Hydrogels for Analyte Sensing.

Hydrogels have emerged as a versatile platform technology for analyte sensing, offering unique advantages in tunable chemistry, for loading with sensors across multiple length scales, and biocompatibility. These smart materials undergo predictable changes in optical properties, conductivity, swelling, and porosity upon analyte interaction, enabling their function as biosensors. While hydrogels can respond to a variety of stimuli, their responses are most effectively quantified through optical and electrical readouts, which enable direct, real-time, and quantitative sensing in complex biological fluids. Optical approaches leverage fluorescence, chemiluminescence, and colorimetry, whereas electrical approaches leverage conductive fillers or redox-active groups. Hybrid platforms integrate multiple readout mechanisms, enhancing sensitivity, robustness, and multiplexing capabilities. Many of these systems were validated in various biological matrices, such as interstitial fluid, sweat, and wound exudates. Beyond technical advances, we discuss translational challenges including selectivity, stability, nonreversibility, signal standardization, device portability, and regulatory approval, as well as emerging opportunities in coupling hydrogel sensors with artificial intelligence for improved data interpretation and clinical integration. Together, these developments position hydrogel-based diagnostics as promising candidates for next-generation, real-time, point-of-care biosensing.