Ultrasensitive detection of glucose oxidase and alkaline phosphatase in milk based on valence regulated upconversion nanoprobes

Fresh milk should undergo sterilization before consumption to eliminate bacteria that can cause foodborne illnesses. Additional antimicrobial measures are beneficial to extend its shelf life. The nanoprobe developed herein can not only inspect the activity of alkaline phosphatase (ALP) for evaluating the degree of pasteurization, but also detect the activity of glucose oxidase (GOD), which is added as a chemical preservative. The facile preparation of the nanoprobe involved introducing gallic acid-Fe complex (GA-Fe) into lanthanide doped upconversion nanomaterials (UCNPs). Based on the alteration of iron’s valence state in the complex through a straightforward redox reaction, both enzyme activities could be determined through colorimetric and luminometric dual-signal readouts. With detection limits of 1.669 × 10 -5 for GOD and 9.81 × 10 -6 U/mL for ALP respectively, this nanoprobe shows merits of easy operation and high sensitivity. Successful application in milk samples demonstrates its potential as an innovative and cost-effective approach to food safety inspection.