Optoelectronic tweezers created to sort cells
researchers to manipulate large numbers of single cells and
particles using optical images projected onto a glass slide coated
with photoconductive materials. The device could prove essential in
a number of pharmaceutical R&D applications.
Rounding up wayward cells and particles on a microscope slide can be difficult particularly if there's a need to separate single individuals from the group. The technique has the 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.
"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," he added.
Wu and his UC Berkeley graduate students, Pei Yu Chiou and Aaron Ohta, used 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 behaviour 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 foetal 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. "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."
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.
This technique, reported in the July 21 issue of the journal Nature.
