A composite sensor assembly for monitoring bio-processes which is suitable for use with a polymeric bioprocess vessel or with downstream equipment, and comprises: i) a port comprising a high surface tension thermoplastic having a hollow tubular portion and a base plate portion, the base plate portion being fusibly sealable to the bioreactor vessel at a hole in the wall thereof; ii) a generally opaque polymeric monitoring sensor assembly including electrical, and/or optical measurement components. The sensor assembly fits inside the bore of the hollow tubular portion of the port, and is adhesively retained therein.