Strategy to improve the reproducibility of colloidal SERS

There is a pressing need to improve the reproducibility of surface enhanced Raman spectroscopy (SERS) measurements, if the technique is to be used routinely for trace analysis. This is particularly true for colloidal SERS, in which data reproducibility is dominated by the final shape and size of metal clusters produced during colloid aggregation. This study presents general guidelines for designing appropriate measurement strategies that can be used to identify and optimise crucial steps in a protocol that leads to better reproducibility of the results. We show that the data reproducibility can be improved by optimising vortexing time during colloid aggregation, which we attribute to the formation of more reproducible metal clusters under conditions of 'forced convection'. The study also investigated the effects of different storage conditions on the data reproducibility of SERS during a 6-month study period. Storage conditions did not significantly influence the SERS reproducibility. However, at the end of 6 months, colloids that were stored (in plastic containers) at room temperature showed a difference in their quality, as mirrored by their different opto-physical properties. This was made apparent through the analysis of UV-vis spectroscopy measurements by principal component analysis. Copyright (C) 2007 John Wiley & Sons, Ltd.