Elisa

ELISA, or enzyme-linked immunosorbent assay, is a plate-based technique used to detect and quantify soluble substances such as proteins, peptides, antibodies, and hormones. In a typical ELISA, a capture molecule (antibody or antigen) is immobilized on a microplate well. The sample is added and any target analyte binds to the capture molecule. Detection is achieved with an enzyme-conjugated antibody or subunit and a chromogenic substrate; the enzyme converts the substrate to a colored product, and the intensity is measured spectrophotometrically to yield quantitative or qualitative results. A standard curve with known concentrations enables determination of the analyte’s amount in the sample.

Common formats include direct ELISA (labeled primary antibody detects antigen), indirect ELISA (unlabeled primary antibody detected by a labeled secondary antibody), sandwich ELISA (capture antibody binds antigen and a labeled detection antibody completes the assay), and competitive ELISA (sample antigen competes with labeled antigen for antibody binding).

ELISA is frequently performed in 96-well microplates. Enzymes such as horseradish peroxidase or alkaline phosphatase are commonly used, with substrates like TMB or pNPP producing a color change read at wavelengths such as 450 nm or 405 nm.

Applications span clinical diagnostics (infectious disease serology, autoimmune markers), measurement of hormones and cytokines, food safety testing, veterinary and environmental testing, and basic research. Advantages include high throughput, sensitivity, and relatively low cost per test. Limitations involve dependence on high-quality antibodies, potential cross-reactivity and interference, need for careful controls and standard curves, and variability from manual handling.

ELISA was developed in the 1970s and is widely used in diagnostics and research to detect and quantify specific biomolecules.