Label-Free Fluorescence Sensing of Lead(II) Ions and Sulfide Ions Based on Luminescent Molybdenum Disulfide Nanosheets

Fluorescent molybdenum disulfide (MoS2) nanosheets were synthesized hydrothermally by employing sodium molybdate and thiourea as the starting materials. Lead(II) ion was introduced as a chemical dopant into the fluorescent nanosheets for the first time, and it was found that the fluorescence of the doped MoS2 nanosheets showed a considerable enhancement compared with that of initial MoS2 nanosheets, implying that lead(II)-doping into the MoS2 nanosheets could result in an increase in the fluorescence quantum yield. In parallel, we exploited the lead(II)-induced fluorescence enhancement of MoS2 nanosheets to design a green and facile fluorescent turn on nanosensor for lead(II) detection. Moreover, we found that the fluorescent intensity of the doped MoS2 nanosheets was drastically quenched by the successive addition of sulfide ions. Hence, the turn off process was used to fabricate a green fluorescence quenching sensor for detection of sulfide ions. Finally, we elucidated the origin of the lead(II)-induced fluorescence enhancement and sulfide-induced fluorescence reduction by using various analytical techniques like scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and UV-vis spectroscopy. The work not only opens a door for the further development of new approaches for the preparation of various fluorescent layered transition metal dichalcogenides with high quantum yields but also provides a versatile and sustainable sensing platform for ion detection.