Preparation of nitrogen-doped carbon quantum dots (NCQDs) and application for non-enzymatic detection of glucose

A hydrothermal method was used for the preparation four kinds of nitrogen-doped carbon quantum dots (NCQDs) by using citric acid as the carbon source and ethylenediamine (EDA), urea (U), melamine (MA) and ammonia solution (AS) as the nitrogen source, respectively. The NCQDs were characterized by TEM, FT-IR and XPS, and the optical properties were studied by UV–vis and fluorescence spectra. It is found that the NCQDs(AS) from ammonia solution (AS) as nitrogen source are uniform size spherical nanoparticles and have prominent optical properties. Influencing factors including solution acidity, interfering substances, Ag+ ions concentration and glucose concentration on the detection of glucose are taken into account. In the presence of Ag+ ions, the fluorescence of NCQDs(AS) in aqueous solution was severely quenched due to the surface energy transfer from NCQDs(AS) to Ag+ ions. In weakly alkaline condition, the detected glucose is oxidized to gluconic acid and Ag+ ions are reduced to Ag in aqueous solution at 60 °C. Thereby, the abscission of Ag+ ions from the surface of NCQDs(AS) results in the fluorescence recovery of NCQDs(AS). The glucose can be analyzed quantitatively by NCQDs(AS) in the presence of Ag+ ions with a wide linear region (0.1 μM–1000 μM) and low limit of detection (LOD) (0.375 μM). Also, the selectivity and anti-interference ability experiment of the NCQDs(AS) in the presence of Ag+ ions for glucose detection were discussed. In addition, cytotoxicity and cell imaging experiments of NCQDs(AS) were researched. Overall, the prepared NCQDs(AS) are expected to be widely used in different biological research fields.