Dual-recognition colorimetric platform based on porous Au@Pt nanozymes for highly sensitive washing-free detection of...

A dual-recognition strategy is reported to construct a one-step washing and highly efficient signal-transduction tag system for high-sensitivity colorimetric detection of Staphylococcus aureus (S. aureus). The porous (gold core)@(platinum shell) nanozymes (Au@PtNEs) as the signal labels show highly efficient peroxidase mimetic activity and are robust. For the sake of simplicity the detection involved the use of a vancomycin-immobilized magnetic bead (MB) and aptamer-functionalized Au@PtNEs for dual-recognition detection in the presence of S. aureus. In addition, we designed a magnetic plate to fit the 96-well microplate to ensure consistent magnetic properties of each well, which can quickly remove unreacted Au@PtNEs and sample matrix while avoiding tedious washing steps. Subsequently, Au@PtNEs catalyze hydrogen peroxide (H2O2) to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) generating a color signal. Finally, the developed Au@PtNEs-based dual-recognition washing-free colorimetric assay displayed a response in the range of S. aureus of 5 × 10¹-5 × 10⁵ CFU/mL, and the detection limit was 40 CFU/mL within 1.5 h. In addition, S. aureus-fortified samples were analyzed to further evaluate the performance of the proposed method, which yielded average recoveries ranging from 93.66 to 112.44% and coefficients of variation (CVs) within the range 2.72-9.01%. These results furnish a novel horizon for the exploitation of a different mode of recognition and inexpensive enzyme-free assay platforms as an alternative to traditional enzyme-based immunoassays for the detection of other Gram-positive pathogenic bacteria.