In Situ Electrodeposition of Gold Nanostructures in 3D Ultra-Thin Hydrogel Skins for Direct Molecular Detection in Complex Mixtures with High Sensitivity

Surface-enhanced Raman spectroscopy (SERS) based on nanostructured metals has promise as a nondestructive tool for sensitive molecular detection. However, metal surfaces are prone to fouling by the nonspecific adsorption of macromolecules, which limits the selective detection of small molecules in complex fluids. Therefore, samples must be purified and enriched before Raman analysis, which makes on-site detection difficult. In the present work, Au nanopillar arrays are encapsulated with ultra-thin hydrogel skins to protect the metal surfaces against macromolecular interferents while selectively allowing the infusion of small target molecules. In addition, densely packed Au nanostructures are produced in situ in the 3D mesh of the hydrogel skin via electrodeposition, which effectively captures targets into dense plasmonic nanogaps, providing rapid and ultrasensitive molecular detection. The synergistic influence of the size-selective permeability of the hydrogel skin and the in situ formation of hotspots enables the direct, highly sensitive detection of pyocyanin dissolved in an aqueous solution of bovine serum albumin and human serum. It is believed that the new nanocomposite materials and techniques will enable rapid and affordable SERS-based on-site analysis and point-of-care testing.