**1. Introduction**

Progress in biomedical technologies has emerged into miniaturization of biomedical devices. The main features in miniaturized biomedical devices are establishment of controlled microenvironment that promotes predictive micro-/nanoparticle behaviors and reduction in required sample volume for characterization of scarce materials, e.g., patient-derived samples, which help to reduce the cost and time for diagnosis and therapy [1]. Miniaturization of these biomedical devices demands for implementation of particular procedures in precise approach, which has

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

distribution, and reproduction in any medium, provided the original work is properly cited.

been extensively studied in micro-/nanofluidic system integrated with active manipulation mechanisms [2–4].

prokaryotic microorganisms, grow and reproduce rapidly through binary fission. They are important in biomedical studies in the development of disease diagnostic tools and in understanding of biological responses under certain stimuli, according to their actions, either as predators, mutualists, or pathogens, in which pathogenic bacteria demonstrate a parasitic association with other organisms to cause infections. Viruses, which are genes enclosed by a protective coat, are infective agents due to lack of metabolic machinery, hence depending on the host for gene expression. They are important in the study of virus detection as well as the study of virus influence to cells. Nucleic acids, which are biomolecules made from nucleotides as monomers, function in encoding, transmitting, and expressing genetic information. There are two types of nucleic acids in living cells, which are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). They are highly essential in the research of replication, repair, storage and modification of DNA, disease biomarkers, and gene delivery. Proteins are biomolecules constructing a single or a number of long chains of amino acid residues. The discovery of their role within living organisms includes catalyzing metabolic reactions, DNA replication, responding to stimuli and transporting molecules from one location to another, and getting

Biological Particle Control and Separation using Active Forces in Microfluidic Environments

http://dx.doi.org/10.5772/intechopen.75714

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remarkable attention in the biomedical research and application these days.

Dielectrophoresis (DEP) is the motion of polarizable particles under a spatially nonuniform electric field that cause momentary polarization of the particle by dipole establishment within, with an unequal Columbic forces at both ends of the particles, causing the particles to move

Dielectrophoretic force, *FDEP*, for a stationary alternative current (AC) field is given by

where *E* is the electric field, *εm* is the permittivity of the suspending medium, *a* is the particle

*CM* <sup>=</sup> *<sup>ε</sup><sup>p</sup>*

<sup>∗</sup> = *ε*<sup>0</sup> *ε<sup>p</sup>*,*<sup>m</sup>* − *j*

*CM* is the Clausius-Mossotti factor which describes relationship between dielectric con-

<sup>∗</sup> − *ε<sup>m</sup>* ∗ \_\_\_\_\_\_ *εp* <sup>∗</sup> + 2 *ε<sup>m</sup>*

*σp*,*m* \_\_\_\_

*CM*]∇|*E*| 2

*CM*] is the real part of the factor [7].

<sup>∗</sup> (2)

*ω* (3)

(1)

**3. Dielectrophoresis**

**3.1. Fundamentals of DEP**

For a spherical particle, *f*

*FDEP* = 2*πa* <sup>3</sup> *ε<sup>m</sup>* Re[*f*

*CM* is governed by

where *ε\** is the complex permittivity, which is determined by

stants of two different media, and the Re[*f*

*f*

*ε<sup>p</sup>*,*<sup>m</sup>*

[2, 6, 7].

radius, *f*

Micro-/nanofluidic system facilitates researchers in creating well-controlled micro-/nanoscale environment and at the same time enables the analysis of micro-/nanoparticles including biological particle (bioparticle) behaviors and responses toward active manipulation mechanisms, in addition to particle-particle reactions and external stimuli [5]. Active manipulation mechanisms make possible the control of bioparticle displacement and motional trajectories in a highly predictable and consistent fashion [2], by introducing tunable external force systems such as dielectrophoresis (DEP) [6, 7], magnetophoresis (MAG) [8], acoustophoresis (ACT) [9], thermophoresis (THM) [10], and/or optical tweezing/trapping (OPT) [11, 12].

In this chapter, description of the fundamental mechanism underlying the phenomenon is presented, covering the theoretical and schematic description, as well as specific implementation into bioparticle manipulation covering from micron-sized material down to molecularlevel particles. Conclusion and future perspectives of this multidisciplinary field are provided at the end of this chapter.
