Oligonucleotide-mediated the oxidase-mimicking activity of Mn3O4 nanoparticles as a novel colorimetric aptasensor for ultrasensitive and selective detection of Staphylococcus aureus in food

Colorimetric detection of pathogenic bacteria in food still faces many challenges. Herein, a novel label-free and ultrasensitive colorimetric aptasensor was firstly established for the detection of food-borne pathogenic like Staphylococcus aureus (S. aureus) based on oligonucleotide-mediated the oxidase-mimicking activity of octahedral Mn3O4 nanoparticles (NPs). The study confirmed that the common oligonucleotide such as SA31 aptamer can adsorb on the surface of octahedral Mn3O4 NPs, and significantly inhibit the oxidase-mimicking activity by blocking their electron transfer to 3,3′,5,5′-tetramethylbenzidine. In the presence of S. aureus, aptamers will preferentially bind to bacterial cell, resulting in the recovery of oxidase-mimicking activity. The naked eye can easily recognize the color change from green to yellow, with the increase concentration of S. aureus from 10 CFU·mL−1 to 2 × 105 CFU·mL−1. The colorimetric aptasensor shows a low detection limit of 3 CFU·mL−1 (S/N = 3). This strategy has excellent selectivity whether the presence of other competitive bacteria, and has been successfully applied to the non-enrichment detection of S. aureus in milk and pork samples.