Near infrared in vivo flow cytometry for tracking fluorescent circulating cells

The in vivo flow cytometry (IVFC) is now a powerful technique in biomedical research, especially for tracking specific cells in circulatory system. The current fluorescence-based IVFC is limited to visible spectrum, while near infrared (NIR) dyes have their advantages, such as deeper penetration, less absorption and less scattering for NIR fluorescence. Here, using an NIR in vivo flow cytometer with a 785 nm laser excitation, the measurement of fluorescent dye IR-780 labeled circulating cells is demonstrated. Representative peaks corresponding to NIR fluorescent circulating cells are detected and quantified. In addition, blood flow information, including the blood flow velocity and flow volume per unit time, is obtained. By simultaneous detection of IR-780 and enhanced green fluorescent protein (EGFP) signals from dual labeled cells, the IR-780 is shown to be a suitable fluorescent dye for multicolor detection by IVFC, including NIR. Thus, the IVFC is extended to the NIR range and shows potential application in biomedical research.