  Vertical optofluidic biosensors based on refractive index sensing promise
highest sensitivities at smallest area foot-print. Nevertheless, when it comes
to large scale fabrication and application of such sensors, cheap and robust
platforms for sample preparation and supply are needed - not to mention the
expected ease of use in application. We present an optofluidic sensor system
using a cyclic olefin copolymer microfluidic chip as carrier and feeding supply
for a complementary metal-oxide-semiconductor-compatibly fabricated Ge PIN
photodetector. Whereas typically only passive components of a sensor are
located within the microfluidic channel, here the active device is directly
exposed to the fluid, enabling top-illumination. The capability for detecting
different refractive indices was verified by different fluids with subsequent
recording of the optical responsivity. All components excel in their capability
to be transferred to large scale fabrication and further integration of
microfluidic and sensing systems. The photodetector itself is intended to serve
as a platform for further sophisticated collinear sensing approaches.
