Portable and label-free optical detection of sweat glucose using functionalized plasmonic nanopillar array.

Continuous glucose monitoring (CGM) is vital for diabetes care, but current invasive electrochemical sensors of blood glucose often cause potential infection and skin irritation. Non-invasive sensors in sweat glucose are promising alternatives but limited by low sensitivity and poor compatibility with complex sweat environments, because the sweat glucose has concentrations of 20 - 600 μmol/L and are 100-fold more dilute than the blood glucose. Here, we report a portable optical sensing system that integrates an optical watch prototype with functionalized plasmonic silver-coated silicon nanopillars substrate for non-invasive and label-free glucose detection in sweat. The nanopillar sensor with wide-range plasmonic hot spots is functionalized with 4-mercaptophenylboronic acid for selective glucose capture and optical signal transduction through both Raman scattering and plasmonic detection. The optical watch system has a compact LED illumination at 623-660 nm and wireless transmission of data to a smartphone application. Significantly, the whole system demonstrated excellent sensitivity down to 22 μmol/L and high selectivity in detecting glucose in artificial sweat, which were validated by human sweat samples to confirm its applicability in real-life scenarios. Our study offers a promising portable and non-invasive alternative to traditional CGM and highlights the potential of integrating nanophotonic sensors with wearable platforms for continuous health monitoring and personalized medicine.