Time-resolved mid-infrared photothermal microscopy for heat transfer dynamics across aqueous interfaces

Photothermal imaging has proven a powerful label-free chemical imaging technique. With time-resolved mid-infrared photothermal imaging heat transfer dynamics across aqueous interfaces can be studied. However, liquid water has been a limiting factor in mid-infrared imaging and spectroscopy due to its high absorption spanning across the molecular fingerprint region so that cellular imaging is often performed in less absorbing heavy water instead. Time-resolved measurements via boxcar detection enable the separation of water background and reveal how heat transfer dynamics across aqueous interfaces strongly depend on hydration and the surrounding environment. Mid-infrared photothermal imaging of extracted axon-bundles from crayfish is presented in a saline solution where the water background can be separated based on its inherently different transient response.