Bradford test for protein

Safety

Method

Results

The Bradford assay is a very good, and simple, method of detecting microgram quantities of protein.

However the test is specific for certain amino acids, principally arginine, so not all proteins give the same reaction. For example albumin, casein and gelatin all give different responses. Gelatin has a very weak response to Bradford reagent since the protein, which is partially hydrolysed collagen, contains very few of the amino acids to which the reagent is sensitive. The standard usually employed is bovine serum albumin, (BSA). This is relatively expensive. We have used powdered egg white from the home-baking section of our local supermarket as the standard with results comparable to BSA.

The reagent contains Coomassie Blue dye which is light brown in the reagent but blue when bound to protein.

	The stock solution contains phosphoric acid (50%).
	Diluted for use the reagent is irritant. The dye will stain skin and clothes.

Dissolve 50mg Coomassie Blue in 20cm3 methanol Add this to 60cm3 phosphoric acid Make up to 100cm3 with water
Label the stock solution 'CORROSIVE' Dilute with 4 volumes of water for use

Add 2.5cm³ of the reagent, (stock solution diluted 1+4 with water), to 0.25cm³ of the sample solution.
Allow the mixture to stand for ten minutes then read the absorbance using red light. Ten minutes allows full development of the colour, longer intervals will not affect the result.

Microassay
The sensitivity can be increased by adding 0.5cm³ of undiluted stock solution to 2cm³ of the solution to be tested. The method will detect concentrations down to about 5µg per cm³.

Egg albumin (powdered egg white) was the standard used for these results.

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