We report a novel patterning technique to direct-write nanoporous gold (NPG) into micron-sized units by projecting laser patterns using a spatial light modulator (SLM) onto a gold/silver alloy film immersed in diluted nitric acid solutions. Heat accumulation induced by the photothermal effect enables localized dealloying in dilute nitric acid solution, which is otherwise impotent at room temperature. Consequently, NPG micropatterns were formed at the irradiated spots while the surrounding alloy remained intact. We have studied the size of the patterned NPG microstructures with respect to laser power and irradiation time. The NPG microstructures become significantly more transparent compared to the original alloy film. The NPG microstructures also exhibit strong localized surface plasmon resonance (LSPR) which is otherwise weak in the original alloy film. Both the light transmission intensity and LSPR peak wavelength have been demonstrated to be sensitive to the local environmental refractive index as quantified by microscopy and spectroscopy.