Intravital images were obtained before injection and then taken at 0.5, 1, 1.5, 2, 2.5, and 3 h after intradermal 0.03% (0.3 mg/mL, 1500μM) MB (10mg/mL Astar) injection using a 0.5-mL 29-gauge insulin syringe needle (Becton, Dickinson and Company, USA). The participant lay down and the skin was imaged 10 cm above the ankle in the lower leg and above the wrist in the middle forearm; three sites in each limb were randomly selected for each time point. SHG or THG captured MB signals with two-photon excitation microscope at the Molecular Biomedical Imaging Research Center of National Taiwan University.
In previous studies, we know methylene blue (MB) stains nerves, and oxidized MB has near-infrared (NIR) fluorescence for fluorescent observation. In this trial we using MB on human skin and combining MB and third-harmonic generation imaging (THG) to label cutaneous nerve fibers.