Plastic light coupler for absorbance detection in silicon microfluidic channels

We present a micro-optical system for ultraviolet/visible absorbance detection in silicon microfluidic channels, which consists of a micro-optical light coupler placed on top of the silicon fluidic channel to probe the molecules under test with laser light. We use nonsequential optical ray-tracing simulations to model the system and to optimize its performance with respect to optical efficiency and system complexity. Deep Proton Writing is used to prototype the plastic light coupler and its spacer baseplate which contains marks to align the micro-optics with respect to the microfluidic channel and which allows for an accurate control of the position of the micro-optics with respect to the excitation source. We demonstrate the proof of concept of this microfluidic light probe by measuring standard samples of coumarin 102 dye with concentrations between 0.6 µM and 6 mM. Calibrating the system yields a detection limit of 4.3 µM. To conclude, we show that the concept of this microfluidic detection system is generic in that it can be applied at different positions on different microfluidic channel configurations.