Two-Photon Polymerized Flow Sensor Integrated in a Microfluidic Channel with Optoelectronic Readout

This paper presents an unrolling microstructure fabricated by two-photon polymerization, that is deflected by the drag force of a liquid flow in a microchannel. Upon deflection the microstructure blocks incident light. The light is focused in the center of the microchannel by perpendicular integrated waveguides with lenses. Applied flow rates from 50 μl/min to 300 μl/min can be determined by measuring a decrease of the transmitted light power through the sensor chip using a photodetector. The microstructure acts as a sensor element in a microfluidic channel. On the silicon chip waveguides and lenses made of SU-8 and air are integrated to focus the light to different points in the channel.