Types of ELISA: Direct, Indirect, Sandwich & Competitive Compared

All ELISA types at a glance

An ELISA (enzyme-linked immunosorbent assay) is an antibody-based test that detects and quantifies a target molecule in a biological sample. Within that broad definition, there are five widely used formats — and three or four specialist variants — each suited to a different combination of analyte size, sample type and sensitivity requirement:

The five sections below break each format down — how it works, when to use it, and which Assay Genie kits and protocols fit.

Sandwich ELISA

Sandwich ELISA is the workhorse format for most modern immunoassays. A capture antibody immobilised on a 96-well plate pulls the target analyte out of solution, and a second detection antibody — labelled with an enzyme such as HRP — binds a different epitope on the same molecule. The analyte is "sandwiched" between the two antibodies.

When to use it. Almost always the right choice for proteins, cytokines, growth factors, and any analyte large enough to host two non-overlapping antibody epitopes. Tolerates complex samples (serum, plasma, lysate) without purification.

Strengths. Highest sensitivity (typically low pg/mL), highest specificity, broad dynamic range, quantitative.

Limitations. Requires a matched antibody pair, which may not exist for novel targets. Vulnerable to the hook effect at very high analyte concentrations.

Read the full sandwich ELISA protocol →

Competitive ELISA

A competitive ELISA uses a single antibody. The sample's analyte and a labelled "competitor" analyte (added by the user) compete for binding to that antibody. The more analyte in the sample, the less competitor binds — so the signal is inversely proportional to concentration.

When to use it. Small molecules under ~5 kDa — hormones, steroids, drugs, residues, small peptides — where the analyte is too small to host two antibodies simultaneously.

Strengths. Works for analytes that sandwich ELISA can't. Less sensitive to matrix effects than sandwich. Single-antibody design simplifies development.

Limitations. Inverse signal can confuse new users. Less sensitive than sandwich for protein-sized targets.

Direct ELISA

The simplest format. The antigen is coated directly on the plate, and a single enzyme-conjugated primary antibody binds it. No secondary antibody, no capture antibody.

When to use it. Quick antigen screening, antibody titer determination, or when you're working with a purified antigen and don't need maximum sensitivity.

Strengths. Fastest format (fewest steps). Lowest cross-reactivity risk. Cheapest reagent setup.

Limitations. Lower sensitivity than sandwich or indirect (no signal amplification). Antigen must be pure to coat efficiently.

Indirect ELISA

The antigen is coated on the plate. An unlabelled primary antibody binds the antigen, and an enzyme-conjugated secondary antibody (anti-immunoglobulin from a different species) binds the primary. The two-antibody amplification gives higher sensitivity than direct ELISA.

When to use it. The standard format for antibody detection from serum — seroconversion testing, vaccine response monitoring, infectious-disease serology, autoimmune antibody screening.

Strengths. Strong signal amplification from secondary antibody binding multiple sites on each primary. Flexible — one labelled secondary works for many primary antibodies.

Limitations. Slightly higher background risk than sandwich because the secondary antibody can cross-react with sample IgG.

Read direct vs indirect ELISA in detail →

Multiplex ELISA

Multiplex ELISA platforms measure many analytes simultaneously from a single well. Two architectures dominate:

• Planar arrays — spatially separated capture antibody spots printed inside each well. Imaged with a fluorescence camera.
• Bead-based arrays — capture antibodies coupled to spectrally encoded microbeads read by flow cytometry.

When to use it. Cytokine panels, biomarker discovery on limited sample volumes, large-scale immunology screens.

Strengths. 4 to 100+ analytes per well. Same sensitivity per analyte as sandwich ELISA. Excellent for small-volume samples.

Limitations. Higher up-front cost per kit. Requires a dedicated reader (Luminex, MSD) or compatible flow cytometer.

Other ELISA formats worth knowing

ELISpot & FluoroSpot

ELISpot counts the number of cells secreting a specific cytokine. Cells are plated on an antibody-coated membrane; secreted cytokine is captured locally, and individual secreting cells appear as discrete coloured spots. FluoroSpot is the same with fluorescent detection, allowing two or three cytokines per well. Mainstays of vaccine immunogenicity testing and TB diagnostics.

CLIA (chemiluminescent immunoassay)

CLIAs use the sandwich ELISA architecture but replace TMB with a chemiluminescent substrate such as luminol or acridinium ester, measured by a luminometer. CLIAs achieve sub-pg/mL sensitivity and are widely used for low-abundance hormones and tumour markers.

Cell-based ELISA

An indirect ELISA performed on intact cells in the well. Cells are plated, fixed, and probed with antibodies as normal. Used to measure cell-surface antigens, phosphorylated signalling proteins, or the effects of treatments without lysing cells.

How to choose the right ELISA format

That rule handles roughly 90% of real research applications. The remaining 10% — cell-surface signalling, fixed-cell assays, samples with unusual matrix interference — usually require pilot experiments comparing two or three formats.

Kit formats: pre-coated vs DIY vs multiplex

Beyond the assay type, ELISA kits ship in three product formats:

Frequently asked questions