FIG. 1.

Model for converting an absorbance assay into a fluorescence quenching method. (A) Chemical structure of quinaldine red (QR). (B) Overlap between QR-phosphomolybdate chromophore and intrinsic fluorescence of white opaque 384-well plates. When irradiated at 430 nm, white plates emit broadly between 450 and 550 nm. (C) Schematic representation of white plate method. Fluorescence emission from white plates is quenched by QR in the presence of molybdate and inorganic phosphate (spheres). (D) Comparison of sensitivity for phosphate between absorbance and fluorescence methods. Results are the average of at least triplicates and error bars are standard error of the mean (some bars are smaller than the symbols).