Fabrication of pyrenetetrasulfonate/layered double hydroxide ultrathin films and their application in fluorescence chemosensors

This paper reports the fabrication of fluorescence indicator/layered double hydroxide (LDH) ultrathin films (UTFs) by alternate assembly of 1,3,6,8-pyrenetetrasulfonat acid tetrasodium salt (PTS) and Zn-Al LDH nanosheets on quartz substrates using the layer-by-layer (LBL) deposition technique, and demonstrates their application as a fluorescence chemosensor for Cu2+. UV-vis absorption spectroscopy indicates a stepwise and regular growth of the PTS/LDH UTFs upon increasing deposition cycles. X-Ray diffraction, atomic force microscopy and scanning electron microscopy demonstrate that the UTFs possess a periodical layered structure perpendicular to the substrates with a thickness of 1.93-1.98 nm per bilayer. Furthermore, the fluorescence chemosensor with film thickness of 48 nm (24 bilayers) exhibits a broad linear response range for Cu2+ solution (0.6-50 mu M), good repeatability (RSD less than 5% in 20 consecutive measurements), high photostability and storage stability (similar to 93.2% of its initial fluorescence intensity remains after one month) as well as excellent selectivity. In addition, the study on mechanism of measurement-regeneration cycle of the fluorescence chemosensor shows that Cu2+ enters/departs from the PTS/LDH UTF with reversible change in chemical composition, surface morphology and fluorescence anisotropy. Therefore, this work provides new opportunities for fabrication and application of chromophore/LDH UTFs which can be used as fluorescence chemosensors.