We report diamagnetic levitation of droplets and/or particles of pico-femtoliter volume and demonstrate their on-chip storage and high precision manipulation (translation, merging, assembling and rotation). We also demonstrate a levitation based microfluidic processor to process droplets/particles with up to a billion times smaller volume than in typical microfluidic devices. The levitated particles can be positioned with up to 300 nm accuracy and precisely rotated and assembled, providing a different physical approach for Micro-Electro-Mechanical-Systems. Force can be applied to the droplets/particles via magnetic or electric fields from electrodes.

The core of Magnetic Micromanipulation Chip (MMC) consists of two 10mmX10mmX h neodymium-iron-boron permanent magnets with height h in the range 0.1mm - 2mm mounted on a steel substrate which contains a set of electrodes directed perpendicular to the slit between the magnets (see Figure). The magnetization of the permanent magnets is directed in-plane, normal to the slit of width and opposite in direction to each other. The magnetic field is estimated to be 0.5T on the magnet surface with a minimum that lies along a line between the magnets. The levitating droplets/particles have a small induced magnetic moment directed opposite to the magnetic field. Interaction of this moment with the magnetic field gradient provides the force which levitates the droplet/particle.

Figure shows five sequentially timed snapshots of back and forth motion of a 30 micron diameter glycerine/water droplet levitated above a substrate with electrodes (5 are shown). The droplet has stable local energy minima between the electrodes. The magnetic field generated by current pulses in the electrodes moves the droplet along the slit from one potential minimum to another (see VIDEO 1, (size 1MB), see also extended version VIDEO 1a (size 4MB), ).

Droplets also can be merged. Figure shows three sequentially timed snapshots (top view) of a controllable merging of 22 micron and 24 micron diameter glycerine/ water droplets moved by currents in the electrodes (3 are shown). The resulting combined droplet is 29micron in diameter. See also VIDEO 2 (size 1MB) , and extended version VIDEO 2a (avi file) (size 1MB) .

We have grown crystals of NaCl from droplets of corresponding water solutions. Crystal anisotropy of the levitated particles permits their precise rotation by application of an AC electric field (10000 V/m) between the two permanent magnets in the trap (see Figure and VIDEO3 (size 1MB), ).