Study of the surface-enhanced Raman spectroscopy of residual impurities in hydroxylamine-reduced silver colloid and the effects of anions on the colloid activity

The paper investigated the residual ions in hydroxylamine-reduced silver colloid (HRSC) and the relationship between the condition of HRSC and the enhanced mechanisms of this colloid. We also detected the SERS of MB and studied the effects of anions on the Raman signal. In the case of HRSC, the bands of residual ions diminish while the bands of Ag-anions increase gradually with increasing the concentrations of Cl− and NO3−. It means the affinity of residual ions on the silver surface is weaker than that of Cl− and NO3− and the residual ions are replaced gradually by the added Cl− or NO3−. The Raman signal of residual ions can be detected by treatment with anions that do not bind strongly to the silver surface, such as SO42−. The most intense band of Ag-anions bonds can be also observed when adding weakly binding anions to the colloid. However, the anions which make up the Ag-anions bonds are residual Cl− and the effect of weakly binding anions is only to aggregate the silver particles. Residual Cl− can be replaced by I− which has the highest affinity. From the detection of methylene blue (MB), the effects of anions on the enhancement of Raman signal are discussed in detail, and these findings could make the conditions suitable for detecting analytes in high efficiency. This study will have a profound implication to SERS users about their interpretation of SERS spectra when obtaining these anomalous bands.

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► The paper studied the SERS of HRSC when adding a great range of anions.
► The SERS of residual impurities in HRSC was further investigated.
► The relationship between the condition of HRSC and the enhancement was studied.
► We detected the SERS of MB and studied the effects of anions on the Raman signal.
► This study makes the conditions suitable for detecting analytes in high efficiency.