Directional immobilization of phage on the palladium-based nanozyme for colorimetric detection of Cronobacter sakazakii in powdered infant formula

Cronobacter sakazakii in powdered infant formula (PIF) can cause infections in newborns that are life-threatening. Establishing a High-performance evaluation method for C. sakazakii in the PIF is urgently needed. In this study, a chromogenic system based on phage-directed immobilized nanozyme for colorimetric measurement of C. sakazakii in PIF was constructed. Initially, our acquired phage EspYZU15 was electrostatically immobilized on the surface of a palladium-based nanozyme to produce EspYZU15 directionally immobilized Pd (EspYZU15@Pd). EspYZU15@Pd possesses outstanding peroxidase-like properties, catalyzing the chromogenic reaction of 3,3 ',5,5 '-tetramethylbenzidine (TMB) in the presence of H2O2. The ability of EspYZU15@Pd to recognize and trap host bacteria allows C. sakazakii to specifically inhibit the TMB chromogenic process catalyzed by EspYZU15@Pd. Based on this detection strategy, a visual quantification method for C. sakazakii ranging from 3.2 x 102 to 3.2 x 107 CFU mL-1 was developed, yielding a low limit of detection (LOD) of 3.6 x 101 CFU mL-1. This method was able to successfully detect C. sakazakii in PIF, with outstanding recoveries ranging from 95.8% to 104.9%. These characteristics indicate that the EspYZU15@Pd-based chromogenic system has considerable promise for the colorimetric determination of C. sakazakii in PIF.