Article pubs.acs.org/Langmuir
Development of Biocompatible and Proton-Resistant Quantum Dots Assembled on Gelatin Nanospheres Longyan Chen,† Alex Siemiarczuk,§ Hong Hai,† Yi Chen,† Guobang Huang,† and Jin Zhang*,†,‡ †
Department of Chemical and Biochemical Engineering, University of Western Ontario, London, Ontario, N6A 5B9, Canada Department of Ophthalmology, Schulich School of Medicine & Dentistry, University of Western Ontario, London, Ontario, N6A 4 V2, Canada § Photon Technology International (Canada) Inc., 347 Consortium Court, London, Ontario N6E 2S8, Canada ‡
S Supporting Information *
ABSTRACT: In this study, biocompatible and protonresistant CdSe quantum dots (QDs) assembled on gelatin nanospheres (GNs) have been synthesized by combining the two-step desolvation method with the layer-by-layer assembly technique. The core−shell fluorescent gelatin nanosphere consists of a gelatin core and a four-layer shell of hydrophilic CdSe QDs assembled through polyelectrolytes (PE). The morphology, microstructures, and photostability of the hybrid spheres were further investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), fluorospectrometery, and confocal fluorescent microscopy (CFM), respectively. The average diameter of the hybrid QDs-gelatin nanospheres (QDs-GNs) is estimated at 484 ± 40 nm. Our results indicate that the 20 ± 5 nm of the shell is attributed to the four−layer of CdSe QDs assembled through the PE. QD-GNs show a strong photoluminescence with the maximum emission (λem) at 613 nm at the excitation wavelength of 470 nm. The core−shell QDs-GNs are able to resist quenching in acidic solution (pH < 4). Furthermore, core−shell QDs-GNs show a longer lifetime in a broad range of pH values, from 9 to 1. The calculated average lifetime (τave) of QDs-GNs is about 889 ± 23 ps, which is 3-fold longer than that of MUA-QDs (263 ± 10 ps) at pH 7.0. The enhanced lifetime of QDs-GNs is almost 9 times of that of CdSe QDs when pH value is 1. Meanwhile, the cell viability study shows that no significant toxic effect is imposed on the NIH/3T3 mouse fibroblast cell line when the concentration of QD-GNs is below 5 mg/mL. It is expected that this new biocompatible fluorescent nanospheres could be an excellent alternative fluorescent imaging agent for cell labeling, especially in acidic conditions.
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INTRODUCTION Group II−VI semiconductor nanocrystals with diameters in the range of 1−10 nm, i.e., quantum dots (QDs), have been extensively studied as light-emitting materials for biological labeling over the past decade because of their strong sizetunable band gap photoluminescence (PL).1−4 CdSe quantum dots (QDs) are one of the most well-studied QDs due to their size-dependent light emission in a visible region, as well as the high PL quantum yield.5,6 However, unsatisfied biocompatibility and instability in aqueous media limit QDs in vitro and in vivo biomedical applications.7−9 Efforts have been attempted to improve the biocompatibility and photostability of QDs by modifying the surface of QDs with amphiphilic molecules,10−14 polymers,15,16 or inorganic materials, such as silica shells.17,18 Gelatin is a natural biocompatible biopolymer derived from collagen. Gelatin nanospheres (GNs) have been used in gene delivery due to its good biocompatibility.19−21 Quite recently, fluorescent gelatin nanospheres (GNs) demonstrate the potential applications in drug delivery and bioimaging at the same time.22−26 Unlike loading organic dye, loading quantum © 2014 American Chemical Society
dots (QDs) within GNs may improve the biocompatibility of QDs and fluorescence properties of GNs. The two-step desolvation process is able to produce well-tailored GNs in terms of uniform size and narrow size distribution. It is noted that a low pH value (
