Preparation of surfactant-free gold nano-particle dispersed aqueous solutions with solution plasma processing for surface-enhanced Raman scattering spectroscopy

Detailed procedure to form gold (Au) thin films from surfactant-free Au nano-particle dispersed aqueous solution prepared by solution plasma processing was investigated for the application of surface-enhanced Raman scattering (SERS) spectroscopy measurement. The averaged diameter, thickness, and the weight of each Au thin film in our experimental conditions from 40 mL of around 0.1 % Au dispersed aqueous solution, were evaluated to be around 2.4 mm, 3 μm and 0.1 mg, respectively. SERS spectra of dye molecules and thiol compounds adsorbed on Au thin film were successfully measured upon excitation at 532 nm of solid type laser and 632.8 nm of He-Ne laser, respectively. These SERS spectra from AuNP film surface were unexpectedly strong as compared to those from Ag surface. The possible application of AuNP thin film for SERS platform on solid/liquid interfaces was demonstrated by observation of SERS spectra from p-nitrothiophenol (PNTP) adsorbed on Au thin film/aqueous solution interface.