A new optical imaging platform represents a significant step toward a longstanding scientific goal: visualizing small biomolecules inside living biological systems with minimum disturbance. A team at Columbia University has developed a general method to image a broad spectrum of small biomolecules, such as molecular drugs and nucleic acids, amino acids and lipids, viewing where they are localized and how they function inside cells. “Our new technique will open up numerous otherwise-difficult studies on small biomolecules in live cells and animals,” said researcher Wei Min, an assistant professor of chemistry at Columbia. “In addition to basic research, our technique could also contribute greatly to translational applications.” Researchers have coupled SRS microscopy with alkyne tags to visualize a broad spectrum of small molecules in live cells and animals, including DNA, RNA, amino acids, lipids and triglycerides. Courtesy of Columbia University. The researchers coupled the laser-based technique stimulated Raman scattering (SRS) microscopy with a small but highly vibrant alkyne tag (a chemical bond that, when stretched, produces a strong Raman scattering signal at a frequency different from natural molecules inside cells). This avoids the perturbation that typically occurs with large fluorescent tags, since fluorophores are frequently larger or at least comparable in size to the small molecules of interest. As a result, they often disturb the normal functions of these small molecules with crucial biological roles. This new technique labels the small molecules with the tiny alkyne tag and obtains high detection specificity and sensitivity by SRS imaging. The unique stretching motion of the carbon-carbon (C=C) bond that is carried by the small molecules produces a 3-D map of them inside living cells and animals. “The major advantages of our technique lie in the superb sensitivity, specificity and biocompatibility with dynamics of live cells and animals for small-molecule imaging,” said lead author Lu Wei, a doctoral candidate in chemistry at Columbia. The researchers plan to apply the technique to other biomedical questions as well, including detecting tumor cells and probing drug pharmacokinetics in animal models. They are also developing other alkyne-labeled biologically active molecules for more versatile imaging applications. The research was funded by the National Institutes of Health Director’s New Innovator Award, the U.S. Army Research Office and the Alfred P. Sloan Foundation. The work is published in Nature Methods. For more information, visit www.columbia.edu.