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Absolute quantity imaging of biomolecules on a single cell level is critical for measurement assurance in biosciences and bioindustries. While infrared (IR) transmission microscopy is a powerful label-free imaging modality capable of chemical quantification, its applicability to hydrated biological samples remains challenging due to the strong water absorption. We overcome this challenge by applying a solvent absorption compensation (SAC) technique to a home-built quantum cascade laser IR microscope. SAC-IR microscopy improves the chemical sensitivity considerably by adjusting the incident light intensity to pre-compensate the IR absorption by water while retaining the full dynamic range. We demonstrate the label-free chemical imaging of key biomolecules of a cell, such as protein, fatty acid, and nucleic acid, with sub-cellular spatial resolution. By imaging live fibroblast cells over twelve hours, we monitor the mass change of the three molecular species of single cells at various phases, including cell division. While the current live-cell imaging demonstration involved three wavenumbers, more wavenumber images could measure more biomolecules in live cells with higher accuracy. As a label-free method to measure absolute quantities of various molecules in a cell, SAC-IR microscopy can potentially become a standard chemical characterization tool for live cells in biology, medicine, and biotechnology., Comment: Body: 19 pages, 5 figures. Supplemental: 11 pages, 6 figures

In electron microscopy, charging of non-conductive biological samples by focused electron beams hinders their high-resolution imaging. Gold or platinum coatings have been commonly used to prevent such sample charging, but it disables further quantitative and qualitative chemical analyses by energy dispersive spectroscopy (EDS). Here we report that graphene-coating on biological samples enables non-destructive high-resolution imaging by scanning electron microscopy (SEM) as well as chemical analysis by EDS, utilizing graphene's transparency to electron beams, high conductivity, outstanding mechanical strength, and flexibility. We believe that the graphene-coated imaging and analysis would provide us a new opportunity to explore various biological phenomena unseen before due to the limitation in sample preparation and image resolution, which will broaden our understanding on the life mechanism of various living organisms.