Feeling the vibes: Vibrational spectroscopic imaging of biomolecular assemblies in their natural environment.

Biomolecular assemblies form via intramolecular interactions and serve important biological functions. The most characterized biomolecular assemblies are amyloid fibrils, which are associated with neurodegenerative diseases. Advances in microscopy techniques enabled characterization of the morphology of these assemblies, but so far, failed in detailed structural characterizations. Vibrational spectroscopic imaging presents unique advantages to studying biomolecular assemblies in their natural environment due to the sensitivity of vibrational spectra to protein structural changes, especially β-sheet enrichment in amyloid fibrils. High-resolution hyperspectral images originating from distinct vibrations of chemical bonds provide label-free characterizations of biomolecules, including proteins, lipids, and nucleic acids. In this review, we first briefly introduce infrared and Raman-based spectroscopy and their biological interpretation. We then review applications adopting Fourier transform Infrared-based, mid-infrared photothermal-based, and Raman-based approaches in tissue and cells, especially live cells. Finally, we discuss how these technologies are evolving to study biomolecular assemblies beyond amyloid fibrils.