Wearable and Flexible Nanoporous Surface-Enhanced Raman Scattering Substrates for Sweat Enrichment and Analysis

Surface-enhanced Raman spectroscopy (SERS), with highsensitivityto a broad range of molecules, can detect molecular "fingerprints"in a complex substance and thereby offers a promising solution fornoninvasive medical diagnostics and personal healthcare monitoring.The eventual realization of such applications relies on SERS substrateswith dense and uniform hot spots, good chemical stability, and highmechanical durability. With these criteria in mind, we developed aflexible nanoporous SERS substrate via the in situ synthesis of goldnanostars (AuNSs) on an ion-track-etched polycarbonate membrane. Thenanoporous SERS substrate can realize analyte enrichment and exhibitexcellent Raman performance by taking the advantage of hot spots onAuNSs. The SERS substrate yields highly repeatable and uniform signalsfor analytes (e.g., methylene blue) over a wide concentration rangefrom 10(-4) to 10(-13) M. The flexibleSERS substrate even can work well after 2000 times bending and exhibitexcellent stability for long-term use. It can be prepared on a largescale with a low-cost and simple fabrication process and can be usedrepeatedly after cleaning to reduce the use-cost further. On-bodyexperiments prove that the sweat SERS substrate allows effective identificationof sweat contents, such as lactic acid and uric acid (UA), and themonitoring of diet-induced variation in sweat UA. The potential ofthe wearable nanoporous SERS substrates in sweat analysis thus hasbeen demonstrated, opening possibilities for autonomous and noninvasivemedical health monitoring.