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 Hg2+ was designed based on g-C3N4 nanosheets. It was found that in the absence of Hg2+, the addition of 6-TG to g-C3N4 nanosheets solution resulted in the fluorescence quenching of g-C3N4 nanosheets (turn off). However, in the presence of Hg2+, the quenched fluorescence of g-C3N4 nanosheets was recovered ( turn on), because the high affinity of Hg2+ and 6-TG resulted in the loss of molecular interactions between 6-TG and g-C3N4 nanosheets. The quantitative detection of 6-TG was obtained via the fluorescence quenching of g-C3N4 nanosheets with a detection limit of 65 nM. Meantime, the 6-TG-g-C3N4 nanosheets system could be used as a fluorescent "turn on" sensor for Hg2+. The detection limit for Hg2+ was 37 nM. The proposed method showed high selectivity for the detection of 6-TG and Hg2+. In addition, it was successfully applied to detect Hg2+ in real water samples. (C) 2017 Elsevier B.V. All rights reserved.