The addition of SDS to the Bradford dye-binding protein assay, a modification with increased sensitivity to collagen.

The standard Bradford protein assay is insensitive to collagen. But if a small, sub-threshold amount of SDS is added to the sample, the response to collagen is increased by at least an order of magnitude, while, on average, the sensitivity for non-collagens is decreased by approximately a factor of 2. As a result, comparable color formation is achieved with both collagen and non-collagens. The addition of protein to a sub-threshold amount of SDS results in the formation of a green color measurable as an increase in absorbance at 700 nm, in contrast to the blue color measured at 595 nm in the standard assay. Depending upon the source, the threshold level for SDS varies from 30 to 50 microgram. The response to protein is linear up to approximately 40 microgram of protein per ml of reagent.