ELISA quality control scenario: If the anti-human Ig enzyme conjugate is not washed out of wells before adding substrate, what outcome would you expect across the plate?

Introduction / Context:
Enzyme-linked immunosorbent assays (ELISAs) rely on sequential binding and thorough washing to remove unbound reagents. Proper washing prevents non-specific signal and ensures that color development reflects true antigen–antibody interactions.

Given Data / Assumptions:

• Secondary reagent is an enzyme-labeled anti-human Ig conjugate.
• Critical wash step before adding chromogenic substrate is omitted.
• Substrate reacts with any enzyme remaining in the well regardless of specific binding.

Concept / Approach:
Without washing, free conjugate remains in solution and adheres nonspecifically to plastic. When substrate is added, the enzyme catalyzes color formation everywhere, collapsing discrimination between positive and negative wells and producing falsely elevated, uniform signals.

Step-by-Step Solution:

Verification / Alternative check:
Controls in ELISA kits include wash verification; insufficient washing classically yields high background, confirming the predicted artifact.

Why Other Options Are Wrong:

• No development: false—development increases, not decreases.
• Normal development: false—background rises markedly.
• Only negatives colorless: opposite of expected.
• Enzyme inhibition by wash buffer: irrelevant since the problem is lack of wash, not buffer effects.

Common Pitfalls:
Under-washing or using worn plate washers; both cause high background. Always validate washer performance and include blanks.

Final Answer:
All wells would show uniform over-development from unbound excess conjugate