Delivered by Publishing Technology to: Korea Advanced Institute of Science & Technology (KAIST) IP: 143.248.118.13 On: Sat, 21 Sep 2013 20:11:05 Copyright: American Scientific Publishers Copyright © 2010 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 10, 487–496, 2010 Preparation and Characterization of CdSe/ZnS Quantum Dots Encapsulated in Poly(ethylene glycol)-b- Poly(D,L-lactide) Micelle Nanoparticles Joohyeon Lee 1 , Jeong Hyuk Im 2 , Kang Moo Huh 2 , Yong-kyu Lee 3 , and Heungsoo Shin 1 * 1 Department of Bioengineering, College of Engineering, Hanyang University, Seoul 133-791, Korea 2 Department of Polymer Science and Engineering, Chungnam National University, Daejeon 305-764, Korea 3 Department of Chemical and Biological Engineering, Chungju National University, Chungbuk 380-702, Korea The final goal of this study is to develop multi-functional organic/inorganic hybrid nanoparticles, which can be utilized as biomedical imaging probes and drug delivery carriers. As an initial step toward this goal, we encapsulated CdSe/ZnS quantum dots (QDs) into poly(ethylene glycol)-b-poly(D,L-lactide) (PEG-PLA) micelles using a solid dispersion method. The size and fluorescent intensity of QDs encapsulated in PEG-PLA micelles depended on the amount of incorporated QDs. For example, when the amount of QDs increased from 0.1 to 1.0 g, the mean diameter increased from 24.2 ± 6.0 to 211.2 ± 6.5 nm and the fluorescent intensity changed from 10.2 ± 1.0 to 469.9 ± 15.6 (RFU). Sta- bility studies showed that the size and zeta-potential (ZP) of QDs encapsulated in PEG-PLA micelles (QEMs) did not change significantly in response to a change in pH conditions or under a 10% serum condition. We also tested the cytotoxicity and cellular uptake of the QEMs. The viability of HeLa cells treated with micelles for 24 h was 80∼100% in various concentration ranges of micelles. Confocal laser scanning microscopic images showed that the QEMs penetrated into the cells, particularly into the cytosolic compartments. Our results suggest that the QEMs may be a promising multi-functional nanocarrier for biomedical imaging and drug delivery. Keywords: PEG-PLA, Micelle, Quantum Dots, Imaging, Drug Delivery Carrier. 1. INTRODUCTION Highly luminescent semiconductor nanocrystals, referred to as quantum dots (QDs), with their unique size and composition-tunable narrow emission and broad absorp- tion spectra, have drawn great attention in the last decade due to their promising applications in molecular imag- ing and biology. 1 2 Recently, a number of approaches for transforming hydrophobic QDs into hydrophilic QDs have consequently been developed for various biomedical appli- cations. Among the new surface modifications of QDs, amphiphilic molecules made through exchange interac- tions with hydrophobic ligands on the surfaces of QDs, such as phospholipids, calixarenes, cyclodextrines, and complex copolymers (in particular polyacrylic acid deriva- tives), have been used for this purpose. 3–5 Alternatively, researchers have also used biocompat- ible materials such as poly(ethylene glycol) (PEG) * Author to whom correspondence should be addressed. and poly(maleic anhydride alt-1-tetradecene) to coat the surface of QDs. 6 7 The strategy of using polymers is generally superior to conventional surface modification techniques because the fluorescent properties of QDs remain unchanged while other functional moieties on the surfaces of QDs can be introduced. 8 9 Polymer micelles have been extensively studied for the solubi- lization of hydrophobic drugs and bioactive agents due to their unique properties, including nano-scaled size, high water solubility, high structural stability, high car- rying capacity of hydrophobic agents, and easiness in introducing functional moieties on the outer shell. 10–13 In particular, poly(ethylene glycol)-poly(D,L-lactide) diblock copolymer micelles are the most frequently used system because of their biocompatibility and biodegradability. 14–16 In this study, luminescent QDs were synthesized and encapsulated in biodegradable amphiphilic poly(ethylene glycol)-poly(D,L-lactide) (PEG-PLA) diblock copolymers for the preparation of water-soluble and biocompatible J. Nanosci. Nanotechnol. 2010, Vol. 10, No. 1 1533-4880/2010/10/487/010 doi:10.1166/jnn.2010.1736 487