Polymer-Based Hydrogels for Chemical Biosensing: From Bioreceptor Integration to Smart Applications

In recent years, flexible, wearable, and implantable chemical sensors and biosensors have become crucial in biomedical engineering. These flexible devices enable the noninvasive, real-time monitoring of biochemical markers in biofluids, from blood to the most accessible ones that enable noninvasive monitoring (sweat, tears, saliva, and interstitial fluid) as indicators of the health status. In their development, polymer-based hydrogels have emerged as the material of choice and have recently started to attract increasing attention due to advantages in terms of biocompatibility, surface area, and chemical tunability. Here, we provide an overview of the structural polymers according to their nature (natural vs synthetic), giving a special focus on the use of conductive polymers. Then, we discuss the strategies to integrate the bioreceptor to provide the hydrogels with the necessary selectivity toward biomarker detection. Finally, we go through emerging trends where hydrogels are employed in smart formats beyond the simple performance of the detection. As an overall, the integration of polymer-based hydrogels with advanced bioreceptor strategies and smart functionalities is driving the development of next-generation wearable and implantable biosensors, paving the way for noninvasive, continuous, and personalized diagnostics.