Microring resonator arrays for label-free biochemical multi-parameter analysis

There exist growing demands for robust, reliable, low-cost and easy-to-use sensor systems capable of performing multi-parameter analysis for biomedical diagnostics. We have recently demonstrated a particularly economic approach to analyze large arrays of microring resonator (MRR) sensor elements coupled to a single bus waveguide. The sensor elements can be individually functionalized to specifically promote the accumulation of target molecules. The binding of target molecules to the surface of a particular MRR results in a resonance displacement to longer wavelengths, which can be measured with high accuracy. In order to measure the response of the individual MRR from an array to external stimuli, we employ a special frequency modulation scheme in which each MRR is independently modulated and phase sensitive lock-in detection is used to filter the respective frequency component from the superimposed complex trans-mission spectrum of the bus waveguide. We fabricated test arrays comprising up to 12 MRR coupled to a single bus waveguide. A silicon nitride based material system was chosen to fabricate the devices. Each element of an array is equipped with a platinum heater electrode for thermo-optical modulation. A clear readout of the individual MRR resonance frequencies was possible by employing the modulation scheme above. Furthermore, we demonstrated a bulk refractive index sensitivity of 190 nm/RIU for a frequency modulated MRR. With our first results, we point out the large potential for multiplexed label-free detection of diverse bio molecular com-pounds. Due to the miniaturization of the multisensor arrays the realization of portable sensor systems will be feasible.