Entrapment in phospholipid vesicles quenches photoactivity of quantum dots

Abstract

Quantum dots have emerged with great promise for biological applications as fluorescent markers for immunostaining, labels for intracellular trafficking, and photosensitizers for photodynamic therapy. However, upon entry into a cell, quantum dots are trapped and their fluorescence is quenched in endocytic vesicles such as endosomes and lysosomes. In this study, the photophysical properties of quantum dots were investigated in liposomes as an in vitro vesicle model. Entrapment of quantum dots in liposomes decreases their fluorescence lifetime and intensity. Generation of free radicals by liposomal quantum dots is inhibited compared to that of free quantum dots. Nevertheless, quantum dot fluorescence lifetime and intensity increases due to photolysis of liposomes during irradiation. In addition, protein adsorption on the quantum dot surface and the acidic environment of vesicles also lead to quenching of quantum dot fluorescence, which reappears during irradiation. In conclusion, the in vitro model of phospholipid vesicles has demonstrated that those quantum dots that are fated to be entrapped in endocytic vesicles lose their fluorescence and ability to act as photosensitizers.

Keywords:

• fluorescence lifetime
• free radicals
• liposomes
• lipodots
• reactive oxygen species

Acknowledgments

This study was financed by the NANOMAT program of the Research Council of Norway (project number 182058). The work of S (Lukoseviciute) Kavaliauskiene was supported in part by the Norwegian Radium Hospital Research Foundation (project number FU0802) and in part by the European Commission’s ERASMUS Lifelong Learning Programme (LLP). Wei Chen would like to acknowledge the support from the startup funds from UTA, the NSF and DHS joint ARI program (2008-DN-077-ARI016-03, CBET-1039068), DOD DTRA08-005, and the US Army Medical Research Acquisition Activity (USAMRAA) under Contracts of W81XWH-10-1-0279 and W81XWH-10-1-0234. The authors thank Sandra Rocha for assistance with TEM technique.

Disclosure

The authors report no conflicts of interest in this work.