Surface enhanced Raman scattering (SERS) effect using flexible and self-closing ZnO nanowire-Au nanoparticle heterostructures

Herein, we demonstrate a novel and flexible Surface enhanced Raman scattering (SERS) substrate comprised of thermally-responsive polymer film coated with ZnO nanowire-Au nanoparticle heterostructures. The heterostructure fabrication involved vapor-solid growth of ZnO nanowires and their subsequent decoration with Au nanoparticles via a wet-chemical and surfactant-free route. These heterostructures were further loaded with an analyte, methylene blue (MB). The mechanism of SERS relied on the Raman laser-based local heating of the thermally-responsive polymer substrate coated with MB-loaded heterostructures. This in-situ heating process caused the substrate to shrink and resulted in suitable hot spots between the heterostructures (“self-closing” mechanism) leading to MB Raman signal enhancement. The SERS effect was studied as a function of the substrate heating duration (0–10 s) and MB concentration (10−5–10−7 M). In addition, SERS substrate reusability was demonstrated by performing multi-spot analysis and photo-decomposition of loaded MB allowed for regeneration of the analyzed spot. The temperature distribution for the polymeric substrate under the incident Raman laser was calculated using finite element method (FEM). The plasmonic characteristics or hot spot formation for the self-closing heterostructures with varying distances between the two heterostructured targets was simulated using discrete dipole approximation (DDA) method.