Label-free imaging of fibroblast membrane interfaces and protein signatures with vibrational infrared photothermal and phase signals

• Published in: Biomedical optics express 2021-01, Vol.12 (1), p.303-319
• Main Authors: Samolis, Panagis D, Langley, Daniel, O'Reilly, Breanna M, Oo, Zay, Hilzenrat, Geva, Erramilli, Shyamsunder, Sgro, Allyson E, McArthur, Sally, Sander, Michelle Y
• Format: Article
• Language: English
• ISSN: 2156-7085; 2156-7085
• DOI: 10.1364/BOE.411888

Label-free vibrational imaging of biological samples has attracted significant interest due to its integration of structural and chemical information. Vibrational infrared photothermal amplitude and phase signal (VIPPS) imaging provide label-free chemical identification by targeting the characteristic resonances of biological compounds that are present in the mid-infrared fingerprint region (3 µm - 12 µm). High contrast imaging of subcellular features and chemical identification of protein secondary structures in unlabeled and labeled fibroblast cells embedded in a collagen-rich extracellular matrix is demonstrated by combining contrast from absorption signatures (amplitude signals) with sensitive detection of different heat properties (lock-in phase signals). We present that the detectability of nano-sized cell membranes is enhanced to well below the optical diffraction limit since the membranes are found to act as thermal barriers. VIPPS offers a novel combination of chemical imaging and thermal diffusion characterization that paves the way towards label-free imaging of cell models and tissues as well as the study of intracellular heat dynamics.