There is an ongoing need to develop ultrasensitive nanomechanical instrumentation that has high spatial and force resolution, as well as an ability to operate in various biological environments. Here, we present a compact nanofiber optic force transducer (NOFT) with sub-piconewton force sensitivity and a nanoscale footprint that paves the way to the probing of complex mechanical phenomena inside biomolecular systems. The NOFT platform comprises a SnO2 nanofiber optic equipped with a thin, compressible polymer cladding layer studded with plasmonic nanoparticles (NPs). This combination allows angstrom-level movements of the NPs to be quantified by tracking the optical scattering of the NPs as they interact with the near-field of the fiber. The distance-dependent optical signals can be converted to force once the mechanical properties of the compressible cladding are fully characterized. In this protocol, the details of the synthesis, characterization, and calibration of the NOFT system are described. The overall protocol, from the synthesis of the nanofiber optic devices to acquisition of nanomechanical data, takes ~72 h.
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This work was supported by the National Science Foundation (ECCS 1150952) and the University of California, Office of the President (UC-LFRP 12-LR-238415). This work was performed in part at the San Diego Nanotechnology Infrastructure (SDNI) of UCSD, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation (grant ECCS-1542148).
The authors declare no competing interests.
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Key references using this protocol
1. Huang, Q. et al. Nat. Photon. 11, 352–355 (2017): https://doi.org/10.1038/nphoton.2017.74
2. Ma, Y. G. et al. ACS Photonics 3, 1762–1767 (2016): https://doi.org/10.1021/acsphotonics.6b00424
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Shi, Y., Polat, B., Huang, Q. et al. Nanoscale fiber-optic force sensors for mechanical probing at the molecular and cellular level. Nat Protoc 13, 2714–2739 (2018). https://doi.org/10.1038/s41596-018-0059-9
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