The Bradford Protein Assay, commonly referred to as the BSA (Bovine Serum Albumin) Assay due to the frequent use of BSA as a protein standard, is a rapid and sensitive method for the quantitation of microgram quantities of protein. Here’s a brief historical development of the assay:

1. Predecessors: Before the development of the Bradford Assay, scientists primarily used the Lowry assay and the Biuret assay for protein determination. Both assays have their advantages, but they also possess several disadvantages such as sensitivity to contaminating substances.
2. Introduction of the Bradford Assay: Developed by Marion M. Bradford in 1976, the Bradford Protein Assay uses an acidic solution of Coomassie Brilliant Blue G-250 dye. When protein is present, the dye, which is brownish-green in its acidic form, binds to the protein and turns blue. The intensity of this blue color is proportional to the amount of protein present and can be measured spectrophotometrically.
3. Principle: The principle behind the Bradford assay’s sensitivity is the binding of Coomassie Brilliant Blue G-250 dye to proteins. Under acidic conditions, the dye gives up protons when it binds to protein, leading to a color change. The dye binds primarily to arginine and lysine residues in proteins.
4. Advantages and Widespread Adoption: The Bradford Assay was quickly adopted in many labs because of its rapidness, simplicity, and reduced sensitivity to common protein contaminants, such as detergents, salts, and reducing agents. Moreover, since it doesn’t rely on certain amino acid side chains like the Lowry assay, it’s considered more general.
5. BSA as a Standard: While the assay is not specific to Bovine Serum Albumin, BSA became a commonly used protein standard for many biochemical assays due to its stability, availability, and well-known structure. Its consistent results in the Bradford assay made it a popular choice as a reference protein.
6. Modifications and Improvements: Over the years, there have been many iterations and variations to the original protocol, optimizing it for different conditions and specificities. However, the basic principle has remained unchanged.

Today, despite the development of many new protein determination methods, the Bradford assay remains a popular choice, especially for quick estimations or when certain contaminants are present. The historical development of the Bradford Assay is a testament to its simplicity, efficiency, and utility in biological research.