Enhancement of Ultraweak Chemiluminescence from Reaction of Hydrogen Peroxide and Bisulfite by Water-Soluble Carbon Nanodots

In this work, carbon nanodots were synthesized through a novel solvothermal route, and the effects of carbon nanodots on the ultraweak chemiluminescence (CL) reaction of hydrogen peroxide (H2O2) and sodium bisulfite (NaHSO3) were explored for the first time. It was found that the CL emission intensity of H2O2–HSO3– was significantly enhanced by carbon nanodots: about 60-fold increase in the CL intensity was obtained. The enhanced CL was induced by the excited-state carbon nanodots (CD*), which could be produced from the electron-transfer annihilation of positively charged carbon nanodots (CD•+) and negatively charged carbon nanodots (CD•–). Radical scavengers such as nitro blue tetrazolium chloride (NBT), sodium azide, thiourea, 5,5-dimethyl-1-pyrroline N-oxide, and ascorbic acid were used to study the intermediate species. The intermediate radicals generated during the reaction of H2O2 and NaHSO3, such as hydroxide radical (•OH), sulfate anionic radical (SO4•–), superoxide anionic radical (•O2–), and sulfur trioxide anionic radical (•SO3–), were key species for producing CD•+ and CD•–. The CL enhancement mechanism was proposed based on the results of the CL emission spectra, fluorescence spectra, and electron spin resonance (ESR) spectra. The CL properties of carbon nanodots will provide a new route to study the novel materials and broaden the use of them in many fields, such as chemistry, biology, microbiology, and biochemistry.