Electrochemiluminescence reactions

This new material was used to design biochips based on the electrochemiluminescence reaction of luminol in the presence of enzymatically... 

The formation of electron donor-acceptor complexes from excited singlet states can lead to triplet formation. In highly polar solvents where radical-ion formation readily occurs, triplets may be produced by recombination (25) of solvent-separated radical ions and of geminate radical ions (Schulten et al., 1976) A- + Dt-> A + D. Such an electron-transfer reaction occurs in many of the electrochemiluminescent reactions discussed earlier. There is also evidence that, in some solvents of medium polarity, triplet production occurs via an exciplex (Orbach and Ottolenghi, 1975). The extent to which each of these processes contributes is obviously highly dependent upon the solvent. 

Ruthenium (II) tris(bipyridyl) (Figure 9-17, B) undergoes an electrochemiluminescent reaction (620 nm) with tripropylamine at an electrode surface, and this chelate is now used as a label in competitive and sandwich electrochemiluminescence immunoassays. Using this label, various assays have been developed in a flow cell using magnetic beads as the solid phase. Beads are captured at the electrode surface, and an unbound label is washed out of the cell by a wash buffer. Label bound to the bead undergoes an electrochemiluminescent reaction, and the light emission is measured by an adjacent photomultiplier tube. ... 

An interesting application of the DCE is in the study of electrochemiluminescent reactions [78]. In this work, the generator and collector electrodes were used to generate the reduced and oxidized forms of diphenylaniline (DPA) according to the equations... 

Reactions between oppositely charged aromatic or heteroaromatic radicals are among the most thoroughly studied electrochemiluminescent reactions. These reactions, which are carried out in aprotic solvents, can be generally written as in reactions [I-V],... 

Electrochemiluminescent reactions are quite rare. Although this may be a drawback if general methods are sought for, it is clearly an advantage if the electroluminescent compound is used for labeling, because of the smaller likelihood of interference. 

Chen Z, Wang J, Lin Z, Chen G (2007) A new electrochemiluminescent sensing system for glucose based on the electrochemiluminescent reaction of bis- 3,4,6-trichloro-2-(pentyloxycarbonyl)-phenyl oxalate. Talanta 72(4) 1410-1415. doi 10.1016/j.talanta. 2007.01.051... 

Light-emitting reactions that take place by the use of an electrical current are designated electrochemiluminescent reactions. 

Demonstration of the phenomenon employed an electrochemiluminescent reaction at the anodes and oxygen reduction at the cathodes, allowing photographic capture of signals, as shown in Fig. 6. This array design has subsequently been applied to nucleic acid detection and is discussed further in a following section of this chapter. 

The mechanism of chemiluminescence is still being studied and most mechanistic interpretations should be regarded as tentative. Nevertheless, most chemiluminescent reactions can be classified into (/) peroxide decomposition, including biolurninescence and peroxyoxalate chemiluminescence (2) singlet oxygen chemiluminescence and (J) ion radical or electron-transfer chemiluminescence, which includes electrochemiluminescence. 

Under optimum conditions electron transfer can produce excited states efficiently. Triplet fluoranthrene was reported to be formed in nearly quantitative yield from reaction of fluoranthrene radical anion with the 10-phenylphenothia2ine radical cation (171), and an 80% triplet yield was indicated for electrochemiluminescence of fluoranthrene by measuring triplet sensiti2ed isomeri2ation of trans- to i j -stilbene (172). 

In this paper the electtode anodic reactions of a number of dihydropyridine (DHP) derivatives, quantum-chemical calculations of reactions between DHP cation-radicals and electrochemiluminescers anion-radicals (aromatic compounds) and DHP indirect ECL assay were investigated. The actuality of this work and its analytical value follow from the fact that objects of investigation - DHP derivatives - have pronounced importance due to its phaiTnacology properties as high effective hypertensive medical product. 

A new cholesterol flow injection analysis biosensor has also been described as an application of the H2O2 ECL sensor56. In that work, the luminol electrochemiluminescence, previously studied in aqueous media, was implemented in Veronal buffer added of 0.3% triton X-100 (v/v), 0.3% PEG and 0.4% cholate to enable the solubilisation of the cholesterol and then its efficient oxidation catalyzed by the immobilized cholesterol oxidase. The ECL reaction occurred thus in a micellar medium and the performances of the H2O2 ECL sensor were investigated. 

Electrochemiluminescence Emission occurring in solution, from an electronically excited state produced by high-energy electron transfer reactions Electrogenerated chemiluminescence Emission produced at an electrode surface Oxyluminescence Emission from polymers caused by oxidative processes (presence of oxygen is required)... 

Electrogenerated chemiluminescence (ECL) is the process whereby a chemiluminescence emission is produced directly, or indirectly, as a result of electrochemical reactions. It is also commonly known as electrochemiluminescence and electroluminescence. In general, electrically generated reactants diffuse from one or more electrodes, and undergo high-energy electron transfer reactions either with one another or with chemicals in the bulk solution. This process yields excited-state molecules, which produce a chemiluminescent emission in the vicinity of the electrode surface. 

Enzyme-coupled ECL enables the selective determination of many clinical analytes that are not in themselves directly electrochemiluminescent, but that can act as substrates for a variety of enzymic reactions. There are two general strategies for ECL the use of dehydrogenase enzymes, which convert NAD+ to NADH, and oxidase enzymes, which produce hydrogen peroxide. 

J. Liu, D. Xing, X. Shen and D. Zhu, Electrochemiluminescence polymerase chain reaction detection of genetically modified organisms, Anal. Chim. Acta, 537 (2005) 119-123. 

Feldberg68,69 has made a valuable analysis of the relationship of the light produced in a double potential step electrochemiluminescence experiment to the current, time, and kinetic parameters involved. The analysis presumes that the reaction which produces excited states is cation-anion radical annihilation which occurs when the radical ions, separately produced, diffuse together in the solution near the electrode. The processes that Feldberg initially considered were eqs. (7)—(13). The assumptions involved are that decay of the excited state... 

As described above, spectroelectrochemical methods are useful in studying the reactivity of radical anions and cations in non-aqueous solutions. Related to this, electrochemiluminescence (ECL), which is often caused by the reaction between radical... 

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. 

Electrochemiluminescence typically involves the electrochemical generation of species that undergo homogeneous reactions to generate electronically excited dissolved compounds. In certain cases, emission can then be observed as these molecular species relax to the ground state. As such, ECL in some sense represents the opposite process of that observed in a photogalvanic cell. 

---