Stability evaluation of oxyhydrogen and hydrogen nanobubbles under thermal and pH stress conditions

Nanobubbles (NBs), gas-dispersed systems < 200 nm in size, are increasingly explored for therapeutic and drug delivery applications but are highly sensitive to environmental conditions. This study evaluated the stability of nanobubbles generated from oxyhydrogen (HHO) and pure hydrogen (H₂) gases under thermal and pH stress. HHO nanobubbles were subjected to heating (80 °C and 100 °C) and freezing (-17 °C), while H₂ nanobubbles were stored at pH 4-9 for seven days. Particle size (mode, mean, D50) and concentration were measured using Nanoparticle Tracking Analysis (NTA). HHO nanobubbles showed significant degradation at 100 °C, with reduced concentration and increased particle size, whereas freezing caused moderate instability. H₂ nanobubbles were most stable at neutral pH (6-7), maintaining size and concentration, while highly acidic (pH 4) and alkaline (pH 9) conditions accelerated particle disintegration. Neutral pH (6-7) is optimal for nanobubble stability, while extreme temperatures (100 °C and freezing) markedly reduce stability. These findings provide insights into designing nanobubble formulations with enhanced environmental resilience for clinical applications such as therapeutic gas infusion and advanced drug delivery.