Abstract: To explore the feasibility of applying nanobodies in colloidal gold immunochromatography assay (GICA) for small-molecule harmful substances, this study systematically investigated the effects of colloidal gold labeling parameters, colloidal gold working buffer and sample pretreatment methods on GICA using the pesticide procymidone as a model. The results showed that the size of colloidal gold particles, labeling pH and the amount of antibody used were the key factors to ensure the stability of the nanobody-gold-labeled probes. Under the optimal conditions, the limit of detection, half-maximal inhibitory concentration (IC50) and visual detection limit of GICA for procymidone were 0.44, 6.29 and 200 μg/L, respectively. The sensitivity was 5.1-fold higher than that of conventional monoclonal antibody-based GICA. The quick, easy, cheap, effective, rugged and safe (QuEChERS) procedure was used for the pretreatment of Chinese leek, cucumber and tomato samples. Based on the excellent organic solvent tolerance of nanobodies, the organic solvent blow-drying procedure was omitted. The average recoveries of the spiked samples ranged from 80.1% to 109.6%, and the results for the actual samples were consistent with those of gas chromatography-mass spectrometry (GC-MS). This study showed that nanobodies are a potential alternative to conventional antibodies for immunoassays for the rapid detection of small molecules. The proposed nanobody-based GICA can be used for the rapid screening of procymidone in vegetables with the advantages of high sensitivity, high accuracy, rapidity and simplicity.

Key words: nanobodies; procymidone; colloidal gold immunochromatography; rapid detection