Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Quantum Dots Go With the Flow

25.05.2010
Quantum dots may be small. But they usually don’t let anyone push them around. Now, however, JQI Fellow Edo Waks and colleagues have devised a self-adjusting remote-control system that can place a dot 6 nanometers long to within 45 nm of any desired location. That’s the equivalent of picking up golf balls around a living room and putting them on a coffee table – automatically, from 100 miles away.

QDs can be moved with “optical tweezers” – a system that sets up a gradient of forces from multiple laser beams – or by electrophoresis, in which a microscopic object with a surface charge can be pushed through a fluid or gel by applying a constant electric field. (Electrophoresis provided an early method of separating DNA for analysis.) To date, however, results from both methods have been insufficiently exact for anticipated applications, and typically move multiple particles at once.

But now a research team headed by Waks and Benjamin Shapiro of UMD’s Fischell Department of Bio-Engineering has invented a fully automated apparatus that controls the position of a single QD by manipulating the fluid in which the dots are immersed. The system exploits a phenomenon called electroosmosis, in which liquids with polar molecules such as water are pulled in specific directions by applied electrical fields.

At the ends of each channel are cylindrical fluid reservoirs, each of which contains a platinum electrode. By altering the voltage between pairs of electrodes, the scientists control the motion of the fluid in two dimensions.

To position a dot, the researchers first identify a single QD with a microscope. This is possible because when a dot is struck by a green laser beam (532 nm), it begins to blink, emitting red photons at 655 nm. The blinking light is detected and the individual dot’s motion is tracked by a microscope. When the dot goes “dark,” the tracking pauses until the next blink. When the QD blinks, its position relative to the target location is re-detected.

The researchers programmed their device to calculate how much voltage will be required to shove the dot by the right amount in the desired direction. At each blink, an appropriate voltage is applied to the electrodes. [See diagram at bottom.] The QD thus proceeds to its intended destination by a series of nudges. Once there, the system can keep it in place for more than an hour.

One potential problem the group faced is that the dots not only move in two dimensions, but also rise and fall within the fluid. As a result, the imaging microscope loses its sharp focus and the dot can be lost. The scientists compensated for this effect by programming their microscope to detect the onset of fuzziness in the image and automatically adjust its distance to the dot accordingly.

The microfluidic array, including reservoirs and electrodes, is about the size of a postage stamp. It fits easily atop a microscope slide which is placed on a small platform with a circular hole in the middle.

The microscope is located beneath the slide, and refocuses using a piezoelectric transducer – a device that allows extremely small displacements of special materials when exposed to electric potential. The microscope image is routed to a digitalcamera that records 20 frames per second. The entire system operates at room temperature and pressure.

Using the device, the scientists were able to move a single dot very accurately along a planned trajectory at an average rate of about two micrometers per second, pausing at intervals between blinks.

This “ability to individually select, characterize and position single nanoscopic objects with nanometer precision,” the team writes, “could enable integration of single quantum dots, or other visualizable nanoscale objects, with photonic structures and enable the development of novel nanophotonic devices and sensors.”

Curt Suplee | Newswise Science News
Further information:
http://www.umd.edu

Further reports about: Dots Flow Structure Quantum laser beam optical tweezer quantum dot

More articles from Physics and Astronomy:

nachricht New quantum liquid crystals may play role in future of computers
21.04.2017 | California Institute of Technology

nachricht Light rays from a supernova bent by the curvature of space-time around a galaxy
21.04.2017 | Stockholm University

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

Im Focus: Quantum-physical Model System

Computer-assisted methods aid Heidelberg physicists in reproducing experiment with ultracold atoms

Two researchers at Heidelberg University have developed a model system that enables a better understanding of the processes in a quantum-physical experiment...

Im Focus: Glacier bacteria’s contribution to carbon cycling

Glaciers might seem rather inhospitable environments. However, they are home to a diverse and vibrant microbial community. It’s becoming increasingly clear that they play a bigger role in the carbon cycle than previously thought.

A new study, now published in the journal Nature Geoscience, shows how microbial communities in melting glaciers contribute to the Earth’s carbon cycle, a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

New quantum liquid crystals may play role in future of computers

21.04.2017 | Physics and Astronomy

A promising target for kidney fibrosis

21.04.2017 | Health and Medicine

Light rays from a supernova bent by the curvature of space-time around a galaxy

21.04.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>