A portable nanozyme-integrated photoelectrochemical and colorimetric dual-mode biosensor for E. coli O157:H7...

Portable, ultra-sensitive, and highly specific detection of foodborne pathogens is significant for food safety. Here, we designed a portable PEC biosensor based on a Bi₇O₉I₃/In₂O₃ type-II heterojunction combined with an isothermal amplification strategy, realizing on-site PEC and colorimetric dual-mode quantitative detection of Escherichia coli O157:H7 (E. coli O157:H7) in milk using Zr-MOF nanozyme. By utilizing a very small U-disk electrochemical workstation with a portable LED lamp as the light source, a portable PEC biosensor was achieved with excellent sensitivity (10^0.3-10^7.2 CFU/mL), low limit of detection (2 CFU/mL), outstanding stability, selectivity and reproducibility. In addition, a colorimetric assay for E. coli O157:H7 was developed based on the phosphatase-like activity of Zr-MOF nanozyme, which hydrolyze 4-nitrophenyl phosphate to produce 4-nitrophenol. The output dual-signals from U-disk electrochemical workstation and RGB values were captured by smartphone-compatible Bluetooth, thus accomplishing on-site testing of E. coli O157:H7 in milk. To validate the suitability of the portable PEC biosensor, a variety of dairy products were spiked for quantitative detection and all showed excellent recoveries, which demonstrated the great potential application of portable PEC analysis for field testing.