Turning water into green disinfectant

Rita Agus © Nadia Barth / EPFL

Rita Agus © Nadia Barth / EPFL

Imagine sterilizing kitchen surfaces and hospital instruments, washing fruits and vegetables, sanitizing hands, or rinsing mouths—all achievable with a single eco-friendly solution: Plasma-activated water (PAW). Rita Agus, a PhD student at the Swiss Plasma Center, is deeply engaged in this research involving PAW, which promises to solve microbial issues without resorting to traditional methods involving heat or chemicals. Recently, she published a paper in the renowned Chemical Engineering Journal, introducing the word’s first portable PAW reactor for academic research, a high-tech tool that could not only transform water, but also our everyday hygiene practices.

Only a few elements form the core of this portable reactor: a supporting structure, two electrodes, a dielectric in between and a glass container. The compact reactor can easily slip into a backpack, ready for use anywhere, in any laboratory setting. For the magic to happen, all you need is some water and an electrical socket. Plug in the reactor, wait ten minutes, and ordinary water becomes a powerful disinfectant, particularly effective against E. coli, a very common microbe residing in our gut. It's so simple, we could envision it on every kitchen counter: “plasma activated water could be used for surface and floor disinfection, as well as cleaning and sanitizing utensils, and even disinfecting laundry,” Rita Agus explained, highlighting the potential of plasma-activated water for household applications.

The portable PAW reactor designed by Rita Agus and her colleagues © Nadia Barth / EPFL

Low-temperature plasma, highly efficient
Working under the supervision of Ivo Furno, adjunct professor at the Swiss Plasma Center, Rita Agus and her colleagues dedicated one year of effort, with assistance from various technicians, to manufacture the world's first portable PAW reactor. But what precisely is “plasma-activated water”, and how does it work?

Rita Agus explains, “PAW water is generated through the exposure of water to low-temperature plasma, where the operating gas remains at room temperature. Operating in air at atmospheric pressure, plasma — the fourth state of matter, where electrons get stripped from their atoms — produces reactive oxygen and nitrogen species. These highly reactive chemical species diffuse into the water, altering its chemical properties and composition, thereby creating PAW. It is highly reactive on its own, serving as a carrier to deliver the reactive species for specific applications.” In other words, this process imbues the water with powerful antimicrobial properties, making it an effective tool for sterilization and disinfection.

PAW's appeal lies in its simplicity and versatility. Unlike typical disinfectants packed with harsh chemicals, PAW offers a natural, eco-friendly alternative. Rita Agus argues that, in contrast to autoclaves, PAW efficiently cleanses heat-sensitive materials and food with less grey energy. Plus, it's cost-effective, needing only basic equipment, water, and electricity. Compared to chemical methods with chlorine and formaldehyde, PAW wins on both cost and safety, eliminating the need for special gear to handle dangerous chemicals.

Establishing plasma selectivity is crucial for the safe and effective use of PAW in various fields

Rita Agus, PhD student at the Swiss Plasma Center

Thanks to its strong innovative potential, PAW received significant attention from researchers over the last decade. Although much progress has already been made, there are still several challenges standing in the way of the widespread adoption and commercialization of PAW-based technologies. One of these is “plasma selectivity”, which refers to the ability of PAW to target bacteria and microorganisms while preserving cells and surrounding environments.

Rita Agus explains, “In my view, establishing plasma selectivity is crucial for the safe and effective use of PAW in various fields such as healthcare, food processing, and sanitation; and would unlock tremendous opportunities for this technology.” Therefore, research efforts focused on understanding the underlying mechanisms of plasma selectivity and identifying optimal operating conditions are critical for advancing PAW-based solutions.

Water recirculation
The research carried out by Rita Agus and her colleagues is a step in this direction. Their portable reactor enables the production of different compositions of plasma-activated water by adjusting certain parameters such as whether or not to recirculate the water, or the duration of water exposure to plasma. These variables affect the effectiveness of the antimicrobial properties of PAW. For example, we know that prolonged exposure enhances their potency, and Rita Agus has demonstrated that water recirculation also significantly increases the antibacterial effect.

PAW could serve as an alternative or complementary approach to antibiotics

Rita Agus, PhD student at the Swiss Plasma Center

Besides its hygiene benefits, PAW has also emerged as a potent tool in fighting harmful microbes. “Some researchers argue that bacterial resistance to PAW is unlikely due to its action on multiple targets. Moreover, experimental evidence supports the efficacy of PAW against multi-drug-resistant bacteria. However, further research is needed to confirm whether PAW can prevent the development of bacterial resistance. Additionally, PAW could serve as an alternative or complementary approach to antibiotics, for example, for the topical treatment of wounds infected by drug-resistant bacteria,” concludes Rita Agus. Further investigation into the mechanism of bacteria inactivation is necessary to assess the potential of safe plasma-based technologies in reducing resistance or persistence development.

While challenges remain, particularly in understanding plasma selectivity and optimizing operating conditions, PAW's potential in combating microbial resistance and enhancing hygiene practices is undeniable.

Short bio

This journey in bio-plasma applications is marked by continual growth and discovery

Rita Agus, PhD student at the Swiss Plasma Center

“I come from Villagrande Strisaili, a small town in Sardinia. As a child, I dreamed of becoming a scientist, even though I had no idea what it meant. However, when I finished high school, I chose engineering over physics because I mistakenly believed that pursuing physics studies would lead me exclusively into research, which I thought was out of my reach.

My educational journey led me to Turin, where I took a bachelor's degree in Energy Engineering at the Polytechnic School. During this period, I learned about fission reactor physics, and I found it so fascinating that I pursued a master's degree in Nuclear Engineering.

It was for my master thesis that I first came to SPC. During my stay, I found out about the topic of bio-plasma applications and the unique interaction between water and low-temperature plasma for the production of plasma-activated water. After getting to know the bio-plasma world I could not picture myself working anywhere else. Luckily, I had the great opportunity to do my Ph.D. within this stimulating lab with Prof Ivo Furno. This journey in bio-plasma applications is marked by continual growth and discovery, into the interaction between microbiology, applied physics, and chemistry. Each day presents new opportunities for exploration and experimentation, fueling my passion for scientific research.”


Rita Agus, Fabio Avino, Lorenzo Ibba, Brayden Myers, Leonardo Zampieri, Emilio Martines, Alan Howling, Ivo Furno, Implementing water recirculation in a novel portable plasma-activated water reactor enhances antimicrobial effect against Escherichia coli, Chemical Engineering Journal, Volume 486, 2024, 149915, ISSN 1385-8947