Surface-Ligand-Dependent Cellular Interaction, Subcellular Localization, and Cytotoxicity of Polymer-Coated Quantum Dots

Abstract

Nanoparticle- and quantum-dot (QD)-based bioprobes are emerging as alternatives to small-molecule probes for in vitro and in vivo applications. However, their cellular interaction and cell uptake mechanism are significantly different from those of small-molecule probes and are extremely sensitive to surface ligands. These present a barrier in the development of nanoparticles and QDs as cellular probes. This work focused on the synthesis of various functionalized QDs with tunable surface charge, hydrophobicity, and functionalization with poly(ethylene glycol) (PEGylation) and their cellular interaction. We found that the surface functional groups of nanometer-sized probes significantly dictated their cellular interaction, subcellular localization, and cytotoxicity. A dose-dependent interaction was observed for all types of QDs, but the cationic surface charge or hydrophobicity would increase the cellular interaction as compared to the anionic surface charge. Cationic QDs rapidly entered cells and induced cytotoxicity, but hydrophobic QDs were stuck to the cell membrane and did not enter the cells. PEGylation of cationic QDs reduced their nonspecific binding and cytotoxicity, and a higher concentration of QDs was required for cellular entry. On the basis of these results, we were able to design different functionalized QD nanoprobes with balanced hydrophobicity and surface charge for cell membrane labeling and subcellular targeting. Mechanistic studies indicated a clathrin-mediated interaction and uptake for all types of QDs. The cellular interaction and uptake of 20−50 nm particles were primarily determined by their surface charges and ability to penetrate the cellular membrane, and the final destinations of the nanoparticles in the cell could be controlled by the appropriate design of surface ligands.

Transport of Nanoparticles through the Placental Barrier

“…The active transport systems play a key role in the intracellular transport of macromolecules and NP. Extensive studies have shown that NP internalization mainly occurs via endocytotic pathways and depends on NP properties (e.g., size, charge, functionalization) as well as on the cellular origin and physiology (Kelf et al 2010;Pi et al 2010;Tan et al 2010). Some authors report presence of transtrophoblastic channels which are thought to be membrane-lined tubular systems that originate from membrane invaginations of the basal syncytiotrophoblastic surface and cross the cell towards its apical surface (Kertschanska et al 1997;Benirschke and Kaufman 2000).…”

“…Nevertheless, the large NP used in the current reports have to be absorbed inside the trophoblast cells to be afterwards transferred to the fetal circulation. It is assumed that NP mainly enter the cells by the active transport, particularly, via the endocytotic pathways (Pi et al 2010;Tan et al 2010).…”

“…Since the NP were modified with a polymer, the size might have increased and the final diameter of the modified NP was undetermined. The influence of NP surface on the interaction with biomolecules and intracellular uptake was investigated in vitro (Tan et al 2010) and in vivo (Choi et al 2007) earlier. The studies showed that negatively charged particles are better endocytized by endothelial vessel cells .…”

“…Neutral NP possess lower protein adhesion, less efficient cellular uptake and longer circulation times in blood (Mosqueira et al 2001). NP hydrophilicity also has a significant effect on endocytotic efficiency (Tan et al 2010). Similarly to these effects, the chemical composition of NP surface should determine NP interaction with the receptors of placental trophoblast cells and, consequently, influence the efficiency of active transport to the fetal capillaries.…”

Ligand exchange on the surface of cadmium telluride quantum dots with fluorosurfactant-capped gold nanoparticles: Synthesis, characterization and toxicity evaluation

“…Therefore, the citrate-capped QDs might have little potential for biological labeling and imaging applications. On the other hand, there have been several researches reported on the great improvement of the ligand exchange procedures [14][15][16]. In this study, we are motivated to explore the possibility of TGA ligand transformation of CdTe QDs without affecting luminescent characteristics of the QDs to meet the future's demand for nanotoxicity studies and bioapplications.…”