With its high penetration depth and amenability for two-photon and multi-photon fluorescence microscopy, near-IR fluorescent protein development is a rapidly developing field. Conceptually, near-IR appears to be more benign than conventional visible wavelength excitation methods given its lower energy and longer wavelength. However, use of near-IR excitable fluorescent protein in two-photon and multi-photon fluorescence microscopy … More Challenges in developing near-IR fluorescent proteins