Acridinium esters derivatives

In an interesting variation of the technology. Law et al, (L2) described a liposome-based TSH assay in which the liposomal membrane surface contained covalently attached antibodies, and a modified membrane-impermeable acridinium ester derivative was encapsulated inside the vesicles. A normal sandwich assay was conducted using magnetic particles as the solid phase and antibody-sensitized liposomes as the label. The total assay time was 5 min, compared with the normal 2.5 hr, and showed superior sensitivity. 

Label amino function in DNA probe with N-hydroxy succinimide derivatives of acridinium esters. 

Methods based on chemiluminescent and bioluminescent labels are another area of nonisotopic immunoassays that continue to undergo active research. Most common approaches in this category are the competitive binding chemiluminescence immunoassays and the immunochemiluminometric assays. Chemiluminescence and heterogenous chemiluminescence immunoassays have been the subject of excellent reviews (91, 92). Detection in chemiluminescence immunoassays is based on either the direct monitoring of conjugated labels, such as luminol or acridinium ester, or the enzyme-mediated formation of luminescent products. Preparation of various derivatives of acridinium esters has been reported (93, 94), whereas a variety of enzyme labels including firefly or bacterial luciferase (70), horseradish peroxidase (86, 98), and alkaline phosphatase are commercially available. 

Indole derivatives have been used for fluorescence (FL), chemiluminescence (CL) and bioluminescence assays. Various indole derivatives were synthesized and their CL characteristics were investigated. However, indole derivatives have not been frequently used compared to the typical FL and CL reagents such as dansyl chloride, fluorescein, luminol and acridinium esters in terms of emission wavelength and intensity. For the selective and highly sensitive FL and CL assays, indole derivatives, which have a long emission wavelength of more than 600 nm and have strong CL intensity, should be developed. 

While luminol and isoluminol require an oxidant plus a catalyst for initiation of the chemiluminescent reaction, esters derived from A -methyl acridinium carboxylic acid require only alkaline hydrogen peroxide (W4). Acridinium esters were first introduced by McCapra s group (M23, M25, S32), based on earlier work on the bioluminescence of the lucigenin/luciferase system (G18), and reviewed in McCapra and Beheshti (M21). From Fig. 19, one can see the structural similarity between lucigenin and a typical acridinium ester. 

Fio. 29. Novel N-alkyl derivatives of phenyl acridinium esters, (a) Taken from Batmangelich et al. (B2) (b) taken from Zomer et al. (Z6). 

Some analytical methods, for example, for detection of trace metals, have been devised based on this reaction. Luminol has also been suggested as a labeling compound for the ECL immunoassay. In addition to luminol there are a number of analogous chemiluminescent compounds that require hydrogen peroxide in their luminescent reactions. Among these compounds the acridine derivatives lucigenin and acridinium esters have been used in ECL methods. 

Different CL reactions in liquid phase have been applied with analytical purposes. These include luminol, tris(2,2 -bipyridyl)ruthenium(II), lucigenin, lophine, peroxyoxa-late derivatives, acidic potassium permanganate, sulfite, gallic acid, morphine, codeine, pyrogallol acridinium esters, and others. Table 19.2 summarizes some of the commonly used CL reactions in liquid phase and their analytical application in different areas. 

Acridinium derivatives, specifically the 9-carboxyacridinium phenyl esters, are one of the most efficient chemiluminescent labels used in immunoassays since 1980 ... 

Chemiluminescence generally arises from chemical reactions in solution in which an oxidation occurs that involves either molecular oxygen or hydrogen peroxide (H2O2). The quantum yield in solution is generally very low because certain derivatives inhibit luminescence, notably oxygen. There are some exceptions such as luminol, acridinium salts, and some oxalic esters. Although the mechanism is poorly understood, the reaction of luminol (5-amino-2,3-dihydro-l,4-phthalazinedione) can be written schematically ... 

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