Abstract
SERRS spectra of cationic 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin (TMPyP) on Ag nanoparticles immobilized to glass via silane or by drying were measured using confocal Raman microspectrometer. The limit of detection (LOD) of TMPyP on Ag silanized glass plates was ~ 1x10-8 M, but spectra suffered from presence of spurious bands originating from carbon species mainly as a result of thermal decomposition of silane.
Ag colloid/TMPyP drops dried on glass show better spectra and fewer spurious bands for the same TMPyP concentration compared to the silanized surfaces. Dried drops form a ring in the edge part of the drop containing high enhancing sites (big aggregates with some ''hot spots'') providing high SERRS signal of TMPyP in extremely short acquisition times (1 s).
Despite the problems with spurious bands, Raman microspectroscopy from immobilized Ag colloidal nanoparticles improves SERS sensitivity and reproducibility in comparison to macro-Raman measurements in Ag colloidal solution.