Nafion or sodium poly(styrenesulfonate) (NaPSS) entrapped in either sol-gel-derived silica or cross-linked poly(vinyl alcohol) (PVA) composite coatings on spectroscopic graphite electrodes were investigated electrochemically with [Re I (DMPE) 3 ] + , where DMPE ) 1,2-bis-(dimethylphosphino)ethane. Among these composite coatings, Nafion-entrapped sol-gel-derived silica (Nafionsilica) exhibited a sensitivity for [Re I (DMPE) 3 ] + ∼4 times higher than that of NaPSS-entrapped sol-gel-derived silica or NaPSS-entrapped PVA. When Nafion was entrapped in cross-linked PVA matrix, however, the voltammetric response was found to be only ∼14% of that of Nafion and Nafion-silica composite coatings. Dispersing Nafion in sol-gel-derived silica matrix improves the slow diffusion of [Re I (DMPE) 3 ] + in Nafion, thus leading to a higher sensitivity than Nafion in a shorter preconcentration time. Such a Nafion-silica composite is promising for both electrochemical and spectroelectrochemical sensing of [Re I (DMPE) 3 ] + . It was also found that increasing the high potential of a cyclic voltammetric scan greatly reduces the amount of [Re II (DMPE) 3 ] 2+ available for reduction in the reverse potential scan, suggesting that the electrochemically generated [Re II (DMPE) 3 ] 2+ was consumed in the more positive potential region.[Re I (DMPE) 3 ] + , where DMPE ) 1,2-bis(dimethylphosphino)-ethane, is a nonradioactive analogue of [ 99m Tc I (DMPE) 3 ] + , which is radioactive and shows potential as a myocardial perfusion imaging agent. 1 Radiopharmaceuticals are routinely used for organ imaging and for radiotherapy in nuclear medicine. One of the fundamental problems associated with the use of radiopharmaceuticals is that, in many circumstances, the composition of an injected radiopharmaceutical is known, but the chemical form of the agent that is actually responsible for the imaging or therapy may be an altered form due to in vivo reactions. 2 This is evidenced by biological studies which show that in vivo redox reactions can markedly affect the biodistributions of technetium-99m and rhenium-186 radiopharmaceuticals. 3,4 Therefore, gaining the information regarding the chemical form that is responsible for imaging or therapy is crucial for developing more efficacious radiopharmaceuticals. By investigating the nonradioactive species, [Re I (DMPE) 3 ] + , information directly applicable to its radioactive analogue can be acquired and information related to other radiopharmaceuticals may also be extracted.We have recently shown the preferential uptake of [Re I -(DMPE) 3 ] + by Nafion, a perfluorosulfonated ionomer, and the potential utility of Nafion as an electrode modifier to enhance electrochemical detection of [Re I (DMPE) 3 ] + . 5,6 [Re I (DMPE) 3 ] + ion strongly partitions into Nafion films, 5 due to the electrostatic interaction and, to some extent, hydrophobic interaction of Nafion ionomer with the hydrophobic cation. However, we have found the partitioning process for [Re I (DMPE) 3 ] + into Nafion films to be slow. 5,6 A slow...
The influence of the initial molar ratio of water relative to tetraethyl orthosilicate (TEOS) precursor and the content of Nafion ionomer in sol−gel-derived silica composites on the voltammetric response of electrodes modified with these composites for [ReI(DMPE)3]+ was investigated. The slow diffusion of [ReI(DMPE)3]+ in Nafion can be significantly improved by dispersing Nafion in sol−gel-derived silica, and the diffusion of [ReI(DMPE)3]+ in such a composite increases with the increase in water/TEOS molar ratio and the decrease in Nafion content. With the mass ratio of Nafion relative to sol−gel-derived silica being 40:100 and the initial molar ratio of water relative to TEOS being 20:1, the electrodes modified with the derived Nafion−silica nanocomposite exhibited an apparent peak current increase rate, during preconcentration of [ReI(DMPE)3]+, that was approximately three times faster than the corresponding Nafion-modified electrode. Compared with bare indium−tin oxide (ITO) glass, the composite-coated ITO glass showed a 25-fold enhancement in voltammetric response to [ReI(DMPE)3]+. The suitability of the developed optically transparent Nafion−silica composite for spectroelectrochemical sensing of [ReI(DMPE)3]+ was demonstrated. The [ReI(DMPE)3]+ extracted into the coating (∼0.4 μm in thickness) was electrolyzed to [ReII(DMPE)3]2+. Under attenuated total reflection mode, the in-situ electrogenerated chromophore [ReII(DMPE)3]2+ was monitored by probing its interaction with the evanescent field of light of a selected wavelength. Thus, the elements required for a spectroelectrochemical sensor with three modes of selectivity were demonstrated: partitioning into the film on an electrode surface and an electrochemically modulated optical signal.
A magnesium ion selective microelectrode based on a synthetic neutral carrier is presented. The selectivity of Mg2+ over Na+, K+, H+, and Ca2+ is sufficient for assays of intracellular magnesium ion activities. The microelectrodes with an optimized membrane composition have a resistance of about 5 x 10(10) omega and a 90% response time of less than or equal to 3 s for a tip diameter around 1 microns. The lifetime of the microelectrode cell assembly is longer than 1 week and the emf drift after equilibration is less than or equal to 0.3 mV/h.
Electrochemical etching of gold using chemical species other than cyanide and thiourea has been investigated. Through complexation with gold ions, chemical species such as chloride and iodide are able to facilitate electrochemical oxidation of gold. It was found that while chloride makes electrochemical oxidation of gold feasible, particularly at highly acidic conditions, the process appeared inadequate for applications in microelectronics as it left microscopic gold residues on areas where gold seed layers were to be removed, most probably due to the limited complexation ability of chloride with gold ions. In contrast, electrochemical etching of gold using iodide resulted in complete removal of gold seed layers. To prevent electrochemical and chemical oxidation of iodide, we envisioned the use of sacrificial stabilizers that are oxidizable at anodic potentials, at which gold is oxidized in the presence of iodide, and are able to convert the generated iodine, if there is any, back to iodide. With the use of such a sacrificial stabilizer, sulfite, we demonstrated that electrochemical etching of gold using iodide is suitable for gold-seed-layer removal in microelectronics applications. The potential and merits of electrochemical etching of gold using other complexing agents such as thiocyanate and bromide are also discussed.
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