How to Run an R&D Systems Quantikine ELISA

critical

Absent Standard Curve Signal with Normal Zero Standard

No detectable signal is observed for standard curve points containing analyte, while the zero standard (maximum binding control) shows normal OD values, indicating complete loss of competitive inhibition.

💡 4 · ✓ 4

critical

No Signal or Weak Signal in ELISA

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.

💡 6 · ✓ 6

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

Poor or Non-Linear Standard Curve

Standard curve shows irregular shape, poor linearity, or inconsistent serial dilution response. R-squared value below 0.95 or curve does not follow expected sigmoidal or linear pattern across dynamic range.

💡 5 · ✓ 5

critical

No Signal for Standard Curve with Normal Zero Standard

All standard concentrations show no signal (high OD in competitive format similar to zero standard), while the zero standard (no competitor) shows normal maximum binding signal.

💡 4 · ✓ 4

critical

Complete Absence of Standard Curve Signal with Normal Zero

All standard concentrations show no detectable signal (very low OD), while the zero standard (B0, maximum binding) produces normal expected signal, indicating complete competition failure.

💡 4 · ✓ 4

severe

Excessive Non-Specific Background Signal in Competitive ELISA

High background optical density readings are observed across wells, obscuring the difference between standards and samples. Signal persists even in wells without primary antibody or sample.

💡 4 · ✓ 4

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

Standard Curve Plateau at High Concentration End

The standard curve reaches a plateau at high analyte concentrations (low OD values in competitive format), showing no further decrease in signal despite increasing standard concentration.

💡 4 · ✓ 4

severe

OD Value of Zero Standard Too Low

The zero standard (maximum binding, no competitor) shows insufficient optical density signal, providing inadequate dynamic range for the competitive assay and poor B/B0 calculations.

💡 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

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

Buffer Components Inhibit Detection Enzyme

No or very weak signal despite correct antibody binding. Signal loss occurs after addition of detection reagent. Other wells using different buffers show normal signal.

💡 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

Poor Dynamic Range Between Signal and Background

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.

💡 5 · ✓ 5

severe

Inadequate Washing Between Assay Steps

High background with retained signal in negative controls. Edge wells may show higher background than center wells. Residual reagents visible in wells.

💡 4 · ✓ 5

severe

Incomplete Standard Reconstitution with Visible Particulates

After adding reconstitution buffer to lyophilized standard, visible undissolved material or particulates remain in the vial, leading to inaccurate standard concentrations.

💡 4 · ✓ 6

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

Inadequate Blocking of Non-Specific Binding Sites

Uniformly elevated background across plate with high coefficient of variation. Background may be particularly high in wells with lower antigen concentrations.

💡 4 · ✓ 4

severe

High Variability Between Replicates (CV >15%)

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.

💡 5 · ✓ 5

severe

Uneven Color Development Across Plate

Color intensity varies significantly between wells that should be identical. Pattern may show edge effects, gradients across the plate, or random spotty appearance indicating incomplete or inconsistent reagent contact.

💡 4 · ✓ 4

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

moderate

Standard Curve Plateau at High Concentration End

The top of the standard curve (high analyte concentration, low OD) shows a plateau with minimal signal change across multiple high-concentration standards, reducing dynamic range.

💡 4 · ✓ 4

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

Incubation Temperature Below Optimal Range

Consistently weak signal across all samples including positive controls. Signal improves when experiment is repeated with attention to temperature. Longer incubations partially compensate.

💡 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 Primary Antibody Concentration Saturating Wells

High background signal with poor signal-to-noise ratio. Standard curve may show compressed dynamic range or plateau at lower concentrations than expected.

💡 3 · ✓ 3

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 CV from Bubbles in Wells

Inconsistent absorbance readings between replicate wells with coefficient of variation >15%. Visual inspection may reveal bubbles present in wells, particularly when using detergent-containing solutions.

💡 4 · ✓ 4

moderate

Biological Sample Not in Detectable Range

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.

💡 4 · ✓ 4

moderate

High Variability Between Experimental Runs

Standard curves or sample values differ significantly between experiments run on different days, despite using the same reagents and protocol, showing poor reproducibility.

💡 5 · ✓ 5

moderate

Edge and Drift Effects on ELISA Plate

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.

💡 5 · ✓ 5

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

Standard Curve Fitting Model Not Appropriate

The recommended curve-fitting model (typically Four-Parameter Logistic) does not adequately fit the standard data points, resulting in poor correlation even with properly prepared standards.

💡 4 · ✓ 5

minor

Sample Values Above Assay Range (Hook Effect Excluded)

Sample absorbance readings exceed the top standard, reading off the curve, while the standard curve itself appears normal with proper shape and dynamic range.

💡 2 · ✓ 3

minor

Plate Contamination or Optical Interference

Random high background in specific wells or patterns. Fingerprints, dust, or residue visible on plate bottom. Erratic readings not following expected pattern.

💡 4 · ✓ 5

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