Quantum dots (QDs) are increasingly attracting attention in recent years due to their potential in biological imaging and drug delivery applications. Despite their significant advantages over organic dyes and fluorescent proteins, cytotoxicity is still a major problem in live-cell QD labeling. In this work, in-vitro characterization of a novel CdTe/2MPA quantum dot capped with CdS-DMSA was conducted on human cervical cancer (HeLa) and mouse fibroblast (NIH/3T3) cell lines. Biocompatibility of this novel particle was evaluated in comparison to a commercial quantum dot (Qdot 565) and various QDs with CdTe core. Cytotoxicity of quantum dots was investigated using XTT and proliferation assays. Cellular internalization and localization of particles were studied using confocal laser scanning microscopy. For quantitative determination of internalization and intracellular QD stability, we also performed uptake and cadmium release assays. Optimal cell imaging concentration with CdTe-CdS/2MPA-DMSA was determined as 10-50 ug/mL in HeLa cells. Localization of the internalized QD particles was observed in the perinuclear region of the cells. XTT and proliferation assays provided identical viability results for the tested QDs. CdS-DMSA capping increased cytocompatibility of CdTe/2MPA by 15% in NIH/3T3 cells. Biocompatibility of this capped particle was further increased by 3-folds with pegylation. For pegylated CdTe-CdS/2MPA-DMSA and commercial Qdot 565, we have not observed QD-related cytotoxicity on NIH/3T3 cells following 24-hr QD exposure at 50 ug/mL. Our in-vitro characterization studies indicate that CdTe-CdS/2MPA-DMSA is a promising live-cell imaging probe which can be effectively excited in the visible range of the electromagnetic spectrum.

Quantum dots are fluorescent semiconductor nanocrystals that have unique optical properties such as high quantum yield and photostability. These nanoparticles are superior to organic dyes and fluorescent proteins in many aspects and therefore show great potential for both in vivo and in vitro imaging and drug delivery applications. However, cytototoxicity is still one of the major problems associated with their biological applications. The aim of this study is in vitro characterization and assessment of biological application potential of a novel silver sulfide quantum dot coated with mercaptopropionic acid (2-MPA). In vitro studies reported in this work were conducted on a mouse fibroblast cell line (NIH/3T3) treated with Ag2S/2-MPA quantum dots in 10-600 &mu / g/mL concentration range for 24 h. Various fluorescence spectroscopy and microscopy methods were used to determine metabolic activity, proliferation rate and apoptotic fraction of QD-treated cells as well as QD internalization efficiency and intracellular localization. Metabolic activity and proliferation rate of the QD treated cells were measured with XTT and CyQUANT&reg / cell proliferation assays, respectively. Intracellular localization and qualitative uptake studies were conducted using confocal laser scanning microscopy. Apoptosis studies were performed with Annexin V assay. Finally, we also conducted a quantitative uptake assay to determine internalization efficiency of the silver sulfide particles. Correlated metabolic activity and proliferation assay results indicate that Ag2S/2-MPA quantum dots are highly cytocompatible with no significant toxicity up to 600 &mu / g/mL treatment. Optimal cell imaging concentration was determined as 200 &mu / g/mL. Particles displayed a punctuated cytoplasmic distribution indicating to endosomal entrapment. In vitro characterization studies reported in this study indicate that Ag2S/2-MPA quantum dots have great biological application potential due to their excellent spectral and cytocompatibility properties. Near-infrared emission of silver sulfide quantum dots provides a major advantage in imaging since signal interference from the cells (autofluorescence) which is a typical problem in microscopic studies is minimum in this part of the emission spectrum. The results of this study are presented in an article which was accepted by Journal of Materials Chemistry. DOI: 10.1039/C2JM31959D.