Rapid and sensitive determination of difenoconazole in cucumber and pear samples using an immunochromatographic assay

Development of a highly sensitive colloidal gold semiquantitative method for the determination of difenoconazole residues in citrus

Introduction

Difenoconazole (DIFE) is a common pesticide used in citrus cultivation; excessive intake can cause neurological damage to the organism, and the existing colloidal gold immunochromatographic test strips cannot meet the requirements for the detection of citrus samples.

Methods

Difenoconazole test strip was prepared based on the colloidal gold immunochromatographic technique (GICT), and its application in citrus samples was investigated; with colloidal gold (CG) as the probe, the optimization of GICT parameters, and the determination of reaction method, the immunochromatographic test strips for the detection of DIFE in citrus was developed, and the limit of detection (LOD), specificity, accuracy, and stability of the test strips were verified.

Results

The results showed that the visual detection limit of the prepared colloidal gold immunochromatographic test strips was 0.2 mg/kg and the quantitative range was 0.06-0.6 mg/kg, and the test strips could specifically identify DIFE and have no cross-reaction with other common triazole pesticides. The detection method established in this study was verified by the GC-MS method, and the detection results achieved good consistency (R2 > 0.98).

Conclusion

The test strips developed in this study have good performance and can be used for highly sensitive detection of citrus samples.

Immunochromatographic assay for miroestrol and deoxymiroestrol, its cross-reactivity, and application in Pueraria mirifica (white Kwao Krua) analysis

INTRODUCTION

Miroestrol (Mi) and deoxymiroestrol (Dmi) are trace, yet potent, phytooestrogens found in white Kwao Krua [Pueraria candollei var. mirifica (Airy Shaw & Suvat.) Niyomdham, PM]. However, the analysis of these substances is difficult because of complex matrix effects and their various analogues. In addition, alteration in the cross-reactivity of a gold nanoparticle (AuNP)-based immunochromatographic assay (ICA) resulting from the electrostatic adsorption between antibodies and AuNPs has not yet been evaluated.

OBJECTIVES

This study aims to develop, characterise, and validate ICA with a monoclonal antibody exhibiting similar reactivity against Mi and Dmi (MD-mAb).

MATERIALS AND METHODS

The ICA performance was validated for cross-reactivity and performance in comparison with those of indirect competitive enzyme-linked immunosorbent assays (icELISAs) with MD-mAb and mAb exhibiting specificity against Mi (Mi-mAb).

RESULTS

The ICA showed a limit of detection (LOD) at 1 and 16 μg/mL for Mi and Dmi, respectively. The cross-reactivity of the ICA with Dmi was lower (6.25%) than that observed with the icELISA (120%). Cross-reactivity of ICA against other compounds of the PM was also correlated with those of icELISA; no false-positive/negative results were observed. The repeatability and reproducibility of the ICA were confirmed. The results obtained using ICA in samples of PM are correlated with the concentrations determined through icELISAs.

CONCLUSION

An ICA with MD-mAb was constructed and validated. However, direct conjugation via the electrostatic adsorption of mAb-AuNPs was expected to alter the cross-reactivity of ICA, especially that of the analyte analogue Dmi.

Identifying fungicide difenoconazole as illegal growth regulator in vegetable: Computer-aided hapten similarity to enhance immunoassay sensitivity

Difenoconazole, a fungicide with broad-spectrum properties, has recently been found to have been used illegally used as a plant growth regulator in Brassica campestris, with the intent of inducing thick stems and dark green leaves. However, analysts have encountered challenges in implementing a rapid surveillance screening approach for this purpose. In this study, a novel hapten was designed to improve the analytical performance of difenoconazole immunoassay. Specifically, the triazole of the original hapten was replaced with a benzene ring, guided by molecular simulation. This led to the development of a very sensitive antibody and the subsequent development of a competitive indirect enzyme linked immunosorbent assay (ciELISA) for the detection of difenoconazole in vegetable samples. The assay exhibited a working range of 0.16 ng mL^-1 to 9.64 ng mL^-1, with a detection limit of 0.05 ng mL^-1. Upon analysis of blind samples, a strong correlation was observed between the ciELISA and HPLC-MS/MS methods. As a result, the proposed technique may prove to be an excellent tool for the rapid detection of difenoconazole overuse and adulteration in vegetables.

Development of a gold-based lateral flow immunoassay for the determination of abscisic acid

The visual cut-off values of the LFIA strip for abscisic acid in food samples were 5 ng mL−1 as observed by the naked eye.