Fluorometric competitive immunoassay for chlorpyrifos using rhodamine-modified gold nanoparticles as a label

Rapid immunoassays for the detection of quinoxalines and their metabolites residues in animal-derived foods: A review

Quinoxalines are a class of veterinary drugs with antibacterial and growth-promoting functions. They are often widely used to treat and prevent animal diseases and are illegally used as animal growth promoters to increase economic benefits. Quinoxalines could be easily metabolized in animals to various residue markers and remain in animal-derived foods, which would pose a serious threat to human health. Consequently, it is necessary to detect the residues of quinoxalines and their metabolites. This article reviewed and evaluated immunoassays for quinoxalines and their metabolites in animal-derived foods, mainly including enzyme-linked immunosorbent assays, fluorescence immunosorbent assays, immunochromatography, and surface plasmon resonance biosensors. In addition, we deeply explored the design of haptens for quinoxalines and their metabolites and analyzed the effect of haptens on antibody performance. This paper aims to provide guidance and references for their accurate and sensitive detection, thereby ensuring food safety and human public health.

The Simultaneous Determination of Chlorpyrifos-Ethyl and -Methyl with a New Format of Fluorescence-Based Immunochromatographic Assay

The improper and excessive use in agriculture of chlorpyrifos-methyl (CPSM) and chlorpyrifos-ethyl (CPSE) may affect the health of human beings. Herein, a fluorescence-based immunochromatographic assay (FICA) was developed for the simultaneous determination of CPSM and CPSE. A monoclonal antibody (mAb) with equal recognition of CPSM and CPSE was generated by the careful designing of haptens and screening of hybridoma cells. Instead of labeling fluorescence with mAb, the probe was labeled with goat-anti-mouse IgG (GAM-IgG) and pre-incubated with mAb in the sample. The complex could compete with CPS by coating antigen in the test line. The new format of FICA used goat-anti-rabbit IgG (GAR-IgG) conjugated with rabbit IgG labeled with fluorescence microspheres as an independent quality control line (C line). The novel strategy significantly reduced nonspecific reactions and increased assay sensitivity. Under the optimal conditions, the proposed FICA showed a linear range of 0.015-64 mg/L and limit of detection (LOD) of 0.015 mg/L for both CPSE and CPSM. The average recoveries of CPS from spiked food samples by FICA were 82.0-110.0%. The accuracy was similar to the gas chromatography-tandem mass spectrometry (GC-MS/MS) results. The developed FICA was an ideal on-site tool for rapid screening of CPS residues in foods.

A Simple Aptamer SERS Sensor Based on Mesoporous Silica for the Detection of Chlorpyrifos

Chlorpyrifos is an organophosphorus insecticide, which can be used to control a variety of chewing and piercing mouthparts pests in agricultural production. It can destroy the normal nerve impulse conduction by inhibiting the activity of acetylcholinesterase or cholinesterase in the nerves, causing a series of poisoning symptoms. In order to achieve the quantitative analysis of chlorpyrifos residues in agricultural products, an aptamer-controlled signal molecule release method was developed in this study. The signal molecule 4-ATP of surface-enhanced Raman spectroscopy (SERS) was loaded into aminated mesoporous silica nanoparticles (MSNs-NH2) prepared by the one pot method, and then coated with an aptamer of chlorpyrifos through electrostatic interaction. The specific binding of the aptamer and chlorpyrifos led to the release of 4-ATP, and the amount of 4-ATP released was positively correlated with the amount of chlorpyrifos. Finally, the standard curve of chlorpyrifos quantitative detection based on SERS was established. Meanwhile, Ag-carrying mesoporous silica (Ag@MSNs) was prepared as the reinforcement substrate for SERS detection. The results showed that there was a good linear correlation between the Raman intensity and the concentration of chlorpyrifos at 25−250 ng/mL, and the limit of detection (LOD) was 19.87 ng/mL. The recoveries of chlorpyrifos in the apple and tomato samples were 90.08−102.2%, with RSD < 3.32%. This method has high sensitivity, specificity, reproducibility and stability, and can be used for the quantitative detection of chlorpyrifos in the environment and agricultural products.

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.

Recent advancements in the detection of organophosphate pesticides: a review

Organophosphorus pesticides (OPPs) are generally utilized for the protection of crops from pests. Because the use of OPPs in various agricultural operations has expanded dramatically, precise monitoring of their concentration levels has become the critical issue, which will help in the protection of ecological systems and food supply. However, the World Health Organization (WHO) has classified them as extremely dangerous chemical compounds. Taking their immense use and toxicity into consideration, the development of easy, rapid and highly sensitive techniques is necessary. Despite the fact that there are numerous conventional ways for detecting OPPs, the development of portable sensors is required to make routine analysis considerably more convenient. Some of these advanced techniques include colorimetric sensors, fluorescence sensors, molecular imprinted polymer-based sensors, and surface plasmon resonance-based sensors. This review article specifically focuses on the colorimetric, fluorescence and electrochemical sensors. In this article, the sensing strategies of these developed sensors, analytical conditions and their respective limit of detection are compiled.

A competitive immunoassay for electrochemical impedimetric determination of chlorpyrifos using a nanogold-modified glassy carbon electrode based on enzymatic biocatalytic precipitation

A direct competitive impedimetric immunoassay for chlorpyrifos (CPF) was developed that is based on the specific affinity of immunoassay and the enzymatic biocatalytic precipitation amplification strategy. The CPF antibody (anti-CPF) was anchored onto an electro-deposited nanogold modified glassy carbon electrode surface by adsorption of the Au-NH₂ bond and Au-SH bond. This improved the electrode reactivity and the loading amount of anti-CPF. Abundant horseradish peroxidase (HRP) and bovine serum albumin-CPF (BSA-CPF) were anchored onto spherical gold nanoparticles (AuNPs, 16 ± 2 nm) to form HRP-AuNP-BSA-CPF (analyte competitor). CPF determination was achieved when the competitive immunoassay occurred between CPF and analyte competitor with anti-CPF. In the presence of H₂O₂ and 4-chloro-1-naphthol, an enzyme-mediated biocatalytic precipitation process was triggered and produced an insoluble 4-chloro-1(4H)-naphthalenone. This insoluble substance increased the Faradaic impedance of the base electrode. The impedimetric signal was determined at the formal potential of 220 mV and alternating voltage of 10 mV. This signal decreased with increasing concentration of CPF over a linear range of 1.0 × 10^-3 ng mL^-1~10 ng mL^-1 with a detection limit of 0.070 pg mL^-1. The immunoassay has been tested for determination of chlorpyrifos in complex matrices such as artificially spiked vegetables with recoveries in the range 85 to 110%. The relative standard deviations were less than 7.5%. Graphical abstractSchematic representation of electrochemical impedimetric immunoassay for chlorpyrifos determination before enzymatic biocatalytic precipitation (BCP, red line) process and after BCP process (blue line).

Displaying of acetylcholinesterase mutants on surface of yeast for ultra-trace fluorescence detection of organophosphate pesticides with gold nanoclusters

Acetylcholinesterase (AChE) has been widely applied on the enzyme inhibition-based detection of organophosphate pesticides (OPs). To improve the sensitivity of fluorometric OPs assay, great efforts were made to change the fluorometric probes or analytical strategies rather than improve the sensitivity of AChE towards OPs. In this work, AChE wild-type (WT) and mutants (E69Y and E69Y/F330L) from Drosophila were successfully displayed on the surface of yeast through a-agglutinin-mediated microbial surface display system. The location of AChE on yeast surface was confirmed by immunofluorescence analysis. Further, a fluorescence OPs detection method was developed by combining yeast surface-displayed AChE mutants and protein-directed electronegative fluorescent gold nanoclusters (Au NCs). Yeast surface-displayed AChE can catalyze the hydrolysis of acetylthiocholine to produce thiocholine. The electropositive thiocholine can not only bind with AuNCs by Au-S bond but also absorb Au NCs by the electrostatic interaction, leading to the aggregation of AuNCs and corresponding fluorescence quenching. When AChE was incubated with paraoxon, a typical model of OPs, the activity of AChE was inhibited and the thiocholine-induced aggregation of AuNCs was reduced. The fluorescence assay based on Au NCs and yest-AChE-E69Y/F330L exhibited the ultra-sensitivity for ultra-trace OPs and 2-6 orders of magnitude lower detection limit (3.3 × 10^-14 M) than those of AChE-WT-based method and other reported methods. In addition, the proposed method showed excellent reliability for the real samples assay. This work would provide an alternative strategy for the improvement of bio-analysis at its source.

Oriented assembly of surface plasmon resonance biosensor through staphylococcal protein A for the chlorpyrifos detection

In this study, we report a direct surface plasmon resonance (SPR) biosensor based on an oriented assembly of antibody for the rapid detection of chlorpyrifos residue in agricultural samples. In this covalent-orientated strategy, staphylococcal protein A (SPA) was first covalently bound to the surface for monitoring chlorpyrifos residue, with subsequent binding of the antibody in an orientated fashion via its fragment crystallizable (Fc) region. Consequently, the SPA-modified biosensor exhibited a satisfactory specificity and a low detection limit of 0.056 ng mL^-1 for chlorpyrifos, with a linear detection range of 0.25-50.0 ng mL^-1. Under optimal conditions, the sensor chip could be regenerated for at least 210 cycles. The results presented here indicate that the SPA-modified sensor chip can successfully improve the sensitivity and obviating the need of the modification of the antibody. The developed SPR biosensor method has the great potential for rapid, sensitive, and specific detection with broad applications in areas of environmental monitoring and food safety. Graphical abstract.

Label-free gold nanoclusters as quenchable fluorescent probes for sensing olaquindox assisted by glucose oxidase-triggered Fenton reaction

Glucose oxidase (GOx) catalyses oxidation of glucose accompanied with the generation of hydrogen peroxide. With the addition of Fe²⁺, hydroxyl radical produced by Fenton reaction between hydrogen peroxide and Fe²⁺ may quench the fluorescence of gold nanoclusters. In this work, a fluorescent enzyme-linked immunosorbent assay with gold nanoclusters was designed with a straightforward signal output, in which the fluorescence of gold nanoclusters was quenched by GOx-triggered Fenton reaction. Olaquindox was selected as a target analyte. Gold nanoclusters capped with bovine serum albumin and GOx-linked olaquindox conjugates were successfully prepared. Olaquindox in samples directly competed with the GOx-linked olaquindox conjugates for binding immobilized antibody. Consequently, the fluorescence signal increased with the amount of olaquindox. Under optimal conditions, the fluorescent enzyme-linked immunosorbent assay exhibited a favorable performance to detect olaquindox in swine feeds, demonstrating a good linear range from 1.0 µg kg^-1 to 150 µg kg^-1 with a reliable correlation coefficient (R² = 0.9918); the limit of detection was 0.68 µg kg^-1. Average recoveries in spiked samples were 85.3% to 113.5%. The proposed strategy is a promising approach for the detection of olaquindox and other harmful small molecules.