Effects of the surface modification of silver nanoparticles on the surface-enhanced Raman spectroscopy of methylene blue for borohydride-reduced silver colloid

The paper further investigated the relationship between the modification of the surface chemistry and the enhancement mechanisms of borohydride-reduced silver particles (BRSC). The bands of residual ions die down while the anomalous bands increase gradually with the increasing of the concentration of Cl− and Br−. It means the residual ions are displaced gradually by the added Cl− or Br− and the two halides can lead to the aggregation of the BRSC to a certain extent. However, the most strongly binding anions – I−, cannot cause any aggregation of silver particles. From the detection of methylene blue (MB), the relationship between the modification of silver surface chemistry and the enhancement mechanisms was discussed. Chloride gives the greatest enhancement while the iodide gives the lowest enhancement among the different kinds of anions. There are also some anomalous bands in the SERS spectra of MB, and these anomalous bands were given rational explanation in this paper.