A highly sensitive immunoassay of pesticide and veterinary drug residues in food by tandem conjugation of bi-functional mesoporous silica nanospheres

A novel type of enzyme-antibody conjugation using mesoporous silicon nanospheres (MSN) was developed, which amplified the labeling signal and highly increased the sensitivity of enzyme-linked immunosorbent assay (ELISA) for the determination of pesticide and veterinary drug residues in food. First, conjugates were prepared through layer-by-layer immobilization of an enzyme and an antibody on an MSN scaffold. Then the MSN scaffold was employed for labeling and signal amplification to develop a sensitive colorimetric immunoassay through the catalytic oxidation reaction of 5,50-tetramethylbenzidine (TMB). When this MSN-based ELISA was applied to detect chloramphenicol, avermectin, tetracycline and streptomycin in food samples, it provided linear ranges of 0.025 ng ml-1-25 ng ml-1, 0.05 ng ml-1-10 ng ml-1, 0.025 ng ml-1-10 ng ml-1 and 0.05 ng ml-1-25 ng ml-1, respectively, with low detection limits down to 0.011 ng mL-1, 0.134 ng mL-1, 0.015 ng ml-1 and 0.106 ng ml-1, respectively. For avermectin, it provided a 16.7-fold decrease of the limit of detection in contrast to that of standard ELISA without the loss of method specificity and accuracy. This novel immunoassay was hypersensitive, simple and easy-to-use, which made it high potential in applying for the accurate analysis of harmful substances in food.