DuoSet ELISA — Sandwich ELISA Hands-on Protocol (Bio-Techne)

critical

No Signal or Weak Signal in ELISA

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.

💡 6 · ✓ 6

critical

No Signal or Weak Signal in ELISA

The ELISA plate reader detects no colorimetric signal or signal intensity is significantly below expected values after substrate development. Wells appear clear or only faintly colored even after standard incubation times of 10-30 minutes.

💡 6 · ✓ 6

critical

Complete Signal Absence

No detectable signal across the entire plate when signal is expected

💡 7 · ✓ 9

severe

Insufficient Signal from Zero Standard (B0)

The zero standard (no competing antigen, maximum antibody binding) produces OD values that are too low, resulting in compressed standard curve with poor sensitivity.

💡 4 · ✓ 4

severe

No or Very Low Signal Due to Poor Plate Binding

No detectable signal or extremely weak signal in ELISA even when target protein is expected to be present. Signal may be inconsistent across wells.

💡 4 · ✓ 4

severe

Detection System Lacks Sensitivity for Target Concentration

Low or no signal despite proper assay setup. High concentration samples may show weak signal while low concentration samples are undetectable.

💡 4 · ✓ 4

severe

Primary and Secondary Antibody Incompatibility

No signal or minimal signal in indirect ELISA despite proper coating and blocking. Positive controls with matched antibodies work correctly.

💡 4 · ✓ 4

severe

Antibody or Reagent Loss of Activity from Improper Storage

Progressive signal loss over time using the same reagents. Previously working protocols suddenly fail. Positive controls that worked before now show reduced or no signal.

💡 5 · ✓ 5

severe

Non-specific Secondary Antibody Binding Causing High Background

Elevated background signal across wells, including negative controls. Signal appears uniformly high rather than specific to target-containing wells.

💡 4 · ✓ 5

severe

High CV from Plate Edge Effects

Outer (edge) wells show systematically different absorbance values compared to inner wells, with CV >15%. Edge wells may show higher or lower signal depending on evaporation or temperature variation. Visual inspection from the side reveals lower buffer levels in edge wells.

💡 5 · ✓ 5

severe

Standard Curve R² Below 0.98 Threshold

The regression coefficient (R²) of the standard curve falls below 0.98, indicating poor curve fit and unreliable quantification of sample concentrations.

💡 5 · ✓ 6

severe

Excessive Signal - Entire Plate Turned Blue

Whole plate turned uniformly blue indicating non-specific signal saturation

💡 5 · ✓ 5

severe

High Inter-Assay CV from Inconsistent Sample Storage

High inter-assay coefficient of variation (>15%) when the same samples are tested across different runs. Sample readings decrease over time or vary unpredictably between runs.

💡 5 · ✓ 5

severe

Low OD Value for Zero Standard in Competitive ELISA

The zero standard (B0, representing maximum antibody binding without competing analyte) produces lower than expected optical density values, reducing overall assay sensitivity and dynamic range.

💡 4 · ✓ 4

severe

Poor Assay-to-Assay Reproducibility

Inconsistent results between different assay runs with same samples

💡 7 · ✓ 9

severe

Poor Reproducibility Between Duplicate Wells

Coefficient of variation (CV) between duplicate or triplicate wells exceeds 10-15%. Individual replicates show inconsistent absorbance values that cannot be attributed to biological variation.

💡 4 · ✓ 4

severe

High Background Signal in ELISA

All wells including negative controls show elevated absorbance readings. Background signal obscures specific signal, reducing signal-to-noise ratio and making data interpretation difficult.

💡 6 · ✓ 6

moderate

Wrong Instrument Settings for Detection Wavelength

No signal or very low signal readings from plate reader despite visible color development or expected fluorescence. Signal does not correlate with visual observations.

💡 4 · ✓ 4

moderate

Over-Washing Removes Bound Detection Reagents

Signal progressively decreases with increased wash steps or aggressive washing. Reducing wash stringency restores signal. Edge wells show lower signal than center wells.

💡 4 · ✓ 5

moderate

Excessive Substrate Concentration or Incubation Time

Rapid color development with all wells turning dark quickly. Signal may exceed linear range of reader (OD >2.0). Background wells show significant color development.

💡 4 · ✓ 5

moderate

Precipitate Formation in Wells Upon Substrate Addition

Visible precipitate or cloudiness appears in wells immediately or shortly after substrate addition. Absorbance readings may be abnormally high or variable.

💡 4 · ✓ 4

moderate

Excessive Signal Amplification in Detection System

Very high signals across all wells including low-concentration standards. Loss of discrimination between different antigen concentrations. Background approaches signal levels.

💡 4 · ✓ 4

moderate

High Background Signal

Elevated background noise across the ELISA plate making it difficult to distinguish specific signals from non-specific binding

💡 3 · ✓ 3

moderate

Poor Duplicate Reproducibility

Duplicate wells showing inconsistent results with high variation between replicates

💡 6 · ✓ 8

moderate

Very Low Readings Across Plate

Consistently low optical density readings across entire plate including standards

💡 5 · ✓ 6

moderate

Signal Drift Across Plate

Gradual change in signal intensity across the plate suggesting time-dependent variation during assay setup

💡 2 · ✓ 2

moderate

Weak Signal from Inadequate Antibody-Antigen Interaction

Signal is present but consistently lower than expected. Positive controls show weak but detectable signal while samples are near background.

💡 4 · ✓ 4

moderate

High Coefficient of Variation Between Standard Replicates

Duplicate or triplicate wells for the same standard concentration show high variability (CV >10-15%), compromising curve fit and confidence in quantification.

💡 5 · ✓ 6

moderate

Poor Standard Curve Discrimination

Standard curve achieved but shows low or flat curve with poor discrimination between concentration points

💡 6 · ✓ 8

minor

Edge Effects on Plate

Wells at the edge of the plate show different readings compared to central wells

💡 1 · ✓ 2

minor

Green Color Upon Adding Stop Solution (Streptavidin-HRP)

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.

💡 2 · ✓ 3