(549h) Lambda-DNA Dielectrophoresis in a 3D Carbon-Electrode Micro-Post Device: Theoretical and Experimental Studies

Dielectrophoresis (DEP) is a transport mechanism where movement of particles depends of their polarizability. In general, the dielectrophoretic migration of molecules can be toward or away from regions of high electric-field gradients depending on the permittivity of the biomolecule and the medium. A typical method to create electric field gradients is introducing metallic posts along the microfluidic device. However, this approach causes electrode reactions at high applied potentials which are one of the main disadvantages of this technique. The use of insulator posts is an alternative method for DEP that generates homogenous electric field gradients over the entire depth of a microchannel. A main issue with this method is the large potentials that may be needed to achieve sufficiently high electric field gradients to manipulate small biomolecules by DEP such as DNA which polarization and its DEP response at different lengths remain unclear. Our approach is to combine advantages of metallic and insulator posts by employing carbon electrodes for DEP also known as carbon-DEP to study DNA DEP. The fabrication process of carbon electrodes gives an additional benefit in terms of materials and processing costs since they are synthesized from inexpensive photoresist, which can be patterned by optical photolithography.

Here, we analyze the DEP behavior of lambda-DNA using carbon-DEP under AC and several flow conditions both numerically and experimentally. Rows of 3D carbon electrodes made of carbonized SU-8 photoresist on fuse silica are electrically connected such that every other row has the same polarity. The experiments were performed using fluorescence microscopy under continuous flow applying AC potential. Finally, numerical simulations using a convection-diffusion model were performed.

We found that trapping and streaming behavior depends on the frequency range and hydrodynamic flow conditions. Experimental results reveal that positive DEP trapping of DNA is observed at low frequencies and small hydrodynamic flow. In contrast, streaming DEP in which DNA is concentrated according to positive DEP is enhanced at higher frequencies and higher pressure drops. We compared these experimental observations with numerical simulations considering DNA DEP as well as a pressure driven velocity component. The numerical model captured the experimentally observed streaming behavior in reasonable quantitative and excellent qualitative agreement. These findings are significant for future analytical applications to concentrate and sort biomolecules by creating streams of different biomolecules in tailored carbon-DEP devices.