Ru(II) Bipyridyl Complex and TiO2 Nanocomposite Based Biomolecule-free Photoelectrochemical Sensor for Highly Selective Determination of Ultra-trace Hg2+ in Aqueous Systems

A biomolecule-free photoelectrochemical(PEC) probe(denoted as Ru-1) was designed, synthesized and coupled with TiO 2 nanoparticles(NPs) for the highly sensitive and selective PEC detection of Hg 2+ , a model analyte with hypertoxicity to both human health and ecosystem. The probe Ru-1 was designed with Ru(II) bipyridyl complex as the chromophore, thiocyanate ligand as the recognition unit, and carboxylate group as the linkage site to connect Ru-1 to TiO 2 nanoparticles. Under irradiation, Ru-1 shows strong affinity to TiO 2 and good photophysical properties of strong visible light absorption, slow electron-hole(e-h + ) recombination, and fast photoelectron injection to TiO 2 nanoparticles via the π -bridge of 4-(2,2′-bipyridin)-4-yl-thiophene moiety. However, the specific coordination of Hg 2+ with Ru-1 via the thiol moiety in the thiocyanate enlarges the band gap of the complex and reduces the photocurrent significantly. The synergistic interaction between TiO 2 nanoparticles and the Ru-1 complex led to a selective PEC sensing strategy for Hg 2+ detection. Detectable linear ranges from 10 −12 g/mL to 10 −7 g/mL and from 10 −7 g/mL to 10 −3 g/mL were obtained without the interference from possibly co-existed metal ions. The good analytical performances indicate the chemical probe based biomolecule-free PEC platform may offer a new route for the detection of biologically and environmentally important small molecules.