Gold Nanoparticle Aggregates Immobilized on High Surface Area Silica Substrate for Efficient and Clean SERS Applications

摘要

A simple synthesis route based on the incipient wetness impregnation method originally designed for catalytic purposes has been developed to synthesize Au/SiO2 samples containing increasing amounts of gold (0—50% by weight). In all cases, nanoparticles having about the same size distribution (with majority about 10 nm) and being randomly scattered in the silica matrix have been obtained. With the increase of Au concentration, the aggregation state of gold particles grows progressively, and for 50 wt % of gold with respect to silica, aggregates predominate over isolated particles. The plasmon resonance of isolated particles is located at about 530 nm while that of aggregates contributes to the rise of a strong and broad absorption in the near-infrared region. It is concluded that the adopted synthesis allows the tuning of the aggregation state in an unprecedented way. The 785 nm laser line was then chosen for Raman measurements of adsorbed pyridine and its derivative to investigate whether and how the presence of aggregates can influence the surface-enhanced Raman spectroscopy (SERS) activity. Relative enhancement factors of 10~2—10~3 with respect to bare silica for some vibration modes were obtained on samples containing gold aggregates. These measurements clearly demonstrate that Au/SiO2 systems can be utilized for SERS applications, and the connection between presence of aggregates and enhancement is fully verified.