Strong Enhancement of the Chemiluminescence of Hydrogen Sulfite-Oxidant Systems in the Presence of N,S-Doped Graphene Quantum Dots, and Its Application to the Determination of Folic Acid in Spinach and Kiwifruit Samples

Abstract

The oxidation of bisulfite by classical oxidants such as hypochlorite, hydrogen peroxide, and permanganate is accompanied by weak chemiluminescence (CL). It is reported here that the CL is strongly enhanced in the presence of nitrogen/sulfur co-doped graphene quantum dots (N,S-GQD), nitrogen-doped graphene quantum dots (N-GQD), or graphene quantum dots (GQD). The weak CL of the NaHSO3-NaClO system and the NaHSO3-H2O2 system in the neutral medium and of the NaHSO3-KMnO4 system in acidic solution is more than 1000-fold enhanced in the presence of N,S-GQD, about sixfold in the presence of N-GQD, and twofold in the presence of GQD. Fluorescence spectra and CL spectra indicate that the N,S-GQD-sensitized enhancement originates from energy transfer and electron transfer annihilation effects on the CL system. It is also reported that folic acid (FA; vitamin B9) causes a notable diminution in the N,S-GQD-NaHSO3-NaClO system. Based on this finding, a sensitive CL method is developed for the determination of FA in food samples. The method works in the 0.5 to 70.0 μmol/L FA concentration range and the limit of detection is 78.0 nmol/L.