In alternating current electrokinetics, electric fields are used to generate forces on particles. Techniques have been applied for the manipulation of particles and the measurement of their dielectric properties. The fields are typically generated by microelectrode structures fabricated on planar surfaces. One particular design, using interdigitated bar electrodes, is used both in dielectrophoretic field flow fractionation and travelling wave dielectrophoresis. This paper presents a Fourier series analysis of the dielectrophoretic force on a particle generated by this type of electrode array, for both dielectrophoresis and travelling wave dielectrophoresis. Simple expressions are derived for the force at a distance of the order of the electrode spacing from the electrodes. A full analytical expression is given for the dielectrophoretic force in two dimensions. Comparisons are made with previously published experimental observations.

This paper reports measurements that characterize the collection of DNA onto interdigitated microelectrodes by high-frequency dielectrophoresis. Measurements of time-dependent collection of 12 kilobase pair plasmid DNA onto microelectrodes by dielectrophoresis show significant reduction in the response as the frequency increases from 100 kHz to 20 MHz. Collection time profiles are quantitatively measured using fluorescence microscopy over the range 100 kHz to 5 MHz and are represented in terms of two parameters: the initial dielectrophoretic collection rate, and the initial to steady-state collection transition. Measured values for both parameters are consistent with trends in the frequency-dependent real part of the effective polarizability measured for the same plasmid DNA using dielectric spectroscopy. The experimentally measured parameters are qualitatively compared with trends predicted by theory that takes into account dielectrophoretic particle movement and diffusion. The differences between experiment and theory are discussed with suggested improvements to theoretical models, for example, including the effects of electrohydrodynamically driven fluid motion.

This paper presents a technique for measuring and quantifying the dielectrophoretic collection of sub-micron particles on planar microelectrode arrays. Fluorescence microscopy and video recording is used to measure the number of particles collecting on an electrode as a function of time for various experimental parameters, such as applied electrode voltage and frequency. Video images are processed using analytical methods that take advantage of the geometrical properties of the electrode array to extract quantitative information which is used to characterize the dielectric properties of particles. The time-dependent collection profiles can be characterized by three parameters: the initial dielectrophoretic collection rate, the initial to pseudo-steady-state transition and the rise time. This method can be used as a general technique to characterize the dielectrophoretic properties of populations of sub-micron-scale particles.

The dielectric properties of 12 kbp plasmid DNA have been measured as a function of temperature in the range 5 degrees C to 40 degrees C. Time domain reflectometry was used to obtain dielectric data over the frequency range from 200 kHz to 3 GHz. Values of the frequency dependent polarisability per DNA macromolecule have been determined from the measurements. Possible mechanisms that could account for the dielectric dispersion are also discussed, in particular the counterion fluctuation model of Manning-Mandel-Oosawa.

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Myosin-actin and kinesin-microtubule linear protein motor systems and their application in hybrid nanodevices are reviewed. Research during the past several decades has provided a wealth of understanding about the fundamentals of protein motors that continues to be pursued. It has also laid the foundations for a new branch of investigation that considers the application of these motors as key functional elements in laboratory-on-a-chip and other micro/nanodevices. Current models of myosin and kinesin motors are introduced and the effects of motility assay parameters, including temperature, toxicity, and in particular, surface effects on motor protein operation, are discussed. These parameters set the boundaries for gliding and bead motility assays. The review describes recent developments in assay motility confinement and unidirectional control, using micro-and nano-fabricated structures, surface patterning, microfluidic flow, electromagnetic fields, and self-assembled actin filament/microtubule tracks. Current protein motor assays are primitive devices, and the developments in governing control can lead to promising applications such as sensing, nano-mechanical drivers, and biocomputation.

In a non-uniform ac electric field, dipole forces cause polarizable particles to experience ponderomotive forces. The particle velocity is a function of the dielectric properties of the particle, the suspending medium, particle volume and the electric field gradient. Measurement of the collection rate of particles can be used to estimate their dielectric polarizability. In this work we have measured the collection rate of sub-micrometer particles collecting at the edges of a planar interdigitated electrode array The Fokker-Planck equation was used to simulate the spatial and temporal accumulation of particles at the electrodes. The experimental data shows that the collection rate decreases with increasing frequency of the applied field, in agreement with the predicted frequency-dependent reduction in the effective polarizability of the particles. Numerical simulations are in broad agreement with experimental results.

A new experimental system and theoretical model have been developed to systematically quantify and analyse the movement of nanoparticles subjected to continuously pulsed, or amplitude modulated, dielectrophoretic (DEP) input signal. Modulation DEP-induced concentration fluctuations of fluorescently labelled 0.5 µm and 1.0 µm diameter latex nanospheres, localized near castellated electrode edges, were quantified using real-time fluorescence microscope dielectrophoretic spectroscopy. Experimental measurements show that the fluorescence fluctuations decrease as the modulation frequency increases—in agreement with model predictions. The modulation frequency was varied from 25 × 10−3 to 25 Hz and the duty-cycle ratios ranged from zero to unity. Two new parameters for characterizing DEP nanoparticle transport are defined: the modulation frequency bandwidth and the optimal duty-cycle ratio. The ‘on/off’ modulation bandwidth, for micrometre scale movement, was measured to be 0.6 Hz and 1.0 Hz for 1.0 µm and 0.5 µm diameter nanospheres, respectively. At these cut-off frequencies very little movement of the nanospheres could be microscopically observed. Optimal fluorescence fluctuations, for modulation frequencies ranging from 0.25 to 1.0 Hz, occurred for duty-cycle ratio values ranging from 0.3 to 0.7—agreeing with theory. The results are useful for automated DEP investigations and associated technologies.