Investigation of optimal size of gold nanoparticles for SERS detection of PAH in water with 671-nm excitation

To investigate the optimal gold colloid film properties for the in-situ detection of polycyclic aromatic hydrocarbon (PAH) in water using 671 nm excitation wavelength, gold substrates with selected sizes of gold nanoparticles were prepared. Heating of (3-aminopropyl)trimethoxysilane (APTMS) methanol solution allowed to control the surface plasmon resonance for surface enhanced Raman spectroscopy (SERS). Shifted excitation Raman difference spectroscopy (SERDS) was applied for effective background removal. Results for pyrene in aqueous solution demonstrate that there is a dependence of SERS activity on the size of gold nanoparticles even though their surface plasmon resonances are almost same and close to the excitation wavelengths, and also confirmed that the improved self-assembly method using controlling the temperature of APTMS solution way can work well. Appling the substrate with the average gold nanoparticles size of 35 nm, different concentrations of pyrene in aqueous solution were detected with SERS supported by SERDS technique. Raman signals of pyrene up to 5 nmol/l on this substrate can be obtained. The quantitative analysis shows the SERS intensities increase with the increasing concentration of pyrene, which is the foundation of quantitative analysis of pyrene in aqueous solution.