Optical sensor for lithocholic acid based on multilayered assemblies from polyelectrolyte and cyclodextrin

Multilayered thin films were prepared by a layer-by-layer (LbL) deposition of sulfonated β-cyclodextrin (s-β-CD) and cationic poly(allylamine) hydrochloride (PAH) on the surface of a quartz slide. A self-assembled fluorescent host, s-β-CD/neutral red was formed by the inclusion interaction of neutral red (NR) with the s-β-CD immobilized on the multilayered films. An optical sensor for lithocholic acid (LA), based on the fluorescence quenching of s-β-CD/NR complex immobilized on the multilayered films, has been developed, in which NR served as a sensitive fluorescence indicator probe. The decrease of fluorescence intensity of s-β-CD/NR complex in the presence of LA was attributed to the formation of an inclusion complex between s-β-CD and LA, which has been utilized as the basis of the fabrication of a LA-sensitive fluorescence sensor. The response mechanism of sensor has been discussed in detail. The analytical performance characteristics of the proposed LA-sensitive sensor were investigated. The sensor can be applied to the quantification of LA with a linear range covering from 2 uM to 60 uM and a detection limit of 1 uM. The sensor exhibits excellent reproducibility, reversibility and selectivity.