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

A ratiometric fluorescence sensor for Be2+ 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 Be2+ with a linear response range in 1.0 x 10(-7)-1.9 x 10(-6) mol L-1 and a detection limit of 4.2 x 10(-9) mol L-1. Furthermore, the ratiometric sensor exhibits good repeatability, high stability (thermal, storage and mechanical) as well as excellent selectivity toward Be2+. XPS and Raman measurements demonstrate that the specific response of the sensor is attributed to the coordination between Be2+ 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 Be2+ in the environmental and biomedical field. (C) 2012 Elsevier B.V. All rights reserved.