High-Sensitivity Optofluidic Sensor Based on Coupled Liquid-Core Laser

The refractive index (RI)-based label-free sensor has attracted tremendous attention in biological and chemical research over the last few decades. Here, we proposed an optofluidic laser for high-sensitivity and low-detection-limit sensing of refractive index. The laser was made by parallel coupling two thin-wall silica capillaries. One of the capillaries served as dye solution channel, while the other worked as the sampling channel. On the one hand, we took the advantage of the Vernier effect due to the coupling of two capillaries to break the upper limit of sensitivity for whispering gallery mode (WGM) cavity sensing. On the other hand, the liquid-core dye laser was applied to reduce the detection noise. As a result, we have achieved an ultra-high sensitivity of 3874 nm/RIU with a noise equivalent detection limit of 2.6 × 10
^-6
RIU. The laser mode in the coupled WGM cavity was also analyzed numerically according to the sensitivity.