A competitive sensitive bio-barcode immunoassay based on bimetallic nanozyme (Au@Pt: gold@platinum) catalysis has been designed for the detection of the pesticide parathion. Gold nanoparticles (AuNPs) were modified with single-stranded thiol oligonucleotides (ssDNAs) and monoclonal antibodies (mAbs) to form AuNP probes; magnetic nanoparticles (MNPs) were coated with ovalbumin (OVA)–parathion haptens as MNP probes, and bimetallic nanozyme (Au@Pt) nanoparticles functionalized with the complementary thiolated ssDNA were used as Au@Pt probes. The Au@Pt probes reacted with the AuNP probes through complementary base pairing. Further, parathion competed with MNP probes to bind the mAbs on the AuNP probes. Finally, the complex system was separated by a magnetic field. The released Au@Pt probes catalyzed a chromogenic system consisting of teramethylbenzidine (TMB). The bimetallic nanozyme-based bio-barcode immunoassay was performed on rice, pear, apple, and cabbage samples to verify the feasibility of the method. The immunoassay exhibited a linear response from 0.01 to 40 μg·kg–1, and the limit of detection (LOD) was 2.13 × 10–3 μg·kg–1. The recoveries and relative standard deviations (RSDs) ranged from 73.12 to 116.29% and 5.59 to 10.87%, respectively. The method was found to correlate well with data obtained by liquid chromatography–tandem mass spectrometry (LC–MS/MS). In conclusion, this method exhibits potential as a sensitive alternative method for the detection of a variety of pesticides, ensuring the safety of fruits and vegetables in agriculture.

An ultrasensitive bio-barcode competitive immunoassay method based on droplet digital polymerase chain reaction (ddPCR) was developed for the determination of triazophos. Gold nanoparticles (AuNPs) were coated with monoclonal antibodies (mAbs) and complementary double-stranded DNA (dsDNA), which included bio-barcode DNA and thiol-capped DNA. Magnetic nanoparticle (MNP) probes were constructed by modifying the MNPs with ovalbumin–hapten conjugates (OVA–hapten). The target pesticide and OVA–hapten on the surface of the MNP probes competed with the AuNP probes simultaneously, and then the bio-barcode DNA was released for quantification by ddPCR. The concentration of released DNA was inversely proportional to the concentration of pesticide to be tested. Under the optimum conditions, the competitive immunoassay exhibited a wide linear range of 0.01–20 ng/mL and a low detection limit of 0.002 ng/mL. Spike recovery tests were carried out using apple, rice, cabbage, and cucumber samples to verify the feasibility of the method. The recovery and relative standard deviations (RSDs) of the technique ranged from 76.9 to 94.4% and from 10.8 to 19.9%, respectively. To further validate the results, a linear correlation analysis was performed between the proposed method and liquid chromatography–tandem mass spectrometry (LC–MS/MS). Consequently, the bio-barcode immunoassay based on nanoparticles and ddPCR, an ultrasensitive method, showed great potential for the determination of target pesticides in real samples.

A rapid, ultra-sensitive and simple fluorescence immunoassay (FLISA) on CdSe/ZnS Quantum dots (QDs) for recognition pesticide triazophos have been established. In this assay, the immunoassay uses (CdSe/ZnS) Quantum dots (QDs) as a probe that carries monoclonal antibody (mAb). The free triazophos and OVA-haptens were competed for binding the mAb on the surface of the QDs. Therefore, the concentration of TRIAZ can get by calculation of the detection of fluorescence value. The assay has a linear response in the 10 ng L −1-25 μg L −1 TRIAZ concentration range, and limit of detection (IC 10) was 0.508 ng L −1. The recovery rate in the case of spiked samples ranges from 82.6% to 96.6%, and the RSD is <20%. FLISA can accurately and sensitively screen out triazophos in representative actual samples that contain trace levels of pesticides, it can play a prominent part in agricultural product and environmental detection.

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