Hydrogel microneedle patch for low-cost, colorimetric, continuous glucose monitoring
Diabetes is a chronic condition characterized by dysregulated blood glucose levels. Continuous glucose monitors (CGMs) enable minimally invasive, real-time monitoring of glucose levels, but broader access requires devices that are both effective and affordable. Popular CGMs such as Dexcom and FreeStyle Libre have high accuracy and are integrated with mobile applications to display real-time data and alerts but are limited by high cost. We developed a low-cost, electronic-free, microneedle hydrogel patch CGM that utilizes colorimetric detection to continuously monitor glucose levels. The proposed patch penetrates the skin and absorbs interstitial fluid (ISF) containing glucose. This glucose reacts with glucose oxidase (GOx) enzyme embedded in the hydrogel, producing gluconic acid and decreasing the pH of the hydrogel. As glucose levels increase, decreasing pH levels are reported by the loaded pH indicator bromocresol purple (BCP) via a color change from purple to yellow. This system was validated through a combination of in vitro experiments and COMSOL computational modeling to assess performance at physiologically relevant glucose concentrations. The resulting hydrogels demonstrated reversible and dynamic color changes in response to glucose levels ranging from 3.5-10 mmol/L (63-180 mg/dL), supporting their potential for continuous monitoring applications. A quantitative, image-based analysis method enabled estimation of glucose concentration from photographs, demonstrating strong predictive performance (RMSE=8.59 mg/dL, R2=0.94). Although optimization of mechanical strength and diffusion kinetics remain necessary, these findings highlight the promise of integrating colorimetric sensing with microneedle-based sampling for affordable, user-friendly glucose monitoring.