Flow sensors for on-chip microfluidics: promise and challenges

This review focuses on flow sensors in microfluidics specific to on-chip detection inside a microchannel. These sensors are distinct from external, off-chip flow sensors that are often associated with microfluidics. We explore the various mechanisms and physical principles involved in their working and compare their pros and cons. We consider the working principles that can be used for sensing at the microscale and prepare a typical designer’s perspective with respect to flow sensors that can be integrated on a microfluidic chip. Developing an accurate on-chip flow sensor would enable autonomous flow control leading to advancements in point-of-care applications of microfluidics. We also highlight some of the challenges that have kept researchers at bay from developing an all-weather on-chip flow sensor for microfluidics. Also included is a brief discussion on the relevant applications of on-chip flow sensors including preventive healthcare, drug development, and microreactors. This review should give an impetus to development of better and larger variety of on-chip flow sensors.