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Unformatted text preview: Fluorescent Silica Nanoparticles H EIKE M ADER , X IAOHUA L I , S AYED S ALEH , M ARTIN L INK , P ETER K ELE , AND O TTO S. W OLFBEIS Institute of Analytical Chemistry, Chemo- and Biosensors, University of Regensburg, Regensburg, Germany We report on the preparation of fluorescent silica nanoparticles (NPs). They have been prepared by (a) modification of the NPs by amino groups and subsequent introduction of amino-reactive fluorophores of various color and (b) by modification of the NPs by either azido groups or alkyne groups and subsequent conjugation to fluorophores by so-called click chemistry, which is a novel approach toward modifying silica NPs. The new NPs were characterized in terms of size and spectral properties. Key words: fluorescence; silica nanoparticles; click reaction; click chemistry Introduction Silica nanoparticles (NPs) represent an interesting class of materials because they are available in well de- fined size and size distribution, are rather affordable, and have fairly good biocompatibility and a surface reactive enough to allow for various kinds of function- alization. While silica NPsin contrast to quantum dotsare not fluorescent by themselves, they can be rendered fluorescent by various methods, such as in- corporation of dyes into the interior of the material, or by methods that are comparable to processes that can be used to modify glass surfaces. One of the most promising applications of silica nanobeads is their use as fluorescent labels in bioassays. In fact, fluorescent NPs have been used for various pur- poses 1 including nanotechnology for gene delivery, 2 , 3 drug delivery, 4 , 5 and scanning probe microscopy-based imaging and sensing techniques. 6 Besides, silica-based NPs have been extensively used in bioanalytical ap- plications, such as immuno and gene assays, 7 , 8 where they are conjugated, for example, to biomolecules for analyte recognition and subsequent signal generation. Numerous methods have been developed for sur- face modification of silica NPs in order to enable the coupling of NPs to biomolecular targets. For example, oligonucleotides, 9 , 10 proteins, 11 and antibodies 12 have been linked to silica NPs which, in turn, enabled sen- sitive fluorometric bioassays. Different types of func- tional groups can be easily introduced onto the NPs for Address for correspondence: Otto S. Wolfbeis, Institute of Analyti- cal Chemsitry, Chemo- and Biosensors, University of Regensburg, D- 93040 Regensburg, Germany. Voice: + 49-943-4065; fax: + 49-943-4064. www.wolfbeis.de, email@example.com conjugation with biomolecules. In addition, the silica surface makes such NPs chemically inert and physi- cally stable....
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