An app for your optical traps
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
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
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
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.
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