The Application Of Tissue Optical Clearing In In Vivo Flow Cytometry

Cancer is one of the major threats to human public health. In ourcountry, more than90%patients die from the metastasis and recurrencewithin five years, which is an important reason for the low survival ofcancer patients. In this process, circulating tumor cells (CTCs) play animportant role in the tumor metastasis, and the quantification of CTCs hasbecome an emerging tool used to diagnose, stratify and monitor patientswith metastatic diseases.In vivo flow cytometry (IVFC) is a novel optical technique. It candetect the dynamics of fluorescently labeled CTCs in the bloodstreamcontinuously and non-invasively, which can be used to diagnose themetastasis of malignant tumor or other severe diseases. However, thedetection depth of IVFC suffers from the strong light scattering of tissue.In this study, we apply the tissue optical clearing to IVFC detection. Aninnovative ear skin optical clearing agent (ESOCA) is employed to themouse ear to improve the signal quality of the IVFC. Our results show thatcompared with commonly used glycerol, topical application of ESOCAcan enhance the transmittance of rat ear significantly in vivo. The labeledred blood cells can be detected by the IVFC with higher signal quality andgreater detection depth and ESOCA has better biocompatibility. IVFC isalso used to distinguish the fluorescent particles with different size andfluorescence intensity.This study is very helpful for potential tumor metastasis studies by theIVFC in deep tissues. With the development of novel optical clearingagents, IVFC may be useful for studying cancer metastasis not only insmall animals, but also in large mammals and potentially human beings.