Highly sensitive detection of triazophos pesticide using a novel bio-bar-code amplification competitive immunoassay in a micro well plate-based platform

•The AuNPs probe and MMPs probe were designed and synthesized.•The barcode strands was detected by gold nanoparticle-catalyzed reduction of silver in a micro well plate-based platform.•The detection system using one monoclonal antibody overcame the obstacles in small molecule detection.•High sensitivity and good selectivity for triazophos detection.•The idea and method will provide a new approach for detection triazophos. 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 40.0ngmL−1, and LOD of the immunoassay was 1.96×10−2ngmL−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.