Single-molecule imaging and spectroscopy using fluorescence and surface-enhanced Raman scattering

We extended single molecule fluorescence imaging and time-resolved fluorometry from the green to the violet-excitation regime to find feasibility of detecting and identifying fluorescent analogs of nucleic-acid bases at the single-molecule level. Using violet excitation, we observed fluorescent spots from single complexes composed of a nucleotide analogue and the Klenow fragment of DNA polymerase I. Also, we implemented Raman imaging and spectroscopy of adenine molecules adsorbed on Ag colloidal nanoparticles to find feasibility of identifying nucleic-acid bases at the single-molecule level. Surface enhanced Raman scattering (SERS) of adenine molecules showed an intermittent on-and-off behavior called blinking. The observation of blinking provides substantial evidence for detecting single adenine molecules.