Label
Definition
The reporter coupled to either the antigen or the antibody so the binding event becomes measurable. Three families dominate: radioisotopes (RIA), enzymes (ELISA, EMIT) and fluorophores (FPIA, FIA).
- Role
- Reporter coupled to antigen or antibody
- Radioisotope-based
- RIA
- Enzyme-based
- ELISA, EMIT
- Fluorophore-based
- FPIA, FIA
Common questions
Why did forensic labs largely move away from radioisotope labels?+
Enzyme and fluorophore labels avoid the radiation handling, licensing, and waste disposal burdens of radioisotopes while still giving a measurable signal, which made them far more practical for routine casework.
How does the choice of label affect what an immunoassay can detect?+
The label's readout method sets the required detector, for example a gamma counter for RIA versus a spectrophotometer or fluorometer for enzyme and fluorophore labels, and each has its own sensitivity and interference profile.
Related terms
- Antibody
- An immunoglobulin (typically IgG) raised to bind a specific antigen. Source decides specificity: polyclonal antibodies recognise many epitopes, monoclonal antibodies recognise one.
- Antigen
- A molecule recognised by the adaptive immune system through specific binding to an antibody or T-cell receptor. Defined by immunogenicity (capacity to...
- Competitive vs Non-Competitive Format
- Competitive: labelled antigen and sample antigen compete for a limited number of antibody sites; signal is inversely proportional to analyte. Non-competitive (sandwich):...
- ELISA
- Enzyme-Linked Immunosorbent Assay. Heterogeneous, plate-based, enzyme label (HRP, alkaline phosphatase), colour or chemiluminescent readout. Four standard formats: direct, indirect, sandwich, competitive.
- Epitope and Hapten
- Epitope is the small surface patch on an antigen the antibody actually binds. A hapten is a small molecule (most drugs of...
- Homogeneous vs Heterogeneous
- Homogeneous assays (EMIT, FPIA) need no wash step, so they run fast on clinical analysers. Heterogeneous assays (ELISA, RIA) require a wash...
- Lateral-Flow Immunoassay
- A point-of-care competitive immunochromatographic format on a nitrocellulose strip. In the absence of drug, colloidal gold-labelled antibody is captured at a test...
- RIA
- Radioimmunoassay. Berson and Yalow, 1959. Heterogeneous, competitive, radioisotope label (most often 125-I). Highest sensitivity historically, now displaced in most Indian labs by...