David J. G. Bakewell

The dielectrophoretic and travelling wave forces generated by interdigitated electrode arrays: analytical solution using Fourier series

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.

Dielectrophoresis of DNA: time- and frequency-dependent collections on microelectrodes

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

Protein Linear Molecular Motor-Powered Nanodevices

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.

Dielectric relaxation measurements of 12 kbp plasmid DNA.

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.

Measuring the frequency dependent polarizability of colloidal particles from dielectrophoretic collection data

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.

Dielectrophoretic manipulation of avidin and DNA

This paper demonstrates the application of dielectrophoresis (DEP) to the manipulation of biological macromolecules such as avidin and plasmid DNA. We report, for the first time, observations of negative dielectrophoresis of these macromolecules which can be used to perform stable trapping. The basic electrokinetic theory and experimental arrangements for realising DEP in microelectrode structures are described. The paper discusses our observations on the DEP manipulation of these macromolecules.

Modelling nanoparticle transport in dielectrophoretic microdevices using a Fourier?Bessel series and applications for data analysis

A Fourier–Bessel (FB) series solution is derived that describes the dielectrophoretic-driven transport of nanoparticles in a microdevice. The solution assumes that the nanoparticles do not interact and is based on a linear Fokker–Planck equation that includes the effects of thermal diffusion. The solution is applicable for a dielectrophoretic force that varies exponentially in the microdevice, such as in the far field of planar interdigitated arrays. Important applications of the FB solution are demonstrated that include simulation and system classification of nanoparticle movement under the action of weak and strong dielectrophoretic forces. Methods are demonstrated for the inverse process of estimating model parameters, such as the dielectrophoretic force, based on nanoparticle concentration data obtained experimentally. Data decomposition into separate spatial and temporal modes is demonstrated and Fourier transformation of the series solution yields a representation in the frequency domain. The frequency response predicted by transforming the time-dependent FB solution indicates the presence of a dielectrophoresis modulation bandwidth that concurs with observations of preliminary experiments.

Advancing image quantification methods and tools for analysis of nanoparticle electrokinetics

Image processing methods and techniques for high-throughput quantification of dielectrophoretic (DEP) collections onto planar castellated electrode arrays are developed and evaluated. Fluorescence-based dielectrophoretic spectroscopy is an important tool for laboratory investigations of AC electrokinetic properties of nanoparticles. This paper details new, first principle, theoretical and experimental developments of geometric feature recognition techniques that enable quantification of positive dielectrophoretic (pDEP) nanoparticle collections onto castellated arrays. As an alternative to the geometric-based method, novel statistical methods that do not require any information about array features, are also developed using the quantile and standard deviation functions. Data from pDEP collection and release experiments using 200 nm diameter latex nanospheres demonstrates that pDEP quantification using the statistic-based methods yields quantitatively similar results to the geometric-based method. The development of geometric- and statistic-based quantification methods enables high-throughput, supervisor-free image processing tools critical for dielectrophoretic spectroscopy and automated DEP technology development.

Fourier-Bessel Series Modeling of Dielectrophoretic Bionanoparticle Transport: Principles and Applications

Principles and applications are described for a Fourier-Bessel series model that predicts the transport of bionanoparticles driven by a dielectrophoretic (DEP) force and randomized by Brownian motion. The model is applicable for a dielectrophoretic force that spatially decays from the electrode array according to a reciprocal-law; that is, in the near field of a planar interdigitated array or in the far field where other long range forces assist DEP transport, e.g., ac electro-osmosis. Capabilities of the model are demonstrated for estimating and decomposing data typical of dielectrophoretic bionanoparticle collection experiments. An important approximation, for moderately strong DEP forces, is that a collection can largely be described by a single exponential profile with a square-law dependence on microdevice chamber height. Applications of the model demonstrate transformation and representation of time-dependent bionanoparticle transport in the frequency domain and prediction of a modulation bandwidth that concurs with experimental observations.

Real-time dielectrophoretic signaling and image quantification methods for evaluating electrokinetic properties of nanoparticles

Real‐time image signaling and quantification methods are described that allow easy‐to‐use, fast extraction of the electrical properties of nanoparticles. Positive dielectrophoretic (pDEP) collection rate analysis enables the dielectric properties of very small samples of nanoparticles to be accurately quantified. Advancing earlier work involving dual‐cycle pulsed pDEP collection experiments, we report the development of a statistical image quantification method that significantly advances the evaluation of nanoparticle dielectric properties. Compared with traditional methods that require information about the geometry of the electrode array to be entered for semiautomated quantification , the new statistical approach described does not require a priori knowledge of device geometry. The efficacy of the statistical method is experimentally demonstrated using 200 nm diameter latex nanospheres, suspended in low conductivity medium, that are attracted by pDEP onto planar castellated electrode arrays with 5‐micron‐sized features. The method is shown to yield estimates for the nanoparticle conductivity and surface conductance, σp=25.8 mS/m and KS=1.29 nS, that concur closely with those obtained using traditional geometric methods previously reported . Consequently, the statistical method is accurate, fast, robust, supervisor‐free, and useful for determining nanoparticle electrokinetic parameters.