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

Abstract

A biomolecule-free photoelectrochemical(PEC) probe(denoted as Ru-1) was designed, synthesized and coupled with TiO₂ nanoparticles(NPs) for the highly sensitive and selective PEC detection of Hg²⁺, 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 TiO₂ nanoparticles. Under irradiation, Ru-1 shows strong affinity to TiO₂ and good photophysical properties of strong visible light absorption, slow electron-hole(e-h⁺) recombination, and fast photoelectron injection to TiO₂ nanoparticles via the π-bridge of 4-(2,2′-bipyridin)-4-yl-thiophene moiety. However, the specific coordination of Hg²⁺ 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 TiO₂ nanoparticles and the Ru-1 complex led to a selective PEC sensing strategy for Hg²⁺ 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.

Keywords

Photoelectrochemical probe / Ru(II) bipyridyl complex / Hg²⁺ detection / Nanocomposites

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