Carbon dots prepared from citric acid and urea by microwave-assisted irradiation as a turn-on fluorescent probe for allantoin determination

Abstract

This research aimed to develop a simple and selective method for allantoin determination to overcome the limitations of existing colorimetric and alternative methods. A fluorometric detection-based method was developed and used carbon dots (CDs) synthesized from citric acid (CA) and urea as a carbon source. CDs selective for allantoin were synthesized from a mixture of 0.5 g CA and 2.5 g urea exposed to 800 watts of microwave-assisted pyrolysis for 9 minutes. A fluorescence emission spectrum of 438.0 nm was obtained when CDs were excited with a 370.0 nm wavelength. Several detection parameters were investigated including pH, sample: reagent ratio, and reaction time. Under optimum conditions, the proposed method resulted in a detection limit of 0.30 mg L⁻¹, a quantitation limit of 0.98 mg L⁻¹, and a detection range of 1.0–100.0 mg L⁻¹. In summary, the application of this method for measuring the allantoin content of skincare products was demonstrated and accurate and selective detection of allantoin was achieved. Furthermore, a mechanism of fluorescent enhancement of CDs by allantoin was also proposed in this research.