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.

Tip enhanced Raman spectroscopy evidence for amorphous carbon contamination on gold surfaces

“…Spectral fluctuations observed in SERS experiments were promptly attributed to single molecules effect [3][4][5], possibly overlooking the contribution due to analyte decomposition occurring by laser damage [6][7][8]. Similarly, a blinking behavior has also been readily observed in TERS experiments on dye molecules and has been interpreted as a signature of single molecule response [9][10][11].…”

“…Surface contaminating carbon may be also formed by photo-degradation of the sample due to the giant electromagnetic field in both SERS and TERS. As shown by Khan et al [6], high laser power can cause heating and burning of the sample during the spectral acquisition. Thus, complex spectra, originating from a range of intermediate surface species, may be observed.…”

Inherent Complexities of Trace Detection by Surface‐Enhanced Raman Scattering

“…The advantages of using minimal laser power have been demonstrated many times in SERS experiments, particularly in cases where there is a chance of molecular resonance or photochemistry. [105][106][107] One method for reducing laser-induced molecular degradation is to lower the sample temperature. For example, by conducting SERS experiments at 40 K, Pang et al [108] have shown that the negative effects of laser exposure can be greatly reduced.…”

Nano-immunoassay with improved performance for detection of cancer biomarkers

“…The origins of this contamination are not fully understood, however such factors as photo-induced or thermal decomposition of the analyte molecules are usually discussed in the literature. 17 Another possible source of carbon contamination is adsorption of airborne hydrocarbons on the metal surface. 18 Other components of our assay such as antibodies and proteins may all contribute to the appearance of the carbonaceous peaks upon their decomposition.…”