Manipulation of Microbeads using DC/AC Electrical Fields What is Dielectrophoresis Forces Involved!! Dielectrophoretic Force Electrohydrodynamic Forces
Ripley, Tom, Contributing Editor has reference to this Academic Journal, PHwiki organized this Journal Manipulation of Microbeads using DC/AC Electrical Fields By, Michael Scharrer Nitin Sharma Neil Krishnan What is Dielectrophoresis Moment of Polarizable particles under the action of AC electrical field. Forces Involved!! Deterministic as long as ces Dielectrophoretic Hydrodynamic Sedimentation R in addition to om Brownian
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Dielectrophoretic Force Gradient in electrical Field Volume of the particles Polarizability of the particles Frequency of AC signal Negative in addition to Positive Dielectrophoresis Electrohydrodynamic Forces Natural Convection Density variation Coulomb Charge gradients Dielectric Permittivity gradients Brownian Force Gives a Gaussian Probability distribution to the particle. Higher the time scale of observation more is the deterministic movement observed.
Procedure Procedure First method cover slide Second method Droplet in addition to probes Third method Wafer flooding First Method : Cover slide Use Gold electrodes Adjust probes to touch the contact pads of electrodes Place a small droplet (2.5l) at the site of interest Cover with a cover slide cut to appropriate size Problems Evaporation Contact
Second Method : Droplet in addition to Probes Use probes as electrodes Position probes to lie flat on cover slide Place a large droplet (0.1 ml) at the site of interest Advantage Dont need to worry about contact Evaporation is much slower Third method : Flooding wafer Glass wafer with gold electrodes placed in a petri-dish Petri-dish flooded with solution till wafer is immersed Same as first procedure Advantages Evaporation effects are minimal Beads are more stable Disadvantages Difficult to position probes Difficult to see beads Results in addition to Discussion Positive DEP was achieved once by Carmen in addition to Changhong. Result could not be repeated. Conditions used:
After changing the procedure by using the probes directly as electrodes, we got some accumulation of beads on the probe tips. Excessive motion of beads made results unreliable in addition to unrepeatable. Problems Complicated set-up (focusing, establishing contact, applying cover slide) Lack of control over experimental variables (conductivity, voltage) Noise from excessive motion of beads Recommendations Implement measuring the conductivity of the buffer/beads solution. (A set-up to do this as long as small amounts of liquid probably exists on campus. We tried to locate the necessary equipment but were not successful in the given time.) Fabricate a glass cover to constrain the liquid in the electrode region, prevent quick evaporation in addition to excessive motion of the beads. This work was started, but not finished in time. It should be straight as long as ward using microscope slides in addition to glue.
Integrating the electrical probes on the microscope stage: This would allow the stage in addition to viewing area to be moved after electrical contact has been established. Redesign wafer to allow all electrodes to be contacted from the same pads: This would allow the probes to quickly be brought into contact after the liquid has been applied in addition to the microscope has been focused. Improve the adhesion of the Au electrodes on the wafer. Currently the electrodes have a tendency to peel off at higher voltages (~4V) which obviously limits the range of conditions that can be applied.
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