Redox Induced Fluorescence On–Off Switching Based on Nitrogen Enriched Graphene Quantum Dots for Formaldehyde Detection and Bioimaging

Tunable optical and fluorescent properties of graphene quantum dots (GQDs) by heteroatom doping and surface functionalization provide tremendous advantages for practical applications. One of these notable issues is the construction of stimuli-responsive GQDs which can be used as smart green nonmetal materials in the field of sensor and biotechnology. In this work, N-doped graphene quantum dots (NGQDs) encapsulated by organic species were obtained through hydrothermal method, of which the quantum yield achieved 22.9%, much higher than that of bare NGQDs (1%). Interestingly, it was found that the functionalized NGQDs exhibited a color oscillation in open air and its fluorescence emission can be reversibly switched “on–off” via redox reactions. Meanwhile, the PL emission would be transformed from excitation-independent to excitation-dependent through modifying the surface states of NGQDs. The origin of PL is then studied, emphatically distinguishing the role of different C–N configurations and surface functi...