Multiple internal reflection photonic lab on a chip

In this work it is shown how the inclusion of the air mirrors allows the implementation of a highly sensitive absorbance based biosensor based on Multiple Internal Reflection (MIR). They have been fabricated in a single-mask step and replicated in Poly(dimethylsiloxane) (PDMS) using soft lithographic techniques. Experimental results confirm the ray-tracing predictions: if the air mirror is accurately defined, the propagating light matches the conditions of Total Internal Reflection (TIR) at the PDMS-air interface, which results in a complete reflection of the light towards the system. Additionally, the shape of the air mirrors can be modified so as to allow the light focusing at concrete places. With the recursive positioning of air mirrors, the optical path length has been meaningfully lengthened without a dramatic increase of the volume. The experimental results also matches with the ray tracing predictions and allows obtaining a LOD of 110 nM. The results are auspicious for the implementation of the absorbance-based photonic lab on a chip systems.