The sensitivity of RhQ for rBSA was further evaluated. Using increasing amounts of rBSA (0-4 μM) the fluorescence intensity of RhQ was enhanced (Figure ). The fluorescence intensity at 590 nm is linearly proportional to the amount of rBSA from 0.2 to 4.0 μM, enabling the quantitative detection of rBSA (Figure ). According to the linear range of the titration plot, the limit of detection was determined to be below 0.2 μM. This result suggests that RhQ could be used for quantifying VDPs.