Integrated Digital and Analog Microfluidics by EWOD and LDEP

EWOD (electrowetting-on-dielectric) and LDEP (liquid dielectrophoresis) are investigated to provide digital and analog microfluidic functions on an integrated chip respectively. By altering the frequency of the applied voltage and the surrounding medium of a EWOD device, we found that when using oil as surrounding medium and applying an AC signal 100 kHz, liquid column would be drawn and follow the thin connecting lines of the EWOD driving electrodes instead of remaining on top of the center of the EWOD driving electrodes. This new phenomenon is described in this paper and is regarded as a LDEP effect. Three fundamental tools for integrated digital and analog microfluidics are developed, including a digital-to-analog converter, an analog-to-digital converter, and a valve. Combining EWOD and LDEP effects, liquids can be pumped on a virtual channel (analog microfluidics), defined by energized thin LDEP electrode lines, continuously from liquid reservoir or from a digitized droplet (digital microfluidics). On the contrary, liquids on LDEP electrodes (analog microfluidics) can also be pumped on a EWOD electrode and be digitized in droplet forms with precise volumes (digital microfluidics). EWOD and LDEP can be selectively programmed on a single chip, making integrated digital and analog microfluidics a reality