Nanozyme sensor based-on platinum-decorated polymer nanosphere for rapid and sensitive detection of Salmonella typhimurium with the naked eye

•A new nanozyme Ps-Pt that can attach protein by covalent binding was designed and synthesized.•Based on the nanozyme, a simple, sensitive colorimetric assay is reported for Salmonella typhimurium (S. typhi) detection.•100 CFU/mL S. typhi could be distinguished from the blank by measuring the absorbance.•The generated color change of 1000 CFU/mL S. typhi could be seen clearly with naked-eye. Increasingly frequent outbreaks of bacteria-caused illness heightened the need to develop a rapid, portable, sensitive, and reliable method for bacteria detection. Herein, a nanozyme Ps-Pt was synthesized by growing Pt nanoparticles (Pt) on the surface of carboxyl functionalized polymer nanospheres (Ps). The Pt endowed the Ps-Pt with ultrahigh peroxidase-like catalytic activity. Meanwhile, carboxyl groups enabled Ps-Pt to attach streptavidin via covalent binding, which showed higher activity and stability than physical adsorption. To get immune Ps-Pt (IPs-Pt), biotin-antibody was attached to the streptavidin modified Ps-Pt. The two-step binding method enabled the IPs-Pt to own more antibodies and possess high stability. Based on the immune nanozyme, a simple, sensitive colorimetric assay was reported for Salmonella typhimurium (S. typhi) detection. With the assay, as low as 100 CFU/mL S. typhi could be distinguished from the blank by measuring the absorbance, and the generated color change of 1000 CFU/mL S. typhi could be seen clearly with the naked eye. Additionally, the assay has been successfully applied to the detection of S. typhi in spiked milk, Luria-Bertani broth, and serum samples. The specificity and sensitivity of the IPs-Pt-based sensor demonstrated its feasibility in practical applications. Most importantly, the results of 24 single-blind milk samples demonstrated the high sensitivity and 100 % accuracy of the assay, indicated that the developed method could detect S. typhi in food samples.