Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Engineers create optoelectronic tweezers to round up cells, microparticles

21.07.2005


Rounding up wayward cells and particles on a microscope slide can be as difficult as corralling wild horses on the range, particularly if there’s a need to separate a single individual from the group.


The images above show selective collection of live cells from a mixture of live and dead cells. In (a), the cells are randomly positioned. In (b) and (c), a series of optically projected concentric circles round up live cells, while dead cells (stained with Trypan blue dye) leak out through the dark gaps and are not collected. The optical pattern has a yellowish colour, while weak background scattered light results in a pinkish hue in the non-patterned areas. Section (d) shows the collection of live cells rounded up by the optoelectronic tweezer. (Courtesy of Wu Lab, UC Berkeley)


Shown is a schematic of the optoelectronic tweezer developed by UC Berkeley engineers. Liquid that contains microscopic particles is sandwiched between the top indium tin oxide (ITO) glass and the bottom photosensitive surface, made up of amorphous silicon (a-Si:H) and silicon nitride. The illumination source is a light-emitting diode operating at a wavelength of 625 nm. The optical images shown on the digital micromirror display (DMD) are focused onto the photosensitive surface and create the non-uniform electric field for manipulation of the particles. (Courtesy of Wu Lab, UC Berkeley)



But now, a new device developed by University of California, Berkeley, engineers, and dubbed an "optoelectronic tweezer," will enable researchers to easily manipulate large numbers of single cells and particles using optical images projected onto a glass slide coated with photoconductive materials.

"This is the first time a single light-emitting diode has been used to trap more than 10,000 microparticles at the same time," said Ming Wu, UC Berkeley professor of electrical engineering and computer sciences and principal investigator of the study. "Optoelectronic tweezers can produce instant microfluidic circuits without the need for sophisticated microfabrication techniques."


This technique, reported in the July 21 issue of the journal Nature, has an advantage over existing methods of manipulating cells, such as optical tweezers that use focused laser beams to "trap" small molecules. Such techniques require high-powered lasers, and their tight focusing requirements fundamentally limit the number of cells that can be moved at the same time.

Wu and his UC Berkeley graduate students, Pei Yu Chiou and Aaron Ohta, also improved upon other cell manipulation tools that use electrokinetic forces to create electric fields that either repel or attract particles in order to move them. Dielectrophoresis, for instance, can move larger numbers of particles. However, it lacks the resolution and flexibility of optical tweezers.

The UC Berkeley engineers found a way to get the best of both worlds by transforming optical energy to electrical energy through the use of a photoconductive surface. The idea is similar to that used in the ubiquitous office copier machine. In xerography, a document is scanned and transferred onto a photosensitive drum, which attracts dyes of carbon particles that are rolled onto a piece of paper to reproduce the image.

In this case, the researchers use a photosensitive surface made of amorphous silicon, a common material used in solar cells and flat-panel displays. Microscopic polystyrene particles suspended in a liquid were sandwiched between a piece of glass and the photoconductive material. Wherever light would hit the photosensitive material, it would behave like a conducting electrode, while areas not exposed to light would behave like a non-conducting insulator. Once a light source is removed, the photosensitive material returns to normal.

Depending upon the properties of the particles or cells being studied, they will either be attracted to or repelled by the electric field generated by the optoelectronic tweezer. Either way, the researchers can use that behavior to scoot particles where they want them to go.

There are many reasons why researchers would want the ability to easily manipulate cells. Biologists may want to isolate and study the fetal cells that can be found in a mother’s blood sample, for instance, or sort out abnormally shaped organisms from healthy ones.

"This sorting process is now painstakingly done by hand," said Wu, who is also co-director of the Berkeley Sensor and Actuator Center. "A technician finds the cell of interest under a microscope and literally cuts out the piece of glass where the cell is located, taking care not to harm the sample."

"Our design has a strong practical advantage in that, unlike optical tweezers, a simple light source, such as a light-emitting diode or halogen lamp, is powerful enough," said Chiou, a Ph.D. student in electrical engineering and computer sciences and lead author of the paper. "That is about 100,000 times less intense than the power required for optical tweezers."

Moreover, since the optoelectronic tweezers generate patterns through projected light, an almost limitless range of patterns are possible. Interested in boxing up individual particles in a grid-like pattern? No problem. Perhaps a star pattern would be more interesting. And there’s no reason why the light needs to be static, so the researchers have even created moving conveyor belts to show how large particles can be automatically sorted from smaller ones.

"We can almost change these patterns on the fly," said Ohta, also a Ph.D. student in electrical engineering and computer sciences. "For other manipulation tools, changing these electrode patterns meant fabricating a new chip. Now, we can just project a new image to generate any type of pattern we want."

The researchers also took advantage of the difference in electrical conductivity between living and dead cells. Living cells with intact membranes in a lower conductive medium are attracted to areas of exposed light. Using a series of ever shrinking concentric circles, the researchers were able to round up living human immune cells while leaving dead ones behind.

Chiou added that while researchers can use the optoelectronic tweezer to study a few single cells, they would also have the choice of manipulating roughly 10,000 cells or particles at the same time, giving statistical weight to their studies.

The researchers are now studying ways to combine this technology with computer pattern recognition so that the sorting process could be automated. "We could design the program to separate cells by size, luminescence, texture, fluorescent tags and basically any characteristic that can be distinguished visually," said Wu.

Part of Wu’s research was conducted while he was an electrical engineering professor at UC Los Angeles, and a co-principal investigator at NASA’s Institute for Cell Mimetic Space Exploration, headquartered at UCLA’s Henry Samueli School of Engineering and Applied Science.

Sarah Yang | EurekAlert!
Further information:
http://www.berkeley.edu

More articles from Life Sciences:

nachricht A Map of the Cell’s Power Station
18.08.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau

nachricht On the way to developing a new active ingredient against chronic infections
18.08.2017 | Deutsches Zentrum für Infektionsforschung

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

A Map of the Cell’s Power Station

18.08.2017 | Life Sciences

Engineering team images tiny quasicrystals as they form

18.08.2017 | Physics and Astronomy

Researchers printed graphene-like materials with inkjet

18.08.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>