Highly fluorescent silver nanoparticles (AgFNP) have been prepared by a facile photochemical method, yielding these materials in just a few minutes and with excellent long-term stability. The method makes use of photogenerated ketyl radicals that reduce Ag(+) from silver trifluoroacetate in the presence of amines. While as functional materials these AgFNP can be described as of nanometer dimensions, we believe that the luminescence arises from particle-supported small metal clusters (predominantly Ag(2)). The materials have been characterized by electron microscopy, fluorescence and absorption spectroscopy, fluorescence lifetime studies, and (19)F NMR spectroscopy. Exploratory work shows that the fluorescence from AgFNP can be efficiently quenched by paramagnetic quenchers, and these studies have been combined with electron paramagnetic resonance work.

Nanomedicine, defined as the application of nanotechnology in the medical field, has the potential to significantly change the course of diagnostics and treatment of life-threatening diseases, such as cancer. In comparison with traditional cancer diagnostics and therapy, cancer nanomedicine provides sensitive cancer detection and/or enhances treatment efficacy with significantly minimized adverse effects associated with standard therapeutics. Cancer nanomedicine has been increasingly applied in areas including nanodrug delivery systems, nanopharmaceuticals, and nanoanalytical contrast reagents in laboratory and animal model research. In recent years, the successful introduction of several novel nanomedicine products into clinical trials and even onto the commercial market has shown successful outcomes of fundamental research into clinics. This paper is intended to examine several nanomedicines for cancer therapeutics and/or diagnostics-related applications, to analyze the trend of nanomedicine development, future opportunities, and challenges of this fast-growing area.

The photochemistry of aromatic ketones through the Norrish type I cleavage of benzoins and via photoreduction generates ketyl radicals that readily reduce many metal ions, including silver and gold. Reduction to Au(0) and Ag(0) leads to the spontaneous formation of nanoparticles (NPs) in aqueous or micellar solutions. Careful consideration of kinetic factors to minimize triplet quenching by metal ions can lead to rapid NP generation. These materials are quite stable and have interesting reactivities due to the essentially unprotected characteristics of the surface.

The association and resulting fluorescence quenching of CdSe quantum dots by 4-amino-2,2,6,6-tetramethylpiperidine oxide (4-amino-TEMPO), a persistent nitroxide, have been examined using electron paramagnetic resonance (EPR) and fluorescence spectroscopy. EPR data suggest binding constants around (8 +/- 4) x 10(6) M(-1) for green (2.4-2.5 nm) nanoparticles, and the application of Job's method indicates that the preferred mode of binding involves one or two quencher molecules per quantum dot, although more quenchers could bind at high concentrations of 4-amino-TEMPO. Fluorescence quenching by 4-amino-TEMPO is at least 3 orders of magnitude more efficient than by TEMPO itself, reflecting the strong binding confirmed by the EPR data. Stern-Volmer plots are nonlinear and in light of the EPR data probably reflect ready accessibility of the CdSe surface to one or two 4-amino-TEMPO molecules, while additional quenchers can only bind if they displace trioctylphosphine oxide ligands. Quantum dot-4-amino-TEMPO complexes can be used as free radical sensors, since the fluorescence (quenched by the nitroxide) is readily restored when radicals are trapped to form alkoxyamines.

Quenching of quantum dot luminescence by nitroxides shows steep exponential behavior and is dependent on nanoparticle size, being most effective for the smaller particles. The interaction of CdSe nanoparticles with TEMPO (non‐binding) and 4‐amino‐TEMPO (binding) has been examined using fluorescence and electron spin resonance techniques. The data suggest that quenching involves an electron exchange mechanism. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The ketone-photoinduced formation of Au, Ag, and Cu nanoparticles from their corresponding ions in solution has been carried out using benzoin photoinitiators. Ketones are good photosensitizers for nanoparticle synthesis not because of the energy they can absorb or deliver, but rather because of the reducing free radicals they can generate. Efficient photochemical nanoparticle generation thus requires a careful selection of substrates and experimental conditions such that free radical generation occurs with high quantum efficiency, where metal ion precursors do not inhibit radical formation. A key consideration to achieve nanoparticle synthesis with short exposure times is to minimize excited-state quenching by metal ions. Applications of nanostructures in catalysis require control of the nanoparticle characteristics, such as dimension, morphology, and surface properties. Part of this article describes the strategies to modify photochemically prepared particles. Finally, we illustrate some of the nanoparticle applications that interest us, with some emphasis on plasmon-mediated processes.

A bis-pyrrolide ligand containing a nonconjugated aromatic ring in the backbone was reacted with ThCl 4 (DME) 2 , affording the corresponding η 6 -{1,3-[(2-C 4 H 3 N)(CH 3 ) 2 C] 2 C 6 H 4 }ThCl 3 ][Li(DME) 3 ] (1) complex. In this species, the π-bonding interaction of the actinide with the ring is probably induced by steric constraint. The bonding mode of the pyrrolide rings was switched from σ to π upon treatment of complex 1 with Et 3 Al. This reaction was also accompanied by deprotonation of the aromatic ring and formation of two similar compounds with the ring σ-bonded to the Th metal center. The two compounds {were isolated and fully characterized. The common feature among these two species is that the switching of bonding mode of the pyrrolide rings, resulting from the coordination of the aluminum residues, is accompanied by deprotonation of the central ring. Attempts to reduce 1 yielded the paramagnetic 3), which on the basis of the connectivity might be regarded as a rare case of Th(III). However, DFT calculation have elucidated the electronic structure of this species, which should be regarded as containing tetravalent Th bonded to the ligand radical anion. The spin density is mainly localized at the ring C atom, which is deformed and deviates from the planarity. Similar reductions carried out under slightly different reaction conditions afforded {η 4). In this complex the metal is surrounded by two ligands, one of which appears as having been partly hydrogenated at the central aromatic ring. Treatment of an in situ generated transient low-valent species with azobenzene as mild oxidizing agent resulted in reoxidation to a tetravalent thorium diphenylhydrazido species, [{η 6 -1,3-[(η 5 -2-C 4 H 3 N)(CH 3 ) 2 C] 2 C 6 H 4 }Th(μ-η 2 -PhNNPh)(μ-Cl)(Cl)Li(DME)][Li(DME) 3 ] (5).

As applications for semiconductor nanoparticle quantum dots (QDs) continue to expand in fields such as biology, imaging, and sensors, 1 it is paramount to have a fundamental understanding of their chemical and electronic interactions. Thiol-stabilized QDs have received considerable attention because they suffer from fewer fluctuations in their properties, and in certain cases their photoluminescence quantum yields show an improvement over trioctylphosphine oxide (TOPO)-capped QDs. 2,3 Further, from the perspective of QDs biological applications, the interaction of RS-H and RS-SR bonds with the surface is of the utmost importance.As part of our study of the interaction of (TOPO)-capped CdSe QDs with free radicals, 4-6 we have found that binding of disulfide biradical C2 to the QD surface provides a unique perspective of the mechanism by which disulfide binding evolves on the surface. By probing the system with fluorescence and EPR spectroscopies, we have found that the disulfide linkage is useful for the attachment of species to the surface of CdSe QDs leading to robust, strong chemical bonds to the particle surface and reporting on the dynamics of surface binding and S-S dissociation.