Bifunctional Fe-MOF@Fe3O4NPs for colorimetric and ratiometric fluorescence detection of uric acid in human urine

Nanozymes as a substitute for natural enzymes have attracted many attention owing to their high stability, low cost, and satisfactory catalytic activity. In this study, a new dual-readout detection strategy was proposed for colorimetric and ratiometric fluorescence detection of uric acid (UA) based on bifunctional metal–organic framework nanocomposite (Fe-MOF@Fe3O4NPs), which functions as fluorescent indicators as well as peroxidase mimics. In the presence of uricase, the decomposition of UA can produce H2O2, and Fe-MOF@Fe3O4NPs catalyzed H2O2 into the OH radicals, which could oxidize o-phenylene-diamine to 2,3-diaminophenazine, accompanied by a fluorescence emission at 600 nm and a UV–vis absorption peak at 450 nm. At the same time, the fluorescence of Fe-MOF@Fe3O4NPs at 460 nmcould be quenched by 2,3-diaminophenazine via Förster resonance energy transfer. Therefore, the fluorescence intensity ratio (I600/I460) and UV–vis absorption intensities are employed to construct the dual-readout biosensor for the determination of UA. The linear range was 0.2–200 μM and the limit of detection for the fluorometric and colorimetric detection were 0.03 μM and 0.18 μM, respectively. Finally, the biosensor was employed to determine UA in urine samples, and satisfactory results were obtained.