Competitive and noncompetitive fluorescence polarization immunoassays for the detection of benzothiostrobin using FITC-labeled dendrimer-like peptides

Peptides obtained from phage display libraries are valuable reagents for small-molecule immunoassays. However, their application in fluorescence polarization immunoassays (FPIAs) is limited by phage particles. Here, monomer, dendrimer-like dimer, tetramer peptidomimetic and anti-immunocomplex tracers were designed and synthesized using lysine as special scaffolds and spacers to develop competitive and noncompetitive FPIAs for benzothiostrobin. The affinity between tracers and monoclonal antibodies or immunocomplexes increased with the tracer valence. A higher signal-to-noise ratio and sensitivity could be generated in the FPIAs based on tetramer tracers. The sensitivities of competitive (50% inhibitory concentration) and noncompetitive (50% saturation concentration) FPIAs were 19.71 ± 4.65 and 40.43 ± 2.73 ng mL −1 , respectively. The spiked recoveries were 78.3%−105.2% with relative standard deviations (RSDs) of 0.7%−15.4% for the competitive FPIA, while 78.7%−115.3% with RSDs of 0.7%−12.5% for the noncompetitive FPIA. The amounts of benzothiostrobin in rice detected by the FPIAs were consistent with those detected by high performance liquid chromatography.