparticles, carbon nanotubes, and graphene for signal amplification; enzyme-based amplification strategies; and the design of three-dimensional electrode architectures. The integration of these sensors into microfluidic and lab-on-a-chip devices has enabled miniaturization and automation, while screen-printed and disposable electrodes have facilitated on-site testing. We analyze the challenges faced in real sample analysis, including matrix effects and the stability of biological recognition elements. Emerging trends such as the application of artificial intelligence for data interpretation and the development of aptamer-based sensors are highlighted. The review also considers the potential for commercialization and the hurdles that must be overcome for widespread adoption. Future research directions are identified, including the development of multi-analyte detection platforms and the integration of sensors with emerging technologies like the Internet of Things. This comprehensive overview provides insights into the current state of the field and outlines promising avenues for future development in organophosphate pesticide detection.

Development of a Portable Cell-Based Biosensor for the Ultra-Rapid Screening for Boscalid Residues in Lettuce

Fungal plant pathogens have posed a significant threat to crop production. However, the large-scale application of pesticides is associated with possible risks for human health and the environment. Boscalid is a widely used fungicide, consistently implemented for the management of significant plant pathogens. Conventionally, the detection and determination of boscalid residues is based on chromatographic separations. In the present study, a Bioelectric Recognition Assay (BERA)-based experimental approach combined with MIME technology was used, where changes in the electric properties of the membrane-engineering cells with anti-boscalid antibodies were recorded in response to the presence of boscalid at different concentrations based on the maximum residue level (MRL) for lettuce. The membrane-engineering Vero cells with 0.5 μg/mL of antibody in their surface were selected as the best cell line in combination with the lowest antibody concentration. Furthermore, the biosensor was tested against another fungicide in order to prove its selectivity. Finally, the BERA cell-based biosensor was able to detect the boscalid residue, below and above the MRL, in spiked lettuce leaf extracts in an entirely distinct and reproducible manner. This study indicates that the BERA-based biosensor, after further development and optimization, could be used for the routine, high-throughput detection of boscalid residue in lettuce, and not only that.

Production and Selection of Antibody–Antigen Pairs for the Development of Immunoenzyme Assay and Lateral Flow Immunoassay Methods for Carbofuran and Its Analogues

To produce a sensitive monoclonal antibody (mAb) for the simultaneous detection of carbofuran, benfuracarb, carbosulfan and 3-hydroxy-carbofuran, 2,3-dihydro-2,2-dimethyl-7-benzofuranmethanamine (DDB) was conjugated to bovine serum albumin (BSA) to prepare the immunogen DDB-BSA and mice were immunized. Coating antigens were prepared by conjugating DDB and 5-methoxy-2,3-dihydrobenzofuran-3-acetic acid (MDA) to BSA and ovalbumin (OVA), respectively. Furthermore, the effect of different antibody–antigen pairs on the sensitivity of ELISA and LFIA methods for the detection of carbofuran was investigated. After the immunization, a high-affinity mAb 13C8 was obtained. The ability of the coating antigen to compete with carbofuran for binding antibodies was found to be significantly different between ELISA and LFIA methods. With the antibody–antigen pair 13C8-MDA-OVA, the IC₅₀ values of the ELISA and QD-LFIA methods for carbofuran were 0.18 ng/mL and 0.67 ng/mL, respectively. The cross-reactivity (CR) values of the two methods for benfuracarb, carbosulfan and 3-hydroxy-carbofuran ranged from 72.0% to 83.7%, while, for other carbamate pesticides, the CR values were less than 1%. The spiked recoveries of carbofuran in vegetables by the QD-LFIA method were 83–111%, with a coefficient of variation below 10%, and the test results of the actual samples were consistent with the HPLC-MS method. Overall, this study provides key materials for the development of immunoassays for carbofuran and its analogues, and the antibody–antigen pair selection strategy established in this study provides useful insights for the development of sensitive immunoassays for other compounds.

Electroactive reduced graphene oxide for highly sensitive detection of secretory non-structural 1 protein: A potential diagnostic biomarker for Japanese encephalitis virus

Fluorine Doped Tin Oxide (FTO) electrode was fabricated with reduced Graphene Oxide (rGO) for sensitive detection of Japanese encephalitis virus (JEV) non-structural 1 (NS1) protein. Beforehand, in-silico 3D structure, stability, and docking of recombinant JEV NS1 antigen (NS1-Ag) and antibody (Ab) was evaluated. The recombinant NS1 Ag of 42 kDa was produced in-house by successful cloning into pET-28a(+) plasmid and further expressed using BL21 Escherichia coli (E. coli) cells. The NS1 Ag was used to raise polyclonal antibodies (Ab) and both were characterized via Sodium Dodecyl Sulphate Polyacrylamide Gel Electrophoresis (SDS-PAGE), Western Blot, Matrix-Assisted Laser Desorption/Ionization-Time of Flight (MALDI-TOF), and Enzyme-Linked Immunosorbent Assay (ELISA). Further characterisation of all binding events such as rGO synthesis, and its conjugation with NS1 Ab, and NS1 Ag were confirmed through Fourier-Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, Energy Dispersive X-Ray Analysis (EDX), Scanning Electron Microscopy (SEM), Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV). The fabricated FTO electrode was optimised for various parameters such as pH, response time, temperature, concentration, and scan rate. The detection of JEV NS1 Ag was performed in buffer (LOD- 0.92 fM) as well in spiked serum (LOD- 1.3 fM) samples. The JEV NS1 Ab showed negligible cross-reactivity with other flaviviral NS1 Ag, provided a rapid response within 5 s, and remained stable up to 4 weeks. Furthermore, the fabricated immunosensor may be a potential candidate for further miniaturisation for accurate and early diagnosis of JEV in clinical samples.

Waveguide-Based Fluorescent Immunosensor for the Simultaneous Detection of Carbofuran and 3-Hydroxy-Carbofuran

Carbofuran (CBF) is an efficient and broad-spectrum insecticide. As testing indicators for water quality and agricultural products, CBF and its metabolite 3-hydroxy-carbofuran (3-OH-CBF) are regulated by many countries. The detection of CBF and 3-OH-CBF is of great importance for the environment and human health. However, an immunosensor detection method for the simultaneous analysis of CBF and 3-OH-CBF remains unavailable. Herein, we report a waveguide-based fluorescent immunosensor for detecting CBF and 3-OH-CBF, synchronously. The immunosensor is based on a broad-spectrum monoclonal antibody with high binding affinity against CBF and 3-OH-CBF. The linear detection ranges for CBF and 3-OH-CBF are 0.29-2.69 and 0.12-4.59 μg/L, with limits of detection of 0.13 μg/L for CBF and 0.06 μg/L for 3-OH-CBF, respectively. The whole detection process for each cycle is approximately 30 min. The results show a good application prospect for the rapid detection of CBF and 3-OH-CBF in water or agricultural products.

Application of Immunoassays for Rapid Monitor of Carbofuran Residue in Vegetables

Carbofuran residue in vegetables is a concern to human health. Direct competitive enzyme-linked immunosorbent assay (dcELISA) and dipstick immunoassay were developed in the present study. The dcELISA showed a 50% inhibition concentration (IC₅₀ ) and working range of 1.3 and 0.2 to 7.5 ng/mL, respectively, while the cutoff value of dipstick immunoassay was 20 ng/mL. Applying the two immunoassays, we achieved the goal of rapid screening of carbofuran residue in commercial vegetables with a simple sample processing method. Among 46 leek, 39 potato, and 39 sweet potato samples, carbofuran residue was detected in 22% of the leek samples, and two samples exceeded the maximum residue limit of China (0.02 mg/kg). In addition, carbofuran residue was found at less than 2.5 ng/g in one potato and one sweet potato samples. The residual level of carbofuran measured by immunoassays agreed well with those determined by ultra-performance liquid chromatography tandem mass spectrometry. To ensure food safety and human health, it is greatly necessary and meaningful to monitor carbofuran residue in commercial vegetables. PRACTICAL APPLICATION: Rapid monitoring of carbofuran residue in vegetables is very necessary and important for consumers, regulatory agencies, and food industry.

Development of a Simple Pretreatment Immunoassay Based on an Organic Solvent-Tolerant Nanobody for the Detection of Carbofuran in Vegetable and Fruit Samples

Nanobodies are one-tenth the size of conventional antibodies and are naturally obtained from the atypical heavy-chain-only antibodies present in camelids. Their small size, high solubility, high stability, and strong resilience to organic solvents facilitate their use as novel analytical reagents in immunochemistry. In this study, specific nanobodies against pesticide carbofuran were isolated and characterized from an immunized library via phage display platform. We further established an indirect competitive enzyme-linked immunosorbent assay (ELISA) using nanobody Nb316 to detect carbofuran in vegetable and fruit samples. The results showed a half-maximal inhibitory concentration (IC₅₀) of 7.27 ng/mL and a detection limit of 0.65 ng/mL. A simplified sample pretreatment procedure omitting the evaporation of organic solvent was used. The averaged recovery rate of spiked samples ranged between 82.3% and 103.9%, which correlated with that of standard UPLC–MS/MS method. In conclusion, a nanobody with high specificity for carbofuran was characterized, and a nanobody-based sensitive immunoassay for simple and rapid detection of carbofuran in real samples was validated.

Advances in electrochemical immunosensors

Immunosensors are compact tools on which antibody and antigen interactions are formed. The specific interaction between antibody and antigen is detected by using a transducer and an electrical signal is measured. This specific interaction between these molecules makes immunosensor very attractive for several applications in different fields. Electrochemical immunosensors are successful devices in selective and sensitive detection of several analytes. Electrochemical transducing methods such as voltammetric, potentiometric, conductometric or impedimetric have been utilized in different applications due to their excellent properties such as being low-cost, sensitivity and simplicity. In this chapter, the fundamentals of electrochemical immunosensors are summarized and different applications in food, environmental and clinical analyses are investigated and discussed.

Trends and Perspectives in Immunosensors for Determination of Currently-Used Pesticides: The Case of Glyphosate, Organophosphates, and Neonicotinoids

Pesticides, due to their intensive use and their peculiar chemical features, can persist in the environment and enter the trophic chain, thus representing an environmental risk for the ecosystems and human health. Although there are several robust and reliable standard analytical techniques for their monitoring, the high frequency of contamination caused by pesticides requires methods for massive monitoring campaigns that are capable of rapidly detecting these compounds in many samples of different origin. Immunosensors represent a potential tool for simple, rapid, and sensitive monitoring of pesticides. Antibodies coupled to electrochemical or optical transducers have resulted in effective detection devices. In this review, the new trends in immunosensor development and the application of immunosensors for the detection of pesticides of environmental concern-such as glyphosate, organophosphates, and neonicotinoids-are described.

Microfluidic-based graphene field effect transistor for femtomolar detection of chlorpyrifos

Chlorpyrifos is one of the most widely used pesticides that acts on the nervous system by inhibiting acetylcholinesterase. Prolonged use of chlorpyrifos causes severe neurological, autoimmune, and persistent developmental disorders in humans. Therefore, in this study, a highly sensitive and robust biosensor platform was devised by fabricating graphene field effect transistors (graFET) on Si/SiO2 substrate for the detection of chlorpyrifos in real samples. Anti-chlorpyrifos antibodies were immobilized successfully on the graphene surface. Under optimal conditions, graFET sensor showed an excellent response for chlorpyrifos detection in the linear range of 1 fM to 1 µM with a limit of detection up to 1.8 fM in spiked samples. The developed graFET biosensor is highly stable, sensitive, and specific for chlorpyrifos as confirmed by its significant ability to detect changes in electrostatic potential. These findings signify useful efficacy of immunobiosensors for the detection of chlorpyrifos and other organophosphates in fruits and vegetables.

Affinity Sensing Strategies for the Detection of Pesticides in Food

This is a review of recent affinity-based approaches that detect pesticides in food. The importance of the quantification and monitoring of pesticides is firstly discussed, followed by a description of the different approaches reported in the literature. The different sensing approaches are reported according to the different recognition element used: antibodies, aptamers, or molecularly imprinted polymers. Schemes of detection and the main features of the assays are reported and commented upon. The large number of affinity sensors recently developed and tested on real samples demonstrate that this approach is ready to be validated to monitor the amount of pesticides used in food commodities.

Sensitive and selective detection of the highly toxic pesticide carbofuran in vegetable samples by a molecularly imprinted electrochemical sensor with signal enhancement by AuNPs

An imprinted electrochemical sensor was constructed for the detection of carbofuran with high sensitivity and selectivity. AuNPs were used as the electron wire for signal amplification, and molecularly imprinted polymer was used as the recognition element. The preparation process of the modified electrode was optimized, and the electrode was characterized using scanning electron microscopy, cyclic voltammetry and differential pulse voltammetry. The results proved that the prepared sensor can selectively detect carbofuran and the AuNPs can increase its sensitivity. The method validation included the systematic evaluation of the linearity, sensitivity, selectivity, reproducibility and stability. The optimized sensor showed a wide linear response to carbofuran in the range from 5.0 × 10⁻⁸ to 4.0 × 10⁻⁴ mol L⁻¹ with a low detection limit of 2.4 × 10⁻⁸ mol L⁻¹. The sensor also exhibited a high selectivity to carbofuran. The real sample analysis for vegetable samples suggested its potential application in the analysis of vegetable samples.

An imprinted electrochemical sensor was constructed for the detection of carbofuran with high sensitivity and selectivity.

Electrochemical immunosensors - A powerful tool for analytical applications

Immunosensors are biosensors based on interactions between an antibody and antigen on a transducer surface. Either antibody or antigen can be the species immobilized on the transducer to detect antigen or antibody, respectively. Because of the strong binding forces between these biomolecules, immunosensors present high selectivity and very high sensitivity, making them very attractive for many applications in different science fields. Electrochemical immunosensors explore measurements of an electrical signal produced on an electrochemical transductor. This signal can be voltammetric, potentiometric, conductometric or impedimetric. Immunosensors utilizing electrochemical detection have been explored in several analyses since they are specific, simple, portable, and generally disposable and can carry out in situ or automated detection. This review addresses the potential of immunosensors destined for application in food and environmental analysis, and cancer biomarker diagnosis. Emphasis is given to the approaches that have been used for construction of electrochemical immunosensors. Additionally, the fundamentals of immunosensors, technology of transducers and nanomaterials and a general overview of the possible applications of electrochemical immunosensors to the food, environmental and diseases analysis fields are described.

An ultrasensitive electrochemical immunosensor for the detection of prostate-specific antigen based on conductivity nanocomposite with halloysite nanotubes

A sensitive label-free amperometric electrochemical immunosensor for detection of prostate-specific antigen (PSA) was proposed in this work. The nanocomposite of halloysite nanotubes with polypyrrole shell and palladium nanoparticles (HNTs@PPy-Pd) was used as a novel signal label. The HNTs with adequate hydroxyl groups are economically available raw materials. PPy, as an electrically conducting polymer material, can be absorbed to the surface of HNTs by in situ oxidative polymerization of the pyrrole monomer and form a shell on the HNTs. The shell of PPy could not only improve the conductivity of the nanocomposite but also absorb large amounts of Pd nanoparticles (NPs). The Pd NPs with high electrocatalytic activity toward the reduction of H₂O₂ and the HNTs@PPy-Pd nanocomposite as the analytical signal label could improve the sensitivity of the immunosensor. Under optimal conditions, the immunosensor showed a low detection limit (0.03 pg/mL) and a wide linear range (0.0001 to 25 ng/mL) of PSA. Moreover, its merits such as good selectivity, acceptable reproducibility, and stability indicate that the fabricated immunosensor has a promising application potential in clinical diagnosis. Graphical Abstract A new label-free amperometric electrochemical immunosensor based on HNTs@PPy-Pd nanocomposite for quantitative detection of PSA.

An ultrasensitive sandwich-type electrochemical immunosensor based on δ-MnO2 and palladium nanoparticles covered natural halloysite nanotubes for the detection of hepatitis B surface antigen

An ultrasensitive sandwich-type immunosensor for the detection of HBsAg based on the multifunctional natural halloysite nanotube nanocomposites (Pd/δ-MnO₂/HNTs).

An ultrasensitive aptasensor for chlorpyrifos based on ordered mesoporous carbon/ferrocene hybrid multiwalled carbon nanotubes

In this study, we designed a novel and ultrasensitive aptamer sensor for the quantitative detection of chlorpyrifos.