Simple method for preparing controllably aggregated silver particle films used as surface-enhanced Raman scattering active substrates

Silver colloids Are, one of the extensively employed surface-enhanced Raman scattering (SERS) active substrates. To obtain the SERS effect, their aggregation upon addition of analyte is necessary. However, problems of instability and irreproducibility in the magnitude of the signal are caused by the formation of aggregates. Considering that the aggregation of silver colloids is essential to induce small silver clusters, in the present study, we develop a drying process to prepare silver particle films (silver clusters) that are supported directly on a glass slide. These silver particle films arise through the aggregation of silver colloids occurring in thin water films supported on a solid substrate. With the evaporation of water, silver clusters are left on the solid substrate. Thus, the assembly meets perfectly the requirement of aggregation of silver colloids and, at the same time, possesses the stability of solidlike SERS-active substrates. We can easily obtain excellent SERS spectra from these silver particle films. These substrates show great potential in practical applications such as ultrasensitive microanalysis with micro-Raman spectroscopy and are suitable for studying the optical properties of silver clusters. 4-Mereaptopyridine (4MPY) was used to test the utility of the proposed method and to compare it with the chemically deposited silver film (silver mirror) method. The intensity of SERS signals of 4MPY on the silver particle films is stronger by about 100 times than that of 4MPY on the silver mirror. In addition, the experimental results of SERS reveal that the activation agent, coadsorbed chloride ions, can further enhance the SERS, signals from both the silver mirror and the silver colloids.