Cation exchange is shown to be a simple and efficient method to prepare nanostructured Ag(2)Se gels and aerogels from CdSe gel precursors. Treatment of CdSe wet gels with AgNO(3) yields, for the first time, Ag(2)Se gels, and these are transformed to high surface area, nanostructured aerogels by supercritical fluid drying. The striking similarity in crystallite size, morphology, and surface area characteristics between CdSe and the corresponding Ag(2)Se aerogels supports a mechanism in which the bonding within the gel network remains globally unchanged, even as the structural attributes of the primary particle components are undergoing a dramatic transformation (hexagonal CdSe to cubic Ag(2)Se). Intriguingly, the rapid exchange also enables exquisite control of composition on the macroscale; reduced concentrations of Ag(+) lead to two-component (i.e., CdSe inside, Ag(2)Se outside) heterogeneous structures of mm-cm dimensions. Overall, this methodology offers a simple approach for the generation of porous nanocrystalline metal chalcogenide networks of known or new compositions.

No abstract

Highly porous CdTe nanoarchitectures (aerogels) were prepared by sol-gel assembly of discrete nanocrystals followed by supercritical CO(2) drying. CdTe nanocrystal surface functionalization (either phosphine oxide or thiolate) is found to be immaterial to oxidation induced gel formation suggesting that the standard thiolate capping procedure is not a necessary step in the gelation process. On the basis of this observation, and reduction induced dispersion of the gel network, the exposure of reactive sites and the subsequent surface oxidation reaction to form polychalcogenide linkages are key steps in the gelation mechanism. Consequently, CdTe aerogels exhibit similar physicochemical properties, regardless of original ligating functionality. The aerogels are mesoporous, with surface area >100 m(2)/g, and exhibit an optical bandgap of 1.92 eV, consistent with quantum confinement within the 3-D linked network. Photoluminescence is suppressed in the aerogels, but can be partially recovered upon heating.

The photoluminescence (PL) response of highly porous CdSe aerogels to triethylamine (TEA) is investigated and compared to results from prior studies on single crystals and nanoparticle-polymer composites. As-prepared CdSe aerogels show significant and reversible enhancement of luminescence intensity upon exposure to TEA relative to the intensity in pure argon carrier gas. The enhancement in the PL response is dependent on the concentration and linear over the range of TEA concentration studied (4.7 x 10(3)-75 x 10(3) ppm). The sensing response of previously tested samples exhibits saturation behavior that is modeled using Langmuir adsorption isotherms, yielding adsorption equilibrium constants in the range 300-380 atm( - 1). The response is sensitively affected by the surface characteristics of the aerogel; when the wet gels are treated with pyridine prior to aerogel formation, the response to TEA is diminished, and when as-prepared aerogels are heated in a vacuum, no subsequent response is observed. Deactivation is attributed to an increase in surface oxide (SeO(2)) and decrease in surface Cd(2 + ) Lewis acid sites. Sensing runs of approximately one hour have little impact on the morphology or crystallinity of the aerogels, but do result in partial removal of residual thiolate ligands left over from the gelation process.

No abstract

No abstract

Urinary 8-hydroxy-2'-deoxyguanosine (8OHdG) is an excellent marker of oxidative DNA damage. Until now, urinary 8OHdG has been measured by high-performance liquid chromatography with electrochemical detection. A simple and sensitive method for the analysis of urinary 8OHdG by capillary electrophoresis with end-column amperometric detection has been developed in our laboratory. A single-step solid-phase extraction procedure was optimized and used for extracting 8OHdG from human urine. To improve the sensitivity of this method, a new focusing technique based on a dynamic pH junction was used. The limit of detection was 20 nM (signal-to-noise ratio S/N = 3), the linear range was 50 nM-10 microM, and the correlation coefficient was better than 0.999. The relative standard deviation (RSD) was found to be 0.57% for migration time, and 4.79% for peak current. To show the usefulness of the method, the urinary concentration of 8OHdG in nine healthy persons and ten cancer patients was determined. The urinary concentration of 8OHdG in cancer patients was significantly higher than that in healthy persons.

Urinary 8-hydroxy-2'-deoxyguanosine (8OHdG) is an excellent marker of oxidative DNA damage. Until now, urinary 8OHdG has been measured by high-performance liquid chromatography with electrochemical detection. A simple and sensitive method for the analysis of urinary 8OHdG by capillary electrophoresis with end-column amperometric detection has been developed and is described in this chapter. A single-step solid-phase extraction procedure was optimized and used for extracting 8OHdG from human urine. To improve the sensitivity of this method, a new focusing technique based on a dynamic pH junction was used. In the end, the urinary concentration of 8OHdG in healthy persons, patients with cancer, patients with diabetic nephropathy, and smokers was determined. Emphasis is focused on the establishment and application of the methods.