Nano-sized fluorescent particles as new tracers for sentinel node detection: Experimental model for decision of appropriate size and wavelength

The concepts of made-to-order and low-invasiveness medicines are becoming widely accepted. A treatment for cancer, with minimum invasive surgery and without lymph nodes dissection based on sentinel lymph node (SN) navigation surgery, would adhere to these concepts. Dyes and/or radioisotopes are employed for SN detection in standard methods, however, each detection method has advantages and disadvantages. To make up for the disadvantages, we aimed at developing a new non-invasive method using fluorescent beads of uniform nano-size that could efficiently visualize SN from outside the body, and conducted experiments to determine the appropriate size and fluorescent wavelength. We examined various bead sizes and fluorescent wavelengths. The sizes were 20, 40, 100 and 200 nm. The fluorescent peak wavelengths of the beads were yellow-green (515 nm), dark red (680 nm), far red (720 nm) and infrared (755 nm). The beads were subcutaneously injected into the foot pad of the hind leg of a rat, and followed by laser scanning of the inguinal area for fluorescence observation. The beads exhibited different times for the fluorescence detection according to their sizes and wavelength. The 40 nm beads were considered to be the most appropriate size for SN detection in rats. The wavelength of near infrared was effective for avoiding attenuation by the tissue. In conclusion, we confirmed that uniformly nano-sized fluorescent beads have the potential to be an alternative to existing tracers in the detection of the SN in animal experiments if we select the appropriate particle size and wavelength.