Recent progress in hydrogel microneedle sensors based on electrochemical and optical sensing

Hydrogel-forming microneedles (HMNs) have emerged as a promising platform for biosensing applications, offering a minimally invasive and highly versatile approach for real-time monitoring of various biomarkers. This review explores the key aspects of HMNs, beginning with an in-depth examination of their fabrication, focusing on the role of crosslinking methods—covalent, ionic, and self-crosslinking—in influencing the hydrogels’ swelling behavior, mechanical properties, and overall performance. The interplay between polymer composition and crosslinking strategies is discussed in the context of tailoring HMNs for specific biomedical applications. We then delve into the integration of electrochemical and optical sensing technologies with HMNs, highlighting their potential for precise, on-site biomarker detection. Electrochemical sensors enable high sensitivity and specificity through aptamer-based, enzyme-based, and redox-mediated detection strategies, while optical sensing methods such as fluorescence, colorimetry, and surface-enhanced Raman spectroscopy (SERS) provide additional versatility. The synergies between these sensing modalities and HMNs are explored, emphasizing their potential for advancing diagnostic accuracy and patient compliance. Finally, the review outlines the diverse applications of HMN sensors, including drug monitoring, glucose and lactate sensing, and the detection of uric acid and cortisol, among others. Emerging innovations in wearable technologies and personalized medicine are discussed alongside the challenges of HMN-based sensors, such as limited diffusion of large biomarkers and potential leaching of sensing reagents. This review underscores the transformative potential of HMN-based electrochemical and optical sensors in healthcare, offering insights into their current advancements and future directions.