Protein Detection: Western, ELISA, and Mass Spectrometry
TL;DR
Protein assays ask a different question from DNA/RNA assays: is the protein present, modified, secreted, bound, or changed in abundance? Western blots are target-specific and visual. ELISA is target-specific and quantitative in fluids or lysates. Mass spectrometry can identify and quantify many proteins or peptides at once, but requires careful sample prep and computational analysis. Sources: [1], [2]
Method comparison
| Method | Strength | Weakness |
|---|---|---|
| Western blot | size + antibody signal | semi-quantitative, antibody dependent |
| ELISA | scalable quantification | one/few targets, matrix effects |
| Multiplex immunoassay | cytokine/panel readout | cross-reactivity and calibration issues |
| LC-MS/MS proteomics | broad protein/peptide discovery | sample complexity, missingness, cost |
| Targeted MS | precise peptide quantification | assay development burden |
Oncology examples
- confirm pathway activation by phospho-protein
- measure secreted cytokines after immune stimulation
- profile serum or plasma proteins
- validate antibody specificity
- detect protein biomarkers in tumor tissue
- quantify drug-target engagement or degradation
What it does not solve
- DNA mutation status by itself
- spatial localization unless paired with tissue imaging
- cell-type attribution in mixed samples
- causality without perturbation
- reliable biology if the antibody or peptide assay is not validated
Computational output
| Assay | Output |
|---|---|
| Western | image, band intensity, normalization |
| ELISA | standard curve, concentration |
| Multiplex assay | analyte matrix |
| Shotgun MS | peptide-spectrum matches, protein groups |
| Targeted MS | transition intensities, absolute/relative abundance |
Developer notes
- Antibody ID, clone, lot, dilution, and validation context are data.
- Western blot band intensity without exposure and normalization metadata is fragile.
- ELISA concentrations depend on standard curves and matrix compatibility.
- Proteomics protein groups can collapse multiple isoforms or homologs.
- Missing values in mass spectrometry are often structured, not random.
- Protein abundance does not automatically imply activity; phosphorylation, localization, and complex formation may matter.
References
- Towbin H, Staehelin T, Gordon J. Electrophoretic transfer of proteins from polyacrylamide gels to nitrocellulose sheets. Proc Natl Acad Sci U S A 1979;76:4350-4354. PMID 388439. https://doi.org/10.1073/pnas.76.9.4350
- Uhlen M, Bandrowski A, Carr S, et al. A proposal for validation of antibodies. Nat Methods 2016;13:823-827. PMID 27595404. https://doi.org/10.1038/nmeth.3995