Photonic Crystal Optofluidic Silicon Microsystems for (Bio)Sensing

Abstract

In this work, feasibility of an optofluidic microsystem (OFM) in which vertical high aspect-ratio (HAR) silicon/air one-dimensional (1D) photonic crystals (PhCs) are employed as transducers for label-free refractive index (RI) sensors is demonstrated. The 1DPhC is integrated in a silicon substrate together with microfluidic channels for managing liquid flow and fiber grooves for alignment/positioning of readout optical fibers. The whole microsystem is fabricated by means of one-step etching thanks to advanced features of electrochemical micromachining (ECM) technology, a low-cost and highly flexible microstructuring technique based on the electrochemical etching of n-type silicon electrodes in HF-aqueous electrolytes. A glass cover, provided with inlet/outlet holes for liquid insertion/extraction, is anodically bonded on top of the micromachined silicon substrate. Optofluidic characterization of PhC-OFMs by pressure-driven operation is carried out through measurement of the reflected power spectra of 1DPhCs upon injection of liquids with different refractive index values in the 1DPhC air gaps, by using readout optical fibers positioned in the on-chip fiber grooves. A best sensitivity value of 357 nm/RIU and limit of detection of 4·10⁻³ RIU are obtained.