Surface-enhanced Raman scattering on aggregates of silver nanoparticles with definite size

Aggregation behavior of colloidal silver nanoparticles for surface-enhanced Raman scattering (SERS) on a hydrophobic surface is investigated. A regular glass slide is used to deposit dicholoromethylsilane in order to inactivate the free hydroxyl groups and increase the hydrophobicity of the glass surface. A submicron volume of colloidal suspension is spotted on the hydrophobic surface. During the evaporation of water from the droplet, the nanoparticles start to form aggregates with a definite size and shape. Increasing colloidal suspension concentration by more than 4 times helped to complete the size of silver nanoparticles aggregates to about 1 mu m diameter. The SERS activity of aggregates was investigated using Rhodamine 6G as a probe. The aggregates formed from higher colloidal suspension concentrations show a significant improvement in SERS activity. The SERS enhancement on the aggregates formed on hydrophobic surfaces is at least 1 order of magnitude greater than the disordered aggregates prepared on the regular glass surface using the same colloidal suspension. The SERS enhancement factor for the aggregates and the limit of detection (LOD) for Rhodamine 6G are estimated as about 3 x 10(5) and 1.0 x 10(-5), respectively. The percent coefficient of variance (CV) improved about 300% by increasing the,colloidal suspension concentration 8-fold on the prepared aggregates. A minimum 2-fold increase in SERS enhancement on the aggregates prepared from silver colloidal suspension containing NaCl and SDS is also observed.