A dissolved oxygen sensor for use with a single use-bioreactor/container is provided. The bioreaction vessel includes a plastic wall defining a bioreaction chamber therein, and having an aperture therethrough. A membrane holder is attached to an inner surface of the plastic wall. The membrane holder has a cylindrical portion passing through the aperture. A sensor window membrane is coupled to the membrane holder proximate the aperture. The sensor window membrane has a high oxygen permeability, but forms a water-tight seal with the membrane holder.