Near-Infrared Quantum Dots For Bioimaging And Targeting Applications
Luminescent semiconductor nanocrystals or quantum dots (QDs) offer attractive characteristics as a new class of fluorescent probes for molecular, cellular and in vivo imaging. While traditional cadmium-containing QDs have been widely used in biomedical research, diagnostics, and drug delivery, the cytotoxicity arising from the release of Cd2+ ions caused by the degradation of the surface coating is deemed to be a shortfall of cadmium-based QDs for long-term cellular and in vivo imaging. Here we report a direct synthesis of silver-doped zinc selenide QDs in water with near-infrared tunable fluorescence emissions, coinciding with the biological window of transmission to offer high signal-to-noise for fluorescence imaging of cells and small animals. Glutathione, which carries both carboxyl and amino groups, serves as a stabilizing ligand and offers the flexibility of decorating the surface of the QDs with moieties such as proteins, peptides and DNA. The cytotoxicity of the as-synthesized QDs was evaluated on macrophage (RAW 264.7) cells and human mesenschymal stem cells using MTS cell viability assay. The results indicated that the silver- doped ZnSe QDs possess low cytotoxicity. In vivo biodistribution study shows that these bare QDs are different from conventional QDs, it traversed through systemic route and could accumulate in the stomach of nude mice. These QDs were conjugated to monoclonal CD44v6 antibody and tested with human gastric adenocarcinoma cell line (AGS). The results indicated the feasibility of modifying the surface properties of these QDs for efficient targeting applications. The QDs were also conjugated to heparin and used to formulate nanocomplexes with chitosan to encapsulate tumor necrosis factor-alpha. Quantitative imaging analysis revealed in vivo trafficking kinetics of the nanocomplexes to the lymph nodes after subcutaneous administration into nude mice. This study demonstrates the potential of incorporation of near-infrared-emitting QDs in nanocarrier drug delivery that allows in vivo trafficking of the biodistriution events and will be of greatly improve the development new drug nanocarrier formulations.
In vivo imaging
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