Abstract
Aggregated Au colloids have been widely used as SERS enhancing media for many years but to date there has been no systematic investigation of the effect of the particle size on the enhancements given by simple aggregated Au colloid solutions. Previous systematic studies on isolated particles in solution or multiple particles deposited onto surfaces reported widely different optimum particle sizes for the same excitation wavelength and also disagreed on the extent to which surface plasmon absorption spectra were a good predictor of enhancement
factors. In this work the spectroscopic properties of a range of samples of monodisperse Au colloids with diameters ranging from 21 to 146 nm have been investigated in solution. The UV/visible absorption
spectra of the colloids show complex changes as a function of aggregating salt (MgSO4) concentration which diminish when the colloid is fully aggregated. Under these conditions, the relative SERS
enhancements provided by the variously sized colloids vary very significantly across the size range. The largest signals in the raw data are observed for 46 nm colloids but correction for the total
surface area available to generate enhancement shows that particles with 74 nm diameter give the largest enhancement per unit surface area.
The observed enhancements do not correlate with absorbance at the excitation wavelength but the large differences between differently sized colloids demonstrate that even in the randomly aggregated
particle assemblies studied here, inhomogeneous broadening does not mask the underlying changes due to differences in particle diameter.
Original language | English |
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Pages (from-to) | 7455-7462 |
Number of pages | 8 |
Journal | Physical Chemistry Chemical Physics |
Volume | 11 |
Issue number | 34 |
DOIs | |
Publication status | Published - 2009 |
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- General Physics and Astronomy