A ''naked-eye'' colorimetric and ratiometric fluorescence probe for uric acid based on Ti3C2 MXene quantum dots.

In this work, we developed a ''naked-eye'' colorimetric and ratiometric fluorescence probe for a very important biomarker of uric acid (UA). The method was based on the oxidation of UA by uricase to allantoin and hydrogen peroxide, and then o-Phenylenediamine (OPD) was oxidized to the yellow-colored 2,3-diaminophenazine (oxOPD) in the presence of horseradish peroxidase (HRP) and hydrogen peroxide. The fluorescence emission of glutathione functionalized Ti3C2 MQDs (GSH-Ti3C2 MQDs) centered at 430 nm overlaps with the UV absorption of oxOPD at 425 nm to a large extent, which facilitates fluorescence resonance energy transfer (FRET) between GSH-Ti3C2 MQDs and oxOPD. With the increase of the UA concentration, the emission at 430 nm of GSH-Ti3C2 MQDs is progressively quenched and the emission at 568 nm of oxOPD was gradually increased. Moreover, the probe we designed is easier to distinguish with color change by naked eye for the detection of UA. This is the first report about the determination of UA by a ''naked-eye'' colorimetric and ratiometric fluorescence method combining GSH-Ti3C2 MQDs and uricase/HRP enzymes. This work enables assays to perform fluorescence and visual detection of biomarker in biological fluids based on Ti3C2 MQDs.