Low-Cost, High-Performance Refractive Index Sensing with Ultranarrow Resonance Line Width for Wearable Sensing

Plasmonic nanostructure-based sensors enable real-time, label-free detection for biomedical applications. Considerable efforts have been made to achieve a sharp plasmon resonance and enhance sensitivity. However, most of the reported sensors are limited in wearable sensing applications due to their reliance on traditional rigid substrates and high fabrication costs. In this study, we fabricated a flexible surface plasmon resonance (SPR) sensor by using laser interference lithography (LIL), making it suitable for wearable devices. Experimental results demonstrate that the sensor exhibits excellent robustness and mechanical stability under different bending radii and incident angles, with an ultranarrow line width (∼6.9 nm) and ultrahigh sensitivity (462.31 nm/RIU). Notably, this sensor is integrated with a microfluidic chip, enabling real-time monitoring of different analytes. Further validation using a portable optical system showed that the sensor can reliably detect air, water, and sweat in nonlaboratory environments, highlighting its potential for real-time, flexible wearable sensing applications.