This paper reports on the performance of a subterahertz (THz) liquid sensor tool coupled to a microfluidic platform. Contactless and on-line measurements are demonstrated for the determination of ethanol concentration and controlling by a micromixer device. The authors have developed a label-free chemical sensing methodology coupling a subterahertz sensor technology to microfluidic devices fabricated on glass and polydimethylsiloxane. They demonstrated on-line sensing and control of ethanol concentration on demand. The THz-microfluidic sensing strategy represents a versatile tool for fast and easy integration in microfluidic devices, for concentration detection and linear control of binary mixture concentration in a contactless mode using microreactors in laminar flow and fast mixing mechanism by convection.