Electro-wetting based sample preparation: An initial study for droplet transportation, creation and on-chip digital dilution.

摘要

The miniaturization of Lab-on-a-chip (LoC) provides unprecedented opportunities for chemical and/or biological process automation with innovative liquid handling techniques. The LoC requires that liquid actuation, dispensing, mixing and detection can be accomplished on chip. Electrowetting-based droplet actuation is a promising technique for liquid handling in LoC, because of its controllability, high speed, reversibility and low power consumption. To enable a fully functional electrowetting-based LoC application, droplet dispensing, droplet on-chip dilution and droplet transport dynamics are studied and presented in this work. Pressure-assisted droplet dispensing with capacitance feedback for volume control and on-chip droplet dispensing without pressure assistance are studied and experimentally demonstrated. The reproducibility of droplet dispensing as a function of fluidic properties and operation parameters is investigated to demonstrate the feasibility of these methods in a biological application. 4--6% reproducibility for pressure-assisted dispensing is demonstrated and 2--3% reproducibility is shown for on-chip dispensing shown. An interpolating dilution architecture is designed and demonstrated for the purpose of large dilution factor control in droplet-based system. Dilution errors for dilution factors of four and eight are evaluated and analyzed to prove the feasibility and deficiency. Droplet transport dynamics are studied to develop a transport model based on an energy dissipation method. It is shown that electrowetting-based droplet transport is mainly a contact-line phenomena. Besides the initiation factor caused by contact line hysteresis, contact line friction is dominant in droplet transport dynamics.