Then we estimated the amount of surfactant existed in the solution from the reported carbon content (TC). In nanobubble experiments the TC of pure water is often given, with a typical value of <50 ppb. Here we chose a typical value of 24 ppb. Since the carbon content mainly comes from organic contaminants in the solution, which is assume to act as surfactants. Thus, we can approximate the concentration of surfactants (contaminants) in water, 𝑐 , by the given TC. The total number 𝑁 of actually contained in 1mL of water can be estimated by 𝑁 = × × 𝑁 ≈ 5 × 10 . Here 𝑀 is the molar mass of the surfactant, having a value of 288 g/mol with reference to SDS, and the Avogadro's constant 𝑁 = 6.02 × 10 𝑚𝑜𝑙 .