Correlation of optical properties with structure of immoblised nanoparticles—a method for probing the mechanism of SERRS

Abstract

A combined surface enhanced resonance Raman scattering (SERRS) and transmission electron microscopy (TEM) method has been developed allowing the same immobilised nanoparticles to be reliably located and studied by both techniques. The method allows large numbers of particles to be analysed by each technique relatively simply and the distribution of Raman enhancement between particles and clusters, as well as the relationship between particle microstructure and Raman enhancement, to be investigated. In addition, the effect of chemical and laser damage on the dye on the surface of the particles and the effect on the particles can be systematically investigated. These effects can cause time dependence fluctuations in Raman signals which could be confused with “blinking” from single molecules. Conditions were identified to enable Raman scattering to be detected without photodegradation to either the analyte molecules or the particles. Measurement outside this range gave rise to alterations in the spectra and to loss of signal. The extent of the damage to the analyte/particle if these conditions are not adhered to gives rise for concern about interpretation of changes in spectra observed unless an attempt is made to assess the limits of the conditions which can be applied before photodegradation or sample drying occurs. The method developed will enable reliable and systematic studies of the enhancement obtained from immobilised single particles by enabling the full power of high resolution TEM to be utilised to aid the development of a reliable SERRS theory.