ABSTRACT:The synthesis and photophysical and biological investigation of Ru(II)-polypyridyl stabilized watersoluble, luminescent gold nanoparticles (AuNPs) are described. These structures bind to DNA and undergo rapid cellular uptake, being localized within the cell cytoplasm and nucleus within 4 h. T he development of functional supramolecular nanostructures for applications in photonics, 1 sensing, 2 catalysis 3 and medicine, 4 etc. is a fast emerging interdisciplinary research field. The design and synthesis of nanoparticles 5 and, in particular, functionalized gold nanoparticles (AuNPs) has been at the forefront of this effort in recent times, with many examples being developed for use in biological and medical applications, 6 due to their biocompatibility, unique size-and shape-dependence, and optoelectronic properties. Similarly, Ru(II)-polypyridyl complexes have been intensively studied due to their photophysical properties, 7 where they have been employed for example in luminescent recognition and sensing, 8 as sensitive and structurespecific DNA probes.9 Luminescent d 6 transition metal ion complexes have often been proposed as useful fluorophores for cellular imaging, 10,11 but until very recently their use in actual applications has remained scarce. With our interest in the development of luminescent novel cellular targeting (therapeutic/ imaging) agents 7a,b,12 and surface modified AuNPs, 13 we envisaged that the combination of Ru(II)-polypyridyl complexes, spatially separated from the surface of AuNPs, by a covalent spacer, could be employed as luminescent probes/imaging agents for various biological applications.15 Herein we describe the synthesis of the Ru(II) complexes 1À3, Figure 1, all of which possess a terminal alkyl thiol group which facilitates their adsorption onto AuNPs, leading to the formation of the three water-soluble systems AuNP-1, AuNP-2 and AuNP-3 (Figure 1). We demonstrate that these luminescent AuNPs offer attractive photophysical properties, ideal for application in cellular imaging, which we demonstrate using HeLa cells. These are, to the best of our knowledge, the first examples of such Ru(II)-polypyridyl functionalized AuNPs to be employed for such cellular applications.The syntheses of 1, 2, and 3 are shown in Scheme S1 (see also full details in Supporting Information) and were achieved in a few steps. The common ligand for all of these complexes is 4, the synthesis of which was achieved by employing peptidic (carbodiimide) coupling of 11-mercaptoundecanoic acid 14a with 5-amino,-1,10 phenanthroline in CH 2 Cl 2 , yielding 4 as an offwhite solid in 78% yield. The microwave irradiation of 4 in the presence of the Ru(II) bispolypyridyl dichlorides Ru(bpy) 2 Cl 2 , Ru(phen) 2 Cl 2 , and Ru(TAP) 2 Cl 2 gave 1, 2, and 3, respectively, after 40 min.14b These were isolated, by precipitation from water, using excess NH 4 PF 6 , followed by purification using automatic column chromatography [flash silica; 40:4:1 CH 3 CN/H 2 O/ NaNO 3 (sat)], yielding 1À3 in 75%, 65%, and 54%, respec...
The development of Ru(II) functionalized gold nanoparticles 1–3·AuNP is described. These systems were found to be mono-disperse with a hydrodynamic radius of ca. 15 nm in water but gave rise to the formation of higher order structures in buffered solution. The interaction of 1–3·AuNP with DNA was also studied by spectroscopic and microscopic methods and suggested the formation of large self-assembly structures in solution. The uptake of 1–3·AuNP by cancer cells was studied using both confocal fluorescence as well as transmission electron microscopy (TEM), with the aim of investigating their potential as tools for cellular biology. These systems displaying a non-toxic profile with favourable photophysical properties may have application across various biological fields including diagnostics and therapeutics.
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