Ions-induced two-photon fluorescence dual-switching for reversible and simultaneous sensing of Cu2+ and Hg2+ based on dual-emitting carbon dot/carbon dot conjugates

Dual-emitting carbon dot/carbon dot (CD1/CD2) conjugates were prepared from combination of poly(ethylenimine)-functionalized CD1 with carboxyl-modified CD2. When excited with a laser of 800 nm, the CD1/CD2 conjugates showed two-photon fluorescence (TPF) emissions peaked at 465 nm (CD1) and 600 nm (CD2). The TPF peak intensities at 465 nm decreased near linearly after the addition of Cu2+ (0-3.2 mu M) due to inner filter effect, with a linear coefficient (R-2) of 0.9933 and a limit of detection (LOD) of 0.05 mu M. The TPF peak intensities at 600nm were almost linearly reduced by Hg2+ (0-8.5 mu M, R-2=0.9970, LOD =0.08 mu M) originating from the nonradiative recombination of excitons through electron transfer. Notably, the TPF peak intensities at 465 and 600nm could be near wholly recovered by respective addition of S2- and I-. Thus, the CD1/CD2 conjugates were developed as a novel TPF dual switching sensor for reversible and simultaneous sensing of Cu2+ and Hg2+. This novel sensor enabled highly selective and sensitive detection of Cu2+ and Hg2+ over other metal ions and biological molecules in real water samples and biological fluids, with high detection recoveries. (C) 2017 Elsevier B.V. All rights reserved.