This paper presents an on-chip thermal flow sensor, patterned in Ni on the outside of a polymer microfluidic channel. The sensor is a low power (low T), no-hysteresis device, with excellent resolution (<30 nl min(-1)) and built-in calibration, covering a wide range of typical Lab on a Chip flow rates. These features, together with the compatibility of the approach with current printing and roll-to-roll techniques, prove a realistic mass-producible solution for direct monitoring of microfluidic protocols inside Lab-on-a-Chip (LoC) devices. In contrast with commercially available flow sensors, its low price allows its use in disposable devices. Functionality of the microsensor is tested over 20 h in a microfluidic cell culture application, where nutrients flow rate had to be monitored and controlled. The results indicate successful performance of the sensor in this highly sensitive environment. Overall, this on-chip sensor approach offers significant improvements over existing sensor devices, both for the academic and commercial applications. (C) 2016 Elsevier B.V. All rights reserved.