Fabrication method of microfluidic circuit, and microfluidic circuit fabricated by method thereof

A fabrication method of a microfluidic circuit having a light transmissive substrate that is composed of thermoplastic resin and that is stacked on a light absorptive substrate, said microfluidic circuit including a microchannel at a bottom face of said light transmissive substrate and/or at a top face of said light absorptive substrate, said method comprising:

• forming, at said light transmissive substrate, a light attenuation region attenuating an amount of light to not more than 80%, wherein said light attenuation region contains a light blocking material composed of carbon black,
• after forming the light attenuation region, welding the light transmissive substrate to the light absorptive substrate by directing light through the light transmissive substrate, wherein the amount of light transmitted toward said microchannel is attenuated, by said light attenuation region, to not more than 80% of an amount of light directed to said light transmissive substrate,
• wherein said light transmissive substrate has a thickness d and a refraction index n, and includes a microchannel of a width w at a bottom face, and a value of (d/w) tan [90−θ−sin−1{(sin(90−θ))/n}] is at least 0.1, where θ is an incident angle of directed light transmitted to said microchannel.