Surface enhanced Raman scattering (SERS)—a quantitative analytical tool?

Abstract

Raman spectroscopy is a widely used analytical tool capable of providing valuable information about the chemical structure and composition of molecules. In order to detect substances also at a very low concentration levels, Surface Enhanced Raman Scattering (SERS) was introduced. The different amplification mechanisms result in extreme sensitivity, however, a quantitative use of SERS appears to be problematic. Especially, when deploying silver sols as SERS substrates, the reproducibility of the signal intensities for a given substance concentration is questionable. Experimental results of an investigation of this problem for low concentrations of adenine are presented. Comparison with results obtained for different SERS substrates by other authors reveals clearly different dependencies. Only in a very limited concentration range reproducible and therefore quantitatively utilizable data could be obtained.

Surface‐enhanced Raman scattering spectroscopy via gold nanostars

“…The solution was kept at room temperature and used within 3 h of preparation. Finally, 2 µl of the prepared seed solution, containing HAuCl 4 .H 2 O, CTAB, AgNO 3 and ascorbic acid, was added to the growth solution as described in the previous paragraph. Similar to nanostars, nanorods are also composed of ca 96% Au, ca 2% Ag and ca 2% Br (see Supporting Information for EDX data).…”

“…There were not enough molecules to cover the surface of the NPs at the lowest concentration. [4] Saturation likely occurred close to a molecular concentration of 1.5 µM owing to full coverage of the NP surface by 2-MPy. Above the saturation point, the excess molecules form additional layers, resulting in lower electromagnetic and chemical contribution to the enhancement and thus a decrease in the observed SERS signal intensity.…”

Detection of the Quorum Sensing Signal Molecule N-Dodecanoyl-DLHomoserine Lactone Below 1 Nanomolar Concentrations using Surface Enhanced Raman Spectroscopy

“…However the fall can also be seen to be non-linear, which is seen in literature and thus why a small concentration range is often chosen [40,42]. After 200nM the intensity increases until 2 nM.…”

“…The increase in enhancement for the low concentrations could be explained by the existence of hot spots in the cluster structures, caused by thermally and non thermally activated diffusion of molecules into and out of hot areas, or trapping and release of molecules in high-field gradients [39]. It could also be due to the different adsorption geometries that can exist at different concentrations, as seen in [40,41]. A major problem in SERS is not only the difficulty in reproducing amplification processes and variations in colloid sizes and shapes, but also the orientations of the adsorbed molecules on the colloid surfaces and whether they change orientation due to pH or other factors which may be changing.…”

Surface-enhanced Raman scattering of SnO2bulk material and colloidal solutions

“…Generally, the SERS induced occurrence of Raman forbidden peaks has been attributed to the lowering of the symmetry of the investigated molecules due to the formation of bonds at the metallic surface or to the presence of a steep field gradient close to the nanoparticles metal surfaces [15][16][17] .…”