RED 660™ protein assay is a single reagent colorimetric assay that outperforms commercial colorimetric assays, including Bradford and improved Coomassie/Bradford assays

This assay is suitable for the simple and rapid estimation of protein concentrations and detects proteins in the range of 50-2000µg/mL. This assay is based on a single proprietary dye-metal complex reagent. The binding of protein to the dye-metal complex under acidic conditions results in a change of color from reddish-brown to green and this change in color density is proportional to protein concentration. The color change is a result of deprotonation of the dye-metal complex at a low pH, which is facilitated by interactions with positively charged amino acid groups. Protein estimation can be performed using as little as 0.5 µg protein. The protein-dye complexes reach a stable end point in five minutes, remaining stable for several days.

The RED 660™ protein assay has sufficient reagents for 500 standard test tube assays or 2,500 standard microwell assays and is compatible with most detergents. Its compatibility can be further enhanced with Neutralizer™ (see graph). Neutralizer™ is a unique chemical that sequesters ionic detergents, including SDS, allowing the solution to be compatible with the RED 660™ protein assay. The Neutralizer™ can also be used with Laemmli loading buffer.

Interference to protein assay: Shown are the agents compatible with the RED 660™ Protein Assay (see table). The table also shows the acceptable concentration of reagents for standard protocols. In most cases, using a correct blank will eliminate or minimize the error caused by interference. *Indicates acceptable concentration when RED 660™ Protein Assay Reagent is supplemented with Neutralizer™.

Protein-to-protein variation: Protein-dye complex color is primarily the result of binding of the dye to the basic and aromatic amino acid residues, especially histidine, arginine and lysine and to a lesser extent tyrosine, tryptophan and phenylalanine; therefore, the RED 660 Protein Assay shows protein-to-protein variations (see table). For greater accuracy, the standard plot should be prepared using a protein sample that has a color response similar to the test sample, ideally, a pure fraction of the test protein.

RED 660™ protein assay offers greater linearity, color stability, and compatibility with detergents, reducing agents and other interfering agents compared to the Coomassie assays. The single, ready-to-use reagent allows for rapid analysis of total protein concentration and generates highly reproducible results.