Electrocatalytic sterilization: nanowires produce localized highly alkaline microenvironments
Harmful microorganisms such as bacteria represent one of the largest threats to human health. Efficient sterilization methods are thus a necessity. In the journal Angewandte Chemie, a research team has now introduced a novel, sustainable, electrocatalytic sterilization method based on electrodes covered with copper oxide nanowires. These generate very strong local electric fields thereby producing highly alkaline microenvironments that efficiently kill bacteria.
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Conventional disinfection methods, such as chlorination, treatment with ozone, hydrogen peroxide oxidation, and irradiation with ultraviolet light have disadvantages, including harmful by-products and high energy consumption. Electrochemical disinfection methods, which rely primarily on a pulsed high-voltage electric field and the electrocatalytic generation of highly oxidative radicals, are more efficient and sustainable. However, they require either high voltage or a significant gas supply, which limits their application in practice.
A team led by Tong Sun and Yuanhong Xu at Qingdao University (China) have now proposed a novel, in situ, electrocatalytic sterilization method that induces localized highly alkaline microenvironments in neutral electrolytes under a constant current at relatively low voltage. Most bacteria cannot survive in such extremely alkaline environments.
The method is successful owing to cathodes made of a copper wire mesh that is coated with copper oxide nanowires. On highly curved structures such as the tips of nanowires, extremely strong local electric fields can form, allowing electrocatalysts to function very effectively. At the cathode, the hydrogen evolution reaction (HER) facilitates the efficient adsorption of hydronium ions (H3O+) by the nanowires, producing a rapid increase in the hydroxide ion concentration (OH-) in their immediate surroundings. This produces a localized, highly alkaline microenvironment. The overall pH value of the sterilization solution is only slightly increased, so it does not require neutralization before disposal.
The resulting highly alkaline microenvironment kills off bacteria within a few minutes, as the team demonstrated with Escherichia coli (E. coli). The bacteria are killed due to collapse of protein transport through the bacterial cell membrane because there are effectively no protons available in this environment. This inhibits ATP synthesis, resulting in an energy deficit and oxidative stress. In addition, the NADPH/NAD+ equilibrium, critical for gene regulation and metabolism, is disrupted. The bacteria die off.
This new approach could be a starting point for the development of high-performance, nanostructured electrocatalysts for efficient, environmentally friendly, and safe electrochemical disinfection strategies for a variety of sterilization applications.
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About the Author
Dr. Yuanhong Xu is a Professor at the College of Life Sciences at Qingdao University and has been working in the field of electrochemistry/biotechnology for more than 20 years. She was honored with the "Yangtze River Scholar Award" from the Ministry of Education of the People's Republic of China and is a German Humboldt Scholar. Dr. Tong Sun is a Professor at the College of Chemistry and Chemical Engineering at Qingdao University. His research interests are in the emerging field of nano-electrochemistry, including electrochemical kinetics, nano- and bio-electrochemistry and scanning electrochemical microscopy.
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