Fluorescent detection of uric acid in biological samples through the inhibition of cobalt(II) catalyzed Amplex UltraRed

A novel fluorescent probe consisting of cobalt(II)/hydrogen peroxide–Amplex® UltraRed (Co2+/H2O2–AUR) for determining uric acid (UA) concentration is reported. In the presence of H2O2, Co2+ ions underwent oxidation to produce Co3+ ions and hydroxyl radicals, which then reacted with the fluorescence reagent, AUR, forming a fluorescence product at a pH of 9.0. If UA was present, it underwent oxidation to form urea, parabanic acid, and allantoin. This inhibited the Co2+ ions-catalyzed oxidation of AUR and resulted in a substantial decreasing in fluorescence intensity that was dependent on UA concentration. The buffer systems, pH values, and the concentrations of Co2+ ions, AUR, and H2O2 were crucial parameters in determining the sensitivity and selectivity of the method for sensing UA. Under optimal conditions, the fluorescence intensity decreased linearly with UA concentration in the 0.05–1.0 μmol L−1 range (R2 = 0.94) with a detection limit of 20 nmol L−1 at a signal-to-noise ratio of 3. The analytical recoveries in urine and human serum samples were 90%–100.7% and 90%–95% respectively. This method is simpler and more cost effective than are other optical methods for the detection of UA in biological samples.