Figure 6.

Cuvette FCS measurements in urea. (A) Normalized plots of CPM (squares) and <N> (circles) are obtained from FCS measurements, and quantum yield (solid line) is obtained from spectrofluorometer measurements on 100 nM rhodamine B in 0–7 M urea. The increase of CPM (squares) is consistent with the urea-dependent increase of quantum yield of rhodamine B fluorescence (solid line). The small (∼15%) increase of <N> may arise because of desorption of the fluorophore from the cuvette windows due to serial dilution of the sample. (B) Plot of τ_D versus viscosity of urea is shown. Linear increase of τ_D with viscosity is consistent with the SE relationship. Titration and mixing of urea have been performed using an autotitrator and a magnetic stirrer, respectively. To see this figure in color, go online.