Spectroscopy of Single Hemoglobin Molecules by Surface Enhanced Raman Scattering

We demonstrate the detection of molecular vibrations in single hemoglobin (Hb) protein molecules attached to isolated and immobilized silver nanoparticles by surface enhanced Raman scattering (SERS). A comparison between calculation and experiment indicates that electromagnetic field effects dominate the surface enhancement, and that single molecule Hb SERS is possible only for molecules situated between Ag particles. The vibrational spectra exhibit temporal fluctuations of unknown origin which appear to be characteristic of the single molecule detection limit.