A small-molecule two-photon probe for nitric oxide in living tissues.

Two-photon microscopy (TPM) has become an indispensable tool in the study of biology and medicine due to the capability of this method for molecular imaging deep inside intact tissues. For the maximum utilization of TPM, a variety of two-photon (TP) probes for specific applications are needed. In this article, we report a small-molecule TP probe (ANO1) for nitric oxide (NO) that shows a rapid and specific NO response, a 68-fold fluorescence enhancement in response to NO, and a maximum TP-action cross-section of 170 GM (GM: 10(-50) cm(4) photon(-1)) upon reaction with excess NO. This probe can be easily loaded into cells and tissues and can real-time monitor NO in living tissues at 100-180 μm depth for longer than 1200 s through the use of TPM, with minimum interference from other biologically relevant species.