Scanning probe electromagnetic tweezers

We present a micromanipulation technique that utilizes integrated microcoils and magnetic microtips for localized positioning of micron-sized magnetic objects. Forces of 10 pN, and. submicron positioning control are demonstrated on the 2.8 mum diameter superparamagnetic beads. The technique also implements an optical illumination scheme that provides a clear viewing of the magnetically trapped objects without including the scattering background from the magnetic manipulator tip. This simple instrument provides a noninvasive, low cost alternative to the optical trapping techniques normally used in micromanipulation. Among the possible advantages are the negligible heating of the manipulated sample, effective decoupling of the manipulation component of the experiment from the optical studies of the systems of interest, and the ability to perform studies in a variety of fluids. (C) 2001 American Institute of Physics.