I prepared polydopamine layers with silver nanoparticles and tested for SERS. SESR intensity of the lowest rhodamine B solution concentration (10-7 mol/l ) is higher than the one of the most concentrated Rhodamine B solution (10-2 mol/l). What causes that?
In principle Raman spectroscopy is a bulk method, but if you cover your substrate with macroscopic amounts of material, it is possible that the SERS active zones, i.e. the deepest points, get effectively shielded off by your material and thus the effect decays.
I can't guarantee that's the reason, but it's a possibility.
I agree with Jürgen Weippert. Also, it could because you have "hotspots" (an area with many silver nanoparticles too close to each other) on the material's surface. If you changed the laser intensity and exposure time while investigating the samples, that could lead to such phenomena.
Barbora Štefková
The degree of chemical enhncement of the SERS depends on the bond strength of the molecule being determined with metal atoms on the surface of active centers. Thus, compounds with a greater affinity for the surface will be better adsorbed and have a more significant amplification of the SERS signal, which increases the selectivity of the method. At a high concentration, rhodomine molecules associate. This leads to a decrease in the interaction of rhodamine with silver nanoparticles. The intensity of SERS decreases.
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