The heart of the measuring sofware designed by PicoTwist relies upon a real-time, nanometer resolution particle tracking system. Fast PC-based computer-assisted videomicroscopy offers a user-friendly measuring device. By clicking on the image of a magnetic bead of interest, the user starts the tracking process which delivers the 3D position of the bead in real time. The X,Y position is obtained using a correlation algorithm which follows the bead image, regardless of whether it is bright or dark, with sub-pixel accuracy. Comparing the diffraction ring pattern which surrounds the bead image, the software also computes the bead Z position for every video frame and with a resolution of a few nanometers.

The software is able to follow several beads simultaneously. Simulatenously tracking the bead of interest and a reference bead glued to the glass surface makes it possible to perform differential tracking which allows us to subtract residual apparatus drifts. The force and angular position of the bead may be modulated at will, while the bead�s 3D postion is acquired over hours, days or even weeks.

<< previous

next >>