Functional live-cell mid-infrared optoacoustic microscopy

Imaging modalities based on vibrational spectroscopy (Raman or mid-IR imaging) have demonstrated high label-free chemical specificity for different biomolecules. Nevertheless, conventional mid-IR microscopy have been limited mostly to dry tissues and fixed cells due to the strong mid-IR absorption of water and due to the use of conventional negative-contrast detection. We introduce positive-contrast Mid-infraRed Optoacoustic Microscopy (MiROM) for label-free metabolic imaging in living cells. We showcase the unique capabilities of MiROM in living cells by monitoring the spatiotemporal distribution of carbohydrates, lipids, and proteins in adipocytes during lipogenesis as well as monitoring the lipid-protein dynamics in brown and white adipocytes during lipolysis. We discuss how MiROM yields unique label-free metabolic imaging abilities for a broader range of bioanalytical studies in living cells and its potential for analytical histology in unprocessed tissues.