A traffic light-fluorescent lateral flow immunoassay with dual-color quantum dot nanobeads for the simultaneous detection of ractopamine and clenbuterol

The abuse of illegal β2-adrenergic agonists in animal feeding poses a threat to human health. Fluorescent lateral flow immunoassay (LFIA) is a promising point-of-care testing (POCT) method for monitoring illicit drug use on farms. Here, a traffic light- dual-color quantum dot nanobeads based fluorescent lateral flow immunoassay (QBs-LFIA) was developed for simultaneously detecting ractopamine (RAC) and clenbuterol (CLE). CdSe/ZnS quantum dot nanobeads that emit red and green fluorescence were introduced in this study. They were conjugated with anti-RAC and anti-CLE monoclonal antibodies, respectively, to prepare traffic light fluorescent probes (QBs-mAbs). The dual-color QBs-mAbs greatly enhanced the analytical performance and solved the restriction that multiple mAbs on the control line cannot be accurately distinguished in traditional single-color LFIA. Under optimal conditions, the limits of detection (LODs) for RAC and CLE were 15.7 and 36.3 pg/mL, respectively. The recoveries in spiked cattle urine ranged from 80.3 to 106.1 % with relative standard deviations (RSDs) less than 13.2 %. Good correlations were observed between the detection results of QBs-LFIA and LC-MS/MS (R 2  = 0.9931). The proposed traffic light QBs-LFIA provides a novel approach for simultaneously detecting RAC and CLE. It is also a promising POCT platform for rapid, sensitive, and on-site detection of multiple drug residues.