Using a light-scattering analysis method called nanoparticle tracking analysis (NTA), scientists at Japan's National Institute of Advanced Industrial and Science Technology (AIST; Tokyo) have shown that in the presence of electrolytes and with the correct physical stimulus, stable nanobubbles can be formed from conventional microbubbles.
Interest in nanobubbles is reportedly growing quickly because of their wide range of potential applications. When formed from ozone and stabilized with electrolyte, nanobubbles promise months-long disinfection and sterilization with potential for food preservation and medical applications. Oxygen nanobubbles have been implicated in the prevention of arteriosclerosis (by inhibiting mRNA expression induced by cytokine stimulation in rat aorta cell lines). And when formed in liquids in capillaries, nanobubbles have been shown to greatly improve liquid flow characteristics. They have also been proposed as contrast agents in scanning techniques as well as cleaning agents in silicon manufacturing processes.
According to AIST researchers Kaneo Chiba and Masayoshi Takahashi, microbubbles tend to either coalesce to larger buoyant bubbles and float away or collapse under intense surface tension-derived pressure to the point that they vanish as predicted by theory. The addition of salt (electrolytes), however, is thought to cause the formation of a counter-ion screen around nanobubbles, which effectively blocks the ability of gases within them to diffuse out. The researchers confirmed this through electrophoresis studies in which the zeta potential of nanobubbles was shown to be related to their stability.
The NTA approach, developed by NanoSight (Salisbury, UK) has proven to facilitate such analyses. In a blind experiment in which three suspension samples (containing high, low, and zero concentrations) were tested in duplicate, NTA's results were found to match exactly those predicted. In addition to concentration per unit volume, the approach enables evaluation of size and size distribution.
Representing another research group, Ichiro Otsuka of Ohu University (Koriyama, Japan) has studied the possible role of nanobubbles in ultra-high diluted samples of active agents in which the phenomenon of succussion is considered to relevant. He used NTA to examine nanobubble formation and concentration in more detail than was possible using an electrozone (Coulter) method or conventional dynamic light scattering (DLS) techniques.
To learn more about nanobubbles and their characterization using NTA, read "NanoBubbles: a new class of structure ready for exploitation?" in the latest issue of NanoTrail, NanoSight's eNewsletter.