FIA (Fluorescent Immunoassay) is a highly sensitive analytical technique that utilizes antigen–antibody interactions combined with fluorescence detection to identify and quantify specific biomolecules. By labeling antibodies or antigens with fluorescent dyes, FIA enables rapid, precise, and reproducible measurement of proteins, hormones, infectious agents, and other clinical biomarkers. Due to its high specificity, wide dynamic range, and adaptability to automated systems, FIA is extensively applied in clinical diagnostics, biomedical research, food safety, and environmental monitoring.