Luminescent and luminometric assays are those which produce an emission of light as a result of the presence of an analyte of interest. The light emission is generally of sufficient duration for it to be measured or detected and thereby allow the determination of the analyte.
There are several major types of assays whereby a chemiluminescent signal can be used to advantage to determine an analyte:
1) Assays where a chemiluminescent compound is used to directly label a specific binding ligand such as proteins, oligonucleotides, antigens, haptens, hormones, nucleic acids and other compounds of biological interest. Chemiluminescence can be detected by adding a peroxidase and an oxidant to the labeled ligand.
2) Assays where catalysts or cofactors of luminescent reactions are used as labels for specific binding ligands. For example, peroxidase can be conjugated to ligands and used to provide a chemiluminescent signal.
3) Assays where chemiluminescent reactions are used to determine the products formed by action of an enzyme label other than peroxidase on suitable substrates. An example of this type of assay is the determination of a glucose oxidase-labeled specific binding ligand by generating hydrogen peroxide in the presence of peroxidase.
4) Non-immunoassays to determine a peroxidase or oxidant such as hydrogen peroxide generated as a result of a non-immunoreactant analyte.
Further details of such assays are provided in extensive literature such as U.S. Pat. No. 4,729,950 (Kricka et al) and publications noted therein.
A common reaction system used to generate chemiluminescent signals is that utilizing a 2,3-dihydro-1,4-phthalazinedione derivative (identified herein as a "DPD"), such as luminol or isoluminol, as a substrate for peroxidative action. Attempts have been made to improve the sensitivity of chemiluminescent assays, including those where a DPD is used. For example, U.S. Pat. No. 4,729,950 (noted above) describes the use of certain aromatic amine enhancers. Similarly, certain aromatic phenols are described for the same purpose in U.S. Pat. No. 4,598,044 (Kricka et al).
This technology has been used commercially to some success, but there is a need for further improvement in sensitivity at very low analyte concentration, increased storage stability of reagents and kinetic stability (that is, duration of constant light output).
The use of micelles to improve chemiluminescence with various systems is described in considerable literature, including U.S. Pat. No. 4,462,931 (Cohen et al), U.S. Pat. No. 4,927,769 (Chang et al) and U.S. Pat. No. 4,959,182 (Schaap) and by Hinze, Contri.Cient.Tecnol. 1985, Numero Espec., pp. 20-23.
It would seem apparent that micelles could be combined with enhancers to obtain even further improvements in chemiluminescence, but it has been observed that such is not true when the enhancers of U.S. Pat. No. 4,598,044 (such as p-iodophenol) are used with micelles.