In vivo flow cytometry system for detecting circulating tumor cells labeled with upconverting nanoparticles

• Online Access: http://hdl.handle.net/2047/D20324106

Early detection of rare circulating tumor cells in the bloodstream is important in the pre-clinical study of cancer metastasis. We recently developed a new instrument for the detection of circulating tumor cells labeled with fluorescent markers, which we call "Diffuse in vivo Flow Cytometry" (DiFC). One of the major technical challenges associated with this is the large, non-specific autofluorescence of surrounding tissue, which can obscure dimly labeled cells. In this work we studied the use of upconverting nanoparticles as a novel means to mitigate this autofluorescence. Upconverting nanoparticles are a unique type of fluorescent label which emit light at shorter wavelength than the light used to excite them, so that autofluorescence in the region of fluorescence emission is negligible. Furthermore, the phenomenon of photon upconversion increases the spectral separation between the excitation and emission light by several hundred nanometers. As such, upconverting nanoparticles in principle allow highly-sensitive detection of weakly labeled cells in circulation. We report on the design and validation of an in vivo flow cytometry system for detecting circulating tumor cells labeled with NaYF4 upconverting nanoparticles, which we call "Upconverting Nanoparticle in vivo Flow Cytometry" (UCNP-FC). This instrument incorporates excitation at 980 nm and detection at 519-700 nm, specific to the upconverting nanoparticles used. We show that we can detect circulating upconverting nanoparticles in a phantom and in vivo with a signal-to-noise ratio exceeding 17dB. Labeling of circulating tumor cells and other cells with upconverting nanoparticles remains a persistent problem. However, if this can be solved, in the future this system can be used to detect circulating tumor cells without any interference from tissue autofluorescence.