Scientists Create First 'Nano-Ear' to Listen in on Sounds of Cells

It’s a marvelous piece of nanotech innovation using gold nano-particles and an existing technology known as “optical tweezers” and it will enable scientists to eavesdrop on the private lives of bacterial cells, and even viruses, as they move about and replicate.

The so-called “nano-ear” is actually an intricate system of lasers and gold nano-particles (note: the term “nano” indicates one billionth of a meter in size or smaller) which harnesses the resonating vibrations of these particles when in proximity to other vibrating particles suspended in water.

Researchers claim that the new technology can detect sounds up to a million times fainter than the bottom range of human hearing (which is about 200 Hz) and predict it will serve as the basis for the new scientific field of acoustic microscopy which will seek to describe cellular states and behaviors in terms of the sounds they emit.

'nano ears' using gold nanoparticles and optical tweezers
The movement of a gold nanoparticle (left) in a set of optical tweezers was used to detect sound waves triggered by the expansion of other nanoparticles nearby. Credit: Ohlinger et al., Phys. Rev. Lett. 108, 018101 (2012)


Applying the ‘Optical Tweezers’ technique

One of the two components of the nano-ear system — the optical tweezers — utilizes a lens-focused laser beam to trap tiny particles and so move them from one location to another. The technique has been used since the mid 1980’s and has become a standard tool in microbiology labs where it is commonly used to inject DNA fragments into cells where it can be further manipulated.

But the tweezers can also be used to monitor minute forces acting on cells and microscopic particles; instead of using the laser to move the objects within cells, researchers use it to hold a particle steady and then use microscopes to observe how said particle moves on its own or in response to internal (or external forces).

How the the Nano-Ear works – Picking up tiny vibrations

Researchers at the Photonics and Optoelectronics Group at the University of Munich in Germany, led by optical physicist Jochen Feldmann, used this approach with gold nano-particles; a single gold particle, measuring just 60 nanometers in diameter, was immersed in water and held fast by the optical tweezers.

The researchers then were able to monitor the back-and-forth movements of this particle in response to acoustic vibrations (or sound waves) resulting from the laser-stimulated heating of multiple gold nanoparticles suspended in water nearby the first particle.

This approach allowed researchers to analyze the movements of the first nanoparticle with “unprecedented sensitivity” and also determine which direction the sounds (the vibrations) were coming from — similar to the direction-detecting ability of an actual, macroscopic ear.

Future medical applications

The researchers envision 3D arrays of nano-ears being used to more precisely listen in on cells and other micro-organisms, like bacteria and even small viruses. All such organisms emit tiny acoustic vibrations as they move and carry out their cellular or viral functions (like replicating).

It may also be possible to determine changes in a cell that could signify malfunction or disease onset, such as a pre-cancerous state.

However, in the near term, scientists will have to work to refine the ‘acoustic microscope’ technique so as to distinguish between the normal, background noise of the cellular environment (molecules are constantly vibrating ‘randomly’) and specific sound waves that could indicate bacterial/viral infection or cellular disease.

Source material for this post came in part from the Science NOW article: Scientists Create World’s Tiniest Ear

For more informaiton on the ‘optical tweezers’ technology, check out A Perfect Lens Makes Perfect Tweezers

Top image: (Cultured MDCK epithelial cells, stained for keratin, desmoplakin, and DNA, visualized by scanning laser confocal microscopy) by Helix84 ; CC – BY – SA 3.0

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