Vibrational microspectroscopy of single proteins

Vibrational infrared absorption of a single protein molecule was detected at a few kelvins as infrared-induced recovery of visible fluorescence of a dye with which the protein was labeled. This sensitive method of detecting infrared absorption was demonstrated for a single bovine serum albumin (BSA) molecule labeled with Alexa Fluor 660 by determining the vibrational infrared absorption spectrum of the backbone vibrations of the α-helical structure in the wavelength region around 6 μm (1650 cm -1). In addition to measuring the vibrational infrared absorption spectrum, the visible fluorescence can be simultaneously used for imaging of the same dye-labeled single protein molecules