Real lab failures, root causes, and fixes — curated and bilingually annotated by our team.
After developing the ELISA plate, wells show no color change or very faint signal that is barely above background, even for positive controls or high-concentration standards.
Standard curves or sample values differ significantly between experiments run on different days, despite using the same reagents and protocol, showing poor reproducibility.
Wells at the plate edges show systematically higher or lower absorbance than center wells, or a gradient pattern appears across the plate, affecting data quality especially for samples in edge positions.
Sample absorbance readings exceed the top standard, reading off the curve, while the standard curve itself appears normal with proper shape and dynamic range.
The difference between maximum signal (high standards) and background (blank wells) is compressed, typically less than 5-fold, making it difficult to distinguish between samples of different concentrations.
Replicate wells for the same sample or standard show high coefficient of variation (>15%), with inconsistent absorbance values that suggest uneven treatment or technical errors.
All wells show elevated absorbance including blanks and negative controls, creating a uniformly high background that reduces signal-to-noise ratio and compresses the standard curve.
When sulfuric acid stop solution is added to wells after TMB substrate incubation, a green color appears instead of the expected yellow, indicating incomplete mixing and pH gradient in the well.
No detectable signal or very weak signal across all wells, including standard wells. The plate reader shows absorbance values near baseline or significantly lower than expected.
Standard curve appears normal, but sample wells show no signal or signal below the lowest standard. This occurs when the analyte concentration in samples is below the assay detection limit.
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