In vivo NIR imaging with CdTe/CdSe quantum dots entrapped in PLGA nanospheres Jin Soo Kim a,1 , Kwang Jae Cho b,1 , Thanh Huyen Tran c , Md. Nurunnabi a , Tae Hyun Moon d , Suk Min Hong e , Yong-kyu Lee a,⇑ a Department of Chemical and Biological Engineering, Chungju National University, Chungbuk 380-702, Republic of Korea b Department of Otolaryngology, Head & Neck Surgery, The Catholic University of Korea, College of Medicine Uijeongbu St. Mary’s Hospital, Kyunggi-Do 480-717, Republic of Korea c Department of Applied Chemistry & Biological Engineering, Chungnam National University, 220, Gung-dong, Yuseng-gu, Daejeon 305-764, Republic of Korea d Mediplex Corp., Seoul 135-729, Republic of Korea e Nano/Bio Chemistry Laboratory, Institute Pasteur Korea, 696 Sampyeong-dong, Bundang-gu, Seongnam-si, Gyeonggi-do 463-400, Republic of Korea article info Article history: Received 8 May 2010 Accepted 23 August 2010 Available online 18 October 2010 Keywords: Quantum dots PLGA nanospheres Imaging Tumor Detection abstract Luminescent near-infrared (NIR) CdTe/CdSe QDs were synthesized and encapsulated in poly(lactic- co-glycolic acid) (PLGA) nanospheres to prepare stable and biocompatible QDs-loaded nanospheres for in vivo imaging. QDs were encapsulated with PLGA nanospheres by a solid dispersion method and opti- mized to have high fluorescence intensity for in vivo imaging detection. The resultant QDs-loaded PLGA nanospheres were characterized by various analytical techniques such as UV–Vis measurement, dynamic light scattering (DLS), fluorescence spectroscopy, and transmission electron microscopy (TEM). Finally, we evaluated toxicity and body distribution of QDs loaded in PLGA nanospheres in vitro and in vivo, respectively. From the results, the QDs loaded in PLGA nanospheres were spherical and showed a diam- eter range of 135.0–162.3 nm in size. The QD nanospheres increased their stability against photooxida- tion and photobleaching, which have the high potential for applications in biomedical imaging. We have also attained non-invasive in vivo imaging with light photons, representing an intriguing avenue for obtaining biological information by the use of NIR light. Ó 2010 Elsevier Inc. All rights reserved. 1. Introduction Quantum dots (nanometer-scale semiconductor nanocrystals, QDs) have attracted significant attentions during the last decades because they can dramatically improve the use of fluorescent markers in biological imaging [1–3]. Due to their unique character- istics such as tunable fluorescence wavelength by size, sharp and symmetrical fluorescence peak, strong and stable emission, high quantum yield, and broad excitation spectra, the QDs can provide distinct advantages over conventional organic dyes in vitro and in vivo [4–6]. However, these QDs are hydrophobic and so usually aggregated in aqueous media. Their luminescences are easily impaired and the QDs are targeted by the mononuclear phagocyte system (MPS) [7]. For more extensive and effective biological applications, QDs have been encapsulated or surface modified to prevent aggregation and make them biocompatible. The various strategies have been used to make them water-soluble, such as surface functionalization with water-soluble ligands [8–10], silanization [11], and encapsu- lation within block-copolymer micelles [12–14]. The strategy of using polymers is generally superior to the surface modification, because: (a) there is no direct interaction with the QD surface atoms and it therefore can preserve the original quantum effi- ciency to a highest extent; (b) the presence of hydrophobic poly- mer domains around QDs may strengthen the hydrophobic interaction to form more steady structures and consequently more stable and water-soluble QDs; and (c) these polymers can be tailor- made to have good stability in aqueous media and other functional moieties can be introduced on their surface. Polymeric encapsula- tion has been extensively studied for solubilization of hydrophobic drugs and bioactive agents due to its unique properties that include a nano-scaled size, high water solubility, high structural stability, high carrying capacity of hydrophobic agents, and easi- ness in introducing functional moieties on the outer shell [15– 17]. Poly(lactic-co-glycolic acid) (PLGA), in particular, is the most frequently used system because of its biocompatibility and biode- gradability [18,19]. In this study, luminescent Near IR QDs were synthesized and encapsulated in biodegradable PLGA nanospheres for the preparation of stable and biocompatible QDs-loaded nanospheres. The nanospheres were characterized by UV–Vis, DLS, fluorescence spectroscopy, and transmission electron micros- copy (TEM). The stable and biocompatible QDs-loaded PLGA nanospheres provided sufficient circulation times and non-toxic imaging agents in vivo. 0021-9797/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2010.08.053 ⇑ Corresponding author. Fax: +82 043 841 5220. E-mail address: leeyk@chungju.ac.kr (Y.-k. Lee). 1 These authors are equally contributed to this article as co-first authors. Journal of Colloid and Interface Science 353 (2011) 363–371 Contents lists available at ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis