Anal. Chem. 2006, 78, 5925-5932
Technical Notes
Silica-Shelled Single Quantum Dot Micelles as Imaging Probes with Dual or Multimodality Rumiana Bakalova,*,†,§ Zhivko Zhelev,† Ichio Aoki,‡,§ Hideki Ohba,† Yusuke Imai,† and Iwao Kanno§
On-Site Sensing and Diagnosis Research Laboratory, National Institute for Advanced Industrial Science and Technology, AIST-Kyushu, 807-1 Shuku-machi, Tosu 841-0052, Japan, Department of Medical Informatics, Meiji University of Medicine, Kyoto 629-0392, Japan, and Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, Chiba 263-8555, Japan
The present study describes a stabilization of single quantum dot (QD) micelles by a “hydrophobic” silica precursor and an extension of a silica layer to form a silica shell around the micelle using “amphiphilic” and “hydrophilic” silica precursors. The obtained product consists of ∼92% single nanocrystals (CdSe, CdSe/ZnS, or CdSe/ZnSe/ZnS QDs) into the silica micelles, coated with a silica shell. The thickness of the silica shell varies, starting from 3-4 nm. Increasing the shell thickness increases the photoluminescence characteristics of QDs in an aqueous solution. The silica-shelled single CdSe/ ZnS QD micelles possess a comparatively high quantum yield in an aqueous solution, a controlled small size, sharp photoluminescence spectra (fwhm ∼30 nm), an absence of aggregation, and a high transparency. The surface of the nanoparticles is amino-functionalized and ready for conjugation. A comparatively good biocompatibility is demonstrated. The nanoparticles show ability for intracellular delivery and are noncytotoxic during long-term incubation with viable cells in the absence of light exposure, which makes them appropriate for cell tracing and drug delivery. The presence of the hydrophobic layer between the QD and silica-shell ensures an incorporation of other hydrophobic molecules with interesting properties (e.g., hydrophobic paramagnetic substances, hydrophobic photosensitizers, membrane stabilizers, lipidsoluble antioxidants or prooxidants, other hydrophobic organic dyes, etc.) in the close proximity of the nanocrystal. Thus, it is possible to combine the characteristics of hybrid materials with the priority of small size. The silicashelled single QD micelles are considered as a basis for fabrication of novel hybrid nanomaterials for industrial and life science applications, for example, nanobioprobes with dual modality for simultaneous application in differ* To whom correspondence should be addressed. Phone/Fax: +81-942813628. E-mail:
[email protected]. † National Institute for Advanced Industrial Science and Technology. ‡ Meiji University of Medicine. § National Institute of Radiological Sciences. 10.1021/ac060412b CCC: $33.50 Published on Web 07/14/2006
© 2006 American Chemical Society
ent imaging techniques (e.g., fluorescent imaging and functional magnetic resonance imaging). Starting from 1998 with the first reports of Alivisatos’s and Nie’s labs about the potential of quantum dots (QDs) in bioimaging,1,2 currently, these nanoparticles also are attracting considerable attention in biosensing, photosensitizing, and drug delivery.3-6 The synthesis of highly fluorescent water-soluble QDs has become a priority, and the efforts are directed at the development of simplified and reproducible methodologies for fabrication of small size (
