Plasmonic Skin as a Wearable SERS Substrate for Direct Chemical Identification

Surface-enhanced Raman spectroscopy (SERS) is a powerful tool to identify fingerprint information on molecules, particularly through the use of the SERS substrate for signal enhancement. However, it is nontrivial to detect chemicals directly from real-world surfaces which are rough and topologically complex due to the challenge to establish intimate contact with the conventional rigid and flat SERS substrate. Here, we report a soft, skin-like SERS platform, termed plasmonic skin (P-skin), comprising a Janus gold nanoparticle (AuNP) array supported by elastic polydimethylsiloxane (PDMS). Unlike traditional rigid and opaque SERS substrates, the P-skin is flexible and finger-wearable, allowing for intimate contact with complex surfaces. Combined with a hand-held Raman spectrometer, the P-skin achieves a detection limit of 5 × 10^-8 M, and as low as 1 × 10^-13 M with confocal Raman microscopy, using methylene blue as a model analyte. We demonstrate the utility of the P-skin for on-site detection of the pesticide thiram on various real-world surfaces including paper, apple, avocado, and carrot. In a touch-and-detection demonstration, we show that thiram concentrations below U.S. environmental protection agency limits can be detected.