Suppression of Luminescence Background in Raman Spectroscopy by Means of Transient Optical Depletion of Causal Impurity Molecules

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Abstract
A simple but highly efficient method of luminescence quenching in Raman spectroscopy is proposed—made on the basis of a newly recognized phenomenon which is ascribable to the optical depletion of luminescent impurity molecules by pulsed-laser excitation. The method has been applied to two typical biological samples: a DNA tetramer (AATT; adenine-adenine-thymine-thymine) and a protein (calmodulin). Suppression of luminescence background by factors of 10–100 was achieved by changing the mode of excitation from cw to pulsed. A model calculation based on semiquantitative estimation of photoexcitation rates successfully accounts for the observed quenching efficiency.