a port assembly for use with a polymeric bioreactor bag said assembly comprising : i ) a hollow port member comprised at least in part of a material suitable to be fusibly affixed to the wall surface of said bioreactor bag ; ii ) at least one fluorophore spot positioned on said port member ; iii ) conduit means for conveying excitation light from an optical source to said fluorophore , said conduit means being an assembly comprising at least one of a lens , an optic fiber , a curved parabolic collimator , a shaped reflector or a wave guide ; iv ) conduit means for conveying fluorescent emission light from said fluorophore to a photo - detector , said conduit means being an assembly comprising at least one of a lens , an optic fiber , a curved parabolic collimator , a shaped reflector or a wave guide .