Superoxide anion turns on the fluorescence of carbon dots-ferric complex for sensing

Superoxide anion (O2•−) is one of the most important reactive oxygen species and its sensitive detection is of great significance and challenging in the field of environmental and hazardous chemicals monitoring. Herein, we report an off-on fluorescent probe based on ferric functionalized carbon dots (CDs) which were synthesized using p-phenylenediamine as starting material for the detection of O2•−. The initial green fluorescence of CDs was greatly quenched by Fe3+ based on energy transfer effect on account of the selective formation of ferric complex on the surface of CDs, but not by other metal ions. Interestingly, the fluorescence of CDs could be readily and selectively recovered upon the addition of O2•−, which can be used for the senstivie detection of superoxide. This type of off-on probe exhibited good photostability and high selectivity toward O2•− among other interfering substances including metal ions, reactive oxygen species as well as reductant substances. The probe showed good linearity with the concentration of O2•−, and the limit of detection for O2•− was estimated down to 25 pM in aqueous solution. Moreover, a paper based sensor for O2•− was fabricated with a visual detection limit as low as 4.4 nM, demonstrating a promising application for practical detection of superoxide anion.