Non-invasive detection of glucose in human urine using a color-generating copper NanoZyme

Renal complications are long-term effect of diabetes mellitus where glucose is excreted in urine. Therefore, reliable glucose detection in urine is critical. While commercial urine strips offer a simple way to detect urine sugar, poor sensitivity and low reliability limit their use. A hybrid glucose oxidase (GOx)/horseradish peroxidase (HRP) assay remains the gold standard for pathological detection of glucose. A key restriction is poor stability of HRP and its suicidal inactivation by hydrogen peroxide, a key intermediate of the GOx-driven reaction. An alternative is to replace HRP with a robust inorganic enzyme-mimic or NanoZyme. While colloidal NanoZymes show promise in glucose sensing, they detect low concentrations of glucose, while urine has high (mM) glucose concentration. In this study, a free-standing copper NanoZyme is used for the colorimetric detection of glucose in human urine. The sensor could operate in a biologically relevant dynamic linear range of 0.5-15 mM, while showing minimal sample matrix effect such that glucose could be detected in urine without significant sample processing or dilution. This ability could be attributed to the Cu NanoZyme that for the first time showed an ability to promote the oxidation of a TMB substrate to its double oxidation diimine product rather than the charge-transfer complex product commonly observed. Additionally, the sensor could operate at a single pH without the need to use different pH conditions as used during the gold standard assay. These outcomes outline the high robustness of the NanoZyme sensing system for direct detection of glucose in human urine. Graphical abstract.