Synthesis, characterization of CdSxSe1-x quantum dots and evaluation of their real-time motions in live cells

Abstract

The use of quantum dots as fluorescent labels in bioimaging is the most intensively studied subject. The aim of this study is to elucidate locations of quantum dots and track their motions in real time through confocal microscopy and to evaluate influence of surface chemistry on diffusions of quantum dots in live cells. In this study, trioctylphosphine oxide (TOPO) capped CdSxSe1-x quantum dots were synthesized and then TOPO molecules were exchanged with 3-mercaptopropionic acid and N-acetyl-Lcysteine to make quantum dots water dispersible for cellular imaging. Human lung adenocarcinoma epithelial cells (A549) and human bronchial epithelial cells (BEAS-2B) were incubated 1 hour with CdSxSe1-x quantum dots with a concentration range of 1-10 g/mL. Localizations and real time motions of quantum dots were tracked by a spinning disc confocal microscope. The center of fluorescent spots of quantum dots was determined by 2D Gaussian fitting with a sub-pixel resolution (<100nm/pixel). The mean square displacements, diffusion coefficients and trajectories in which quantum dots made motions were analyzed by the software ImageJ with a plug in Spot Tracker. Confocal images showed that both MPA and NAC cappped quantum dots were observed in the cytoplasm of cells. Trajectories of quantum dots in cellular environment demonstrated that the quantum dots performed various types of motions in live cells. Unimodal, trimodal and multimodal distribution histograms of the diffusion coefficeints were obtained for different capping agents (MPA and NAC) and cell types (A549 and BEAS-2B). We conclude that the surface chemistry regulates the motion of the quantum dots in the cellular environment.