Soft-lithography and plasma etching with reactive ions were used to fabricate a polymer microfluidic cell-culture bioreactor with integrated optical oxygen sensor. Platinum (II) octaethylporphyrin ketone (PtOEPK) suspended in a microporous polystyrene (PS) matrix was spin-coated to form sensor films of variable thickness from 1.1 µm to 400 nm on glass substrates. Sensor films were found to be smooth and well adhered. Arbitrary patterns with a minimum feature size of 25 µm could be routinely replicated in the PtOEPK/PS layer using polydimethylsiloxane (PDMS) elastomer stamps as etch masks in a reactive ion etcher. No effect of plasma patterning and sensor integration by plasma bonding on the sensor signal could be observed. Detection of different gaseous and dissolved oxygen concentrations with the patterned sensor followed linear Stern-Volmer behavior. Dynamic measurement of sensor intensity as a function of different oxygen concentration showed good reproducibility and a nearly instantaneous response to gas changes. For gaseous and dissolved oxygen measurement with a patterned 400 nm thick film I0/I100 ratios of 3.2 and 2.7 were found, respectively.