Electrochemiluminescence Electrochemistry

Photonic electrochemistry, taken in its most general sense, involves the intimate interaction of light with electrochemical processes. Thus, piocesses in which illumination of the electrode-electrolyte interface produces charge-transfer events as well as electrochemical reactions that produce light as a product (electrochemiluminescence, ECL) fall in this category. A third related area is the elec-troanalytical detection of transient species formed by a photochemical process which takes place in solution. Techniques such as spectroelectrochemistry are excluded from consideration, since they utilize photons as a nonperturbing probe of purely electrochemical processes. 

The distinction in previous sections of electroanalysis, inorganic electrochemistry (particularly metal systems), and electroorganic synthesis leaves out a number of other electrochemical systems. Ultrasound has been applied to many of these, to interesting effect, and this section concerns a number of such systems. There is, of course, overlap in any attempt at compartmentalization, and here some studies on batteries, electrochemiluminescence, and micellar systems could be considered as contributing to electroanalysis, while other multiphase electrolyses might be considered as electrosynthesis. In addition, most multiphase electrolysis is directed to the destruction of haloorganics and is aimed at waste treatment. There are also one-off applications of ultrasound in electrochemistry, which are collected at the end of this section. 

Ultrasound influences multiphase systems such as the production of microemulsions. It is useful in electrosynthesis involving immiscible materials—this effect has been particularly exploited for several applications in environmental science. Ultrasound can also enhance electrochemiluminescence systems, and has been applied to many other aspects of electrochemistry, including the as yet unexplained benefits of pre-treating electrolyte solutions. It has even been proposed to enhance electrochemical cold-fusion . 

On-chip detection firstly relied on optical techniques, such as ultraviolet (UV) absorbance, fluorescence or laser-induced fluorescence (LIF).1,2 The latter technique in particular has a sensitivity in the (sub)micromolar range which is suitable for microfluidic applications. Besides optical techniques, electrical-based techniques are also widely used for on-chip detection due to their sensitivity, e.g. detection based on conductivity,3 electrochemistry,4 electrochemiluminescence,5 etc. The main advantage of these techniques is that they... 

ACE, affinity capillary electrophoresis CEC, capillary electrochromatography CL, chemiluminescence EC, electrochemistry ECL, electrochemiluminescence FAD, flavin adenine dinucleotide FMN, flavin mononucleotide HCV, hepatitis C vims HIV-1 RTase, reverse transcriptase of human immunodeficiency vims type 1 LC, liquid chromatrography LIE, laser-induced fluorescence MALDI-TOF, matrix-assisted laser desorption ionization-time-of-ilight mass spectrometry UV, UV-visible spectram. 

The abundance of work in this area of electrochemistry precludes any attempt at comprehensive coverage in the space presently available. Indeed fully representative coverage is not claimed instead some of the factors already mentioned will be illustrated by examples which particularly interest the author. Some topics such as electrochemiluminescence, which is reviewed elsewhere, will not be treated. A fairly comprehensive source of literature references to electroanalytical and mechanistic aspects is provided by the recent book of Mann and Bames. ... 

Electrochemistry can be coupled with other physical methods such as fluorescence spectroscopy. An XO-based electrochemiluminescent biosensor for hypoxanthine has been reported. The enzyme was immobilized in a carbon paste electrode with bovine serum albumin cross-linked with glutar-aldehyde. The working principle of the biosensor is illustrated in Scheme 5.6. As already shown (eqn (5.3a)), H2O2 is produced by the catalytic reaction between hypoxanthine and XO immobilized on the electrode surface. In an alkaline or neutral solution, luminol is electrochemically oxidized to a compound that reacts spontaneously with H2O2 to generate chemiluminescent luminol and the ensuing luminescence was used to quantify the amount of hypoxanthine present. 

Yuan B, Zheng C, Teng H, You T (2010) Simultaneous determination of atropine, anisodamine, and scopolamine in plant extract by nonaqueous capillary electrophoresis coupled with electrochemiluminescence and electrochemistry dual detection. J Chromatogr A 1217(1) 171-174. doi 10.1016/j.chroma.2009.11.008... 

The primary cathodic step of hot electron-induced electrochemiluminescence (HECL) was postulated to be an injection of hot electrons into aqueous electrolyte solution by tunnel emission through an insulating barrier, followed by reduction reactions induced either by presolvated hot electrons or by fully hydrated electrons [37, 38]. The introduction and details of this kind of hot electron electrochemistry and HECL has been reviewed very recently [33] and only short descriptions of the basic features are given here. 

Conductive electrodes based on metal oxide, e.g., indium-tin oxide (TTO), are widely used in electrochemistry as a support for surface modification with the goal to develop sensors with electrochemical transduction or combined spectroscopic and electrochemical responses or electrochemiluminescence. Inorganic thin films can also be prepared from the assembly of two-dimensional layered inorganic solids, such as cationic clays and layered double hydroxides (LDHs, also defined as anionic clays). These materials can be used to preconcentrate species on the basis of ion-exchange reactions and applied to heavy metal determination or for the detection of organic pollutants. 

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