Semiconductor laser fluorimetry for enzyme and enzymatic assays

Near-infrared semiconductor laser fluorimetry is applied to assays of xanthine and xanthine oxidase. The fluorescence of indocyanine green in the near-infrared region is quenched by hydrogen peroxide. Xanthine is converted to uric acid by xanthine oxidase, in a reaction which also produces hydrogen peroxide; xanthine can be determined by measuring the decrease in fluorescence intensity of the dye added to the sample solution. The calibration graph for xanthine is linear from 5 × 10^?5 M to 5 × 10^?7 M. The enzyme activity can also be determined.