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Herein, a novel visual method for detecting triazophos based on competitive bio-barcode immunoassay was described. The competitive immunoassay was established by gold nanoparticles (AuNPs), magnetic microparticle (MMPs) and triazophos, combined with biochip hybridization system to detect the residual of triazophos in water and apple. Because AuNPs carried many bio-barcodes, which hybridized with labeled DNA on the biochip, catalyzed signal amplification using silver staining was detected by grayscale values as well as the naked eye. Notably, the grayscale values decreases with increasing the concentrations of triazophos, and the color change weakened gradually. The detection range was in between 0.05 and 10 ng/mL and the minimum detection limit was set at 0.04 ng/mL. Percent recovery calculated from spiked water and apple samples ranged between 55.4 and 107.8% with relative standard deviations (RSDs) of 12.4-24.9%. It has therefore been shown that this protocol provides a new insight for rapid detection of small molecule pesticides in various matrices.

This study reports a novel bio-bar-code amplification competitive immunoassay for the detection of pesticide residue combined with a micro well plate. The sensing competitive immunoassay was made up of two types of particles: (1) the gold nanoparticles (AuNPs) with recognition elements (monoclonal antibody: McAb) and hundreds of thiolated single-strand oligonucleotide bar-codes; and (2) the magnetic microparticle (MMPs) with competition elements (hapten-OVA) for the target pesticide. Target pesticide and pesticide hapten competed with McAb labeled on the surface of AuNPs. The bar-code strands were released by dithiothreitol. Then a simple method based on micro well plate was used for the quantification of the bar-code strands. The bar-code strands with the half-complementary biotinylated DNA and half-complementary DNA-modified gold nanoparticles probe were immobilized onto the surface of a streptavidin-coated micro well plate, and the signal was amplified by silver enhancement. Triazophos (TAP), as a pesticide model, was detected by the proposed immunoassay. The linear range was from 2.5 × 10 −2 to 40.0 ng mL −1 , and LOD of the immunoassay was 1.96 × 10 −2 ng mL −1 . The correlation was further studied between this method and GC–MS analysis. Therefore, this method provided a promising approach for rapid detection and screening of pesticide residue. [ABSTRACT FROM AUTHOR]

A simple and highly sensitive immunoassay based on a competitive binding and bio-barcode amplification was designed for detection of small molecules, triazophos. The gold nanoparticles (AuNPs) were modified with monoclonal antibodies and 6-carboxyfluorescein labeled single-stranded thiol-oligonucleotides (6-FAM-SH-ssDNAs); the fluorescence of 6-FAM was quenched by AuNPs. Ovalbumin-linked haptens were coated on the bottom of microplate to compete with the triazophos in the sample for binding to the antibodies on the AuNP probes. The fluorescence intensity was inversely proportional to analyte concentration. Parameters of AuNP probes preparation and immune reaction were optimized. At the optimal conditions, the salting process was shortened to 1 h and 166 ± 9 ssDNAs were loaded onto a single AuNP. The competitive fluorescence bio-barcode immunoassay was performed on water, rice, cucumber, cabbage and apple samples. The linear range of the method was 0.01–20 μg L −1 and the limit of detection (LOD) was 6 ng L −1 . The recovery and relative standard deviations (RSDs) ranged from 85.0 to 110.3% and 9.4–17.4%, respectively. Good correlations were obtained between the results of the developed method and liquid chromatography-tandem mass spectrometry (LC-MS/MS). In conclusion, it is suggested that the competitive fluorescent bio-barcode immunoassay had the potential to be used as a sensitive method for detection of a variety of small molecules in various samples. [ABSTRACT FROM AUTHOR]

A highly sensitive chemiluminescent enzyme immunoassay (CLEIA) method was developed in this study for efficient screening of triazophos residues in a large number of samples. Based on the maximum residue limits (MRLs) set by China and CAC for triazophos in different agro-products, the representative apple, orange, cabbage, zucchini, and rice samples were selected as spiked samples, and the triazophos at the concentrations of the MRL values were spiked to blank samples. Subsequently, the five samples with the spiked triazophos standard were measured by CLEIA 100 times, and the detection results indicated that the correction factors of the apple, orange, cabbage, zucchini, and rice were determined as 0.79, 0.66, 0.85, 0.76, and 0.91, respectively. In this experiment, 1500 real samples were detected by both the CLEIA and the GC-MS methods. With the GC-MS method, 1462 samples were identified as negative samples and 38 samples as positive samples. Based on the correction factors, the false positive rate of the CLEIA method was 0.13%, and false negative rate was 0. The results showed that the established CLEIA method could be used to screen a large number of real samples. [ABSTRACT FROM AUTHOR]