An app for your optical traps

Caren B. Les, caren.les@photonics.com

Scientists and nonspecialists alike now can easily manipulate microparticles, particularly for research in molecular biology, right on their iPads, thanks to a new app called iTweezers.

The application was developed by optics researchers at the universities of Glasgow and Bristol in the UK and documented in the March 4, 2011, Journal of Optics. The new technique represents an advance over traditional joystick- or mouse-controlled optical tweezer systems, which are limited in their ability to control several particles in 3-D at once.

The Apple iPad application iTweezers provides intuitive control of holographic optical tweezers, or “traps.” Courtesy of Graham Gibson. (Below) An artist’s impression of a bead in an optical trap. Photo courtesy of Richard Bowman.

The Apple iPad-based interface allows intuitive control of a holographic optical tweezing system using a dedicated application on the iPad and a modified version of the tweezers’ control software running on a host computer. The use of a spatial light modulator to steer and multiplex a laser beam allows multiple particles to be interactively manipulated in three dimensions, according to the report.

A microscope image is displayed on the iPad’s 10-in. color touch screen, overlaid with markers that represent optical traps. The researchers used the jpeg compression available in National Instruments’ Vision library to stream about 10 fps from a control personal computer to the iPad over a wireless network.

Users can drag up to 11 optical traps simultaneously around on the screen, which has a capacitive touch sensor. With a double tap on the screen, they can create, remove or move the traps, and with a “pinch” gesture, can move a particle up or down. They also can move single or multiple particles from left to right and rotate them. Tilting the iPad will move the particles as well. Inexperienced users can perform all these actions and translate the microscope stage as well, the researchers say.

Trap positions are synchronized over the wireless network with a desktop computer that controls the spatial light modulator using LabView software. The wireless capability also provides benefits in terms of laser safety and contamination control.

Holographic optical tweezers are becoming a standard tool, and the technology is now routinely used by nonspecialists. Optical tweezers have been used to trap particles such as dielectric spheres, viruses, bacteria and living cells in applications including cell sorting, the tracking of particle movement in bacteria and the altering of larger structures, such as cell membranes, and in the study of molecular motors and the physical properties of DNA.

And now, there’s an app for that.