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New Nanofibers Detect Motion of Individual Bacteria, Muscle cells

Engineers have built a nanoscale stethoscope, basically.

by Michael Byrne
May 15 2017, 3:00pm

Rhett Miller/UC Regents

With a diameter of about .5 micrometers, H. pylori is among the smaller bacteria. At these scales, approaching the wavelength of infrared radiation, we even start to have a hard time talking about "things" at all. Observing the interactions and changes associated with those things typically requires an atomic force microscope, and, even then, is imprecise.

Thanks to engineers at the University of California San Diego's Sirbuly Lab we have a new window into this supertiny world in the form of a nanoscale optical fiber. The new fiber, which is about 100 times smaller than a human hair, can detect the motions of individual H. pylori. It can register sounds from beating heart cells down to -30 decibels, a thousand times quieter than can be detected by the human ear. The group's work is described this week in the journal Nature Photonics.

Why do we care so much what happens at these scales? Because this is where very bad things start. Cancer starts in a single cell, often as the result of some mechanical change or deformation, itself possibly caused by an external trauma (like cigarette smoke). Viral infections likewise start at the cellular level as just a single virus particle commandeering just a single cell, starting a chain reaction of viral reproduction and cellular takeover that might eventually swamp entire physiological systems.

To quote from the Sirbuly Lab website: "As research pushes the frontiers of medicine and bioengineering, tracking and quantifying molecular-level forces, displacements, and torques will be become a critical component to unraveling the mysteries of the cell and Nature's marvelous ability to sustain life. Furthermore, measuring nanomechanical events or mechanical responses is essential for developing novel label-free diagnostic devices and analytical probes. Most molecular machines and biological systems operate in the piconewton range and in complex media which puts immediate constraints on instrumentation."

Properly, the fiber is known as a nanofibre optic force transducer (NOFT). It consists of a thin strip of tin oxide coated in a polymer layer (polyethylene glycol, which is kind of in everything) which itself is embedded in tiny gold dots. The fiber is dipped into a solution containing some target cells and then has a beam of light sent down its length. The light signals that bounce back encode information about the motions of cells in the solution

This works because the cells in the solution push up against the gold particles as they do their normal cell stuff. This pushing means that the light beam will interact with the gold particles differently, resulting in a different signal being returned. The polymer is key as it acts like a "spring mattress," naturally squishing and deforming under even tiny bits of pressure. What's more, the fiber can be tuned to register different intensities of forces.

The result is an "ultra-sensitive biological stethoscope." I probably wouldn't expect to see it in your local diagnostic lab anytime soon, but the Sirbuly team imagines its NOFT eventually becoming a key tool in understanding biomechanics and the biology of the very small.