Nanofibre optic force transducers with sub-piconewton resolution via near-field plasmon-dielectric interactions

Ultrasensitive nanomechanical instruments, including the atomic force microscope (AFM)^1-4 and optical and magnetic tweezers^5-8, have helped shed new light on the complex mechanical environments of biological processes. However, it is difficult to scale down the size of these instruments due to their feedback mechanisms⁹, which, if overcome, would enable high-density nanomechanical probing inside materials. A variety of molecular force probes including mechanophores¹⁰, quantum dots¹¹, fluorescent pairs^12,13 and molecular rotors^14-16 have been designed to measure intracellular stresses; however, fluorescence-based techniques can have short operating times due to photo-instability and it is still challenging to quantify the forces with high spatial and mechanical resolution. Here, we develop a compact nanofibre optic force transducer (NOFT) that utilizes strong near-field plasmon-dielectric interactions to measure local forces with a sensitivity of <200 fN. The NOFT system is tested by monitoring bacterial motion and heart-cell beating as well as detecting infrasound power in solution.