Fabrication of nano-indented cavities on Au for the detection of chemically-adsorbed DTNB molecular probes through SERS effect

Micro/nano-lithographic techniques are usually employed as a straightforward process for roughening a thin-film Au surface for surface-enhanced Raman scattering (SERS). However, a topographical pattern with deepened edges is difficult to control in a rapid and environmental-friendly way. In this study, a simple physical procedure is proposed for tailoring a thin-film Au surface with triangular nanostructures using nano-indentation technique. The as-fabricated nano-indented cavities on Au (nAu) were structured as a characterization substrate for SERS. By calculating the geometries of nAu and the increase of surface area as a function of the concentration of chemically adsorbed 2-nitro-5-thiobenzoic acid (NTB), a combined chemical and electromagnetic effect was estimated. Particularly-made nAu was adjusted for examining chemically adsorbed NTB molecules with differently intensified Raman-active groups by tuning the indentation depth and the tip-to-tip displacement. SERS enhancement factor on a specific NTB/nAu could be increased to 2.1×10⁶.