Abstract: A planar waveguide-based optofluidic sensor and use thereof are provided, wherein the optofluidic sensor includes a substrate, an adhesive layer, a waveguide plate, and a microfluidic module layer. The adhesive layer is disposed on both sides of the substrate, the waveguide plate s disposed on the adhesive layer to be bonded with the substrate, and a hollow gap is formed between the substrate and the waveguide plate by the adhesive layer, and the microfluidic module layer is disposed on the waveguide plate and has a microfluidic channel, a fluid sample injection port, and an output port. The optofluidic sensor may detect the refractive index of the fluid sample with high sensitivity.