Abstract: Fluorescent probe labeling is easy to operate and the sensitivity of fluorescence detection is 3–4 orders of magnitude higher than traditional methods such as ultraviolet visible (UV-Vis) spectroscopy. The absorption and distribution of chitosan oligosaccharide (COS) monomers with different degrees of polymerization (DPs) in mice was analyzed by fluorescent probe labeling. In this study, we analyzed the differences in the absorption and distribution of COS monomers with DPs of 2–5 in mice gavaged with fluorescein isothiocyanate (FITC) labeled COS monomers through fluorescence signal detection by a small animal intravital optical imaging system and fluorescence quantification. The results showed that at 1 h after administration, the fluorescence signal in the mice reached its peak level. COS could be absorbed into the blood and cross the blood-brain barrier to distribute into the brain tissue. COS mainly distributed into the kidney and liver, followed by the heart and spleen, and a small amount of COS distributed into the lung and brain. The distribution of COS monomers in the kidney and liver was positively correlated with the DP, while the peak distribution in serum, heart, spleen, lung, and brain in decreasing order was as follows: chitobiose > chitotetraose > chitotriose > chitopentose. The findings of this study are meaningful for guiding future study of the structure-activity relationship of functional COS and provide a reference for further study of the functional mechanism of COS, which will accelerate the development and application of COS in functional foods.

Key words: chitosan oligosaccharide; degree of polymerization; fluorescein isothiocyanate; absorption and distribution; in vivo imaging