Alkali metals (Na, K) doped ZnO/CuO composite films for real-time tracking of sweat loss

Real-time sweat rate monitoring provides clinically proper directives for preventive medicine and disease diagnosis. This research represents an attempt to develop a semiconductor-based nanostructured sensor for monitoring sweat rate using a ZnO/CuO composite thin film. A series of alkali metals (sodium, Na; potassium, K) doped ZnO/CuO composite samples were fabricated on soda lime glass substrates by the Successive Ionic Layer Adsorption and Reaction method. The sweat solution sensing response characterization exhibited promising sensing behavior under room conditions. The Na- and K-doped samples showed a pronounced response at low and high concentrations of the sweat solution. While the undoped composite film responds to the high concentration sweat solution (117.90 mM) with a sensitivity of 4.10, this value increases up to 9.15 for the 2.0% Na-doped samples. In addition, the response time shortens from 6 s to 4 s for 2.0% Na substitutions. Pristine, 2.0% Na and 2.0% K-substituted ZnO/CuO composites exhibit great linearity with linear regression ranges, R2, of 0.958, 0.971, and 0.984, respectively. We concluded that doping of ZnO/CuO composites with alkali metals Na and K is a good candidate for real-time tracking of sweat loss as biological evidence.