Researchers from South Ural State University have developed a new highly sensitive method for detecting mercury ions in aqueous solutions. The innovation is based on a specially modified electrode capable of identifying the toxic metal, even at ultra-low concentrations, within just two minutes.
According to the developers, the uniqueness of the method lies in modifying the electrode with a high-entropy oxide containing the rare-earth element praseodymium. This composition enables the electrode to detect mercury at concentrations starting from one nanomole. For context, this level is below the maximum permissible concentration and corresponds to approximately 200 nanograms per litre.
“We modified a standard glassy carbon electrode (the basis for many electrochemical sensors) using a special nanopowder,” explains Roman Morozov, researcher at the SUSU Laboratory for Studying Environmental Problems in Post-industrial Agglomerations. “Imagine the electrode surface as a desert. A conventional electrode is like smooth sand, where a drop containing mercury simply rolls off. The modified electrode resembles a porous sponge, and thanks to such structure, its active surface area has increased threefold. We intentionally introduced praseodymium (Pr) into the oxide structure. This element creates “vacancies” (empty spots where oxygen atoms are missing) in the crystal lattice. These vacancies act as traps, actively attracting mercury ions. Once captured, the ions more easily undergo reduction to metallic mercury. And the device detects it.”
Mercury contamination of water remains a critical global issue. The metal accumulates in living organisms and can cause severe diseases. A well-known example is Minamata disease in Japan, caused by industrial mercury discharge. Detecting mercury in drinking water, soil, or food products (such as tea and coffee) is particularly challenging, as the maximum permissible concentration set by the World Health Organization is extremely low—just 0.001 mg/l.
Scientists all over the world are working on this problem. The method developed by the Chelyabinsk researchers demonstrates impressive results: the sensor reliably detects mercury in a concentration range of 1 to 5 nanomoles (nM), with a detection limit as low as 0.15 nM. This makes it possible to identify even trace amounts of the toxin. Importantly, the sensor maintains high selectivity and accuracy even in the presence of competing ions (such as lead, copper, and iron) and organic substances (urea, phenol).
The scientists tested the device under real conditions by adding trace amounts of mercury to samples of tap water, soil, and extracts of tea and coffee. In all cases, the sensor demonstrated high accuracy, with recovery rates ranging from 85% to 95%.
In addition to the accuracy, the Chelyabinsk development offers two major advantages: speed and affordability. Unlike traditional techniques requiring complex and expensive equipment (such as atomic emission spectrometers or chromatographs costing tens of millions of roubles), the new approach relies on a compact device.
The experiments were conducted using a stationary potentiostat costing about 1.5 million roubles. Researchers are currently testing a portable version priced at approximately 300,000 roubles, which can operate with a standard laptop or even a smartphone. The electrode itself is disposable, but requires less than one milligram of the rare-earth metal, making the technology highly cost-effective.
“Although the base components (electrodes and portable devices) are currently manufactured in Taiwan, establishing production in Russia would not be difficult,” the developer notes. “As for rare-earth elements, the quantities required are so small that they do not significantly affect the cost or affordability of the method.”
According to the researchers, potential users of the technology include environmental monitoring services. The portable analyser can significantly reduce the time and cost of testing, ensuring rapid on-site analysis with reliable results. It can also be used by producers of tea, coffee, and seafood to quickly check raw materials for mercury contamination.
This method also looks promising for medical diagnostics: by adapting the material for other biomarkers, it could be used to develop sensors for analysing urine or sweat. Additionally, the technology is suitable for real-time monitoring of industrial wastewater, particularly in chemical, mining, and leather industries.
The results have been published in the Colloids and Surfaces A: Physicochemical and Engineering Aspects international journal.