Enzyme-Linked Immunosorbent Assay (ELISA) is a widely used laboratory technique for detecting and quantifying soluble substances such as peptides, proteins, antibodies, and hormones. It is based on the principle of antigen-antibody specificity, where either the antigen or antibody is immobilized on a solid surface typically a microplate and then bound by a corresponding antibody or antigen linked to an enzyme. Upon addition of a chromogenic substrate, the enzyme catalyzes a color change that is directly proportional to the amount of target analyte present in the sample. ELISA is highly sensitive, specific, and suitable for high-throughput screening, making it a standard method in diagnostics, vaccine development, drug testing, and various fields of biomedical research.