Advances and future perspectives in hydrogel-based sensing technologies: a comprehensive review

Hydrogels, with their high water content, biocompatibility, and responsiveness to environmental stimuli, have gained significant attention as promising materials in sensor technology. Hydrogel-based sensors are increasingly utilized in environmental monitoring, healthcare diagnostics, and wearable devices. This review comprehensively synthesizes recent advancements in conductive hydrogel sensors, addressing a critical literature gap by integrating material design, functionalization, and deployment in multifunctional platforms, unlike prior reviews that focus narrowly on specific hydrogel types or applications. Key findings include the development of highly stretchable and conductive hydrogels through conductive polymers, carbon nanofillers, and ionic conduction, enabling precise human motion detection and innovative cancer monitoring via non-invasive sweat analysis and intraoperative tumor tracking, and sensitive UV monitoring through colorimetric and photoelectrochromic mechanisms for skin health and environmental applications. The review critically evaluates challenges, such as mechanical fragility limiting durability in load-bearing applications, inconsistent sensitivity/specificity, and long-term stability issues. Emerging directions, including 'smart' hydrogels responsive to multiple stimuli and their integration with bioelectronics for real-time physiological monitoring, and advanced UV sensors for wearable and environmental monitoring, are explored. By offering a robust framework for researchers and engineers, this review aims to accelerate the development of versatile, durable hydrogel sensors, enhancing their impact in personalized healthcare, environmental sensing, and soft robotics.