Drop-Shaped Optical Microfiber Enabled Biomechanical Sensor

Microforce sensing plays a pivotal role in biomechanics. However, existing microforce sensors face limitations in conducting biomechanical sensing on living organisms due to cumbersome operational procedures and limited measurement flexibility. To overcome this challenge, we developed a microforce sensor using a drop-shaped optical microfiber. Leveraging its small bending radius and the bending-radius-dependent output light intensity, the microforce sensor features a small footprint, a low spring constant, and enables nanonewton-level force sensing by monitoring variations in output light intensity. To prevent contact induced surface contamination, a PDMS microsphere is integrated at the sensor tip to isolate the waveguide evanescent field and boost microforce detection sensitivity. The sensor exhibits a force resolution of 24 nN in the range of 0-10 µN. As proof-of-concept demonstrations, Young's modulus characterization of onion epidermal cells and Caenorhabditis elegans are realized. The sensor demonstrated here is promising to offer a precise, flexible, and reliable solution for biomechanical characterization and is configurable to cater to a broad spectrum of applications.