Applications of vibrational tags in biological imaging by Raman microscopy

Abstract

As a superb tool to visualize and study the spatial-temporal distribution of chemicals, Raman microscopy has made big impacts to many disciplines of science. While the label-free imaging has been the prevailing strategy in Raman microscopy, recent development and applications of vibrational/Raman tags, particularly when coupled with stimulated Raman Scattering (SRS) microscopy, have generated intense excitement in biomedical imaging. SRS imaging of vibrational tags has enabled researchers to study a wide range of small biomolecules with high specificity, sensitivity and multiplex capability, at single live cell level, tissue level or even in vivo. As reviewed in the article, this platform has facilitated imaging distribution and dynamics of small molecules such as glucose, lipids, amino acids, nucleic acids, and drugs that are otherwise difficult to do with other means. As both the vibrational tags and Raman instrumental development progress rapidly and synergistically, we anticipate that the technique will shed light onto an even broader spectrum of biomedical problems.

Volumetric chemical imaging by clearing-enhanced stimulated Raman scattering microscopy

“…Second, label-free SRS enables probing chemical structures in tissues without exogenous labels, free from the difficulties of probe delivery for fluorescence microscopy. Third, the emerging bioorthogonal chemical imaging platform with vibrational tags (such as DO-SRS) allows visualization of metabolic dynamics of biomolecules, such as proteins, lipids, and nucleic acids, inside tissues and organisms (33,40,41). Therefore, volumetric chemical imaging by clearing-enhanced SRS microscopy can be a valuable tool for characterizing 3D structures, compositions, dynamics, and functions in diverse biological contexts.…”

“…The interplay between proteins and lipids has important implications in cancer (36,37) and Alzheimer's disease (38,39). For the cell-silent window, many emerging vibrational tags reside in this region (40)(41)(42)(43)(44), allowing imaging of metabolic dynamics of small metabolites and also super multiplexed imaging (45,46). Hence, our first criterion requires the clearing reagents to make tissues optically transparent without introducing Raman peaks in the CH region or the cell-silent region.…”

“…Compared with 2D cultures, tumor spheroids are considered to better mimic the 3D tumor microenvironment and are thus increasingly used to study tumor cell physiology and response of tumors to radiotherapy and chemotherapy in a 3D multicellular context (50,51). In addition to the two-color label-free imaging, we further introduced a third color for bioorthogonal chemical imaging (40,41). This method allowed imaging not only the spatial distributions of preexisting proteins and lipids, but also the metabolic activity of newly synthesized lipids by incubating spheroids with deuterated palmitic acid (d-PA) (SI Appendix, Fig.…”

Imaging the invisible—Bioorthogonal Raman probes for imaging of cells and tissues

“…Raman spectroscopy in combination with bioorthogonal tags has also been used for studies of the metabolic activity of eukaryotic cells. Labeled molecules were designed for various cellular constituents, which provided the possibility to investigate their uptake behavior, metabolism and other cellular reactions [21,41,84].…”

Raman Imaging of Nanocarriers for Drug Delivery

“…However, recently, small chemical tags have been developed as a way to enhance contrast. This topic was reviewed in 2017 by Zhao et al [68]. There are no peaks in the Raman spectrum of a cell between 1800 and 2800 cm −1 , and various bond stretches, such as carbon–deuterium (C–D), alkynes (C≡C), and nitriles (C≡N) generate peaks in this region, meaning they can be imaged without interference from the cellular background [69].…”