Indirect Competitive Determination of Tetracycline Residue in Honey Using an Ultrasensitive Gold-Nanoparticle-Linked Aptamer Assay

Tetracycline residue in honey has become an increasingly important food safety problem. In this work, an ultrasensitive gold nanoparticles (AuNPs)-linked aptamer assay was developed to determine the tetracycline residue in honey. First, a tetracycline–bovine serum albumin conjugate coating was applied to a microplate. Then, with the incubation of AuNPs-linked aptamer, the fixed tetracycline in the microplate competed for the limited aptamer with the free tetracycline in the sample. Higher amounts of free tetracycline in the sample were associated with more competitive binding of aptamer-AuNPs, and the aptamer-AuNPs binding with tetracycline-BSA was lower. Finally, as a kind of nanozyme, AuNPs exhibited peroxidase activity and oxidized 3,3′,5,5′-tetramethylbenzidine, transforming it from colorless to blue, and achieving the measurement at 652 nm. The analytical performance—including linearity, limit of detection, selectivity, precision, repeatability, and accuracy—has been investigated. It was successfully applied to the determination of tetracycline in honey samples with high accuracy and sensitivity.

Enzyme-Linked Immunosorbent Assay for Streptomycin in Animal Feeds

Polyclonal antibody against streptomycin was prepared by using a streptomycin–bovine serum albumin conjugate for the immunization of rabbits. Using this antibody, we developed quantitative assays for streptomycin by means of an indirect competitive enzyme-linked immunosorbent assay (icELISA). Fifty percent inhibition concentration (IC50) for the antibody was 3.6 ng/ml. The detection limit was 0.4 ng/ml. The average of recoveries for all samples was 86.14% and the coefficients of variation of intra- and inter-assays were below 18%. The detection limit using the kit was 15 ng/ml in animal feeds.