A biomarker is only clinically useful once there's a reliable assay — typically an antibody that selectively captures it — that can turn its presence into a quantifiable signal.
signal ~ [bound antigen] * detectionSensitivity (ELISA-style readout)
- Antigen molecules — the biomarker molecules present in a patient sample (blood, serum, urine).
- Capture antibody sites — immobilized antibody spots on the plate that specifically recognize the target biomarker.
- Binding affinity — how strongly the capture antibody holds onto the antigen once they collide.
- Detection sensitivity — how much measurable signal (colorimetric, fluorescent) each captured antigen produces.
This capture-and-detect logic underlies essentially every clinical immunoassay in routine use, from pregnancy tests to troponin assays for heart attack diagnosis, differing mainly in what antibody and detection chemistry are used.