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 New manufacturing process for SiC power devices opens market to more competition
14.09.2017 | North Carolina State University

nachricht Quick, Precise, but not Cold
17.05.2017 | Fraunhofer-Institut für Lasertechnik ILT

All articles from Process Engineering >>>

The most recent press releases about innovation >>>

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

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Rainbow colors reveal cell history: Uncovering β-cell heterogeneity

22.09.2017 | Life Sciences

Penn first in world to treat patient with new radiation technology

22.09.2017 | Medical Engineering

Calculating quietness

22.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>