Two-photon fluorescent probes for metal ions in live tissues.

Two-photon microscopy (TPM) is a new imaging tool that can detect biological targets deep inside a live tissue. To faciltate the use of TPM in biomedical research, a variety of two-photon (TP) probes for specific applications are needed. In this Forum Article, we describe the design strategy, photophysical properties, and biological imaging applications of a selection of our recent studies in the development of TP probes for metal ions. Small-molecule TP turn-on probes, organelle-targeted probes, and multicolor emissive probes for dual-color imaging are briefly reviewed.