Development of an Imaging System Using Fluorescent Labeling Substances Excited by Infrared Rays

An indocyanine green (ICG) derivative (ICG N‐hydroxy sulfosuc‐cinimide ester; ICG‐sulfo‐OSu) has been developed as an antibody labeling substance suitable for vital immunohistochemical staining. However, an appropriate fluorescence imaging system for ICG‐sulfo‐OSu using infrared rays has not as yet been reported. Therefore, we developed such a system. The absorption maxima of ICG and ICG‐sulfo‐OSu in buffer solution are both at 795 nm, the excitation maxima of their fluorescence spectra in buffer solution at 768 nm, and their emission maxima at 807 nm. An imaging system using an excitation filter with transmission at 710‐790 nm and a barrier filter with transmission at 810‐920 nm was constructed, and fluorescent images of ICG‐sulfo‐OSu labeled anti‐epithelial membrane antigen (EMA) antibody were obtained with this system. Thus, vital immunohistochemical staining of microcancers under infrared ray excitation should now be possible, by exciting an ICG‐sulfo‐OSu labeled antibody specific to the tumor cells with infrared rays, using this imaging system.