Simultaneous fluorescence analysis of the different carbohydrates expressed on living cell surfaces using functionalized quantum dots

The aberrant expression of carbohydrates has been associated with the occurrence, growth, progression and metastasis of tumors. Tumor-associated carbohydrates may have great potential as tumor markers for the early diagnosis of hepatocellular carcinoma (HCC). Therefore, characterizing HCC-associated carbohydrate expression is of great importance to assist the early diagnosis of HCC. A fluorescence method for characterizing carbohydrates expressed on both normal human cells (LO2 cells and endothelial cells) and HCC cells (HepG2 cells) using functionalized quantum dots (QDs) has been proposed in this study. The QDs were successfully fabricated and covalently conjugated with Datura stramonium agglutinin (DSA) or Lens culinaris agglutinin (LCA) via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) coupling reaction. The formed functionalized QDs (lectin-QDs conjugates) were characterized using ultraviolet and fluorescence spectra, agarose gel electrophoresis, hemagglutination activity tests, lectin competitive-binding assay and carbohydrate inhibition assays. The functionalized QDs were found to retain stable fluorescence and carbohydrate recognition abilities. Significant differences of carbohydrates expressed between on the normal cells and the HepG2 cells were evaluated by fluorescence imaging and flow cytometric analysis. The experimental results illustrate that the functionalized QDs could be used as promising tools for monitoring in situ cell surface carbohydrate expression and evaluating the differences in the carbohydrates expressed on normal cells and tumor cells surfaces, which is very important for helping the early diagnosis of HCC.