Efficiently and Sustainably Killing Bacteria

A research team has 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.

How to Kill Bacteria Efficiently and Sustainably

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 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.

A Highly Alkaline Microenvironment

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 by the nanowires, producing a rapid increase in the hydroxide ion concentration 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. 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 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, the authors say.