Label-Free Transient Absorption Microscopy for Red Blood Cell Flow Velocity Measurement in Vivo.

Red blood cells have intrinsic transient absorption property at the near-infrared region, allowing for label-free detection and imaging. We present a new approach to measure the blood flow velocity in vivo with a transient absorption microscope and correlation analyses of signal sequences. With specific scan modes, we have quantitatively obtained the flow velocity in capillaries, arteries, and veins in a live zebrafish with accuracy of about 30 μm/s. In addition, a high-resolution three-dimensional vessel network can be reconstructed through this approach with spatial resolution of 1 μm.