Hindawi Publishing Corporation Journal of Pharmaceutics Volume 2013, Article ID 848275, 6 pages http://dx.doi.org/10.1155/2013/848275 Research Article Quantum Dot-Loaded Liposomes to Evaluate the Behavior of Drug Carriers after Oral Administration Kohei Tahara, 1 Shiho Fujimoto, 1 Fumihiko Fujii, 2 Yuichi Tozuka, 1,3 Takashi Jin, 2,4 and Hirofumi Takeuchi 1 1 Laboratory of Pharmaceutical Engineering, Gifu Pharmaceutical University, 1-25-4 Daigaku-Nishi, Gifu 501-1196, Japan 2 Immunology Frontier Research Center, Osaka University, 3-1 Yamadaoka, Suita, Osaka 565-0871, Japan 3 Laboratory of Formulation Design and Pharmaceutical Technology, Osaka University of Pharmaceutical Sciences, 4-20-1 Nasahara, Takatsuki, Osaka 569-1094, Japan 4 Quantitative Biology Center, RIKEN, 6-2-3 Furuedai, Suita, Osaka 565-0874, Japan Correspondence should be addressed to Hirofumi Takeuchi; takeuchi@gifu-pu.ac.jp Received 25 March 2013; Accepted 2 July 2013 Academic Editor: Waquar Ahsan Copyright © 2013 Kohei Tahara et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We have developed submicron-sized liposomes modifed with a mucoadhesive polymer to enhance peptide drug absorption afer oral administration. Liposomal behavior in the gastrointestinal tract is a critical factor for efective peptide drug delivery. Te purpose of this study was to prepare quantum dot- (QD-) loaded submicron-sized liposomes and examine liposomal behavior in the body afer oral administration using in vivo fuorescence imaging. Two types of CdSe/CdZnS QDs with diferent surface properties were used: hydrophobic (unmodifed) QDs and hydrophilic QDs with glutathione (GSH) surface modifcations. QD- and GSH- QD-loaded liposomes were prepared by a thin flm hydration method. Transmission electron microscopy revealed that QDs were embedded in the liposomal lipid bilayer. Conversely, GSH-QDs were present in the inner aqueous phase. Some of the GSH-QDs were electrostatically associated with the lipid membrane of stearylamine-bearing cationic liposomes. QD-loaded liposomes were detected in Caco-2 cells afer exposure to the liposomes, and these liposomes were not toxic to the Caco-2 cells. Furthermore, we evaluated the in vivo bioadhesion and intestinal penetration of orally administered QD-loaded liposomes by observing the intestinal segment using confocal laser scanning microscopy. 1. Introduction Liposomes are a very attractive drug delivery system because they are physically and chemically well-characterized struc- tures that can be delivered through almost all routes of administration and are biocompatible [1–3]. We have devel- oped a submicron-sized (100–200 nm) mucoadhesive lipo- somal system by modifying the liposome surface with a mucoadhesive polymer such as chitosan to achieve an oral peptide formulation [4, 5]. Te efectiveness of polymer- modifed liposomes was confrmed by the enhanced and prolonged pharmacological efect of peptide drugs such as insulin, which was orally administered in a polymer-coated liposomal form to rats. Terefore, it is important to charac- terize the mucoadhesive properties of oral liposomal systems in vivo based on liposomal behavior in the body [6]. In a previous study, we examined the mucosal layer of the rat intestine to detect organic dye-labeled liposomes by confocal laser scanning microscopy (CLSM) afer administering these particulate systems [4]. In in vivo experiments, near-infrared (NIR) optical imag- ing is a powerful tool for real-time observation of the dynamic behavior of liposomes because it is a minimally invasive, nonionizing method that permits sensitive deep tissue imaging [7, 8]. However, traditional NIR dyes have several disadvantages for use as fuorescent probes, such as low solubility in aqueous solution, low quantum yield, and low photostability [9]. Semiconductor nanocrystals known as quantum dots (QDs) are fuorescent nanoparticles with diameters of 1– 10 nm [10]. QDs have been extensively investigated as optical probes for various biomedical applications in vitro and in vivo