Novel materials for the phototherapeutic release of the bioregulator nitric oxide (nitrogen monoxide) are described. Also reported is a method for scanning these materials with a focused NIR beam to induce photouncaging while minimizing damage from local heating. The new materials consist of poly(dimethylsiloxane) composites with near-infraredto-visible upconverting nanoparticles (UCNPs) that are cast into a biocompatible polymer disk (PD). These PDs are then impregnated with the photochemical nitric oxide precursor Roussin's black salt (RBS) to give UCNP_RBS_PD devices that generate NO when irradiated with 980 nm light. When the UCNP_RBS_PD composites were irradiated with NIR light through filters composed of porcine tissue, physiologically relevant NO concentrations were released, thus demonstrating the potential of such devices for minimally invasive phototherapeutic applications.

Reported are quantitative studies of the energy transfer from water-soluble CdSe/ZnS and CdSeS/ZnS core/shell quantum dots (QDs) to the Cr(III) complexes trans-Cr(N(4))(X)(2)(+) (N(4) is a tetraazamacrocycle ligand, X(-) is CN(-), Cl(-), or ONO(-)) in aqueous solution. Variation of N(4), of X(-), and of the QD size and composition allows one to probe the relationship between the emission/absorption overlap integral parameter and the efficiency of the quenching of the QD photoluminescence (PL) by the chromium(III) complexes. Steady-state studies of the QD PL in the presence of different concentrations of trans-Cr(N(4))(X)(2)(+) indicate a clear correlation between quenching efficiency and the overlap integral largely consistent with the predicted behavior of a Förster resonance energy transfer (FRET)-type mechanism. PL lifetimes show analogous correlations, and these results demonstrate that spectral overlap is an important consideration when designing supramolecular systems that incorporate QDs as photosensitizers. In the latter context, we extend earlier studies demonstrating that the water-soluble CdSe/ZnS and CdSeS/ZnS QDs photosensitize nitric oxide release from the trans-Cr(cyclam)(ONO)(2)(+) cation (cyclam = 1,4,8,11-tetraazacyclotetradecane) and report the efficiency (quantum yield) for this process. An improved synthesis of ternary CdSeS core/shell QDs is also described.

Carbon disulfide, a potentially therapeutic small molecule, is generated via oxidative cleavage of 1,1-dithiooxalate (DTO) photosensitized by CdSe quantum dots (QDs). Irradiation of DTO−QD conjugates leads to λ irr independent photooxidation with a quantum yield of ∼4% in aerated pH 9 buffer solution that drops sharply in deaerated solution. Excess DTO is similarly decomposed, indicating labile exchange at the QD surfaces and a photocatalytic cycle. Analogous photoreaction occurs with the O-tert-butyl ester t BuDTO in nonaqueous media. We propose that oxidation is initiated by hole transfer from photoexcited QD to surface DTO and that these substrates are a promising class of photocleavable ligands for modifying QD surface coordination.S emiconductor quantum dots (QDs) exhibit size and composition dependent optical properties, strong absorption cross sections, high photoluminescence (PL) quantum yields, and customizable solubility through surface ligand exchange. 1 These properties position QDs as attractive sensitizers for photodynamic therapy, 2 photoactivated drug delivery, 3 solar energy conversion, 4 and photocatalysis. 5 Here we describe the photocatalytic cleavage of 1,1-dithiooxalate (DTO) to CS 2 and CO 2 mediated by CdSe QDs. This process serves to "uncage" carbon disulfide (CS 2 ), a potentially therapeutic agent. Similar reactions are observed with the DTO ester t BuDTO, and light activated cleavage of such ligands suggests strategies for the controlled modification of quantum dot surfaces.Fragmentary evidence points toward possible therapeutic roles for carbon disulfide. 6 For example, CS 2 may react with biological amines to form dithiocarbamates, known inhibitors 7 of nuclear factor κB (NF-κB), 8 a crucial mediator in inflammation induced tumor growth and progression. 9 Indeed, dithiocarbamates have been proposed as anticancer agents. 10 Physiological responses to CS 2 or dithiocarbamates include cell growth, apoptosis, and neurotransmission, which are also functions of the small molecule bioregulators NO, CO, and H 2 S. 11 Like each of these, CS 2 is considered toxic at higher concentrations, although epidemiological data are contradictory. 12 Thus, the benefit of balancing the therapeutic and toxic effects of CS 2 make the prospect of controlled, targeted delivery an attractive goal.In these contexts, we are probing DTO−QD conjugates as photochemical CS 2 precursors. These were readily prepared by exchanging DTO dianions for the myristate ligands (n-C 13 H 27 CO 2 − ) originally terminating the QD surface (see Supporting Information (SI) for procedures). Ligand exchange is evidenced by the solubility shift from organic to aqueous media as dianionic DTO replaces the hydrophobic myristate. Purified conjugates show a very strong UV absorption band (∼335 nm) nearly the same as free DTO (λ max ∼335 nm, ε max = 1.5 × 10 4 M −1 cm −1 in aq. solution) and a QD exciton band red-shifted by as much as 40 nm (Figure 1, SI Table S-1).Analogous red shifts in exciton absorptions have been seen when...

Lanthanide-modified CdSe quantum dots (CdSe(Ln) QDs) have been prepared by heating a solution of Cd(oleate) 2 , SeO 2 , and Ln(bipy)(S 2 CNEt 2 ) 3 (bipy = 2,2′-bipyridine) to 180−190 °C for 10−15 min. The elemental compositions of the resulting CdSe(Ln) cores and CdSe(Ln)/ZnS core/shell QDs show this route to be highly reproducible. The optical absorption spectra of these composite materials are similar to those of the unmodified nanocrystals, but the QD-centered band edge photoluminescence (PL) is partially quenched. The time-gated emission and excitation spectra of the CdSe(Ln) cores display sensitized lanthanide-centered PL upon higher energy excitation of the nanocrystal host but not upon excitation at the lowest energy QD absorption band. Growth of the ZnS shell led to the depletion of about 60% of the lanthanide ions present together with depletion of nearly all of the lanthanide-centered PL. On these bases, we conclude that the lanthanide-centered PL from the CdSe(Ln) cores originates with Ln 3+ -related trap states associated with the QD surface.

Semiconductor quantum dots (QDs) are attractive for potential use as photosensitizers for a variety of applications. These nanomaterials have very high absorption cross-sections and often display strong photoluminescence (PL). Furthermore, QD absorption and emission spectra can be tuned simply by varying their size, and QD surfaces can be modified to access multiple sites for attaching potential acceptors as well as other functionalities. Here we provide an overview of recent studies concerned with the photosensitization of transition metal centers and other acceptors. Particular focus is directed towards potential therapeutic applications and to our own interest in the delivery of small molecule bioregulators to physiological targets. Studies that have addressed factors that control likely energy and charge transfer processes between QD donors and acceptor molecules are also discussed. Understanding the mechanisms of these photosensitization processes can provide design guidelines for successful applications.