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iPad Lets Scientists Drag, Pinch and Swipe Real Molecules

* By Lisa Grossman Email Author
* March 3, 2011 |
* 7:03 pm |
* Categories: Physics, Tech
*



Using laser beams to control individual molecules is a precise, difficult operation rendered nearly impossible by the limitations of the computer mouse.

Unless you have the right iPad app.

New software called iTweezers lets scientists drag molecules around the screen as easily as shooting angry birds at pigs.

“It’s cool because it takes something that normally lives on a lab bench, and makes it so simple,” said physicist Richard Bowman of Scotland’s University of Glasgow, lead author of a paper in the March 4 Journal of Optics describing the new software. “We have visitors who have never seen an optical tweezer before in their lives, and they happily move particles around.”
The new app is an interface for controlling optical tweezers, an instrument that uses laser light to trap and move microscopic objects. It works a little like a sci-fi tractor beam: The radiation from a tightly focused beam of light applies enough pressure to tiny objects like cells or proteins to pin them to the spot or push them around.

The invention of optical tweezers won Secretary of Energy Steven Chu a Nobel Prize in Physics, and they have proven their worth in biology labs, where they have been used to trap and manipulate everything from viruses to DNA. They have helped measure some of the smallest forces ever recorded, detected how DNA’s double helix unzips, and watched molecular motors move matter around inside cells.

But most of the early experiments with optical tweezers could only focus on one spot at a time.

“Up till now, people typically controlled things using a mouse,” said physicist Gordon Love of Durham University in England, who was not involved in the new work. “A mouse is great for moving around one thing like a cursor on a screen, but it’s no good for moving around multiple things.”

The multitouch interface was born when Bowman’s colleagues at England’s University of Bristol struggled to control a tiny rod about 300 nanometers wide. To keep the rod from flipping over, the physicists needed to pin the rod down in several places at once.

In 2009, the team built a custom table that let them drag and drop microscopic glass beads just by swiping their fingers along a layer of paper coated with silicon rubber. The device was clunky and complicated, but it mostly worked.

But soon the team found a more elegant setup: the iPad.

“When the iPad came out we thought, well hey, this is just like the big table, except it’s small and works really well,” Bowman said.

The physicists shine laser light through a high-powered microscope onto a slide holding whatever objects the scientists are interested in. Bowman’s lab usually uses glass beads about two microns across, which are used in many experiments as a handle for harder-to-grasp molecules.

Before entering the microscope, the laser beam bounces off a tiny LCD screen that splits the beam and steers it around to focus on several beads at once.

A computer tells the LCD screen to display specific holograms designed to bend the laser light in specific ways. The app Bowman and colleagues use to write the holograms is available on iTunes as iHologram.

“It’s fun to use and quite visually attractive,” Love said. “My young daughters play with it. They have no idea about optical tweezers, but they think it’s fantastic.”

The iPad displays the view through the microscope, and wirelessly sends the computer the information on where the user’s fingers are. A user can select up to 11 different objects by tapping them, move them around by dragging them, and use the pinch-zoom feature to move the objects up and down in space.

Theoretically, scientists could be sitting on the couch with an iPad at home moving beads or molecules in the lab. But so far, the method hasn’t made it out of the University of Glasgow physics lab. The researchers hope to bring it into other labs to help biologists and chemists run complicated experiments without stressing about the technology.

“The interface makes it really easy,” Bowman said. “If somebody comes along and sees my computer program with about a bajillion controls on it, it’s a bit off-putting. Whereas the iPad lets you get stuck right in there and move stuff around, without having to worry about setting up all the physics behind it.”

Feeling like you can directly touch cells and molecules can also help build an intuitive sense of the microscopic world, Bowman says. His lab has also developed a way to manipulate molecules with a joystick that transmits the forces the molecule feels to the user’s hand, like a video game with tactile feedback. Bowman says you can even feel water molecules jiggling around your trapped molecule.

“The interface stuff is fun, but I think you can learn stuff by physically connecting in a different way,” he said. “You get a feel for how things work.”