This article will discuss how we optimized the efficacy of nanobubble immersion therapy. Specifically, it will detail how we determined and improved factors influential to nanobubble therapy such as zeta potential, size of bubbles, concentration, as well as our methods of production and measuring of nanobubbles. Additionally, it explores how nanobubbles supersaturate water with oxygen and how this compares to microbubbles.
Zeta potential is an important variable of consideration when dealing with nanobubbles because of its effects on the concentration and stability (or lifespan) of bubbles. The more stable a bubble is, the less likely it is to coalesce with other bubbles, meaning it won’t rise to the top of the water and burst. Zeta potentials farther from 0 (that is, the more negative and more positive zeta potentials) have higher stabilities. Zeta potentials are a measure of the potential difference (difference in voltage) in a region outside the bubble known as the “slipping plane,” as shown below. The slipping plane lies outside the Stern Layer, which contains all particles attracted to the charges lying on the surface of the bubble. By nature, this region of nanobubbles has negative potential difference, meaning the desired zeta potentials of nanobubbles are lower (more negative), since these values are farther from zero.
Factors Leading to Nanobubbles Having a Lower (More Negative) Zeta Potential:
1. Higher pH [1, 2, 3, 5]
In general, pH is linearly related, and its change in zeta potential is fairly significant over even something as small as ±1 in pH.
Though the pH of skin is around 5.5, it is however considered safe (even desirable) to bathe in alkaline water with a pH of 8 – 9. Additionally, while the majority of cosmetic and skincare products have a pH that lies under 7 to match with that of skin, there are several of these products with an alkaline pH.
Thus we at Oval.Bio use a slightly alkaline pH water when conducting nanobubble immersion therapy– a pH of 8 ± 0.5; in order to optimize Zeta Potential while still being well within the safe range for humans.
There is evidence that zeta potentials of pH levels greater than 8 are ideal, with 10 being the best (6), before decreasing in magnitude. A pH of 8 is ideal because it is a safe pH while facilitating a great zeta potential for the nanobubbles.
2. Lower salt levels [1, 3, 5]
Salts are detrimental to zeta potential — salts and zeta potential are linearly related and relatively easy for us at oval.bio to control. Our water simply is saltless in order to improve the overall zeta potential of the nanobubbles in water.
3. Low temperatures 
Temperature is not the most influential factor in determining zeta potential, however it does affect it up until 20 degrees C, based on this graph. Because a temperature under 20 degrees C can restrict blood flow, among other factors, we have set our nanobubble water to be a comfortable 30 degrees C.
4. Smaller size 
Size is important up to a certain extent (i.e. having too small of a size would lead to the bubbles becoming unstable, and collapsing thus becoming dissolved oxygen which lowers the total super saturation levels, as dissolved oxygen has an upper limit).
Size, as shown above, is another critical variable which is correlated with zeta potential, since bubbles of larger size tend to coalesce as microbubbles and escape the water.
In general, because a decrease in size can lead to a more negative Zeta potential, it is ideal to have them in the lower nanometer range, within the “island of stability” (the 50 – 200 nm range). Additionally, the most widely studied nanobubble distributions have an average nanobubble size under 200 nm (7).
To read more about what nanobubbles are and the “island of stability” .
Size is important because it is the primary determinant in a bubble’s ability to remain in water and not escape. Because air is less dense in water, bubbles with greater volumes of air (i.e. bigger bubbles) escape water very easily, since their large buoyant forces overtake gravitational forces, pushing them upward and forcing them to leave the water. In contrast, nanobubbles’ small size allows for their buoyant and gravitational forces to be relatively equal and opposite– increasing their stability in water. What this means is that nanobubbles can stay in water much, much longer than larger bubbles.
We at Oval.Bio already have a nano bubbler with a pre-set nanobubble diameter distribution that lies in the ideal range as shown below. Our nanobubbler is engineered to make nanobubbles within range of the ideal diameter (73nm), letting us focus more on the concentration of the nanobubbles themselves.
The Importance of Nanobubble Concentration
In addition to size, another crucial factor is the concentration of nanobubbles. At Oval.Bio, we employ our nanobubbler to achieve higher concentrations of oxygen nanobubbles by cycling through the same water multiple times. Each cycle produces about 30 million nanobubbles per milliliter, but our target is 400 to 600 million nanobubbles per milliliter.
Technically, the body absorbs the most oxygen at these higher concentrations . Osmosis, a phenomenon where higher oxygen levels in water and lower levels in the body facilitate the transfer of oxygen into the body, is responsible for this. The higher the oxygen concentration in water, the higher the equilibrium concentration.
To determine the nanobubble concentration in our water, we used a dissolved oxygen meter capable of measuring supersaturated water levels. Among dissolved oxygen meters, optical meters are most advantageous for nanobubble immersion therapy as they don’t require stirring for accurate measurements .
Optical dissolved oxygen meters illuminate blue light on luminescent dyes to measure oxygen molecules. If no oxygen is present, the luminescent dye emits light as electrons. When oxygen is present, the intensity of the dye’s electrons is altered and limited by oxygen molecules, recorded by the photodetector. More oxygen results in greater alteration of the emitted electrons .
Scientific literature has employed dissolved oxygen meters to measure oxygen concentration in nanobubbles submerged in water. Here are some examples:
Maximizing Water Oxygenation with Nanobubble: Unleashing the Potential for Supersaturation
Liquids like water are limited in the amount of dissolved gas they can hold. The maximum dissolved gas concentration of a liquid is known as its saturation point. The saturation point of a liquid is proportional to the partial pressure above the liquid– a principle known as Henry’s Law. Nanobubbles, however, are not considered to be “dissolved” in water, and thus do not contribute to the saturation point of water– they are more like cavities in the water. What this means in practice is that nanobubbles offer the ability to supersaturate water. Because nanobubbles can supersaturate water with oxygen, we are able to increase the amount the body can absorb because of osmosis, as previously mentioned.
Normal dissolved oxygen content in water can range from 1 mg/L to 20 mg/L depending on the temperature, pressure and salinity of water. The dissolved oxygen content in room temperature is 8.68 mg/L at 100% saturation .
One study found that oxygen concentration went from 7.7 mg/L in distilled water to 31.7 mg/L in oxygen-nanobubble water after running the nano bubble aerator with 100 L water for 30 min .
Comparing Dissolved Oxygen Levels: Nanobubbles vs. Microbubbles in Water Therapy
In a study, the level of dissolved oxygen in physiological saline was initially 6 mg/L but increased to 45 mg/L after oxygen micro/nano-bubble dispersion .
Microbubble oxygen therapy, while claimed to dissolve high oxygen concentrations, lacks the ability to supersaturate water like nanobubbles. Unlike nanobubbles, microbubbles do not contribute to the dissolved saturation levels of water because the oxygen in nanobubbles is not dissolved in water. In contrast, microbubbles rise to the water’s top and offer limited therapeutic value. In simple terms, nanobubbles can boost water’s saturation concentration by containing dissolved oxygen content and the oxygen in the nanobubbles themselves, whereas oxygen in microbubbles simply escapes the water.
Nanobubbles hold an advantage due to smaller diameter bubbles being more permeable, facilitating easier absorption by the skin.