Peak multiphoton excitation of mCherry using an optical parametric oscillator (OPO).

mCherry is a red fluorescent protein which is bright, photostable, and has a low molecular weight. It is an attractive choice for multiphoton fluorescence imaging; however, the multiphoton excitation spectrum of mCherry is not known. In this paper we report the two photon excitation spectrum of mCherry measured up to 1190 nm in the near infrared (NIR) region. Skin tissues of transgenic mice that express mCherry were used in the experiments. mCherry in the tissues was excited with a Titanium:Sapphire laser and an optical parametric oscillator pumped by the Titanium:Sapphire laser. We found that the peak excitation of mCherry occurs at 1160 nm.