Enzyme-Linked Immunosorbent Assay (ELISA)

What is ELISA?

ELISA (enzyme-linked immunosorbent assay) is a method used to quantitatively detect an antigen within a sample. An antigen is a toxin or other foreign substance, for example a flu virus or environmental contaminant, that causes the vertebrate immune system to mount a defensive response. The range of potential antigens is vast, so ELISAs are used in many areas of research and testing to detect and quantify antigens in a wide variety of sample types. Cell lysates, blood samples, food items, and more can be analyzed for specific substances of interest using ELISAs.

Types of enzyme-linked immunosorbent assays (ELISAs)

There are four major types of ELISAs: direct, indirect, competitive and sandwich. Each type is described below with a diagram illustrating how the analytes and antibodies are bonded and used.

  • Direct ELISA

    Direct ELISA

    In a direct ELISA, the antigen is bound to the bottom of the microplate well, and then it is bound by an antibody that is specific to the antigen and also conjugated to an enzyme or other molecule that enables detection.

    Indirect ELISA

    Indirect ELISA

    In an indirect ELISA, the antigen is bound to the bottom of the microplate well, then an antibody specific to the antigen is added. A secondary antibody, conjugated to an enzyme or other detection molecule, is then bound to the first antibody.

  • Competitive ELISA

    In a competitive ELISA, a reference antigen is bound to the bottom of microplate wells. Sample plus antibody are added to the wells, and if there is antigen present in the sample, it competes with reference antigen for binding to the antibody. Unbound material is washed away. The more antigen was in the sample, the less antibody ends up bound to the bottom of the wells by the reference antigen, and the lower the signal.

    Sandwich ELISA

    Sandwich ELISA

    For the sandwich ELISA, two antibodies specific to two different epitopes on the target antigen are used. The capture antibody is bound to the bottom of the microplate well and binds one epitope of the antigen. The detection antibody binds to the antigen at a different epitope and is conjugated to an enzyme that enables detection. (If the detection antibody is unconjugated, then a secondary enzyme-conjugated detection antibody is required).

Steps to run a sandwich ELISA assay

Most sandwich ELISAs are run in microplates, with the bottom of the microplate wells serving as the solid surface to which antibodies and other reagents bind. A ELISA microplate washer is used to wash away non-specific material in the wells, and a microplate reader detects the color change produced when target antigen is present. An ELISA plate reader software is used to plot standard curves and calculate results.

The illustration below shows a workflow for a typical sandwich ELISA assay:


ELISA analysis and techniques


Enzyme-linked immunosorbent assay is a commonly used analytical technique performed in many research and biotech labs. Below is a collection of application notes, research and technology related to significant ELISA assays and applications.


  • Chemiluminescent VEGF ELISA

    Chemiluminescent VEGF ELISA

    Chemiluminescent VEGF ELISA Using the SpectraMax L Microplate Luminometer

    Vascular endothelial growth factors (VEGFs) are a family of secreted polypeptides that have been implicated in mammalian vascular development and in disease processes involving abnormal blood vessel growth.

    Read Application Note  

    ELISA for Gluten Quantitation

    ELISA for Gluten Quantitation

    Quantifying gluten in beer using an ASBC-approved ELISA method

    Gliadin levels in six commercially available beers were tested to determine gluten levels with the RIDASCREEN Gliadin competitive ELISA.

    Read Application Note  

  • ELISA – Cytokine Interleukin-22

    Cytokine Interleukin-22

    Protein quantitation with the EMax Plus Microplate Reader

    A performance comparison is made between the EMax Plus Microplate Reader and the EMax Endpoint Reader using a sandwich ELISA to quantitate levels of the cytokine Interleukin-22 (mouse/rat IL-22).

    Read Application Note  

    Faster Results with ELISA Kits

    Faster ELISA results with CatchPoint SimpleStep ELISA kits

    A typical ELISA protocol is time-consuming, with multiple incubation and wash steps. CatchPoint SimpleStep ELISA kits give users a 90-minute ELISA workflow, a nearly two-thirds reduction in time compared to conventional ELISAs.

    Read Application Note  

  • Melamine Detection with ELISA Kit

    Melamine Detection with ELISA Kit

    High-throughput melamine detection with Abraxis Melamine ELISA Kit and Molecular Devices Absorbance readers

    The Abraxis Melamine enzyme-linked immuno-sorbent assay (ELISA) is an immunoassay for quantitative screening of melamine; based on the recognition of melamine by antibodies.

    Read Application Note  

    Quantitate Interleukin-8 ELISA

    Quantitate interleukin-8 concentrations in just 90 minutes

    Learn how to run the Human IL-8 SimpleStep ELISA on the SpectraMax® ABS Plus Microplate Reader using a convenient preconfigured protocol.

    Read Application Note  

Workflow of an ELISA protocol

The workflow of a typical ELISA protocol has multiple reagent addition, incubation and wash steps. The ELISA workflow shows how a typical sandwich ELISA is run. Each step breaks down the ELISA process and highlights the instrumentation and tools needed to conduct the ELISA assay including a microplate washer, absorbance ELISA reader and plate reader software.


Workflow: ELISA Assay Protocol
Antibody Binds to Well


First, the capture antibody is bound to the bottom of the microplate well.

Microplate wells


Most ELISAs are run in 96- or 384- well microplates, a 96-well plate being the most common and sometimes referred to as an ELISA plate. The bottom of the microplate wells serve as the solid surface to which antibodies and other reagents attach. Microplates are typically included in an ELISA kit.


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add sample
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Sample is added to the well, and antigen within the sample binds to the capture antibody.

wash microplate
wash microplate mobile


Unbound material is washed away, leaving only the antigen of interest and minimizing the potential for high background signal.

ELISA Plate Reader and Washer

ELISA Plate Reader And Washer

Complete solution for your ELISA workflow using the EMax plus Microplate Reader with SoftMax Pro data and acquisition software and MultiWash+ Microplate Washer.

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add detection antibody
add detection antibody mobile


Enzyme-conjugated detection antibody binds to a second site on the antigen of interest, providing the means to detect the antigen.

wash microplates
wash microplates mobile


Unbound antibodies are washed away, leaving only those specific for the target of interest and again minimizing the potential for background signal.

AquaMax Microplate Washer

ELISA Plate Washer

The AquaMax Microplate Washer: Aspiration and dispensing of 96- and 384-wells occur simultaneously in all wells leading to high-precision assays and faster microplate processing without mechanical plate indexing or quadrant processing.

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add substrate
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Substrate is converted by the enzyme on the detection antibody, producing a color change, with intensity proportional to the amount of antigen present.

Depending on the enzyme and substrate used, the readout can also be fluorescent or luminescent.

read microplate
read microplate mobile


The microplate reader detects the colored reaction product and outputs optical density (OD) values that indicate how much light is absorbed by the contents of each well.

ELISA Plate Reader Principle

ELISA Plate Reader

An ELISA plate reader, like the SpectraMax ABS Plus Absorbance ELISA Microplate Reader, detects the color change produced when target antigen is present. It does so by measuring how much of the light passed through the wells of the microplate is absorbed by the material within the wells. The more antigen is present, the higher the absorbance value.

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ELISA Plate Reader Software

ELISA Plate Reader Software

An ELISA plate reader software, like our SoftMax Pro data analysis software, is used to plot standard curves and calculate results from the absorbance values provided by the microplate reader.

A standard curve is run so that the amount of antigen in each sample can be accurately calculated. A preconfigured protocol, helps save time by calculating results automatically.

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calculate result
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The amount of antigen in each sample is calculated, and different samples—for example, cells subjected to different treatment conditions—can be compared.



Resources for ELISA

Videos and Demos

SpectraMax ABS and ABS Plus Absorbance Microplate Readers

SpectraMax ABS and ABS Plus Absorbance Microplate Readers

SoftMax Pro 7 Software

SoftMax Pro 7 Software

AquaMax Microplate Washer

AquaMax Microplate Washer

ELISA Workflow using the EMax plus Microplate Reader

ELISA Workflow Using the EMax plus Microplate Reader and MultiWash+ Microplate Washer

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