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This review describes principles and analytical applications of ion-exchange voltammetry (IEV) at polymer modified electrodes. Results of mechanistic studies which are relevant to the development and optimization of IEV methods are discussed. Useful examples of IEV determinations of traces of inorganic and organic electroactive ions of interest for environmental, biomedical or pharmaceutical analysis are given along with future prospects for this technique.

This work is aimed at developing an electrochemical sensor for the sensitive and selective detection of trace levels of perfluorooctanesulfonate (PFOS) in water. Contamination of waters by perfluorinated alkyl substances (PFAS) is a problem of global concern due to their suspected toxicity and ability to bioaccumulate. PFOS is the perfluorinated compound of major concern, as it has the lowest suggested control concentrations. The sensor reported here is based on a gold electrode modified with a thin coating of a molecularly imprinted polymer (MIP), prepared by anodic electropolymerization of o-phenylenediamine (o-PD) in the presence of PFOS as the template. Activation of the sensor is achieved by template removal with suitable a solvent mixture. Voltammetry, a quartz crystal microbalance, scanning electron microscopy and elemental analysis were used to monitor the electropolymerization process, template removal, and binding of the analyte. Ferrocenecarboxylic acid (FcCOOH) has been exploited as an electrochemical probe able to generate analytically useful voltammetric signals by competing for the binding sites with PFOS, as the latter is not electroactive. The sensor has a low detection limit (0.04 nM), a satisfactory selectivity, and is reproducible and repeatable, giving analytical results in good agreement with those obtained by HPLC-MS/MS analyses.

Ensembles of nanoscopic disk-shaped electrodes have been shown to offer enhancements in electroanalytical detection limits relative to electrodes of macroscopic dimensions (e.g., disk electrodes with diameters of ∼1 mm). Enhancements in electroanalytical detection limits have also been observed at macroscopic electrodes that have been coated with films of ion-exchange polymers. In this paper we combine these two concepts. We demonstrate that a nanoelectrode ensemble (NEE) that has been coated with a thin film of the Kodak ion-exchange polymer AQ 55 shows enhanced electroanalytical detection limits relative to the uncoated NEE and to the coated macroscopic electrode. To our knowledge, this is the first investigation of the electrochemistry, and the electroanalytical advantages, of polymer film-coated NEEs.A new approach for preparing ensembles of nanoscopic diskshaped electrodes has recently been described. 1 These nanoelectrode ensembles (NEEs) are prepared using a membranebased method, 2 in which the pores in a nanoporous membrane act as templates for the nanoelectrodes. The membranes employed contain monodisperse, cylindrical pores that run the complete thickness of the membrane. A nanoscopic wire of gold is deposited within each pore of the membrane. 1 The disk-shaped ends of these Au nanowires (at one face of the membrane) define the ensemble of nanodisk electrodes. Ensembles of Au nanodisks with diameters as small as 10 nm have been prepared using this template-based method. 1 The number of Au nanodisks per square centimeter of membrane surface area is determined by the density of the pores in the template membrane. Typically these membranes have high pore densities; for example, the membranes used to prepare the NEEs described in this paper had a pore density of 6 × 10 8 pores cm -2 . As a result, these NEEs operate in the "total overlap" electrochemical limiting case, 1,3 in which the diffusion layer created at each disk-shaped element overlaps with the diffusion layers created at its neighboring elements. As a consequence of this total overlap situation, conventional peak-shaped voltammograms are obtained at these NEEs.It is well known that NEEs operating in this total overlap regime can show enhanced electroanalytical detection limits relative to an electrode of conventional dimensions (e.g., a diskshaped electrode with a diameter of 1 mm; we call such electrodes "macroelectrodes"). 1,3 This enhancement in detection limit occurs because Faradaic currents are proportional to the geometric area of the NEE, while the background signal (the double-layer charging current) is proportional only to the sum of the active electrode area. We have shown that the detection limit is decreased by a factor equivalent to the fractional electrode area, which is the sum of the active electrode area divided by the geometric area of the NEE. 1,3 It occurred to us that detection limits at the NEE could be further enhanced by coating the NEE surface with a film of an ion-exchange polymer. This is because an ion-exchange...

a b s t r a c tEnsembles of copper nanowire electrodes (CuWNEEs) are prepared via electrodeposition in track-etched polycarbonate membranes. Three different preparation methods are compared showing that the better results in terms of sensor durability and reproducibility are achieved by pre-sputtering a thin gold film on the templating membrane and attaching it to a supporting electrode by exploiting the adhesion property and ionic conductivity of a thin Nafion interlayer. SEM-EDS analyses together with double layer charging currents measurements indicate that these arrays are formed by copper nanowires with 400 nm diameter, 10 m length distributed with a spatial density of 1 × 10 8 nanowires/cm 2 . The voltammetric reduction of nitrate at CuWNEEs is characterized by a well-resolved cathodic peak at approximately −0.680 V vs Ag/AgCl, whose current scales linearly with the nitrate concentration in the 10-400 M range. The limit of detection (LOD) achieved by simple linear sweep voltammetry is in the 1.7-3.0 M range, depending on the CuWNEE preparation method, such LOD values being among the lowest reported up to now in the literature. The possibility to use CuWNEEs in chloride and nitrite containing water samples is demonstrated.

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Template synthesis is a relatively simple and easy procedure which has made the fabrication of rather sophisticated nanomaterials accessible to almost any laboratory. Template synthesis requires access to instrumentation capable of metal sputtering and electrochemical deposition. The characterization of the fabricated nanostructures can be done using instrumental techniques including spectrophotometry, voltammetry, optical microscopy, atomic force microscopy, and electronic microscopies (scanning electron microscopy (SEM) and transmission electron microscopy (TEM)).The method is based on the simple but effective idea that the pores of a host material can be used as a template to direct the growth of new materials. Historically, template synthesis was introduced by Possin (1) and refined by Williams and Giordano (2) who prepared different metallic nanowires with widths as small as 10 nm within the pores of etched nuclear damaged tracks in mica. It was further developed by Martin's group (3-5) and followed by others (6) with the number of examples and applications (7) continually increasing. The nanoporous membranes usually employed as templates are alumina or track-etched polymeric membranes which are widely used as ultrafiltration membranes. Recently, metal nanostructures have also been obtained using the pores created by self-assembly in block copolymer structures under the influence of electric fields and high temperatures (8, 9).The first part of this section focuses on the main characteristics and fabrication techniques used for obtaining templating membranes and depositing metal nanostructures by suitable electroless and electrochemical procedures. Methods such as sol-gel (10-12) or chemical vapor deposition (10, 13), which have been used primarily for the template deposition of carbon, oxides, or semiconducting-based materials, will not be considered here in detail. The second part of the section focuses on the electrochemical properties of the fabricated nanomaterials with emphasis on the characteristics and applications of nanoelectrode ensembles (NEEs). Templating membranes 16.2.2