Fabrication of Fluorescent Cellular Probes: Hybrid Dendrimer/Gold Nanoclusters
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1007-S15-07
Fabrication of Fluorescent Cellular Probes: Hybrid Dendrimer/Gold Nanoclusters Chang Zhong1, Yuping Bao1, Dung M. Vu2, R. Brian Dyer2, and Jennifer S. Martinez1 1 Center for Integrated Nanotechnologies, Los Alamos National Laboratory, MS K771, Los Alamos, NM, 87544 2 Physical Chem & Applied Spectroscopy, Los Alamos National Laboratory, MS J567, Los Alamos, NM, 87544
ABSTRACT Fluorescent metal nanoclusters, which consist of collections of small numbers of noble metal atoms, are of great interest in photochemistry and photophysics due to their strong sizedependent emission. Historically their generation was confined to gaseous and solid phases; however, recently a unique organic/inorganic hybrid materials approach was developed that utilizes dendrimers as templates to protect nanoclusters from solution based fluorescence quenching. These hybrid dendrimer/gold nanoclusters are water-soluble and highly fluorescent. Yet there are several intrinsic deficiencies in their synthetic method: first, NaBH4, a toxic chemical, was used as reducing agent in the reaction; and second, the reaction yield was low due to the concurrent formation of large, non-emissive, gold particles. Here we report a particle-free method to produce dendrimer-encapsulated gold nanoclusters in high-yield. Proof of concept is demonstrated using OH-terminated poly(amidoamine) dendrimer and Au(PX3)3Cl (X = Ph, Me), but the approach can also be extended to the combination of other dendrimers and organic noble metal salts. Our approach yields fluorescent clusters with homogeneous size distribution. These clusters can be transferred to aqueous solution and used directly for biological applications. INTRODUCTION Development of small luminescent nanostructures is of great importance for singlemolecule spectroscopy and imaging, biomedicine, and biolabeling.[1] Semiconductor quantum dots have held great promise for these applications, yet their use has been limited because of their potential toxicity and large size.[2] Small clusters of metals develop unique molecule-like properties (i.e. fluorescence) as their size decreases, and are thus promising alternatives to quantum dots.[3] Many different synthetic procedures have been developed to produce fluorescent gold nanoclusters ranging from 3-30 metal atoms.[4] The major drawback of these clusters has been their low quantum yields which preclude their application as biolabels.[5] A breakthrough was made by Dickson and co-workers by using poly(amidoamine) (PAMAM) dendrimer to confine and protect gold nanoclusters. Size-tunable clusters with discrete emission and high quantum yield (0.1 to 0.7) were created.[6,7] While preliminary, Leblanc and colleagues have begun to utilize similar clusters for immunoassays.[8] Albeit exciting, the broad application of this emergent technology requires large scale and high yield synthesis of gold nanoclusters; yet, there are several intrinsic deficiencies in Dickson’s original synthetic method:[9] first, NaBH4, a toxic chemical, was used as reducing agent in the reac
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