A ratiometric fluorescence sensor for Be2+ based on Beryllon II/layered double hydroxide ultrathin films

A ratiometric fluorescence sensor for Be(2+) has been fabricated via alternate assembly of 2-(3,6-disulfo-8-hydroxynaphthylazo)-1,8-dihydroxynaphthalene-3,6-disulfonate (Beryllon II) and MgAl-LDH nanosheets on quartz substrates using the layer-by-layer (LBL) deposition technique. UV-vis absorption and the fluorescence emission spectroscopy indicate a stepwise and regular growth of the Beryllon II/LDH UTFs upon increasing deposition cycle. The film of Beryllon II/LDH possesses a periodic layered structure perpendicular to the substrate revealed by X-ray diffraction and scanning electron microscopy. Atomic force microscopy images show that the film surface is continuous and uniform. The Beryllon II/LDH UTFs display ratiometric fluorescence response for Be(2+) with a linear response range in 1.0×10(-7)-1.9×10(-6) mol L(-1) and a detection limit of 4.2×10(-9) mol L(-1). Furthermore, the ratiometric sensor exhibits good repeatability, high stability (thermal, storage and mechanical) as well as excellent selectivity toward Be(2+). XPS and Raman measurements demonstrate that the specific response of the sensor is attributed to the coordination between Be(2+) and Beryllon II in the UTF. The Beryllon II/LDH UTFs in this work can be potentially used as a chemosensor for the detection of Be(2+) in the environmental and biomedical field.