Bimetallic Deep Eutectic Solvent-Driven Ce-Fe Oxide Nanozyme Based on Electron Transfer for the Colorimetric Detection of E. coli O157:H7 in Food

Sensitive detection of Escherichia coli O157:H7 (E. coli O157:H7) in food matrices remains an important analytical challenge. Here, a colorimetric biosensor was constructed based on a bimetal oxide nanozyme composed of Ce-Fe oxide. This biosensor achieved sensitive detection of E. coli O157:H7. The Ce-Fe oxide synthesized on the basis of deep eutectic solvents (DESs) had the advantages of low solvent consumption and short preparation time. By regulating the two key factors of metal valence and oxygen vacancy content, the peroxidase (POD) activity of the nanozyme was significantly improved. Compared with the single-metal oxide nanozyme Fe oxide, the addition of Ce increased the Fe2+/Fe3+ ratio from 0.37 to 0.49, implying a possible enhancement of electron transfer between Fe2+ and Fe3+. The detection limits (LODs) of the biosensor based on Fe oxide and that based on Ce-Fe oxide were 102 CFU/mL and 101 CFU/mL, respectively, comparable to existing validated methods. Moreover, these two biosensors achieved satisfactory recovery rates (91–104%) and RSDs (1.2–8.8%) in the spiked lake water, juice, and lettuce samples of E. coli O157:H7, indicating their high potential for application in spiked sample detection. In summary, the method proposed in this study for improving the POD activity of nanozymes through electron transfer in DES solutions is beneficial to the development of metal oxide nanozymes.