Colorimetric and fluorescence dual-mode sandwich biosensor for visual detection of multiple foodborne pathogens with concanavalin A modified magnetic nanoparticles and CdTe quantum dots

Salmonella ( Sal ) and Escherichia coli ( Esc ) are two common foodborne pathogens that cause significant harm to humans. Therefore, strict control of Esc and Sal in food and the environment is essential. Herein, we developed a colorimetric/fluorescence dual-mode strategy for the detection of two pathogenic bacteria. Taking advantage of the characteristic that concanavalin A (ConA) can capture bacteria via the recognition of the sugar residues, it was coupled with magnetic nanoparticles (MNPs) to form MNPs@ConA as the capture probe. In addition, the antibody (Ab) can specifically recognize the bacteria, and after coupling with CdTe quantum dots (QDs), QDs@Ab was employed as the signal probe. This study shows that MNPs can catalyze 3,3′,5,5′-tetramethylbenzidine (TMB) to generate blue oxTMB to be recognized by the naked eye, while QDs exhibited strong fluorescence, which can also be observed by the naked eye, allowing for a clear differentiation in Sal and Esc detection. The signal was linearly correlated with the target bacteria with a satisfied visualized results. The practicability of the method was verified using milk tea, milk, and juice samples, with recovery rates ranging from 93.5 % to 106 %. The feasibility of this method for the detection of Sal and Esc was validated, and it poses a significant potential for food safety monitoring.