To realize their full potential as intracellular imaging and sensing reagents, robust and efficient methods for the targeted cellular delivery of luminescent semiconductor quantum dots (QDs) must be developed. We have previously shown that QDs decorated with histidine-terminated polyarginine cell-penetrating peptides (CPP) are rapidly and specifically internalized via endocytosis by several mammalian cell lines with no cytotoxicity. Here we demonstrate the long-term intracellular stability and fate of these QD-peptide conjugates. We found that the QD-peptide conjugates remain sequestered within endolysosomal vesicles for up to three days after delivery. However, the CPP appeared to remain stably associated with the QD within these acidic vesicles over this time period. Hence, we explored a number of techniques to either actively deliver QDs directly to the cytosol or to facilitate the endosomal release of endocytosed QDs to the cytosol. Active methods (e.g., electroporation) delivered only modest amounts of QDs to the cytosol that appeared to form aggregates. Delivery of QDs using polymer-based transfection reagents resulted primarily in the endosomal sequestration of the QDs, although one commercial polymer tested delivered QDs to the cytosol but only after several days in culture and with a considerable degree of polymer-induced toxicity. Finally, a modular, amphiphilic peptide containing functionalities designed for cell penetration and vesicular membrane interaction demonstrated the ability to deliver QDs in a well-dispersed manner to the cytosol. This peptide mediated rapid QD uptake followed by a slower efficient endosomal release of the QDs to the cytosol that peaked at 48 hours post-delivery. Importantly, this QD-peptide conjugate elicited minimal cytotoxicity in two cell lines tested. A more detailed understanding of the mechanism of the peptide's uptake and endosomal escape attributes will lead to the design of further QD conjugates for targeted imaging and sensing applications.

Date Published: 17 February 2010
PDF: 7 pages
Proc. SPIE 7575, Colloidal Quantum Dots for Biomedical Applications V, 75750S (17 February 2010); doi: 10.1117/12.842434

Published in SPIE Proceedings Vol. 7575:
Colloidal Quantum Dots for Biomedical Applications V
Marek Osinski; Wolfgang J. Parak; Thomas M. Jovin M.D.; Kenji Yamamoto M.D., Editor(s)