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We report the rational design of a chitosan-based drug delivery system. The chitosan derivative N-[(2-hydroxy-3-trimethylammonium)propyl]chitosan chloride (HTCC) was ionically cross-linked by sodium tripolyphosphate (TPP) to form sub-200-nm microgels that are responsive to pH changes. When these microgels were loaded with methotrexate disodium (MTX), a cytotoxic drug for cancer treatment, and conjugated to the targeting biomolecule apo-transferrin, a protein known to enter cells via receptor-mediated endocytosis, enhanced killing of immortalized HeLa cells was observed. In this intracellular delivery method, the microgel was exposed to low-pH environments that caused the chitosan to swell and release the drug. This rational drug delivery design may be useful in enhancing cancer therapy and reducing side effects.

Semiconductor quantum dots (qdots) are emerging as a new class of fluorescent labels. The unique optical properties of qdots make them appealing in laboratory diagnosis; however, qdot-based probes remain to be developed and evaluated for clinical laboratory applications. In this study, 2 different approaches were employed to label hematopoietic cells with qdots. The first was based on a generalized intracellular delivery of qdots using qdot-transferrin conjugates through receptor-mediated endocytosis. Hematopoietic cells from umbilical cord blood or bone marrow were successfully labeled with qdot-transferrin in cell cultures. The fluorescence signal of qdot-transferrin was detected in the cytoplasmic location. The second approach was to use qdot-antibodies for labeling cell surface markers. The monoclonal antibodies to CD5, CD19, and CD45 surface antigens were conjugated to qdots with distinct emission spectra. The qdot-linked antibodies were shown to bind successfully to specific cell markers on lymphocytes. The signal obtained from the labeling of cells was detectable by using fluorescence microscopy and flow cytometry. The qdot signals were shown to be target specific, bright, and photo stable. The results of this study demonstrated the feasibility of using qdots for cell labeling and surface marker analysis of hematopoietic cells. Given the superior optical properties of qdots as compared to conventional fluorescence dyes, the qdot-based probe offers a promising tool for hematology analysis in clinical laboratories.

Recent developments in quantum dot (QD) technology have paved the way for using QDs as optical contrast agents for in vivo imaging. Pioneering papers showed the use of QDs as luminescent contrast agents for imaging cancer and guiding cancer surgery. The possible future use of QDs for clinical applications is expected to have a significant impact, however many challenges in this field have yet to be overcome.