Panagis D. Samolis 1 , 2 , Daniel Langley 3 , 4 , Breanna M. O’Reilly 5 , 6 , Zay Oo 3 , 4 , Geva Hilzenrat 3 , 4 , Shyamsunder Erramilli 2 , 7 , 8 , Allyson E. Sgro 5 , 6 , 7 , Sally McArthur 3 , 4 , Michelle Y. Sander 1 , 2 , 5 , 8 , *
14 December 2020
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.