Rohm of Kyoto, Japan, has received US Patent No. 8,377,389, "Microfluidic circuit." A method of fabricating a microfluidic circuit is provided. The circuit includes a microchannel that is located at the bottom face of a light-transmissive substrate or at the top of the light-absorptive substrate, which are stacked together. A light attentuation region is formed on the light-transmissive substrate that is capable of transmitting light toward the microchannel when light is directed at it.