In-vivo and label-free imaging of cellular and tissue structures in mouse ear skin by using second- and third-harmonic generation microscopy

A video-rate multimodal microscope, which can obtain second- and third- harmonic generation (SHG and THG) images simultaneously, is developed for investigating cellular and tissue structures in mouse ear skin. By utilizing in-vivo video-rate epi-detected SHG and THG microscopy, we successfully demonstrate that combined images of subcutaneous cellular components and peripheral nerve fibers, together with the collagen fiber, in the mouse ear pinna can be obtained without employing fluorescent probes. We also show that the flow of red blood cells and the diameter change of arteriole-like blood vessels can be visualized with femtosecond laser pulses with a wavelength of 1036 nm. In particular, the epi-THG contrast images of the blood-vessel walls display clearly the difference between the arteriole-like and the venule capillary-like blood-vessel types. We should emphasize that our newly-developed microscope system has a unique feature in that it can produce simultaneous in-vivo label-free SHG and THG images in contrast to the conventional confocal and two-photon microscopes.