Study about Overall Adhesion-Spreading Process of Liposomes on a Gold Electrode. Influence of the Presence of CdTe Quantum Dots

Abstract

The utilization of quantum dots (QDs) it has been grown up into the material science area, because these nanoparticles have particular optical and electronic properties. These properties are dependent on the particle size, which can be controlled by the modification of some experimental conditions: temperature, reaction time, pH and molar ratio of precursors. QDs present a wide absorption spectrum, narrow emission fluorescence spectrum, high photo-stability, tunable band gap, high quantum yield, among others. These properties have allowed its application in different areas such as photovoltaic cells, biomedicine, chemical analysis, biosensors and biomarkers. However, particularly in the medicine field is very important to know what is the effect of QDs in contact with cell membranes. An approximation to this process could be the utilization of structures like lipid vesicles or liposomes, which also can be used as drug and biomarkers carriers. Some authors [1], [2] have used electrochemical methods in the study of liposomes, because the vesicles deposition process (adhesion and spreading processes) on metallic electrodes are similar to the lipid membranes fusion, providing information about e.g. exo- and endocytosis processes. In this context, this work is related with the influence of the interaction between CdTe QDs and 1,2-dimyristoyl-sn-phosphatidylcholine (DMPC) liposomes on the overall adhesion-spreading processes of liposomes modified by QDs. Synthesis of CdTe QDs was carried out in aqueous media, by using CdCl2 and Na2TeO3 as precursors, mercaptosuccinic acid (MSA) as capping agent and NaBH4 as reducing agent. Using a Doehlert’s experimental design was possible the optimization of the QDs sizes controlling the synthesis variables, i.e. temperature, reaction time, pH and molar ratio of precursors. After QDs were purified through ultracentrifugation with 1:1 water:isopropanol mixture and re-suspended in a buffer solution (borate buffer; pH 9.20). Finally, these were characterized by UV-Vis spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). On the other hand, DMPC liposomes were prepared by dissolving DMPC in chloroform, then evaporating solvent with Argon and suspending the lipids in borate buffer. Lipid suspension was cooled with liquid nitrogen and then heated below the phase transition temperature. Finally, lipids were extruded to obtain large unilamellar vesicles. After, the DMPC liposomes were deposited on gold electrode and characterized by CV observing the coverage degree by charge analysis. Additionally, the overall adhesion-spreading process of liposomes on gold electrode was characterized by means of chronoamperometry technique analyzing the corresponding current-time transients. Both analysis were performed after the mixing with CdTe QDs. The results show a decrease in the constant rate values of the adhesion-spreading processes of DMPC liposomes on gold electrode suggesting that the interaction CdTe(QD)-DMPC produces an increase in the activation energy of the lipid membranes fusion