Biology

The most common method for measuring protein concentration is the Bradford assay. In this assay, a known quantity of protein is mixed with a colored dye in a cuvette, and the absorbance of the mixture is measured at 595nm with a spectrophotometer. If the sample contains a known amount of protein, then the intensity of the measured absorbance can be used to calculate the concentration of the protein in the unknown solution. Another method to measure protein concentration is the Lowry assay, which uses a combination of acid and alkaline precipitants to separate the protein from the cell lysate, after which the sample is measured using a spectrophotometer as above. Additionally, enzyme linked immunosorbent assays (ELISAs) or immunoassays can be used to measure the concentration of specific proteins in a sample. An ELISA is performed by coating a specific antibody to the protein of interest on a plate, adding standard amounts of the protein and then performing a colorimetric readout of the bound protein. This technique is specific for certain proteins and requires the availability of a specific antibody as well as standards for the protein of interest.