High performance microreactor

A microfluidic reaction device (10) includes a thermal buffer fluid passage (16) and a reactant passage (22) having mixing and dwell time sub-passages all defined within an extended body, the dwell-time sub-passage having at least 1 ml volume, and the mixing sub-passage being in the form of a unitary mixer not requiring precise splitting of flows to provide good mixing. The device is desirably formed in glass or glass-ceramic. The unitary mixer is structured to generate secondary flows in the reactant fluid and is preferably closely thermally coupled to the buffer fluid passage by sharing one or more common walls.