A fast, simple procedure is described for obtaining an assembly of silver sulfide nanoparticles (Ag(2)S NPs) on a glass substrate through reaction of a template of an assembled layer of silver nanoparticles (Ag NPs) with hydrogen sulfide (H(2)S) gas. The Ag NP template was prepared by assembling a monolayer of spherical Ag NPs (mean diameter of 7.4 nm) on a polyethylenimine-treated glass substrate. Exposure to pure H(2)S for 10 min converted the Ag NPs of the template to Ag(2)S NPs. The resulting Ag(2)S NP assembly, which retains the template nanostructure and particle distribution, was characterized by optical absorption spectroscopy, atomic force microscopy, transmission electron microscopy (TEM), scanning high resolution TEM, energy dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy. The Ag(2)S NPs have a crystal structure of monoclinic acanthite, and while they retained the spherical shape of the original Ag NPs, their mean particle size increased to 8.4 nm due to changes to the crystal structure when the Ag NPs are converted into Ag(2)S NPs. The measured optical absorption edge of the Ag(2)S NP assembly indicated an indirect interband transition with a band gap energy of 1.71 eV. The Ag(2)S NP assembly absorbed light with wavelengths below 725 nm, and the absorbance increased monotonically toward the UV region.
Thin films derived from nanocrystal cores and functionalized linkers provide a large surface area-to-volume ratio and three-dimensional ligand framework. This paper describes the results of an investigation of the interfacial mass flux and binding properties of such thin films using an electrochemical quartz crystal nanobalance technique. The hydrogen-bonding assembly from gold nanocrystals and 11-mercaptoundecanoic acid was studied as a model system. The results reveal four distinctive mass response characteristics upon pH tuning or metal ion binding. First, the protonation-deprotonation characteristic of the carboxylic acid groups in the nanostructured framework is dependent on particle core size and film thickness. Second, the pHtunable cationic redox reaction across the electrode|film|electrolyte interface is accompanied by a large cationic electrolyte mass flux. Third, the spontaneous complexation to copper ions by the nanostructured carboxylate framework is reflected by a mass increase of the film. Fourth, the redox reaction of copper loaded in the nanostructured film is accompanied by fluxes of electrolyte cations across the electrode|film|electrolyte interface which compensate electrostatically the fixed negative charges. On the basis of the mass change detected in the presence of a series of electrolyte cations, a linear relationship was determined between the mass increase and the atomic mass of the cation, and a concurrent flux of solvent molecules was also revealed. Implications of the findings to the delineation of the design parameters of the nanostructured ligand framework for controlled release and environmental monitoring or removal of metals are also discussed.
Nanostructured thin film assemblies derived from metal or oxide nanocrystal cores and functionalized molecular shells provide large surface-to-volume ratio and three-dimensional ligand frameworks. In this article, we report results of an investigation of the nanostructured materials for electroanalysis. Monolayer-capped gold nanoparticles of 2-nm core diameter and carboxylic acid-functionalized alkyl thiols were assembled on electrode surfaces via an exchangecrosslinking-precipitation reaction route, and were studied as a model system. The network assemblies exhibit open frameworks in which the void space forms channels with the nanometer sized cores defining its size and the shell structures defining its chemical specificity. Such nanostructures were exploited to demonstrate the viability of responsive materials for interfacial incorporation and fluxes of ionic species. The nanomaterials were characterized by an array of techniques, including cyclic voltammetry, electrochemical quartz-crystal nanobalance, flow injection analysis, and surface infrared reflection spectroscopy. The current responses and mass loading as a result of the incorporation of ionic species into the nanostructure have been analyzed. The potential application of the nanostructured thin films for electrochemical detection in microfluidic systems is also discussed.
There is a need for novel, effective, and cell- and gene-specific therapeutics for cancer. Modified oligonucleotides can be used to modulate specifically and potently the expression of several genes that are upregulated in breast and prostate cancer and have been found to be causal to the tumor phenotype. Synergistic downregulation of these genes may be a potent therapeutic intervention. We are investigating the use of boranophosphate (BP) analogues of RNA as promising candidates for enhancing the potential of three relatively new, gene-specific, anticancer strategies: (1) Tumor-targeted borane siRNA against a combination of genes that control metabolism and transduction; (2) Tumor-specific modified aptamers against prostate specific membrane antigen (PSMA) and ERB2 in breast cancer as delivery agents; and (3) Cancer cell obliteration by cell-specific radiation therapy: Boron-Neutron-Capture-Therapy.
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