Insulator-based Dielectrophoresis of Protein Particles Using Direct Current Electric Fields

Dielectrophoresis is a method of rapid response with sufficient selectivity for manipulation and separation of bioparticles, such as: microorganisms and biomolecules. Due to the great importance of proteins in the biotechnological and pharmaceutical processes, the present study demonstrates the potential of the insulator-based dielectrophoresis (iDEP) and DC electric fields to manipulate and concentrate protein solutions, using bovine serum albumin as a model. Samples containing fluorescently labeled bovine serum albumin protein were manipulated inside a microchannel made from glass that contained an array of cylindrical insulating structures. DC electric fields were applied and the dielectrophoretic response of the particles was observed. It was shown that the magnitude of the applied electric field and the conductivity and pH of the suspending medium have a strong effect on the dielectrophoretic response of the protein particles. Introduction Miniaturization has brought important advantages to bioseparation technology. Numerous fields, including environmental, pharmaceutical and biochemical, have beneficiated from the advances of microanalytical systems. There is a growing interest on the development of separation techniques that can applied in microscale. Dielectrophoresis (DEP) is a nondestructive electrokinetic transport mechanism, widely employed in microfluidics to manipulate bioparticles. DEP is the movement of particles in a nonuniform electric field, due to polarizations effects, and it can occur in alternating current (AC) or direct current (DC) electric fields. This technique was described for the first time by Pohl in 1951 [1]. The majority of the studies reported in literature, have been carried out employing electrodes, where non-uniform electric fields are generated using an array of electrodes and AC fields [2-3]. However, it is also possible to generate non-uniforms electric fields by means of electric insulator materials. Insulator-based DEP (iDEP) is an alternative to the traditional electrode-based-DEP. In this technique, only two electrodes are needed since the nonuniformity of the electric field is generated with insulating structures [4]. There are a number of advantages offered by iDEP: fabrication microdevices for iDEP are economical and simpler, leading to more robust devices that can conserve their functionality in despite of fouling. The manipulation of protein molecules has been demonstrated with electrode-based DEP. Washizu et al. in 1994 [5], reported the dielectrophoretic manipulation of the proteins: avidin, concanavalin, chymotripsinogen, and ribonuclease A, employing a set of corrugated electrodes and AC electric fields. In 1998 Bakewell and collaborators [6] demonstrated the dielectrophoretic manipulation of the avidin, using polynomial electrodes. In 2004, Zheng and col. [7], reported the dielectrophoretic manipulation of protein of bovine serum albumin (BSA), using quadrupole electrodes. The manipulation of proteins molecules has not been demonstrated with iDEP. The present study reports the manipulation and concentration of BSA employing insulator-based-DEP and DC electric fields. The protein BSA was concentrated inside a glass microchannel containing an array of cylindrical insulating posts. These results showed that the magnitude of the applied electric field and suspending medium properties (conductivity and pH) have a strong effect on the dielectrophoretic response of the protein particles. The results presented here are the first demonstration on manipulation and concentration of protein employing DC-iDEP. Theory of dielectrophoresis The magnitude of the dielectrophoretic force depends on the intensity of the applied electric field, particle size, and on the dielectric properties of particles and suspending medium [8, 9]. The dielectrophoretic force acting on a spherical particle is defined as:   ( ) E E f r F CM m DEF ⋅ ∇ = Re 2 3 0ε πε (1) where 0 ε is the permittivity of free space, m ε is the relative permittivity of suspending medium, r is the particle radio and   CM f Re it is the real part of the Clausius-Mossotti (CM) factor. According to Hughes [10] when low frequency electric field are used (frequency ≤ 100 kHz), the CM factor can be written as: