New light on Ag‐colloid preparation for surface‐enhanced FT‐Raman spectroscopy: the role of aggregation

Abstract

Abstract Silver‐colloid solutions have been used as the medium for surface‐enhanced Raman spectroscopy (SERS) for over two decades. UV‐Vis absorption is often used to determine the state of aggregation of the colloid, considered a critical parameter for a successful SERS experiment, especially when using an IR excitation source such as an Nd:YAG laser. We present results from parallel studies of silver colloid aggregation and UV‐Vis absorption showing that a significant change in the aggregation state of the colloid does not necessarily translate into a better SERS substrate when using an IR excitation source. Conversely, we show that a small addition of chloride ions sufficient for inducing FT‐IR SERS does not produce any detectable colloid particle aggregation. These results may give new insight into how to optimize experimental conditions for SERS when using a near‐IR excitation source. Copyright © 2005 John Wiley & Sons, Ltd.