Green synthesis of surface-group-tunable red emissive carbon dots and their applications for Fe3+ and pyrophosphate detection

Red emission carbon dots (R-CDs) have great potential applications in optical and electronic devices, but few studies have focused on synthesizing R-CDs with tunable functional groups. In this study, p-phenylenediamine and hydroquinone were selected as precursors with specific hybridized carbon structures for synthesizing R-CDs with tunable functional groups by hydrothermal method. The proportion of precursors in the reaction system were adjusted to successfully synthesize R-CDs with various contents of oxygen and amino groups. Experimental results showed that the fluorescence of the R-CDs was effectively quenched by Fe3+ through the formation of R-CDs/Fe3+ complex. The fluorescence quenching ability of Fe3+ for R-CDs with different N/O ratios were also investigated. The fluorescence quenching efficiency of Fe3+ for R-CDs increased with the oxygen content of the R-CDs. By selecting R-CDs with oxygen-containing surface groups (R-O-CDs) as nanoprobe, an "on–off-on" fluorescent sensor has been developed for dual-detection of Fe3+ and pyrophosphate (PPi). A detection limit of 0.527 μM for Fe3+ and 0.24 μM for PPi were achieved. The as-developed R-O-CDs/Fe3+ nanoprobe was also successfully used to detect Fe3+ and PPi in real samples. Furthermore, an IMPLICATION logic gate was designed.