Benchtop IR\nImaging of Live Cells: Monitoring the\nTotal Mass of Biomolecules in Single Cells

Absolute quantity imaging of biomolecules on a single\ncell level\nis critical for measurement assurance in biosciences and bioindustries.\nWhile infrared (IR) transmission microscopy is a powerful label-free\nimaging modality capable of chemical quantification, its applicability\nto hydrated biological samples remains challenging due to the strong\nIR absorption by water. Traditional IR imaging of hydrated cells relies\non powerful light sources, such as synchrotrons, to mitigate the light\nabsorption by water. However, we overcome this challenge by applying\na solvent absorption compensation (SAC) technique to a home-built\nbenchtop IR microscope based on an external-cavity quantum cascade\nlaser. SAC-IR microscopy adjusts the incident light using a pair of\npolarizers to precompensate the IR absorption by water while retaining\nthe full dynamic range. Integrating the IR absorbance over a cell\nyields the total mass of biomolecules per cell. We monitor the total\nmass of the biomolecules of live fibroblast cells over 12 h, demonstrating\npromise for advancing our understanding of the biomolecular processes\noccurring in live cells on the single-cell level.