Terbium(III)/gold nanocluster conjugates: The development of a novel ratiometric fluorescent probe for mercury(II) and a paper-based visual sensor

In this work, a novel ratiometric fluorescent probe was developed for rapid, highly accurate, sensitive and selective detection of mercury(II) (Hg²⁺) based on terbium(III)/gold nanocluster conjugates (Tb³⁺/BSA-AuNCs), in which bovine serum albumin capped gold nanoclusters (BSA-AuNCs) acted as the signal indicator and terbium(III) (Tb³⁺) was used as the build-in reference. Our proposed ratiometric fluorescent probe exhibited unique specificity toward Hg²⁺ against other common environmentally and biologically important metal ions, and had high accuracy and sensitivity with a low detection limit of 1 nM. In addition, our proposed probe was effectively employed to detect Hg²⁺ in the biological samples from the artificial Hg²⁺-infected rats. More significantly, an appealing paper-based visual sensor for Hg²⁺ was designed by using filter paper embedded with Tb³⁺/BSA-AuNC conjugates, and we have further demonstrated its feasibility for facile fluorescent sensing of Hg²⁺ in a visual format, in which only a handheld UV lamp is used. In the presence of Hg²⁺, the paper-based visual sensor, illuminated by a handheld UV lamp, would undergo a distinct fluorescence color change from red to green, which can be readily observed with naked eyes even in trace Hg²⁺ concentrations. The Tb³⁺/BSA-AuNC-derived paper-based visual sensor is cost-effective, portable, disposable and easy-to-use. This work unveiled a facile approach for accurate, sensitive and selective measuring of Hg²⁺ with self-calibration.