"Turn-on" fluorescent sensor for oleanolic acid based on o-phenyl-bridged bis-tetraphenylimidazole.

Fluorescent sensors had been extensively applied on sensing various biomolecules effectively, but no fluorescent sensor for oleanolic acid was presented up to now. In this work, the first fluorescent sensor for oleanolic acid was designed and synthesized based on o-phenyl-bridged bis-tetraphenylimidazole (PTPI). PTPI was prepared by bridging two tetraphenylimidazole units and o-phenylenediamine via Schiff-base condensation in yield of 86%. PTPI showed high sensing selectivity for oleanolic acid among 26 biomolecules and ions. The blue fluorescence at 482 nm was enhanced by 4.5 times after sensing oleanolic acid in aqueous media. The fluorescence sensing ability of PTPI for oleanolic acid maintained stable in pH = 5-9. The detecting limitation was as low as 0.032 µM. The detecting mechanism was clarified as 1:1 binding stoichiometry by fluorescence Job's plot, mass spectrometry, 1H nuclear magnetic resonance and fourier transform infrared spectroscopy. The detecting ability of PTPI for oleanolic acid was successfully used for paper test and real samples of grapes and Kuding tea with recoveries in the range of 96.0%-106.0%, indicating the good application potential for on-site detecting oleanolic acid in real samples of fruits and food.

An effective fluorescent sensor for ClO- in aqueous media based on thiophene-cyanostilbene Schiff-base.

Although some reports on sensing ClO- had been presented, the ClO- sensor with high selectivity and sensitivity in aqueous media was still expected. Herein, an effective fluorescent sensor for ClO- in aqueous media was designed and synthesized by simple procedure based on cyanostilbene derivative (TCS). TCS exhibited strong fluorescence in aqueous media, which could be selectively quenched by ClO- among various species. The detection limit was as low as 3.2 × 10-8 M. The sensing mechanism of the oxidation of sulfur in thiophene unit was confirmed by the FT-IR spectrum, fluorescence Job's plot, 1H NMR spectrum and MS spectrum. This sensor was successfully applied on detecting ClO- in real sample and living-cell imaging, suggesting its potential application for sensing ClO- in both vitro assay and vivo environment.