Protein Assays for Accurate Protein Quantification and Sample Normalization

Protein Assays covers the colorimetric and UV-based methods used to determine total protein concentration in a sample, including the Bradford dye-binding assay, the copper-based BCA and Lowry assays, and non-destructive UV absorbance at 280 nm. Each method differs in sensitivity, linear range, and tolerance for common interfering substances such as detergents and reducing agents, making assay selection dependent on sample composition and downstream requirements. Academic and core laboratories quantifying protein prior to gel loading, normalization, purification, or other analytical workflows can benefit from guidance when choosing the most appropriate quantification method.

Explore available protein assay reagents or request a quotation by contacting customerservice@mbpinc.net. Our team can help identify the appropriate Bradford, BCA, Lowry, or UV-based protein quantification solution for your workflow and sample type.

Protein Assays

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What are Protein Quantification Assays?

Protein quantification assays determine the total protein concentration in a sample using different detection principles. Common methods include the Bradford assay, BCA assay, Lowry assay, and UV absorbance at 280 nm.

What you will find:

Bioluminescence Assays and Reagents: High-sensitivity tools like the Luciferase Assay Kit (G287), engineered for the rapid detection of reporter gene expression and transcriptional activity in cellular models.
Crosslinking, Labeling and Protein: Specialized purification and control reagents, including high-capacity Ni-IDA Agarose Resins (G250) for His-tagged protein isolation and GFP Purified Protein (000033P) for accurate fluorescent standardization.

How to Choose a Protein Quantification Assay

Match Assay Sensitivity to Your Expected Protein Concentration

Bradford assays typically perform across approximately 1–1000 µg/mL, while BCA assays offer higher sensitivity and a broader linear range for dilute samples.

Check for Detergents in Your Sample

BCA assays tolerate higher concentrations of common detergents such as SDS, Triton X-100, and Tween-20, making them suitable for samples prepared in lysis buffers. Lowry assays are less detergent tolerant.

Check for Reducing Agents Before Using Copper-Based Assays

BCA and Lowry assays can be affected by reducing agents such as DTT or β-mercaptoethanol, while Bradford assays are generally unaffected by these compounds.

Consider UV Absorbance When Sample Preservation Matters

UV absorbance at 280 nm is non-destructive and does not consume sample material, although accuracy may be affected by nucleic acid contamination or variations in aromatic amino acid content.

Evaluate Protein-to-Protein Variation

BCA assays generally show less variation between different proteins than dye-binding methods such as Bradford because the signal is based primarily on peptide bond content.

Specifications context

A modern dilution-free rapid BCA format can reduce assay setup time by up to 80% compared with a standard BCA or Bradford protocol by eliminating the sample and standard dilution step while preserving sensitivity and linearity. As of 2026, BCA remains the most broadly recommended default for detergent-containing or low-concentration samples, while Bradford is used for fast routine measurements of relatively clean protein samples.

Refine your protein quantification—contact the MBP team today for a quote on our professional assay solutions.

FAQ

BCA is generally the best default when you need high sensitivity, a wide linear range, and your sample contains detergents, since it tolerates up to 5% SDS, Triton X-100, or Tween-20 without interference. Bradford is faster and simpler for routine quantification of purified protein with minimal detergent, while Lowry is still chosen when sensitivity at low concentrations matters and the sample lacks interfering reducing agents, detergents, or chelators.

BCA and Lowry are both copper-based assays where reduced copper ions drive the colorimetric reaction, and reducing agents like DTT or beta-mercaptoethanol can independently reduce copper ions, artificially inflating the measured protein concentration. The Bradford assay relies on a dye-binding absorbance shift rather than copper reduction, so it isn't sensitive to reducing agents in the same way, though it is sensitive to detergents instead.

BCA tolerates up to 5% SDS, 5% Triton X-100, and 5% Tween-20 without interference, substantially more than the Lowry method, which only tolerates 1% SDS, 0.03% Triton X-100, and 0.062% Tween-20 before results become unreliable. This makes BCA the more practical choice for samples prepared with detergent-containing lysis buffers.

UV absorbance at 280 nm measures the intrinsic absorbance of aromatic amino acids, primarily tryptophan and tyrosine, so proteins with unusually high content of these residues can show artificially elevated absorbance relative to their actual mass concentration. Contaminating nucleic acids and lipids in the sample can also interfere with the 280 nm reading, further complicating accurate quantification by this method.

BCA chemistry develops a colorimetric signal in proportion to the number of peptide bonds in a protein, which is relatively consistent across different proteins, while Bradford's dye-binding signal depends more heavily on a protein's specific amino acid composition, which varies more between different proteins. This means BCA results are generally more comparable across samples containing different proteins than Bradford results would be.

A dilution-free rapid BCA format eliminates the standard sample and standard dilution step required in conventional BCA protocols, reducing overall assay setup time by up to 80% while preserving the sensitivity and linear range associated with standard BCA chemistry. This is useful when processing many samples and minimizing hands-on time is a priority without sacrificing assay quality.

Nucleic acid contamination can interfere with UV absorbance at 280 nm specifically, since nucleic acids also absorb strongly in that wavelength range, but colorimetric assays like BCA, Bradford, and Lowry are generally less affected by nucleic acid contamination since they rely on different chemistry. If nucleic acid contamination is a concern, a colorimetric assay is often the more robust choice over UV absorbance.

Yes, MBP offers academic and bulk pricing for BCA, Bradford, Lowry, and related protein quantification assay kits, with specialist support for matching a method to your sample's specific composition. Orders ship from MBP's US office in Houston, Texas, with stock available in both USD and CAD.

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