a port assembly for use with a polymeric bioreactor bag includes the following components : i ) a hollow port member made from a material which can be fusibly affixed to the wall surface of the bioreactor bag ; ii ) at least one fluorophore spot positioned on the port member ; iii ) a conduit for conveying excitation light from an optical source to the fluorophore , which conduit can be a lens , a curved parabolic collimator , a shaped reflector or a wave guide ; and iv ) a second conduit for conveying fluorescent emission light from the excited fluorophore to a photo - detector , which second conduit although different from the first , can likewise be a lens , a curved parabolic collimator , a shaped reflector or a wave guide .