(185i) Protein Streaming Via Insulator-Based Dielectrophoresis in a Microfluidic Platform | AIChE

(185i) Protein Streaming Via Insulator-Based Dielectrophoresis in a Microfluidic Platform

Authors 

Nakano, A. - Presenter, Arizona State University
Camacho-Alanis, F., Arizona State University
Ros, A., Arizona State University


Protein Streaming
via Insulator-based Dielectrophoresis in a Microfluidic Platform

Asuka Nakano,
Fernanda Camacho-Alanis, Tzu-Chiao Chao, Alexandra Ros

Department of Chemistry and Biochemistry, Arizona
State University, Tempe AZ, 85287

            Rapid and reliable
separation and analysis of proteins is of great interest. This becomes
especially challenging when only small sample volumes are available,
concomitantly with low concentrations of proteins. Time critical situations such
as surgeries and rapidly degrading samples pose additional challenges. Due to
these challenges, conventional macro-scale separation techniques reach their
limitations. While microfluidic devices require only pL-nL sample they offer
several advantages such as speed, efficiency, and high throughput.

            Here, we propose to
elucidate the capability to manipulate proteins in a rapid and reliable manner
with a novel migration technique, namely dielectrophoresis (DEP). We
demonstrate a detailed study of various factors influencing protein DEP, employing
immunoglobulin G (IgG) under DC conditions. DEP has been extensively employed
as a separation, fractionation, and pre-concentration technique for large
biological objects such as cells and recently for DNA. In contrast to the other
existing separation techniques, DEP relies on a particle's polarizability in an
inhomogeneous electric field. This additional parameter has great potential to
improve separation when employed as a primary separation method as well as a
component of a multi-dimensional separation. Improved separations are in demand
especially when the sample becomes complex. To generate a non-uniform electric
field, we specifically utilize insulator-based DEP (iDEP) where the dielectrophoretic
response of proteins is provoked in a tailored microfluidic device with
integrated arrays of insulating posts. Unlike DNA and cells, protein DEP behavior
is not well understood; therefore our detailed study of protein DEP provides
novel information to eventually optimize this protein migration method for pre-concentration
and other analytical techniques.

            First, we performed numerical
simulations to predict protein migration behavior considering electrokinesis,
protein diffusion, and DEP.  With small sized (~nm) proteins, high electric field
strength as well as corresponding large electric field gradient needs to be
created. For this purpose, multiple post geometries were tested by numerical
simulation and as a result, we found the maximum field strength of 8×105 V/m and
maximum ∇E2
value of 3×1017
V2/m3 with the triangular post geometry. Based on the
calculated electric field, E, and ∇E2,
we simulated the protein concentration profiles and found that the protein concentrates
in streamlines between the rows of posts in the positive DEP case, whereas
protein is depleted at the exact same regions for negative DEP.

            Experimentally, we investigated
the DEP behavior of IgG under various buffer conditions differing in pH and
conductivity. We observed streaming DEP only at pH 6.5~8 with a maximum DEP
streaming enrichment of 70 %. This concentration profile was in excellent
qualitative agreement with numerical simulations performed with the assumption
of monomeric IgG species. Furthermore, pH dependent DEP streaming is also in
agreement with the numerical simulations suggesting that the variation of
protein charge and electroosmotic flow influences protein DEP streaming. Additionally,
we observe micelle induced negative DEP streaming for proteins, which is also in
agreement with numerical simulations. This micelle formation was further confirmed
by dynamic light scattering experiments. Our study thus provides valuable
information to eventually improve novel protein DEP devices for separation,
pre-concentration, and fractionation.

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