Visualizing Bioactive Small Molecules by Alkyne Tagging and Slit-Scanning Raman Microscopy.

An understanding of the intracellular distribution of bioactive small molecules provides insight into their target organelles and biomolecules, and throws light on their molecular mechanisms of action and specificity. Many studies in this area have employed fluorescence imaging, using molecules of interest labeled with fluorescent dyes. However, modification with a bulky fluorophore may significantly alter the properties, including bioactivity, of small molecules. To address this issue, we have recently developed Raman scattering microscopy of alkyne tags to visualize small molecules in biological systems. The tiny alkyne tag should have a minimal effect on the properties of the tagged molecule, and the unique alkyne vibrational properties allow observation of the Raman signals of the tagged molecules in a wavelength region where there is little interference from Raman signals of endogenous biomolecules. Here we summarize the methodology for Raman imaging of alkyne-tagged bioactive small molecules in living biological systems including the development of slit-scanning Raman microscope, which is useful for fast imaging of alkyne-tagged molecules.