Piecemeal Rekindling of Coumarin 6 Fluorescence on Stepwise Unfolding of Protein by Surfactant.

Coumarin 6 (C6) briskly aggregates in water, and as a result, rapidly loses fluorescence. However, vicinal hydrophobic cavity can induce disintegration of the aggregates, and thus reviving the fluorescence. It is shown that carrier protein, such as bovine serum albumin (BSA), can disintegrate the microcrystals of C6 to smaller fragments and trap them inside the hydrophobic domain of the folded protein. This results into a 12-fold enhancement in the fluorescence signal of C6. However, on unfolding BSA by micelles, the C6 microcrystals break into single molecules by getting trapped in the micelles, and hence emission enhances by more than 100-folds.