ELISA plate knowledge base
Every question the ELISA guides answer, organized by topic, plus the two troubleshooting topics covered in full here: high background and signal at the edges.
ELISA questions are usually troubleshooting questions: a background that will not come down, a curve that moved, edges that read hot. This page indexes the answers across this guide and the sister guides by topic, and covers high background and edge effects in full below.
Start here
- What is an ELISA plate? The surface, and its four jobs in the assay.
- The complete guide to ELISA plates: the five families and how to choose.
- The ELISA plate guide: binding surfaces and picking a plate.
Coating and blocking
- Coating and binding surfaces: grades, coating volumes, blocking choices, strip storage.
- Binding grades as families: medium against high, chosen per analyte.
Setup, standards, and controls
- Assay setup: layouts, standard curves on every plate, and what the controls check.
- Plate map templates on the 96 guide: layouts recorded before the run.
Washing
- Washing in the coating guide: 3 to 5 washes, about 300 microliters per well, soak times, and why the validated protocol overrides general rules.
High background: causes and fixes
Background is signal where no analyte should be, and it has a short list of usual causes. Blocking gaps: too little blocker, too short a block, or a blocker mismatched to the assay leaves bare surface for detection reagents to stick to. Washing shortfalls: too few washes, low volumes, or no soak leave unbound enzyme conjugate in the wells. Reagent behavior: detection antibody too concentrated, or cross-reacting with the coating or blocker, manufactures signal honestly. Contamination: buffers made with dirty water or reused reservoirs, and plates handled by the well rims, add what looks like analyte. Over-development: substrate left too long raises every well, blanks included. Work the list in that order, changing one variable per run, and include a no-analyte control row so background has nowhere to hide.
Signal at the edges
ELISA plates show the general edge effect in assay form. Edge wells evaporate faster during the long incubations ELISA is built from, concentrating reagents there; they also develop at slightly different rates when a plate cools unevenly out of the incubator, and stacking plates in the incubator insulates the middle ones and exaggerates both. The fixes are housekeeping: seal the plate for every incubation, equilibrate reagents to room temperature before they go on, do not stack plates during incubation or development, and put the standard curve and controls in the plate interior where they calibrate the wells the samples should have had. The general treatment is in the microplates knowledge base.
Related guides
Common questions
Why is my ELISA background high?
Work the short list: blocking gaps, too little washing, detection antibody too concentrated or cross-reacting, contaminated buffers, and over-development. The full treatment above orders the checks; a no-analyte control row tells you which wells the background lives in.
Why do standard curves differ between plates?
Because binding, incubation, and development vary plate to plate, which is why the curve runs on every plate: it calibrates that plate, and the controls only mean something against it. A curve borrowed from yesterday calibrates a plate that no longer exists.
How many washes does an ELISA need?
Typically 3 to 5 washes of about 300 microliters per well, with a 30 to 60 second soak where the protocol calls for it. The validated protocol for the specific assay overrides any general number.
Can I read an ELISA plate with the seal on?
Only with an optical film made for reading; ordinary adhesive seals scatter and absorb light and distort absorbance. Standard practice is to remove the seal before reading, or apply a rated optical seal if the workflow requires reading sealed.