Introduction to Chemiluminescence Immunoassay (CLIA) and its Principle -part 1

Chemiluminescence immunoassay (CLIA) first appeared in the mid-1970s. Initially, it faced challenges due to short light signal duration and low sensitivity, preventing its widespread use in clinical detection. However, subsequent research found that compounds like horseradish peroxidase, acridine esters, adamantane derivatives, and nanoparticles could enhance CLIA's luminescence intensity. This led to the development of CLIA as an advanced and widely applied ultra-sensitive detection method.


CLIA is characterized by high sensitivity, strong specificity, a wide linear range, simple operation, low cost, low sample requirements, and high throughput. It has become a crucial detection method in the field of medicine. Notably, CLIA is often fully automated, allowing the instrument to complete quantitative detection within 40 minutes, reducing the probability of false-positive results due to experimental mishandling. Commonly used chemiluminescence systems include the luminol chemiluminescence system, KMnO4 chemiluminescence system, luminol-enhanced chemiluminescence system, peroxyoxalate chemiluminescence system, cerium(IV) chemiluminescence system, and pyridine ruthenium(II) luminescence system. These systems find widespread applications in clinical research, food safety, detection of veterinary drug residues, environmental monitoring, and more.


Basic Principles of Chemiluminescence Immunoassay


CLIA comprises two main components: the immunoreaction system and the chemiluminescence analysis system.


1. Immunoreaction System:

Immunoreaction is based on the formation of an antigen-antibody complex through the specific binding of an antigen and an antibody. This complex is highly selective and serves as the basis for analysis. Immunoreaction methods can be classified into non-labeled and labeled immunoassays. Non-labeled immunoassays rely on changes in physical or chemical properties, such as visible precipitates or agglutination, after the formation of the antigen-antibody complex. Labeled immunoassays involve marking a substance, such as a radionuclide (e.g., 125I), non-radioactive alkaline phosphatase, horseradish peroxidase, lanthanide elements, etc., on the antigen or antibody. Detection is then performed on the labeled substance, indirectly measuring the analyte.


2. Chemiluminescence Principle:

Chemiluminescence is the light radiation produced by a chemical substance during a specific chemical reaction. It involves the formation of singlet molecules excited by the decomposition of high-energy intermediates in a chemical reaction. These excited molecules, being unstable, release excess energy to return to the ground state, some of which is emitted as light. Thus, chemiluminescence reactions consist of two processes: excitation and luminescence. The overall efficiency of chemiluminescence (φcL) is influenced by chemical reaction efficiency (φc), energy transfer efficiency (φe), and fluorescence efficiency (φf).