Novel nanozyme-catalyzed and magnetically assisted colorimetric biosensor for Staphylococcus aureus detection with a low matrix effect from complex environments

The accuracy and sensitivity of current strategies for pathogens detection in complex environments still face significant challenge. Herein, the vancomycin-modified magnetic nanoparticles (Fe3O4 @Au-Van MNPs) were prepared to capture and separate bacteria from complex environments. Combined with aptamer inhibition effect on the oxidase-like activity of octahedral Mn3O4 NPs, a robust, sensitive and highly selective colorimetric biosensor was firstly constructed for S. aureus detection. The presence of S. aureus will quickly bind with SA31 aptamer in sensing solution and it can be effectively captured by Fe3O4 @Au-Van MNPs, leading to a significant decrease of unbound aptamer quantity after magnetic separation. Consequently, the oxidase-like activity of octahedral Mn3O4 NPs is no longer inhibited, and can oxidize the chromogenic substrate to form a yellow product, which exhibits a characteristic absorption peak at 450 nm. The colorimetric biosensor displays excellent selectivity and sensitivity, and the minimum detection limit is calculated as 2 CFU·mL−1. Interesting that the absorbance variation is higher than 0.1 once S. aureus contents exceed 100 CFU·mL−1, which can be easily distinguished by naked eye. Besides, the biosensor has been successfully applied to detect S. aureus in several complex environments and biological samples.