Colorimetric detection of Staphylococcus aureus with enhanced sensitivity based on phage covalently immobilized CoO nanozyme through synergistic inhibition effect.

Staphylococcus aureus (S. aureus) is a common foodborne pathogen, posing a serious threat to public health. Consequently, it is crucial to establish a platform for sensitive and specific determination of S. aureus in food. Herein, phage SapYZUH, isolated by our lab, was covalently immobilized on CoO to synthesize SapYZUH@CoO. Notably, SapYZUH@CoO exhibited remarkable oxidase-like activity, enabling the catalysis of dissolved oxygen to generate superoxide anion free radicals and accelerate the TMB chromogenic reaction. Upon introduction of S. aureus, specific capture by SapYZUH@CoO resulted in inhibiting its oxidase-like activity and decelerating the 3,3',5,5'-tetramethylbenzidine (TMB) chromogenic reaction. Moreover, S. aureus can be lysed to release the reductive bacterial contents, which can further inhibit the TMB chromogenic reaction. Based on this principle, SapYZUH@CoO + TMB reaction system was employed for detection with enhanced sensitivity of S. aureus, yielding an equation: A =  - 0.092 Log (C) + 0.79 (R = 0.987), with an ultralow limit of detection (LOD) of 28 CFU mL. This system exhibited remarkable specificity and anti-interfere towards S. aureus, owing to the excellent affinity of SapYZUH towards S. aureus. In addition, S. aureus in the actual food samples was detected using this system, yielding recoveries ranging from 96.34 to 109.43%, demonstrating its exceptional accuracy. Hence, our proposed covalent immobilization of phage on the nanozyme can realize sensitive and specific colorimetric determination of S. aureus in food samples.