Labeling Cells with Silver/Dendrimer Nanocomposites
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Labeling Cells with Silver/Dendrimer Nanocomposites Wojciech Lesniak1, Xiangyang Shi1, Anna Bielinska1, Katarzyna Janczak1, Kai Sun2 James R. Baker Jr.1, and Lajos P. Balogh1,3,4 1 Center for Biologic Nanotechnology, 2Electron Microbeam Analysis Laboratory 3Department of Biomedical Engineering, 4Macromolecular Science and Engineering, University of Michigan, Ann Arbor, MI 48109 Abstract We have developed water-soluble, biocompatible, fluorescent, and photostable silver/dendrimer nanocomposites that have a potential to be used for in vitro cell labeling. A PAMAM_E5.NH2 dendrimer was used as a template to prepare first a silver-dendrimer complex in an aqueous solution at biologic pH=7.4. Conversion into nanocomposite was achieved by irradiating the solution of the [(Ag+)25-PAMAM_E5.NH2] complex by UV light to reduce the bound Ag+ to zero-valent Ag0 atoms, which were simultaneously trapped in the dendrimer network. Results indicate that the {(Ag0)25-PAMAM_E5.NH2} silver/dendrimer nanocomposite forms positively charged single particles of 4-5 nm under the experimental conditions used. The dendrimer nanocomposite proved to be fluorescent. Toxicity testing of {(Ag0)25PAMAM_E5.NH2} nanocomposite revealed a behavior similar to the template dendrimer. Intracellular internalization of the silver nanocomposite and cell labeling capabilities was confirmed by confocal microscopy. Introduction Nanostructured materials have gained increasing attention in the past decades due to their unique properties that provide outstanding opportunities for application in photonics, biology, and medicine. Dendrimer nanocomposites (DNC) [1-3] are nanosized inorganic/organic hybrid composite particles containing topologically trapped guest atoms/molecules/nanocrystals immobilized by dendritic polymer hosts of well-defined size, charge, and terminal functionality. Our goal here is to describe the synthesis, characterization and use of a particular class of silver nanocomposites that can be used as cell labels in in vitro experiments. Noble metal nanoparticles have been shown to demonstrate a strong, discrete emission quantum yield that is comparable to bright organic fluorophores, as they exhibit features useful in the biological imaging [4-5]. The properties of metal nanocomposites strongly depend on their size and shape [6-8]. Thus, control of nanoparticle morphology plays an essential role in their future applications. Nanocomposites that can be used in biological systems are required to be water soluble, biocompatible, and photostable. It is well documented that poly(amidoamine) (PAMAM) dendrimers hold great promise in this regard due to their highly regular, symmetrically branched structure with variable surface functionalities, which permits optimization for toxicity. PAMAMs can host inorganic ions or atoms/molecules by forming dendrimer complexes and nanocomposites [9]. Fabrication of metal/dendrimer nanocomposites requires two steps: (1) binding of metal ions to form complexes that act as precursors for consequent nanoclusters fo
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