Fast and efficient "on-off-on" fluorescent sensor from N-doped carbon dots for detection of mercury and iodine ions in environmental water.

A kind of nitrogen doped carbon dots (N-CDs) was facilely fabricated from polyethyleneimine and anhydrous citric acid, and which was adopted to develop a neoteric "on-off" and "off-on" fluorescent sensor for rapidly and efficiently sensing Hg and I. The fluorescence of N-CDs was notably quenched (off) in the existence of Hg derived from strong interaction and the electron transfer between N-CDs and Hg, while the quenched fluorescence of the N-CDs and Hg system was strikingly regained by addition of I (on) resulted from the separation of N-CDs and Hg due to the higher binding preference between Hg and I. Under optimal conditions, the linear detection ranges were 0.01-20 μM for Hg and 0.025-7 μM for I, respectively. Meanwhile, the detection limits could be down to 3.3 nM for Hg and 8.5 nM for I, respectively. Satisfied recoveries had also been gained for measuring Hg and I in practical water samples. The constructed "on-off-on" fluorescent sensor provided a simple, rapid, robust and reliable platform for detecting Hg and I in environmental applications.