A ratiometric fluorescence chemosenser for Hg2+ based on Primuline and layered double hydroxide ultrafilms

The fabrication of fluorescence indicator/layered double hydroxide (LDH) ultrathin films (UTFs) by alternate assembly of Primuline and Mg-Al LDH nanosheets using the layer-by-layer (LBL) deposition technique has been reported, and their application as a raitometric fluorescence chemosensor for Hg2+ is demonstrated. The Primuline/LDH UTFs show a stepwise and regular growth of upon increasing deposition cycles proved by UV–vis absorption and fluorescence emission spectroscopy, and a periodical layered structure perpendicular to the substrates with a thickness of 2.41–2.48 nm per bilayer observed by X-ray diffraction and scanning electron microscopy. Furthermore, a linear correlation between the fluorescence intensity ratio (I422/I377) of the UTF and the concentration of Hg2+ is obtained (I422/I377 = 2.63–0.01c nM, r2 = 0.99), with a detection limit of 0.13 pM. The results have also exhibited that the ratiometric fluorescence chemosensor possess a good repeatability, high stability (light, storage and mechanics) as well as excellent selectivity. In addition, the mechanism of measurement–regeneration cycle for the ratiometric fluorescence chemosensor indicates Hg2+ enters/departs from the Primuline/LDH UTF giving rise to reversible change in chemical composition, surface morphology and fluorescence anisotropy of the UTF. Therefore, this work provides new opportunities for fabrication and application of chromophore/LDH UTFs as ratiometric fluorescence chemosensors.