Comparison between Gold Nanoparticles Produced by Low-temperature Heating of Dry Residues of a Solution of HAuCl<sub>4</sub> in Air and in a Low Vacuum

In this study, by performing simultaneous low-temperature heating of the dry residue of a droplet of an HAuCl4 solution on a quartz glass substrate and an indium tin oxide (ITO) thin film on a borosilicate glass substrate placed opposite to the dry residue in air or in a low vacuum, gold nanoparticles were produced on ITO thin films. Scanning electron microscope (SEM) observation and total reflection X-ray fluorescence (TXRF) analysis of gold nanoparticles produced in air and in a low vacuum were performed in order to compare the gold nanoparticles produced under the different pressure conditions. The results of the SEM observation and TXRF analysis showed that the production of gold nanoparticles in a low vacuum led to a reduction in the size of gold nanoparticles and an improvement in the purity of gold nanoparticles. Gold nanoparticles produced in air and in a low vacuum were used as surface-enhanced Raman scattering (SERS) substrates for the measurement of a droplet of a solution containing 0.1 g L−1 of nicotinamide. Although the production in air reduced the purity of gold nanoparticles, the use of the gold nanoparticles produced in air enhanced the intensity of a Raman peak originating from nicotinamide compared with the use of the gold nanoparticles produced in a low vacuum when a droplet of the nicotinamide solution on gold nanoparticles was irradiated with the laser beam with a wavelength of 785 nm.