Highly-sensitive optical biosensor based on equal FSR cascaded microring resonator with intensity interrogation for detection of progesterone molecules

We report a refractive index sensing system with a high sensitivity of 1579 dB/RIU and a low refractive index detection limit of 9.7 × 10−6 RIU. The sensing system was based on cascaded-microring resonators (CMRR) using intensity interrogation. The free spectrum range (FSR) for the reference ring was designed to be equal to the sensing ring. The sensing ring of the CMRR was modified with molecularly imprinted polymers (MIPs) for the detection of progesterone. The achieved limit of detection (LOD) was as low as 83.5 fg/mL.