Berberrubine, A plant alkaloid derivative for superb-selective colorimetric quantification of aqueous mercury (II) in real samples and in aquatic plants

Abstract

A new colorimetric sensor, berberrubine (BER-OH), was designed and synthesized based on berberine for superb selective sensing of Hg²⁺ in aqueous medium, addressing limitation of existing probes. The sensor exhibited high selectivity and sensitivity to Hg²⁺ in aqueous solution (CP buffer solution, pH 7.2) over other common metal ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Fe³⁺, Co²⁺, Fe²⁺, Cu²⁺, Al³⁺, Ba²⁺, Pb²⁺, Cd²⁺, Zn²⁺ and Sr²⁺). Upon addition of Hg²⁺, a distinct color change from reddish-orange to yellowish was observed due to complexation between BER-OH and Hg²⁺ in 1:1 stoichiometry. The binding of Hg²⁺ with BER-OH resulted in increasing absorbance at 347 and 430 nm with concurrent decreasing absorbance of the sensor at 377 and 487 nm. The limit of detection (LOD) values were calculated at absorption bands 347, 377, 487 nm and also using absorbance ratio, A₃₄₇/A₃₇₇. The sensor quantitatively analysed Hg²⁺, and the lowest LOD was found to be 46 nM with the range of 0.1 to 1.0 μM. The analytical tools confirmed that the proposed sensing mechanism involves the coordinate bond between lone pair of oxygen atoms of BER-OH and Hg²⁺. The sensor has great utility to detect trace Hg²⁺ in real samples like tap water, river water, and drinking water. A noteworthy application of the sensor is to quantify Hg²⁺ in aquatic plants which can absorb mercury from freshwater ecosystem. This simple yet effective sensing approach may offer a potential platform for the design of plant alkaloid-based sensing probes for environmentally hazardous elements.