Enzyme-triggered inner filter effect on the fluorescence of gold nanoclusters for ratiometric detection of mercury(II) ions via a dual-signal responsive logic

Abstract

Herein a novel ratiometric fluorescence strategy based on enzyme-triggered inner filter effect (IFE) was described to sensitively detect mercury ions (Hg2+) for the first time by using l-proline-protected gold nanoclusters (AuNCs) and 2,3-diaminophenazine (DAP) as IFE fluorophore and absorber. The IFE was derived from the overlap between the emission band of AuNCs and absorption band of DAP and confirmed by fluorescence lifetime decay tests. Based on IFE principle and ratiometric strategy, laccase (LACC)-catalyzed o-phenylenediamine (OPD) oxidation was utilized to produce DAP, whereas the activity of LACC can be monitored by Hg2+. In this way, the existence of Hg2+ could depress the emission of DAP while restore that of AuNCs, achieving the dual signal response of Hg2+, and their emission intensity ratio was dependent on the concentration of Hg2+. Under the optimized detection conditions, the linear range for Hg2+ determination was from 0.8 to 35 μM with a detection limit of 0.27 μM. Besides, it was successfully applied to the analysis of tap water and Yangtze river water. Our strategy can be used to assess the activity of LACC, and it also provided a novel way to construct other enzyme-based biosensors.