A consideration of silver nanoparticle aggregates with a view to SERS

It has been well documented that ideal SERS conditions occur in the nano sized gaps between metal nanoparticles(1,2). Aggregation of the nanoparticles is a very simple and effective way to form these gaps(3,4). We have investigated the 2 salts most commonly used throughout the literature as aggregating agents. Their absorption spectra were measured over time as the nanoparticles gradually aggregate and fall out of suspension, as well as their effects on SERS spectra. It was found that adding these salts to colloidal silver nanoparticles causes them to form large clusters which provide huge enhancement to the SERS spectra. This is due to the analyte molecules being situated in newly formed "hot spots" between the nanoparticles. This method is shown to be a cheap and simple way to achieve very large SERS enhancement.