Optical Nanofiber-Enabled Self-Detection Picobalance

Highly sensitive and compact microforce sensors with piconewton-level resolution are essential in various fields. However, these sensors face the challenge of delicate fabrication, expensive instruments, and complicated signal processing. Here, we report an ultrasensitive microforce sensor with a nanonewton-scale working range and piconewton-level resolution (picobalance) using a 500 nm diameter U-shaped silica optical nanofiber (ONF) as the cantilever beam and a gold microflake as the sample tray. The ONF can detect its deflection upon microforce by monitoring the change of its transmittance, making it a self-detection picobalance with a linear response to microforce in the range of 0–11.2 nN based on theoretical calculation. Benefiting from the extremely low spring constant of the ONF (e.g., 0.15 mN/m), the picobalance achieves a force resolution of 3.3 pN in an experiment measuring the radiation pressure. As proof-of-concept demonstrations, measuring nanogram-level microparticles and radiation pressure are realized. We believe that this easy-to-use picobalance has great potential for biological sensing, biomechanical research, and environmental monitoring.