Suspended micro-ring resonator for enhanced biomolecule detection sensitivity

Silicon micro-ring biosensors demonstrate great potential for high sensitivity and multiplexed lab-on-chip systems. In this work, we characterize the sensing performance of suspended TM-mode silicon micro-ring resonators, 5 μm in radius, and demonstrate an enhanced sensitivity to molecular binding on the ring after suspension. In the TM-mode, the overall field intensity exists primarily outside of the waveguide core, with high electric field intensities present near the top and bottom surfaces. In traditional micro-ring resonators, only the top surface of the ring is available for surface analyte attachment, while the electric field intensity near the bottom surface dissipates by leaking into the underlying silicon dioxide substrate. In our approach, we suspend the TM-micro ring resonators in order to increase the surface area for binding events and increase the light-matter interaction with analytes. The suspended rings demonstrate excellent mechanical stability to multiple rinsing, soaking and nitrogen drying steps during the sensing procedure. We show that the resonance shift achieved by the suspended micro-rings after attachment of small chemical molecules and DNA is at least twice that of micro-rings supported by the silicon dioxide substrate.