Generation and Application of Ultra-Fine, Long-Term Stable Nanobubble Water: An Evaluation of Inclusion Effects on Aromatic Components and Antimicrobial Activity

Nano- and pico-bubble water (NPB), containing hydrogen or ozone, is widely used as a cleaning agent due to its bactericidal and antiviral properties. However, some products—such as certain hydrogen waters—contain only large bubbles or have an extremely low bubble count, making them sometimes indistinguishable from ordinary drinking water. To accurately evaluate NPB activity, we developed a method for producing ultra-nano–pico-bubble water (NanoGAS water [NGW]), an ultra-fine bubble water that is stable and non-volatile over extended periods. By combining a mixed gas–liquid fluid rotary mixer and a shear filter, we produced ultra-fine bubbles that could be sealed in water. This method produced bubbles that remained stable in water even after 10 years since production. NGW has been clinically evaluated as a solvent for fecal microbiota transplantation (FMT) and has been demonstrated to be effective at improving bacterial engraftment in the intestinal tract in patients with autism spectrum disorder (ASD). Furthermore, encapsulating specific gases (hydrogen and ozone) can achieve more diverse effects. In this study, we evaluated the aroma-encapsulating effects, as well as the strength and persistence of the antimicrobial activity, of novel NGW formulations (Air-NGW, H2-NGW, S-O3-NGW, and L-O3-NGW). Both H2-NGW and O3-NGW generated in this study demonstrated slight inclusion activity with volatile aromatic compounds (citral). Furthermore, both H2-NGW (at ≥10% dilution) and O3-NGW (even at a 1% dilution) exhibited sustained antibacterial efficacy against general viable bacteria for 24 weeks. Moreover, additive effects were observed when combined with antibacterial and antiviral compounds (polyoxometalates) developed by the authors. While further consideration, including cost-effectiveness, is needed to translate these findings into practical applications, they provide a fundamental framework for future research.