Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Optical control technique could enable microfluidic devices powered by surface tension

06.08.2003


Video images under monochromatic illumination show the optical selection and control of thin film flow patterns on horizontal substrates. For each of the first three images, the film pattern is shown at two different times. The lower third of each image displays a thin film those contact line is initially straight.
Image copyright: Physical Review Letters


Schematic illustration of microflow that is optically driven via the thermocapillary effect. An intensity-modulated beam from a light source illuminates a substrate that supports a tiny quantity of liquid at one end. Temperature variations arise from light absorption and induce surface tension gradients that drive the flow from the brighter (hotter) to darker (cooler) regions on the substrate.
Image copyright: Physical Review Letters


Reprogammable microarrays

Physicists at the Georgia Institute of Technology have demonstrated a new optical technique for controlling the flow of very small volumes of fluids over solid surfaces. The technique, which relies on changes in surface tension prompted by optically-generated thermal gradients, could provide the foundation for a new generation of dynamically reprogrammable microfluidic devices.

A paper describing the technique is the cover story for the August 1 issue of the journal Physical Review Letters. The research has been supported by the National Science Foundation and the Research Corporation.



Existing microfluidic devices, also known as "labs-on-a-chip," use tiny channels or pipes etched into silicon or other substrate material to manipulate very small volumes of fluid. Such "micropipe" devices are just beginning to appear on the market.

The Georgia Tech innovation could allow production of a new type of microfluidic device without etching channels. Instead, lasers or optical systems similar to those used in LCD projectors would produce complex patterns of varying-intensity light on a flat substrate material. Absorption of the light would produce differential heating on the substrate, creating a pattern of thermal gradients. Surface tension, a relatively strong force at micron size scales, would then cause nanoliter volumes of fluid to flow from the cooler areas to warmer areas through thermocapillary action.

"We envision that this could move multiple droplets or packets of fluid simultaneously, allowing arrays of drops to be moving at the same time at multiple locations," said Michael Schatz, a Georgia Tech associate professor of physics. "We could avoid putting detailed architectures onto the substrate. Instead, we would take advantage of advances in the miniaturization of optoelectronics to pattern the substrate with surface tension forces."

Because the temperature gradients would be formed by computer-controlled light patterns, pathways for the droplets could be quickly changed, allowing a reconfiguration not possible with existing microfluidic devices. And because the surface tension effects are strong at the micron scale, they could produce flow rates higher than channel-based microarrays, which must overcome large frictional forces. Finally, the substrate could be easily cleaned between uses, avoiding contamination.

In their paper, Schatz and colleagues Roman Grigoriev and Nicholas Garnier report their studies of how thermal gradients affect thin films of silicone oil on a surface of glass. The bottom of the glass had been painted black to absorb light, and a heat sink provided to prevent overheating.

The technique could theoretically also use liquid surfaces, where droplets of an immiscible liquid would be moved across a "substrate" fluid by the same surface tension forces. In a liquid-on-liquid system, the underlying fluid would also move, allowing higher flow rates.

In biological applications, fluids of interest are based on water, but Schatz says the optical principle could apply to most liquids. "This technique could apply to many fluid systems because it builds on an intrinsic property that nearly every fluid has – the temperature dependence of surface tension," he noted.

Though many technical hurdles remain, Schatz and his collaborators believe their technique could be the basis for a miniaturized lab-on-a-chip used for genetic or biochemical testing in the field. The easily reconfigurable system would be able to transport, merge, mix and split off streams of fluid flowing across a flat surface.

"If we can build devices that move fluids at small scales in a reconfigurable way, then in principle we can do all kinds of assays in the field at very high densities," Schatz explained. "This approach could be applied in a lot of different conditions."

Ultimately, the miniaturization of microfluidic devices could do for fluid handling what the modern semiconductor technology has done for electronics, allowing assays, chemical studies and other macro-scale processes to become smaller, cheaper and faster. "The shrinking of devices using microfluidics could be as revolutionary to our daily lives as microelectronics has been," Schatz said.

Unlike microelectronics, however, the drive to make microfluidic devices smaller and denser faces an immediate fundamental limit – the size of cells, DNA samples or protein molecules. If those are to be moved in fluid form, the microarray features can’t be much smaller than a few microns.

Among the challenges ahead for building optically-driven microfluidic devices are controlling evaporation, developing interfaces to get the tiny volumes of liquid onto the surface, and choosing the right combination of substrate and heat sink to provide distinct temperature gradient patterns without overheating the fluids, notes Grigoriev, an assistant professor in the School of Physics.

"We are at the point of testing strategies for constructing the building blocks, much like the transistors of microelectronics," he said. "Once those pieces are in place, it will be much more straightforward to bring them together into a working microfluidic device."

Technical contact: Mike Schatz, E-mail: michael.schatz@physics.gatech.edu

John Toon | EurekAlert!
Further information:
http://gtresearchnews.gatech.edu

More articles from Process Engineering:

nachricht Laser Processes for Multi-Functional Composites
18.02.2019 | Fraunhofer-Institut für Lasertechnik ILT

nachricht Efficient reactor dismantling by laser beam cutting?
05.02.2019 | Laser Zentrum Hannover e.V.

All articles from Process Engineering >>>

The most recent press releases about innovation >>>

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

Im Focus: (Re)solving the jet/cocoon riddle of a gravitational wave event

An international research team including astronomers from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has combined radio telescopes from five continents to prove the existence of a narrow stream of material, a so-called jet, emerging from the only gravitational wave event involving two neutron stars observed so far. With its high sensitivity and excellent performance, the 100-m radio telescope in Effelsberg played an important role in the observations.

In August 2017, two neutron stars were observed colliding, producing gravitational waves that were detected by the American LIGO and European Virgo detectors....

Im Focus: Light from a roll – hybrid OLED creates innovative and functional luminous surfaces

Up to now, OLEDs have been used exclusively as a novel lighting technology for use in luminaires and lamps. However, flexible organic technology can offer much more: as an active lighting surface, it can be combined with a wide variety of materials, not just to modify but to revolutionize the functionality and design of countless existing products. To exemplify this, the Fraunhofer FEP together with the company EMDE development of light GmbH will be presenting hybrid flexible OLEDs integrated into textile designs within the EU-funded project PI-SCALE for the first time at LOPEC (March 19-21, 2019 in Munich, Germany) as examples of some of the many possible applications.

The Fraunhofer FEP, a provider of research and development services in the field of organic electronics, has long been involved in the development of...

Im Focus: Regensburg physicists watch electron transfer in a single molecule

For the first time, an international team of scientists based in Regensburg, Germany, has recorded the orbitals of single molecules in different charge states in a novel type of microscopy. The research findings are published under the title “Mapping orbital changes upon electron transfer with tunneling microscopy on insulators” in the prestigious journal “Nature”.

The building blocks of matter surrounding us are atoms and molecules. The properties of that matter, however, are often not set by these building blocks...

Im Focus: University of Konstanz gains new insights into the recent development of the human immune system

Scientists at the University of Konstanz identify fierce competition between the human immune system and bacterial pathogens

Cell biologists from the University of Konstanz shed light on a recent evolutionary process in the human immune system and publish their findings in the...

Im Focus: Transformation through Light

Laser physicists have taken snapshots of carbon molecules C₆₀ showing how they transform in intense infrared light

When carbon molecules C₆₀ are exposed to an intense infrared light, they change their ball-like structure to a more elongated version. This has now been...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Global Legal Hackathon at HAW Hamburg

11.02.2019 | Event News

The world of quantum chemistry meets in Heidelberg

30.01.2019 | Event News

Our digital society in 2040

16.01.2019 | Event News

 
Latest News

JILA researchers make coldest quantum gas of molecules

22.02.2019 | Physics and Astronomy

Understanding high efficiency of deep ultraviolet LEDs

22.02.2019 | Materials Sciences

Russian scientists show changes in the erythrocyte nanostructure under stress

22.02.2019 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>