Optical tweezers setup.

Light from a titanium-sapphire laser (λ = 830 nm) is reflected by a dichroic mirror and is focused onto the objective lens of the inverted microscope to trap the bead. A charged-coupled device (CCD) camera collects 10% of the light for image visualization. The CHO cell and VWF-coated bead are in a solution chamber mounted onto a piezoelectrically driven translational stage.