Study of biomolecules by Surface-enhanced Raman microspectroscopy

This work deals with study of biomolecules using surface-enhanced Raman scattering (SERS) microspectroscopy. For that purpose surfaces based on gold and silver colloidal nanoparticles immobilized either by silane or by drying on glass plate were tested. As a model molecule cationic free-base 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin was chosen. The aim was primarily to improve sensitivity and spectral reproducibility of the mentioned SERS-active systems using an integrated Raman microspectrometer which has several advantages (better signal-to-noise ratio, shorter collection time, mapping, confocality) over a classical Raman spectrometer. The obtained results show that gold and silver nanoparticles immobilized by silane give the limits of detection of porphyrin ~ 1×10-8 M, moreover in the intact free-base form. While gold surfaces also show excellent spectral reproducibility, in the case of silver surfaces there is a great problem of frequent presence of spurious bands originating apparently from contamination by carbonaceous compounds and decomposition of silane or porphyrin itself. In the case of silver nanoparticles, drops that form a ring of aggregates with extremely high SERS enhancement after drying on glass proved more suitable