Abstract: An apparatus for producing a composition that includes nano-bubbles dispersed in a liquid carrier includes: (a) an elongate housing comprising a first end and a second end, the housing defining a liquid inlet, a liquid outlet, and an interior cavity adapted for receiving the liquid carrier from a liquid source; and (b) a gas-permeable member at least partially disposed within the interior cavity of the housing. The gas-permeable member includes an open end adapted for receiving a pressurized gas from a gas source, a closed end, and a porous sidewall extending between the open and closed ends having a mean pore size no greater than 1.0 ?m. The gas-permeable member defines an inner surface, an outer surface, and a lumen. The housing and gas-permeable member are configured to form a composition that includes the liquid carrier and the nano-bubbles dispersed therein.