Research On Applying Constant Current/voltage To Control Sample Loading And Dispending In Microfluidic Chips

Loading and dispending sample are called sample injection. The controllability and stability of the injection are very important to ensure the results of the microfluidic analysis as reproducible as possible. The electric-driven sample injection is commonly used in the microfiuidic analysis at present. The fluid in microchannels is driven by the electroosmotic flow in this method.The velocity of the electroosmotic flow is determined by the electric potential difference per unit length (Electric Field Strength) that applied on the microchannels. The universal method adopted in the experiments is applying different voltage to the inlets of microchannels to control sample injection. Then the equivalent resistance mode of microchannls must be involved to calculate the electric field strength in each microchannel. The current in a microchannel is proportional with the electric flied strength in it. So the current parameters applied to the inlets of microchannels can express the velocity of the electroosmotic flow more directly than the applied voltage parameters. And constant current conditions will be more suitable to control sample injection than constant voltage conditions.CFD-ACE+ is used to found the model of the "double T" microchannels. The constant current and constant voltage boundary conditions loaded in simulation are calculated basesd on the three group of electric field relations, which are corresponded to different pinched injections. Then the distributions of the sample concentration in loading and dispending sample process are calculated under the six electric conditions. The numerical results show that that the concentration and amount of the sample plug injected to the saperating microchannel are decreasing along with the applied current and voltage increasing. Nevertheless, the variability of the concentration of the sample plug in three obvious disparate current conditions is less hyposensitive than in three disparate voltage conditions. Likewise, the volume of sample plug injeted to the separating microchannel will decrease smoothly responding to the increasing of the current, and it will be abrupt declining in particular with the voltage increasing.In order to carry out sample injection driven by constant current and research on the difference of sample injection controlled by constant current and constant voltage, we developed a constant voltage/current dual-function high voltage power supply. The performance of the HV power supply is tested in the paper. The display precision of current mode is± 1μA (the output current range is -160 - 160μA), and the display precision of voltage mode is ±5V (the output voltage range is 0 - 4000V). Three plastic microfluidic chips with "double T" structure are chosen to study on the controllability and stability of sample...