With the development of a nano-scale optic fiber detector around 100 times thinner than a human hair, researchers at the University of California San Diego (UCSD) have created a tiny super sensitive nanofiber device, which can detect forces down to 160 fems to newtons. Practically, it can sense from the turbulence generated by swimming bacteria to the sound waves made by the beating of heart cells.

This work could open up new doors to track small interactions and changes that couldn’t be tracked before, said study author and nanoengineering professor Donald Sirbuly at the UC San Diego Jacobs School of Engineering.

Nanofiber could be used for detecting the presence and activity of a single bacterium, monitoring bonds forming and breaking, sensing changes in a cell’s mechanical behavior or a mini stethoscope to monitor cellular acoustics in vivo.

This is an artist’s illustration of nano-optical fibers detecting fem to newton-scale forces produced by swimming bacteria. Image Credit: Rhett S. Miller/UC Regents

To measure biological forces in very small vessels, scientists need an instrument that can sit amidst cells, record the microscopic forces, so they can correlate them with how cells react. Since such tools don’t exist, UCSD researchers started to develop a nanofiber capable of being temporarily deformed by the microscopic forces.

If we compare to the atomic force microscope (AFM), which is an instrument that can measure infinitesimally small forces generated by interacting molecules, the optical fiber is at least 10 times more sensitive. Unlike AFM, this nanofiber is only several hundred nanometers in diameter, because it is made of an extremely thin fiber of tin dioxide.

To test their device, the UCSD researchers submerged it in a solution containing cells or bacteria. Then pumped light along the length of the optical fiber where it strongly interacted with the embedded gold nanoparticles and scattered. The intensity of this scattering changed when movement forces or acoustic waves from the cells struck the gold nanoparticles, forcing them into the layer of the polymer directly surrounding the fiber. These changes in intensity were then able to be detected by a conventional optical microscope, with the scientists calibrating the device to match signal intensities with distinct levels of sound or force.

We’re not just able to pick up these small forces and sounds, we can quantify them using this device. This is a new tool for high-resolution nanomechanical probing, Sirbuly said.

The UCSD researchers intend to improve the capabilities of their device to produce exceptionally sensitive biological stethoscopes, and further develop the acoustic response capabilities for use in new imaging techniques.