One-pot synthesis of N-doped carbon dots from microwave-irradiated egg white: application to raspberry ketone assay by photo-induced charge transfer fluorescence sensing

In this article, we designed one-step economic eco-harmonious microwave-assisted procedure to prepare nitrogen-doped carbon dots. We selected egg white as a cheap glycoprotein-based carbon source without the assistance of any chemicals. The synthetic process requires only 3 min during which carbonization and nitrogen doping are realized at the same time. The fabricated carbon dots were characterized for particle size, structure and photoluminescence behaviour. The nanodots were amorphous carbon-rich naturally nitrogen-doped particles with plentiful attached hydrophilic functional groups. They had average particle size 2.98 +/- 1.57 nm, emitted strong blue fluorescence and showed excitation-dependant emission behaviour. What is more, the practical use of this system for raspberry ketone determination in commercially available weight loss dietary supplement product is demonstrated successfully. In ethylene glycol medium, the addition of raspberry ketone enhances the emission intensity of the synthesized carbon dots. The effect of reaction time and solvent was investigated. After optimization, the intensity enhancement was linear to the amount of raspberry ketone added to the assay solution in the concentration range of 100-1000 ng/ml, with detection and quantitation limits of 15.10 and 45.45 ng/ml, respectively. The method was validated in accordance to International Conference on Harmonization (ICH) guidelines and further applied to raspberry ketone capsules showing excellent results.