We demonstrate a nanophotonic sensor for real-time monitoring of fluid flows. The sensor is based on a silicon photonic crystal cavity with a well aligned micro fluidic channel for fluid-injection. The simulated resonant wavelength shift of the sensor with residual oil in holes is 9.0 nm, and the observed experimental shift under the same condition is 10.0 nm. An alternating fluid delivery is applied in a dynamic sensing experiment with syringe pump controlled ratios of water and oil. Excellent agreement between the measured data and the video images of fluidic streams in the optofluidic cell is found.

A planarized on-chip nanophotonic sensor based on a photonic crystal cavity is realized in this work. The sensor was embedded in a solid protecting material (flowable oxide) with perfect filled holes: this eliminates problems of fouling in practical applications. The functional area of the sensor is created by carefully removing the protecting material only on the top surface of the cavity. A wavelength shift of 7.5 nm was observed in experiment which is very close to a simulation result of 9.0 nm for sensing water (n=1.33) and crude oil (n=1.45) samples. Swift and accurate sensing was verified by a real-time dynamic measurement with rapidly alternating analytes in a microfluid channel.