Integrated optical diffractive micrograting-based injection force sensor

We present a micrograting-based injection force sensor integrated with a surface micromachined silicon-nitride injector. The injector is supported by springs of known spring constant, and the injection force is determined from displacement measurements using a high-resolution, miniaturized optical encoder. The sensor exhibits configurable sensitivity and dynamic range, allowing monitoring over a wide range of forces. The periodicity of the encoder response can be used for calibration and to obtain information about the deformation of the target. We used an injector with a measured spring constant of 1.85N/m for penetration experiments on Drosophila embryos, and found a penetration force of 52.5+/-13.2% muN and a membrane displacement of 58+/-5.2% mum.