Individual evaluation of DEP, EP and AC-EOF effects on λDNA molecules in a DNA concentrator

Bio-concentrators have been proposed to concentrate and detect tiny amount of cells, DNAs, or proteins in a microfluidic system. Concentrating processes have been experimentally studied and discussed as a result of concentration caused by multiple electrokinetic phenomena. Here, we have investigated individual electrokinetic phenomenon in a DNA concentrator to propose a design guide for a micro-bio-concentrator. Three dominant electrokinetic phenomena: dielectrophoresis (DEP), electrophoresis (EP), and AC electroosmotic flow (AC-EOF) are experimentally and theoretically evaluated. DNA mobility due to DEP was separately studied by utilizing quadrupole electrodes generating a uniform field gradient, which enables us to derive a DEP force on the order of 10−13 N acting on a single DNA molecule. Using the theoretical model the DEP force on the order of 10−12 N, close to the experimental result, was calculated. The EP force estimated from the average charge per base pair of DNA molecule was on the order of 10−9 N. Compared with these two forces, AC-EOF generating a flow velocity of 100–200 μm/s, globally dominates the manipulation of DNA molecules throughout the concentrator. However, the three-dimensional observation of molecule distribution reveals that the EP force has a significant role in holding the DNA molecules at the electrode centre. The results not only support the proposal that the biomolecular concentrator should be designed to utilize AC-EOF and EP [1,2], but also provide approximate estimates for the DEP and EP forces, and the AC-EOF velocity which will allow us to design a concentrator with a given experimental condition.