Helical microrobot for force sensing inside microfluidic chip

Microfluidic platforms used for biology studies are in need of embedded mobile sensing tools. However, tethered actuators and sensors are almost impossible to use in closed microscopic environments. In this paper we propose a microfluidic platform combined with a helical microrobot control setup to perform such tasks. The microrobot used in this paper is 50 μm long and 5 μm in diameter. It is designed with a helical tail that propels it through rotation. This rotation is induced by a homogeneous magnetic field, which is provided by a setup compatible with microscopy techniques. We first propose to use this robot as a force sensor. For this we report a characterization protocol inside the microfluidic chip to link in an open-loop way the robot rotation to the applied force on an object. This approach provided accurate force sensing in the range of 10-40 pN, with measurement error of 12%. Secondly, we demonstrate how this helical microrobot can be used to selectively isolate a particle from a solution and how we can investigate the impact of the particle on the robot propulsion force. Finally, we show that this robot can be stored, ready to use, on a dried microfluidic chip, thus allowing long-term storage and simple transport. This platform opens up the opportunity to develop helical microrobots on various scale that can as untethered sensors and actuators inside microfluidic environment.