An in situ reduction method for preparing novel surface-enhanced Raman scattering substrates

Abstract

Surface-enhanced Raman scattering (SERS)-active substrates with high enhancement were prepared by an in situ reduction method. First, NH 2OH·HCl was added as complexing agent to AgNO3 solution, then NaI was dropped in to produce an AgI colloid. Second, the self-assembly technique was used to transfer the AgI nanoparticles on to the solid substrate and then they were reduced in situ. The UV-visible spectra show that the absorption band is asymmetric, indicating that the Ag nanoparticle size distribution on the substrate is wide, which was further confirmed by atomic force microscopy (AFM) measurements. The SERS-active substrates with different coverages can be formed in a layer-by-layer electrostatic assembly by exposing positively charged surfaces to colloid solutions containing oppositely charged AgI nanoparticles. The results of AFM and UV-visible spectroscopy show that the Ag nanoparticles grow with increase in the degree of coverage and that most of them remain isolated even at high coverage. Consequently, the surface optical properties are dominated by the absorption due to the isolated Ag nanoparticles. The new substrate presents high SERS enhancement and the SERS enhancement factor was estimated to be 109. By comparison with our previous work, the important effects of stabilizers on the formation and transfer of nanoparticles are confirmed. Copyright © 2005 John Wiley & Sons, Ltd.