IntroductionIn the past 25 years, integrated circuit (IC) and microelectromechanical systems (MEMSs) technologies have moved much beyond the microdomain, and into the submicro-, nanoscopic, and, even, the molecular scales. Today, we have the capability to fabricate, manipulate, and assemble matters at the micro-, nano-, or molecular scales. This progress into "seeing" and manipulating matters that are smaller than visible light wavelength scale is impacting a range of fields including semiconductor physics, biological studies, pharmaceutical development, and many other scientific and technological applications. A range of new methods to generate physical forces have been developed in the process. For example, mechanical forces can now be applied to micro-, nano-, and biological entities using atomic force microscope probes [1], microgrippers [2], or pipettes [3]. However, disadvantages of these approaches, including inflection of mechanical damages on objects being manipulated and their relatively low manipulation speed, make manipulation of large quantities of objects difficult. In order to address these disadvantages, noncontact or noninvasive methods for micro-, nano-, and biological manipulation have also been explored in the past two decades.Manipulation devices based on magnetic forces [4], acoustic waves [5,6], hydrodynamic flows [7], light waves [8], or electrokinetic forces [9] are among the major noninvasive technologies available today. Each of them has its own advantages and disadvantages. Methods based on magnetic fields need premodification on objects with magnetic beads which constrains their application domain. In addition, movement controlled by permanent magnets is not precise enough for many proposed applications. Also, the high resistance of the magnetic coil generates significant heat during manipulation [10]. Acoustic traps show good selectivity but cannot achieve parallel manipulation of single entities. Microfluidic devices exploiting hydrodynamic flows are suitable for cell population sorting, but have difficulties in trapping or controlling specific single objects.Electrokinetic forces generated from patterned electrodes capable of inducing the desired spatial distribution of electric field have been exploited to control