High Uniform Background Signal

Symptom

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.

1. 1 Insufficient washing (residual unbound antibody/HRP) or inadequate blocking of plate surface
2. 2 Primary or secondary antibody concentration too high
3. 3 TMB substrate solution prepared too early and turned blue before addition, or plate read after delay
4. 4 HRP-conjugate concentration too high
5. 5 HRP contamination in reused plastics (reservoirs, plate sealers, pipette tips) or buffers

1. 1 Increase wash cycles and/or duration; add 30-second soak between washes; add 0.01-0.1% Tween-20 to wash buffer
2. 2 Increase blocking time or blocker concentration (BSA, casein, or gelatin)
3. 3 Decrease primary/secondary antibody concentration through titration
4. 4 Mix TMB substrate immediately before adding to plate; read plate immediately after stop solution
5. 5 Use fresh plastics for each step; prepare fresh buffers; check and adjust HRP-conjugate dilution

Related Video (3)

Bilibili (China-Accessible Mirrors) ★ 82

R&D Systems Quantikine ELISA Operation Guide

"Official R&D Systems Quantikine hands-on walkthrough directly matches the R&D Guide failure case, showing the wash and blocking steps where uniform background originates."

Bilibili (China-Accessible Mirrors) ★ 80

How to Run an R&D Systems Quantikine ELISA

"Quantikine ELISA protocol video includes troubleshooting guidance, useful for seeing correct washing/blocking technique that prevents elevated background."

Bilibili (China-Accessible Mirrors) ★ 72

ELISA Experimental Protocol Complete Series (5 Episodes)

"Comprehensive 5-episode protocol series covers full benchwork including wash and block steps, giving the operational context for this failure."