Characterization of surface enhanced Raman scattering (SERS) substrates fabricated from colloidal printing inks

Surface enhanced Raman scattering (SERS) is now a well-established technique to greatly amplify the normally weak Raman scattering signals. The amplification is achieved by using SERS substrates - specially structured metallic substrates with nano-scale morphological features. One of the most widely used methods for SERS amplification employs nanoparticles of silver or gold either in colloidal suspension or in dry-drop form. In such substrates SERS amplification factors (AF) exceeding 10(12) have been reported. The reproducibility of the colloid-based substrates, however, is a problem. The lack of reproducibility can be caused by a variety of factors that can change the interparticle distances. In this paper we show that thermal annealing of SERS substrates fabricated using commercially available nano-particle inks can be used to create thermally stable substrates with high reproducibility. It appears that thermal annealing destroys the unstable hot-spots with very high AF's but still leaves the sample with high AF sites yielding spatially averaged substrate AF's exceeding 10(8).