ELISA (Enzyme-Linked Immunosorbent Assay)
Definition
A plate-based immunoassay format in which a target antigen is captured by an antibody bound to a solid surface, detected by a second enzyme-labelled antibody, and quantified by colorimetric substrate conversion. The most widely used laboratory immunoassay format in forensic serology for confirmation of body fluids.
- Format
- Solid-phase antibody capture, enzyme-conjugated detection
- Readout
- Colorimetric substrate conversion, read by plate spectrophotometer
- Use in forensics
- Confirmatory test for body fluids (semen, saliva, blood)
- Sensitivity
- Detects nanogram-range antigen quantities
- Field
- Forensic serology and immunology
Common questions
How does ELISA differ from a presumptive test?+
A presumptive test (such as a color or luminescence reaction) only flags that a stain might be a given body fluid. ELISA targets a specific protein antigen with an antibody, so a positive result is far more specific and is treated as confirmatory rather than screening evidence.
Can ELISA distinguish human from animal body fluids?+
Yes, when the capture and detection antibodies are raised against human-specific antigens. Cross-reactivity with closely related primate proteins is a known limitation, so species-specific validation of the antibody pair matters before results are relied on in casework.
What can cause a false negative on an aged stain?+
Target proteins degrade over time and with heat, humidity, or microbial activity, reducing antigen levels below the assay's detection threshold. A negative ELISA on an old or environmentally exposed stain does not rule out the body fluid, only that intact antigen was not detected.
Related terms
- 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...
- Precipitin Test
- A serological method in which an antiserum specific to one species' proteins is mixed with an extract of an unknown specimen. Formation...
- Cross-Reactivity
- The capacity of an antibody raised against one analyte to bind structurally related compounds. In RIA, cross-reactivity is the main driver of...
- Antibody (Immunoglobulin)
- A Y-shaped glycoprotein produced by B lymphocytes that binds a specific antigen at its variable regions. Antibodies used as forensic reagents are...
- Antigen
- A molecule recognised by the adaptive immune system through specific binding to an antibody or T-cell receptor. Defined by immunogenicity (capacity to...
- Antigen-Antibody Reaction
- The specific non-covalent binding between an antigen (a molecule capable of eliciting an immune response) and the antibody produced against it. In...
- Chain of Custody
- The documented chronological record of who collected, handled, transferred, and examined a piece of evidence. For digital evidence, chain of custody includes...
- CITES
- The Convention on International Trade in Endangered Species of Wild Fauna and Flora, a multilateral treaty signed in 1973 now with over...
- DNA Barcoding
- Species identification using a short, standardised region of the mitochondrial genome. For animals, the primary barcode marker is a 648-base-pair segment of...
- Immunochromatographic Strip (Lateral-Flow Assay)
- A single-use membrane device in which sample migrates by capillary action past a conjugate pad containing labelled antibody and a test line...
- Monoclonal Antibody
- An antibody produced from a single B-cell clone, recognising a single specific epitope. In forensic species identification, monoclonal antibodies offer higher specificity...
- Monoclonal Antibody (mAb)
- An antibody produced by a single hybridoma clone, so that every molecule in the preparation is identical, targets the same epitope, and...
Explained in these topics
- The Role of Immunology in Forensic ScienceAn immunoassay format in which one binding partner is adsorbed to a solid surface (usually a microtitre plate), the sample is added, and detection is achieved...
- Immunological Testing in Wildlife Crime and Food Fraud InvestigationsA plate-based immunoassay in which a target antigen is captured by a coated antibody and detected by a second enzyme-labelled antibody. The enzyme converts a s...
- Modern Immunological and Molecular Approaches to Species IdentificationA plate-based immunoassay in which antigen or antibody is immobilised on a solid surface, and detection depends on an enzyme-conjugated antibody that produces...
- Scope of Forensic Immunology: Specimens and Contexts