Nonenzymatic electrochemical sensors via Cu native oxides (CuNOx) for sweat glucose monitoring

Diabetes is a chronic disease, which is the seventh leading cause of death worldwide. The increased risk to the health of diabetic patients, with comorbidities in harsh situations like COVID-19 pandemics, necessitates real-time monitoring of blood glucose. Monitoring of blood glucose is invasive, hence, sweat glucose monitoring can be an alternative approach to address the invasive issue in blood glucose monitoring. This work reports a facile, low-cost, high-performance copper (Cu) native oxide (CuNOx)-based nonenzymatic electrochemical sensor for sweat glucose sensing. We utilized a very thin Cu native oxide of ~10 nm on Cu thin film for the sensing because of the excellent catalytic oxidation behavior of cuprous oxide (Cu2O) to glucose. The anodic sweep of cyclic voltammetry of glucose showed that the hydroxyl ions from sodium hydroxide convert the electrode surface into different oxides [Cu(I), Cu(II) Cu(III)], which electro-oxidize glucose to gluconolactone, then eventually to gluconic acid resulting in oxidation current. The CuNOx sensors exhibited a sensitivity of 603.42 μA mM−1 cm−2, a linear range beyond the desired limit of 7.00 mM with excellent linearity, and a low limit of detection of 94.21 μM. Excellent repeatability and stability (stable >1 year) with relative standard deviation (RSD) of 2.67%, and 2.70%, respectively were achieved for 1 mM glucose. The selectivity with common interferants of glucose in human sweat and blood showed an RSD of 3.56%. We believe the electrocatalytic efficacy of the CuNOx sensors for glucose sensing can open a new prospect in the fabrication of wearable sweat glucose sensors.