Facile fabrication of wafer-scale flexible SERS substrate via cryo-transferring SiO2 nanosphere multilayer into waterborne polyurethane (WPU) film

Abstract

Preparing flexible Surface-Enhanced Raman Scattering (SERS) substrates with close-packed nanosphere monolayer has attracted considerable interest. Regrettably, although nanosphere (NS) multilayer can be much more easily assembled at a large area than monolayer, it has not yet been employed in the SERS field. Herein, we report the facile fabrication of wafer-scale flexible SERS substrate with NS multilayer for the first time. In detail, we cryo-transferred SiO2 NS multilayer which was easily spin-coated on host Si substrate completely into waterborne polyurethane (WPU) film, followed by air plasma etching to remove part of WPU to make only one layer of embedded SiO2 NS exposed. Cauliflower-like Au nanostructure with abundant “hot spots” was formed on NS crowns by e-beam evaporation, finally enabling the 2-inch flexible SERS substrate with a rhodamine 6G (R6G) detection limit of 10-9 M and the corresponding enhancement factor (EF) of ∼108.