Characterisation of a SapYZU11@ZnFe2O4 biosensor reveals its mechanism for the rapid and sensitive colourimetric detection of viable Staphylococcus aureus in food matrices

Although bacteriophage-based biosensors hold promise for detecting Staphylococcus aureus in food products in a timely, simple, and sensitive manner, the associated targeting mechanism of the biosensors remains unclear. Herein, a colourimetric biosensor SapYZU11@ZnFe2O4, based on a broad-spectrum S. aureus lytic phage SapYZU11 and a ZnFe2O4 nanozyme, was constructed, and its capacity to detect viable S. aureus in food was evaluated. Characterisation of SapYZU11@ZnFe2O4 revealed its effective immobilisation, outstanding biological activity, and peroxidase-like capability. The peroxidase activity of SapYZU11@ZnFe2O4 significantly decreased after the addition of S. aureus, potentially due to blockage of the nanozyme active sites. Moreover, SapYZU11@ZnFe2O4 can detect S. aureus from various sources and S. aureus isolates that phage SapYZU11 could not lyse. This may be facilitated by the adsorption of the special receptor-binding proteins on the phage tail fibre and wall teichoic acid receptors of S. aureus. Besides, SapYZU11@ZnFe2O4 exhibited remarkable sensitivity and specificity when employing colourimetric techniques to rapidly determine viable S. aureus counts in food samples, with a detection limit of 0.87 × 102 CFU/mL. Thus, SapYZU11@ZnFe2O4 has broad application prospects for the detection of viable S. aureus cells on food substrates.