(141g) Modulating DNA Adsorption On Silica Beads in An Electrically Actuated Microfluidic Device

DNA adsorption/desorption on solid surfaces serves as the underlying mechanism for the vast majority of DNA preconcentration and separation techniques that are available for genetic analysis of biological samples. Silica surfaces are the most common ones. Here, we present a strategy for active tuning of DNA adsorption/desorption on silica beads (10 µm diameter) using an electrical switch in a microfluidic chip. In our design, we applied electricity through gold surface microelectrodes to alter pH in a packed bed of silica beads based on electrolysis of water. Since pH has a strong influence on the adsorption of DNA on silica surface, we were able to switch the state of bead surface between being adsorptive and being desorptive without changing the buffer. We tested the device with 100 pM of YOYO-1 labeled λ-DNA molecules in 25 mM acetate buffer solutions (pH 7.0 and 4.0) at various flow rates. Two processes of reversible adsorption-desorption could be successively conducted in our device. The surface concentration of DNA molecules increased continuously, and a drop was immediately observed after a DC voltage of 22 V was applied. In pH 7.0 buffer, the trends at 1 µL/min and 2 µL/min were very similar. However, the electrochemistry created much less change in the hydroxide concentration at 3 µL/min. In pH 4.0 buffer, the response to the applied voltage was more rapid. However, the increase of flow rate (from 0.3 to 1 µL/min) led to less change in the DNA adsorption upon the electric actuation, which was similar to that in pH 7.0 buffer. Our approach shows great potentials for on-chip genetic analysis involving DNA extraction and concentration.