Electrochemical sensing

There are three types of electrochemical sensors potentiometric, amperometric, and potentiodynamic sensors. 

Potentiometric sensors are based on the measurement of the voltage of a cell under equilibrium-like conditions, the measured voltage being a known function of the concentration of the analyte. Potentiometric measurements involve, in general, Nernstian responses under zero-current conditions that is, the measurement of the electromotive force of the electrochemical cell. 

Amperometric sensing is based on the record of the current response of an electrode in contact with the system to be analyzed under the application of a given potential input. Amperometric sensors operate under conditions where mass transport is limiting. 

Potentiodynamic sensors are based on the measurement of the current response of the working electrode under no mass transport limiting conditions. Potentiodynamic methods typically involve accumulation (or preconcentration) steps, such as in stripping voltammetry for analyzing trace metals in solution. 

Social demands (e.g., miniaturization for monitoring processes in vivo) involve 

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Generally, plastics have excellent resistance to weak mineral acids and are unaffected by inorganic salt solutions—areas where metals are not entirely suitable. Since plastics do not corrode in the electrochemical sense, they offer another advantage over metals most metals are affected by slight changes in pH, or minor impurities, or oxygen content, while plastics will remain resistant to these same changes. 

Transition metal complexes with 2,2 -bipyridine ligands in anion-selective recognition and optical/electrochemical sensing 96CC689. 

Wood is particularly valuable for many conditions which are corrosive to common metals (e.g. acids and external exposure), and for contact with foodstuffs and beverages. It is not subject to corrosion in the electrochemical sense of the term applied to metals, but in saline conditions it can be attacked by the products of metal corrosion (alkali and iron salts) where poor technology or unsuitable wood species are used. Although wood is attacked by both extremely alkaline and acid conditions, particularly those which are oxidising, it can be employed over a wider pH range than most other materials. 

Other coordination modes of trans-diammac have been identified where one (154) or both (155) primary amines are free from the metal.721 725 An extension of this concept involves attachment of active functional groups such as crown ethers selectively at one primary amine to generate ditopic ligands capable of electrochemically sensing alkali metal ions through their inductive effect on the Co11111 redox potential. One example is provided by (156) further, the 15-crown-5 and 18-crown-6 analogs were also prepared.726... 

Cobaloxime(I) generated by the electrochemical reductions of cobaloxime(III), the most simple model of vitamin Bi2, has been shown to catalyze radical cyclization of bromoacetals.307 Cobalt(I) species electrogenerated from [ConTPP] also catalyze the reductive cleavage of alkyl halides. This catalyst is much less stable than vitamin Bi2 derivatives.296 It has, however, been applied in the carboxylation of benzyl chloride and butyl halides with C02.308 Heterogeneous catalysis of organohalides reduction has also been studied at cobalt porphyrin-film modified electrodes,275,3 9-311 which have potential application in the electrochemical sensing of pollutants. 

Prussian blue (PB ferric ferrocyanide, or iron(III) hexacyanoferrate(II)) was first made by Diesbach in Berlin in 1704.88 It is extensively used as a pigment in the formulation of paints, lacquers, and printing inks.89,90 Since the first report91 in 1978 of the electrochemistry of PB films, numerous studies concerning the electrochemistry of PB and related analogs have been made,92 with proposed applications in electrochromism1 and electrochemical sensing and catalysis 93... 

A.L. Ghindilis, P. Atanasov, M. Wilkins, and E. Wilkins, Immunosensors electrochemical sensing and other engineering approaches. Biosens. Bioelectron. 13, 113-131 (1998). 

CNTs have been one of the most actively studied electrode materials in the past few years due to their unique electronic and mechanical properties. From a chemistry point of view, CNTs are expected to exhibit inherent electrochemical properties similar to other carbon electrodes widely used in various electrochemical applications. Unlike other carbon-based nanomaterials such as C60 and C70 [31], CNTs show very different electrochemical properties. The subtle electronic properties suggest that carbon nanotubes will have the ability to mediate electron transfer reactions with electroactive species in solution when used as the electrode material. Up to now, carbon nanotube-based electrodes have been widely used in electrochemical sensing [32-35], CNT-modified electrodes show many advantages which are described in the following paragraphs. 

M. Zhang, A. Smith, and W. Gorski, Carbon nanotube-chitosan system for electrochemical sensing based on dehydrogenase enzymes. Anal. Chem. 76, 5045-5050 (2004). 

M. Zhang and W. Gorski, Electrochemical sensing platform based on the carbon nanotubes/redox medi-ators-biopolymer system. J. Am. Chem. Soc. 127, 2058-2059 (2005). 

C. Hu, X. Chen, and S. Hu, Water-soluble single-walled carbon nanotubes films preparation, characterization and applications as electrochemical sensing films. J. Electroanal. Chem. 586, 77-85 (2006). 

Except for the development of on-line systems for nutrients monitoring, the measurement of other inorganic non-metallic constituents is rather rare. Some commercial systems based on electrochemical sensing are proposed for the measurement of cyanide. A simple and rapid procedure for sulphide measurement in crude oil refinery wastewater has been developed [ 32 ]. Based on the de-convolution of the UV spectrum of a sample, this method has a detection limit of 0.5 mg L 1 and has been validated for crude oil refinery wastewater. 

The current responses may be displayed as a function of time, as in Figure 1.1c, or as a function of potential, as in Figure 1.1c. The latter presentation is generally preferred and is what is meant in short by the phrase cyclic voltammetry. The fact that the response is symmetrical about the potential axis provides a clear indication of the reversibility of the system, in both the chemical sense (the electron transfer product is chemically stable) and the electrochemical sense (the electron transfer is fast). If the electron transfer product were unstable, the anodic current would be less than the cathodic current, eventually disappearing for high instabilities. For a slow electron transfer and a chemically stable product, the current-potential pattern is no longer symmetrical about the vertical axis, the anodic peak potential being more positive than the cathodic peak potential. 

Despite the asymmetry between the forward and reverse current or charge responses, reversibility may be strictly defined by the transformations depicted in Figure 1.4. The anodic trace is first measured against the prolongation of the forward trace (the trace that would have been obtained if the forward scan had been prolonged beyond the inversion potential), as symbolized by a series of vertical arrows. After symmetry about the horizontal axis, the resulting curve is shifted to the initial potential in the case of the time dependence representation. Alternatively, in the case of the potential dependence representation, another symmetry about E = E° is performed. In both cases, reversibility, in both the chemical and electrochemical senses, is demonstrated by the exact superposition of the hence-transformed reverse trace with the forward trace. 

Freeman R, Li Y, Tel-Vered R et al (2009) Self-assembly of supramolecular aptamer structures for optical or electrochemical sensing. Analyst 134 653-656... 

Beer P. D. (1996) Anion Selective Recognition and Optical/Electrochemical Sensing by Novel Transition-Metal Receptor Systems, Chem. Commun. 689—96. 

Merkoci A, Pumera M, Llopis X, Perez B, Valle M del, Alegret S (2005). New materials for electrochemical sensing VI Carbon nanotubes. Trac-Trends in Anal. Chem. 24 826-838. 

Qiu, J.-D., et al., Controllable deposition of a platinum nanoparticle ensemble on a polyaniline/graphene hybrid as a novel electrode material for electrochemical sensing. Chemistry - A European Journal, 2012.18(25) p. 7950-7959. 

Wu, C.-H., et al., Unique Pd/graphene nanocomposites constructed using supercritical fluid for superior electrochemical sensing performance. Journal of Materials Chemistry, 2012. 22(40) p. 21466-21471. 

Yu, A., et al., Silver nanoparticle-carbon nanotube hybrid films Preparation and electrochemical sensing. Electrochimica Acta, 2012. 74(0) p. 111-116. 

Dong, X., et al., Synthesis of graphene-carbon nanotube hybrid foam and its use as a novel three-dimensional electrode for electrochemical sensing. Journal of Materials Chemistry,... 

We must be careful, though the two aquo ions are different in an electrochemical sense, and so have different standard electrode potentials with iron, i.e. Fe + Fe V, whilc 2+ = -0.44 V. We therefore need to be certain... 

As a rule of thumb , reversibility (in the electrochemical sense) implies that the electron-transfer reaction is sufficiently swift for the current to obey equation (6.6) instantly and that no chemical processes accompany the electron-transfer reaction - see Section 6.3.4. 

CNTs-nanoparticles composites have also been exploited for electrochemical sensing applications [17, 118, 119[. Incorporation of metal and oxide nanoparticles has been demonstrated to enhance the electrocatalytical efficiency. A wide range of particles have been used (Pt, Pd, Co, FeCo alloy, Co, Cu, Ag, Cu) and in some cases such CNT/nanoparticles have been combined together with charged polymers [17]. 

Keywords DNA Adsorption Materials Graphite Carbon Composite Nanotube Electrochemical sensing... 

Ulyanova YV, Blackwell AE, Minteer SD. Poly(methylene green) employed as molecularly imprinted polymer matrix for electrochemical sensing. Analyst 2006 131 257-261. 

The low stability of the magnesium porphyrins has precluded most potential applications. Other metallotetrapyrroles have found industrial uses for oil desulfurization, as photoconducting agents in photocopiers, deodorants, germicides, optical computer disks, semiconductor devices, photovoltaic cells, optical and electrochemical sensing, and molecular electronic materials. A few scattered examples of the use of Mg porphyrins in nonlinear optical studies have appeared" and magnesium phthalocyanines have been used in a few studies as semiconductor or photovoltaic materials" " One of the few... 

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