A fluorescence and colorimetric dual-mode immunoassay for sensitive detection of marbofloxacin based on gold and silver nanoclusters

Marbofloxacin (MBF) is widely used in veterinary medicine for the prevention and treatment of various infectious diseases. However, improper use of MBF may leave residues in edible animal tissues and milk, posing a potential hazard to human health. Here, we developed a fluorescence and colorimetric dual-mode immunoassay for the detection of MBF based on the inner filter effect between gold-silver bimetallic nanoclusters (AuAgNCs) and the oxidation products of 3,3',5,5'-tetramethylbenzidine (oxTMB). In this immunoassay, horseradish peroxidase (HRP) catalyzes the oxidation of TMB to oxTMB, which can further quench the fluorescence of AuAgNCs. Thereby, the color change of oxTMB and the fluorescence change of AuAgNCs can be utilized as the dual signals for MBF analysis. Under optimal conditions, the detection limit of the fluorescence enzyme-linked immunosorbent assay was 9   ng   L -1 , with a 50% inhibitory concentration (IC50) of 0.80   µg   L -1 . Additionally, this immunoassay demonstrated high specificity for MBF and satisfactory recovery rates in pork samples (fluorescence mode: 84.00-104.40%; colorimetric mode: 90.54-107.63%) and milk samples (fluorescence mode: 88.00-104.00%; colorimetric mode: 86.15-115.22%). Hence, the developed immunoassay has great application potential for sensitive detection of MBF residues in foods.