The deposition of solid-state polymer-encapsulated optical oxygen sensors has been demonstrated using simple casting and spin-coating techniques. This chapter focuses on intensity-based oxygen measurement. It utilizes the PtOEPK/PS optical sensor system as an example to discuss the limitations of existing fabrication methods. The chapter discusses the T-Sensor in particular has been used extensively to measure the diffusion coefficients of solutes between adjacent flow streams and this is demonstrated for oxygen. It shows a schematic of the sensor fabrication process using spin coating and soft lithography. Extending the sensor patterning to smaller dimensions is desirable in particular for cell biological applications. With the full range of sensor patterning now available, integrated oxygen sensing can be realized in a variety of microfluidic devices and novel applications. A schematic of the modified sensor fabrication process using spin coating and sacrificial metal masks. The sensor film is deposited with high film thickness uniformity and repeatability on a standard spin coater.