Phenanthridine based rapid "turn-on" fluorescent sensor for selective detection of Th⁴⁺ ion and its real-time...

A new and highly sensitive and selective phenanthridine based sensor, 9-(7,8,13,14-tetrahydrodibenzo[a,i]phenanthridin-5-yl)benzo[h]quinolin-10-ol (PHBQ), was developed for the fluorescent ''turn-on'' detection of Th⁴⁺ ion in acetonitrile: water (8:2) medium. The fluorescence intensity of PHBQ diminished in the region of pH 1 to 3 and could be recovered by adjusting the pH to above 4. The sensor PHBQ showed distinct spectral changes in response to Th⁴⁺ ion over other competitive metal ions. The fluorescence displayed good linearity with the Th⁴⁺ concentration in the equivalence of 0-0.5 equivalents. The detection limit was calculated to be as low as 99 nM, which was less than that of previously reported sensors. The recognizing mechanism of PHBQ towards Th⁴⁺ was investigated in detail using HR-MS, NMR, and IR spectroscopy. The economically viable Whatman filter paper was fabricated with PHBQ to develop a paper-based fluorescence kit to detect the Th⁴⁺ in an aqueous medium efficiently. Furthermore, the application of sensor ligand in fluorescence imaging was studied in E-coli cells due to its minimal cytotoxicity and good optical properties. The obtained data suggest that the ligand PHBQ can be used as a fluorescent sensor for tracking Th⁴⁺ in multiple applications.