Collaboration strategy-based fluorescence sensor for efficient detecting Al3+ and Hg2+

Abstract

Developing economical sensors and methods to efficiently detect metal ions like Hg2+ and Al3+ is still significant. Hg2+ is notorious for its strong neurotoxicity, while, Al3+ is a risk factor for Alzheimer's disease (AD) in humans. To improve the selectivity and sensitivity of Hg2+ and Al3+, in this research, the collaboration effect has been successfully applied to the design of chemosensors to enhance the detecting ability of the sensor. According to this strategy, quinoline-8-yloxy acetohydrazone and hydroxy‑naphthyl groups have been rationally introduced into one sensor molecule, based on the collaboration of these functional groups, the obtained chemosensor (QN) shows efficient “off-on-off” response for Al3+ and Hg2+. QN can ultra-sensitively detect Al3+ with fluorescent “turn-on” response, the limit of detection (LOD) of QN towards Al3+ is 4.34×10-9 M. Interestingly, after coordination with Al3+, the obtained complex QN-Al can detect Hg2+ sensitively, the LOD of QN towards Hg2+ is 5.70×10-8 M. The Al3+ and Hg2+ sensing process shows nice selectivity, and the detecting procedure cannot be interfered with by other common metal cations. The possible recognition mechanism of QN for Al3+ and Hg2+ was carefully investigated via experimental and theoretical studies. According to these studies, the selective and sensitive sensing of Al3+ and Hg2+ is based on the collaborative coordination of quinoline acetohydrazone and hydroxy‑naphthyl groups. The relay sensing procedure of Al3+ and Hg2+ is attributed to the competitive coordination of these two cations. The fluorescent response of Al3+ might be attributed to excited state intra-molecular proton transfer (ESIPT) and photoinduced electron transfer (PET), meanwhile, the Hg2+ response mechanism may be ascribed to the chelation enhancement quenching effect (CHEQ). Moreover, the detection of real samples is conducted to determine the aluminum content in food to prove that chemosensor QN is suitable for the detection of Al3+ from food samples, and the QN-based test kits for convenient detection of Al3+ and Hg2+ were also successfully prepared.