Macrophage Chemokine Ligand 9 (CXCL9) Competition ELISA Kit (MTS-1123-HM111)

In a competitive ELISA, the antibody binding sites are limited, so CXCL9 in your sample competes with a labeled CXCL9 tracer for binding. When your sample contains more CXCL9, it occupies more antibody sites and displaces the tracer, producing a lower colorimetric signal. This inverse relationship is expected and is handled by constructing a standard curve where higher analyte concentrations correspond to lower OD values. Competitive formats are useful when only one high‑quality antibody epitope is available or when the analyte's structure makes two‑antibody capture challenging. To interpret results confidently, run standards and controls on every plate and ensure consistent incubation times and temperatures because competitive assays can be sensitive to small procedural differences.

The competition assay can be used with typical immunology matrices such as culture supernatants, serum, plasma, and clarified tissue homogenates, provided the sample is free of visible debris. Because competitive assays can saturate when analyte levels are very high, we recommend performing an initial pilot with serial dilutions-such as 1:2, 1:5, 1:10, and 1:20-to bring measurements into the working range of the standard curve. Use the same dilution buffer for standards and samples whenever possible to reduce matrix effects. If you observe non‑parallelism (sample curve shape differs from standards), further dilution often improves linearity. Consistent handling-centrifugation, avoiding hemolysis, and minimizing freeze-thaw-will also improve reproducibility across biological replicates.

A competitive ELISA workflow is often faster than sandwich assays and can typically be completed in roughly 1.5 hours, depending on incubation settings and plate washing efficiency. The most common sources of run‑to‑run variability are inconsistent wash performance, timing drift between wells, and temperature differences during incubations. Because competitive formats rely on fine differences in binding, precise pipetting and uniform mixing are especially important. We recommend using a multichannel pipette where possible, keeping plate handling consistent, and ensuring the plate washer (manual or automated) fully removes residual fluid without drying out wells. Finally, always include internal controls and replicate standards; if your standard curve shifts, recalibrate your reader and verify reagent storage conditions before proceeding with sample interpretation.