New label-free method tracks molecules and drugs in ...(at the growing imbalance of saturated an...)

SRS microscopy could also prove useful in neuroimaging, since neurons are coated with fatty myelin sheaths.

The researchers' use of SRS microscopy to analyze skin tissue could also open new frontiers in drug development. Xie and colleagues used SRS microscopy to view how well retinoic acid, a topical acne medication, is absorbed into skin cells. They also used the technique to capture deep-skin penetration by dimethyl sulfoxide (DMSO), a compound added to many topical medications and ointments to enhance absorption.

Scientists currently use a variety of techniques to visualize biomolecules, but most have significant limitations that are sidestepped by SRS microscopy. A jellyfish protein first discovered in 1962, green fluorescent protein (GFP), is now used extensively as a label for observing the activity of biomolecules. GFP labeling provides sharp images, but the bulky protein can perturb delicate biological pathways, especially in cases where its heft overwhelms smaller biomolecules. Also, GFP's characteristic glow subsides with time, making it infeasible for long-term tracking.

Much like SRS microscopy, conventional infrared (IR) and Raman microscopies measure the vibrations of chemical bonds between atoms. But they are low-sensitivity imaging techniques, and require either desiccated samples or high laser power, which limits use in imaging live specimens. Coherent anti-Stokes Raman scattering (CARS) microscopy, a field pioneered by Xie's own group, cannot provide clear enough contrast for most molecules.

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