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Star-shaped gold nanoparticles modified with cyanine 5.5 derivatives were studied as optical tags for bioimaging by surface-enhanced Raman scattering (SERS). Obtained tags showed a plasmon resonance band at 640 nm in the absorption spectra which ensures them a maximum efficiency when excited by red lasers. SERS measurements were carried out for the modified particles in the solution phase and after incubation with the PANC-1 cell line. The SERS spectra of the solutions revealed a characteristic signal of cyanine 5.5 amino derivative in the range of 100-1000 cm-1, where there is no high fluorescent background. In cell samples, the SERS spectrum of the dye was recorded from the cytoplasm and was not detected outside the cells. In order to confirm the intracellular localization of the tags, the SERS spectra were also scanned in height. The test on cytotoxicity showed that the studied tags are not toxic in the concentration range from 0.05 to 1 mg/l on atomic gold. Keywords: surface-enhanced Raman scattering, gold nanostar, cyanine, optical tags, bioimaging

In this work, we study the mechanism of peptide photodissociation by ultraviolet irradiation at 193 nm wavelength and discuss the role of ionization proton in this process. We found that substituting the ionization proton for the alkali metal cations (sodium) in the peptide ions results in significant changes of the photodissociation spectra. The experimental data obtained in this work revealed that the photodissociation process can be described using the mobile proton model introduced earlier for peptide collision dissociation. The results can be used in proteomics research for optimization of mass spectrometer's parameters to increase the efficiency of peptide dissociation and in developing sequence-specific models for peptide fragmentation prediction.