Fluorescence assay of catecholamines based on the inhibition of peroxidase-like activity of magnetite nanoparticles Original Research Article

We report a fluorescence approach for the highly selective and sensitive detection of catecholamines using magnetite nanoparticles (Fe3O4 NPs) in the presence of Amplex UltraRed (AUR) and H2O2. Fe3O4 NPs catalyze H2O2-mediated oxidation of AUR. The resulting product fluoresces (excitation/emission maxima, ca. 568/587 nm) more strongly, relative to AUR. When catecholamines bind to Fe3O4, the complexes that are formed induce decreased activity of Fe3O4 NPs, mediated through the coordination between Fe3+ on the NP surface and the catechol moiety of catecholamines. As a result, Fe3O4 NPs-catalyzed H2O2-mediated oxidation of AUR is inhibited by catecholamines. The limits of detection for dopamine (DA), l-DOPA, norepinephrine, and epinephrine were 3 nM, 3 nM, 3 nM, and 6 nM, respectively. The Fe3O4 NPs-H2O2-AUR probe exhibited high selectivity (>1000-fold) toward catecholamines over other tested biomolecules that commonly exist in urine. Four catecholamines had similar sensitivity because the inhibition of the Fe3O4 NPs activity relies on the presence of the catechol moiety. This approach also allowed the determination of tyrosinase activity because tyrosinase catalyzes the conversion of l-tyrosine to l-DOPA. We validated the practicality of the use of the Fe3O4 NPs-H2O2-AUR probe for the determination of the concentrations of DA in urine samples.