Optical torque wrench imitates communication between neurones
Using an optical torque wrench, an international team of researchers have shown that rotating microscopic cylinders are excitable. This system therefore demonstrates dynamic properties based on the same physical properties as, for example, neurones when these communicate with each other by means of action potentials. The researchers have also demonstrated that this optomechanical system can detect microscopic particles in fluids. The researchers from the Kavli Institute of Nanoscience at Delft University of Technology and the Institut Non Linéaire de Nice, published the results of this FOM-funded research on the website of Nature Physics on 19 December 2010.
Many non-linear systems in nature are excitable, and the best-known example of this is the neuronal cell. The word 'excitable' characterises the response of such systems to external disturbances: if any disturbance occurs above a critical value, the response of an excitable system always takes the form of a pulse with a constant amplitude. Neurones, for example, communicate with each other by means of voltage pulses of constant amplitude (also known as action potentials) that are a consequence of their excitable character.
An optical torque wrench is a unique instrument that can measure both the force and the impulse moment exerted on microscopic objects and therefore on the biological molecules attached to it such as DNA. By constructing and using such an instrument to study the rotation of quartz nanocylinders (see Figure), the researchers could demonstrate that such rotating micro-objects have an excitable character. With this behaviour the optomechanical system exhibits dynamic characteristics that are based on the same physical principles as the functioning of neurones, for example.
In the optical torque wrench that undergoes an interaction with a quartz microcylinder, the impulse moment detected on the cylinder is directly analogous to the action potential in neurones. Disruptions with sufficient amplitude, in the form of changes in the local viscosity of the fluid in which the cylinder is located, elicit a response in the form of a pulse in the detected impulse moment. The analogy with the neuronal dynamics agrees in theory: the equations that accurately describe this optomechanical system are identical to the equations that are used in simulations of simple neuronal networks.
The researchers also demonstrated that this microscopically excitable system can be used for the detection of microscopic particles. If such a particle comes close to the rotating microcylinder then it has a disruptive effect that gives rise to a simple detectable response in the impulse moment. This provides a method for detecting, counting or separating cells or other microscopic particles in a liquid.
This research was funded by FOM and forms part of the FOM programme 'DNA in Action – Physics of the Genome'.
Meer informatie
Dr. Francesco Pedaci (Department of Bionanoscience, Kavli Institute of NanoScience, Delft University of Technology); (015) 278 35 52.
Prof.dr. Nynke Dekker (Department of Bionanoscience, Kavli Institute of NanoScience, Delft University of Technology); (015) 278 32 19.
Reference
F. Pedaci*, Z. Huang*, M. van Oene, S. Barland and N.H. Dekker (* = equal contribution) 'Excitable Particles in an Optical Torque Wrench' Nature Physics (2010).