Ultrasensitive electrochemical sensor for mercury ion detection based on molybdenum selenide and Au nanoparticles via thymine-Hg2+-thymine coordination

Ecofriendly ratiometric colorimetric determination of mercury(II) ion in environmental water samples using gallic acid-capped gold nanoparticles

Today, the monitoring and determination of heavy metal pollutants in the environment is an essential requirement for the environmental and research communities. Mercury ion is one of the most hazardous heavy metals, and scientists are trying to develop new methods for its detection. In this study, a new colorimetric sensor based on aggregation gallic acid-capped gold nanoparticles (GA-AuNPs) for the determination of mercury ions in environmental water samples was presented. The green synthesized GA-AuNPs exhibited a sharp surface plasmon resonance peak at 515 nm. The addition of mercury ions changed the surface properties of GA-AuNPs, resulting in the formation of a new peak near 670 nm due to the aggregation of GA-AuNPs, and an obvious color change from red to purple occurred. Thus, mercury ions were detected based on the change in the absorbance ratio (A670/A515). The developed sensor can determine the mercury ions in the concentration range of 78.0 nM to 8.3 µM with a detection limit of 5.5 nM. Based on the Environmental Protection Agency (EPA) and the World Health Organization (WHO) reports, the amount of Hg2+ ions in fresh water should be between 10.0 and 30.0 nM. The results indicate that the developed sensor can detect and determine trace amounts of Hg2+ ions in environmental water samples.

A highly sensitive electrochemical biosensor for Hg2+ based on entropy-driven DNA walker-based amplification

Herein, a sensitive electrochemical biosensor based on an enzyme-free and entropy-driven DNA walker is presented for the determination of Hg²⁺. This biosensor uses Hg²⁺ as a key to induce a mismatch between thymine-rich oligonucleotides to start the DNA walker, and it utilizes the entropy change of the sensing system to continuously drive the hybridization of oligonucleotides as a driving force for its walking. As the DNA walker runs, the detection signal is amplified to improve the sensitivity of the biosensor. Square wave voltammetry (SWV) of this biosensor shows a linear response of the methylene blue (MB) oxidation signal with an increase of Hg²⁺ concentration in the range of 0 to 80 nM with a detection limit of 0.136 nM, which satisfactorily meets the sensitivity requirement of the U.S. Environmental Protection Agency (EPA). The biosensor also exhibits excellent selectivity over a spectrum of interfering ions and performs well in real water samples, suggesting that it is a promising candidate for Hg²⁺ detection.

Three-dimensional gold nanowires with high specific surface area for simultaneous detection of heavy metal ions

Traditional detection methods to detect heavy metal ions are time-consuming, complicated, and expensive. Here, we developed a simple electroless plating method to prepare three-dimensional gold nanowire (Au NW) films with high specific surface area. In an aqueous plating bath, tetrachloroauric acid, 4-dimethylaminopyridine and formaldehyde are used as precursor, ligand, and reducing agent, respectively. An electrochemical sensor based on a Au NWs/SPE could be applied for simultaneous detection of lead (Pb(II)), arsenic (As(III)), and mercury (Hg(II)) ions. The detection limits of Pb(II), As(III), and Hg(II) are 2.6, 1.5, and 4.2 μg L^-1, all lower than the permissible limits of the WHO for drinking water (the permissible level of Pb(II) and As(III) is 10.0 μg L^-1, and the permissible level of Hg(II) is 6.0 μg L^-1), respectively. This work presents a simple and novel method to prepare gold nanowires for quick detection of trace heavy metal ions.