<title>Optical trapping forces calculation by dielectrophoresis</title>

Abstract

In this work we present a laser trapping system based on an Ar⁺ laser and the calibration method we used for the optical trapping force measurements on polystyrene spheres. The method uses the dielectrophoretic force exerted on a dielectric particle from an inhomogeneous electric field for the calculation of the optical force. We used polystyrene microspheres on a dielectrophoretic chamber with planar electrodes in the optical tweezers setup. For the determination of the dielectrophoretic force the method is based on Green's theorem. A sphere is trapped in the optical tweezers at various laser powers. An electrical field is applied between the electrodes and thus a dielectrophoretic force is exerted on the particle. The electric field is increased very slowly until the cell is pulled out from the trap. At this moment the optical force equals the dielectrophoretic force, which can be theoretically calculated. This algorithm is repeated several times and the optical force is graphically represented as a function of laser power. Forces of some pN were calculated.