Label-free biological sensors based on ring resonators

This paper reports the progress (design, fabrication and measurement) in label-free biological sensors based on ring resonator technology originally developed for telecommunication. These sensors are made in silicon-on-insulator (SOI), a high index contrast material platform that provides enhanced sensitivity and allows compact waveguide geometries by employing very small bend radii. A double spiral shape allows designing millimetre-long resonator in a compact size (100-150 mum) compatible with spotting technology used for large biochip assays. The detection limit estimated from the resonance shift measurement is ~5 fg of streptavidin adsorbed on the sensor surface functionalised with biotin.