A novel “on-off-on” fluorescent sensor for 6-thioguanine and Hg2+ based on g-C3N4 nanosheets

A facile fluorescence “on-off-on” approach for sensing 6-Thioguanine (6-TG) and Hg 2+ was designed based on g-C 3 N 4 nanosheets. It was found that in the absence of Hg 2+ , the addition of 6-TG to g-C 3 N 4 nanosheets solution resulted in the fluorescence quenching of g-C 3 N 4 nanosheets (turn off). However, in the presence of Hg 2+ , the quenched fluorescence of g-C 3 N 4 nanosheets was recovered (turn on), because the high affinity of Hg 2+ and 6-TG resulted in the loss of molecular interactions between 6-TG and g-C 3 N 4 nanosheets. The quantitative detection of 6-TG was obtained via the fluorescence quenching of g-C 3 N 4 nanosheets with a detection limit of 65   nM. Meantime, the 6-TG-g-C 3 N 4 nanosheets system could be used as a fluorescent “turn on” sensor for Hg 2+ . The detection limit for Hg 2+ was 37   nM. The proposed method showed high selectivity for the detection of 6-TG and Hg 2+ . In addition, it was successfully applied to detect Hg 2+ in real water samples.