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Here, we studied the effect of calcium ions on the physicochemical properties and cellular uptake of CdSe/ZnS quantum dots encapsulated with poly(maleic anhydride-alt-1-tetradecene), modified to a varying extent by quaternary ammonium groups. It was shown that quantum dots carrying negatively charged carboxyl groups in the polymer shell change their physicochemical and optical characteristics in the presence of Ca2+ and Ba2+ ions. As the negatively charged carboxyl groups in the shell are completely replaced by positively charged quaternary ammonium groups, these effects gradually decrease. A change in the physicochemical properties of nanoparticles leads to a change in their cellular uptake in the presence of calcium ions. Nanoparticles carrying only negatively charged groups in the shell in the presence of Ca2+ agglomerate and form conglomerates of nanoparticles and cells. The positively charged quaternary ammonium groups in the polymer shell of the nanoparticles increase their aggregative stability in the presence of Ca2+ and contribute to their uptake by cells. The mechanisms of uptake depend on nanoparticle’s charge. Nanoparticles with a positive ζ potential are absorbed by calcium-dependent mechanisms, which are suppressed by inhibition of the calcium-dependent enzyme dynamin or in the presence of calcium chelator EGTA. The uptake of nanoparticles with a negative ζ potential, in contrast, is enhanced by the chelation of calcium ions. This indicates the different role of cellular calcium-dependent mechanisms in the uptake of positively and negatively charged nanoparticles.

We present here a novel method for formation of laterally-oriented monolayers of plasmonic silver nanoplates and their electrostatic ensembles with semiconductor quantum dots. Monolayers were electrostatically deposited on the surface of thin polymeric film containing different amount of tertiary amino groups. This method allows simultaneously investigate optical properties and morphology of silver nanoplates using transmittance electron microscopy. The optical density of films and surface concentration of silver nanoplates is proportional to the percentage of tertiary amino groups in the polymeric film. A surface ligand exchange was used for functionalization of the surface of silver nanoplates toward formation of electrostatic ensembles with colloidal quantum dots. We observed a straight correlation between the red shift of surface plasmon resonances in silver nanoplates and alkyl chain length of ligand molecules.

Here, we prepared water-soluble highly luminescent CdSe/ZnS quantum dots having different surface charge and examined how zeta potential of quantum dots affected their uptake by cancer cells. Water soluble quantum dots with varied zeta potential were prepared through encapsulation with amphiphilic polymer poly(maleic anhydride-alt-1-tetradecene) (PMAT) containing ziwitterions formed by spatially separated carboxyl and quaternary amino groups. Varying the ration of negatively charged carboxyl and positively charged quaternary amino-groups during chemical modification of PMAT we control the sign and magnitude of zeta potential of encapsulated quantum dots. Quantum dots having nearly equal amount of carboxyl and quaternary amino groups possess pH-controlled zeta potential which can vary from negative to positive value when pH changes from basic to acidic condition. Cellular uptake of encapsulated quantum dots has been found to be strongly dependent of their surface charge: positively charged quantum dots efficiently internalized by cells, while negatively charged adsorbed mostly at the cell membrane. Zwitterionic QDs do not demonstrate any charge-dependent cellular toxicity at least within few hours. Long-term incubation of cells stained with zwitterionic quantum dots results in the decrease of the fluorescence signal mainly due to the cell proliferation.