Development of red fluorescent carbon dots for optical and smartphone imaging dual-mode determination of metabisulfite and pH monitoring

A new type of red photoluminescent carbon dots (R-CDs) with high quantum yield of 46.9% was favorably developed by introducing the luminophore of resazurin into the framework. The obtained R-CDs exhibit excitation-independent behavior, advantageous dispersion and outstanding optical performance. It is worth noting that the proposed R-CDs demonstrate a particular response to S 2 O 5 2- over other competitive species accompanied by a naked-eye color change from red to orange. Fluorescence quenching of R-CDs is determined to be S 2 O 5 2- concentrations dependence with ultra-fast response time and low detection limit. The as-developed R-CDs is further employed in building a smartphone imaging colorimetry platform for portable recognition of S 2 O 5 2- in real samples with considerable accuracy. Furthermore, the specially   prepared R-CDs also display a significant fluorescence enhancement behavior with the increase of pH in the linear range of 5.4–6.2 with a pKa of 5.86. These findings may offer a distinctive strategy for the development of long-wavelength emission carbon dots and help to expand their application in food safety inspection.