Chemiluminometric techniques in clinical chemistry

Abstract

Luminescent phenomena are widespread in nature and found in glow worms, luminous fish, and bacteria, when metabolic energy is partly converted to cold light, and in plants. Most of these phenomena can be explained by chemiluminescence. Chemiluminescence is characteristic for a variety of organic compounds oxidizable by H₂O₂. In those chemiluminescence reactions light is produced by oxidation of an aromatic compound (usually luminol or lucigenin) in the presence of H₂O₂ by a peroxidase. Bioluminescence, a subset of chemiluminescence, may be classified in four different forms: pyridine nucleotide linked in bacteria occurring with coupling of a redox and luciferase reaction; adenine nucleotide linked in fireflies in which oxygen, ATP and luciferin react under the influence of luciferase; furthermore enzyme substrate linked and photoprotein linked bioluminometric processes are observed in arthropods and in jelly fish.

In clinical chemistry chemiluminometric assays based either on direct or coupled reactions utilizing ATP, NAD(P)H, FMNH₂ or H₂O are used. A variety of methods for substrates and enzymes have been described. Furthermore the application of chemiluminometry for the detection of cell functions is of relevance for clinical research. The testing of fertility and of chemosensitivity will be discussed as practical examples. The most promising field are the chemiluminesence immunoassays for measurement of hormones and proteins, since these tests are—at least—sensitive and specific as radioimmunoassays.

For detection luminometers with sensitive photomultipliers are used; either the counts at the maximum (peak measurement) are detected or the light intensity is integrated during a certain time period.