Colorimetric and fluorometric determination of uric acid based on the use of nitrogen-doped carbon quantum dots and...

A dual-read detection system is described for non-enzymatic and non-aggregation based analysis of uric acid (UA). Silver triangular nanoprisms (AgTNPs) were used as colorimetric probes, while the reduction in the fluorescence of nitrogen-doped carbon quantum dots (N-CQDs) served as the fluorometric readout. The absorption band of the AgTNPs overlaps the emission band of N-CQDs (with a peak at 440 nm). Therefore, fluorescence is reduced owing to an inner filter effect. The AgTNPs are etched if exposed to H₂O₂, and round nanodiscs are formed. In the presence of UA, etching of the AgTNPs is suppressed because the facets of the AgTNPs are coated with UA. The absorbance, best measured at 683 nm, increases with the concentration of the pre-added UA. The colorimetric assay works in the 0.1-45 μM UA concentration range, and the fluorometric assay between 1 and 42 μM of UA. The respective detection limits are 50 and 200 nM, respectively. The probe can be used for direct visualization of UA. The method was successfully applied to the determination of UA in urine samples. Graphical abstract The fluorescence of nitrogen-doped carbon quantum dots (N-CQDs) is quenched by AgTNPs (silver triangular nanoprisms). As the AgTNPs are etched by H₂O₂, fluorescence recovers in the system after H₂O₂ is added, and also undergoes a color change. Uric acid (UA) protects the AgTNPs from etching because the facets of the AgTNPs are coated with UA. The fluorescence of N-CQDs decreases. Thus, a dual-read probe is developed for determination of UA.