www.afm-journal.de FULL PAPER www.MaterialsViews.com © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1733 wileyonlinelibrary.com © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Funct. Mater. 2011, 21, 1733–1740 Faisal Mahtab, Yong Yu, Jacky W. Y. Lam, Jianzhao Liu, Bei Zhang, Ping Lu, Xixiang Zhang, and Ben Zhong Tang* 1. Introduction Nanoparticles with both efficient fluorescence and strong magnetization may find high-technological applications in ultrasensitive assays, living cell labeling, biological separation, site-specific drug delivery, magnetic resonance imaging, and magnetocytosis. [1] Little effort has, however, been devoted to the development of such nanoparticles, in comparison to the great wealth of the studies on the particles with a single attribute of either fluorescence or magnetization. [2–17] Silica and polymer are favorable host materials for the inclu- sion of chromophores and nanoclusters because of their optical transparence and biological compatibility. The encapsulation can protect the dye molecules from external perturbations such as oxygen and ions dissolved in solutions. For magnetic nanoclusters, the encapsula- tion can prevent them from agglomerating into large chunks. The silica/polymer matrix also provides a useful platform for surface chemistry, enabling the nano- particle surfaces to be chemically modi- fied for further functionalization. Many commercially available organic dyes, such as rhodamine, ethidium bro- mide, and Nile Red, emit efficiently in the dilute solutions but become weakly fluorescent or even nonemissive when aggregated in the solid state. [18–23] This phenomenon is very common and has been attributed to the nonradiative decay of sandwich-shaped excimers and exciplexes formed among the closely packed dye molecules in the aggregates. A low dye loading in the particle may be free of aggregation but can only offer weak emission. The light emission cannot be enhanced by putting more dye molecules into a particle because of the noto- rious effect of aggregation-caused quenching (ACQ). Various chemical, physical, and engineering approaches and processes have been developed to mitigate the ACQ effect. The attempts have, however, met with only limited success. [24–26] Such prob- lems can be avoided by the use of semiconductor quantum dots (e.g., CdSe). However, quantum dots generally show small Stocks shifts (hence heavy self-absorbtion) and low fluorescence quantum yields, in addition to their high toxicity. [27–30] Many research groups have incorporated magnetic nanoclusters into the nanoparticles but the magnetizations of the clusters are commonly low, which greatly limit the scope of their potential applications. [31–34] We have worked on the development of luminescent materials with efficient light emissions in the solid state and observed a novel phenomenon of aggregation-induced emis- sion (AIE): a group of nonemissive, propeller-like molecules are induced to emit efficiently by aggregate formation. [35–39] The AIE effect can boost the fluorescence quantum yields ( Φ F ’s) of the molecules by up to two orders of magnitude. Taking advantage of such effects, we have utilized the AIE dyes for the fabrication of highly emissive fluorescent silica nano- particles (FSNPs) with core–shell structures. [40] The FSNPs pose Fabrication of Silica Nanoparticles with Both Efficient Fluorescence and Strong Magnetization, and Exploration of Their Biological Applications Nanoparticles with both efficient light emission and strong magnetiza- tion (MFSNPs) are fabricated by one-pot, surfactant-free sol–gel reaction of tetraethoxysilane and silole-functionalized siloxane in the presence of citrate-coated magnetite nanoparticles. The MFSNPs are uniformly sized with smooth surfaces. They possess core–shell structures and exhibit appreciable surface charges and hence good colloidal stability. The MFSNPs are superparamagnetic, exhibiting no hysteresis at room temperature. UV irradiation of the suspension of MFSNPs in ethanol gives strong green emission at 486 nm, thanks to the novel aggregation-induced emission char- acteristics of the silole aggregates in the hybrid nanoparticles. The MFSNPs can selectively stain the cytoplasmic regions of the living cells. Addition of (3-aminopropyl)triethoxysilane during the fabrication of MFSNPs has gener- ated MFSNP-NH 2 with numerous amino groups decorated on the surface, enabling the nanoparticles to immobilize bovine serum albumin efficiently. DOI: 10.1002/adfm.201002572 Dr. F. Mahtab, Y. Yu, Dr. J. W. Y. Lam, Dr. J. Liu, Dr. P. Lu, Prof. B. Z. Tang Department of Chemistry The Hong Kong University of Science & Technology Clear Water Bay, Kowloon, Hong Kong, China Fax: +852–2358-1594 E-mail: tangbenz@ust.hk Prof. B. Z. Tang Department of Polymer Science and Engineering Zhejiang University Hangzhou 310027, China Prof. B. Zhang, Prof. X. Zhang Department of Physics The Hong Kong University of Science & Technology Clear Water Bay, Kowloon, Hong Kong, China