Two-Photon Fluorescence Imaging.

Two-photon fluorescence imaging is a powerful tool for observing the dynamics of cells in vivo in intact tissue and is well suitable for imaging neuronal activity for neuroscience research. Due to the nonlinear two-photon absorption, the optical sectioning ability is inherent, resulting in two-photon images with high signal contrast and signal-to-noise ratio with efficient illumination. In addition, the longer wavelength excitation light in two-photon imaging compared to one-photon imaging suffers less scattering and absorption by tissue, which allows deeper penetration. Today, two-photon microscopy is being rapidly developed to adapt to various biological applications for high-speed, high-resolution, large-volume, long-term imaging in freely behaving animals.