|Twisting and Stretching
||Adding a twist to DNA
Parallel illumination and camera
Another unique and extremely powerful feature of PicoTwistís magetic
tweezers apparatus is its ability to measure the Z position of the
bead of interest in real-time. To achieve this goal, the microscope is
illuminated with a parallel light beam emitted by a high-brightness
LED. Under these conditions, the bead image is decorated with a series
of diffraction rings whose shape and number vary regularly as the
image is progressively defocussed. Using a lookup table of the beadís
diffraction pattern, the acquisition software has been designed to
evaluate the bead z position from the defocussed image of the
diffraction rings. LED illumination provides a very stable, easily
adjustable light source whose spatial coherence is sufficient to
obtain a sharp ring pattern and which is sufficiently low power to
avoid spurious interference effects.
The image of the bead is obtained through a fast CCD camera coupled to the microscope. The standard device is proposed with a 768 x 576 pixels 60 Hz camera, we can also provide it with a 1380 x 1040 pixels 31 Hz camera.
For further information please contact picotwist.