Hydrogel-based colorimetric power-saving sensors for on-site detection of chloride ions and glucose in sweat

Noninvasive diagnostics play a crucial role in health monitoring and disease detection. Sweat is a representative sample type containing various clinical biomarkers that provide information on certain disease risks. We developed a hydrogel-based colorimetric sensor for sweat analysis using a low-power battery. The hydrogel-based sensor comprised highly flexible bacterial cellulose (BC), highly water-absorbent carboxymethyl cellulose (CMC), and antibacterial chitosan (Ch), which functioned independently or in conjunction with a reusable three-dimensional printed polydimethylsiloxane-based microfluidic device. The highest tensile strength of 4.16 N for the hydrogel material of BC-CMC under the 0.6% Ch reaction indicated that this material had the best properties for absorbing sweat and measuring Cl^- and glucose concentrations while attached to the surface of human skin. Our sensor was able to detect chloride ions (Cl^-) and glucose concentrations in sweat. The sensor exhibited a linear relationship between the Cl^- concentration and b∗ value with a detection limit of 0.56 mM and a detection range of 20-100 mM, encompassing the critical diagnostic window of cystic fibrosis. For glucose detection, color changes were observed visually, and there was a linear relationship between the glucose concentration and the -b∗ value. The detection limit of 0.1 μM and wide detection range of 6.25-500 μM were suitable for the diagnosis of diabetes. The as-prepared sensor maintained stability for one month under specific storage conditions, suggesting the potential of this analytical method for excellent water absorption and selectivity. The sensor can be used for real-time diagnostics to detect cystic fibrosis and its potential complications, such as diabetes, in clinical medicine.