Using capacitance measurements in EWOD devices to identify fluid composition and control droplet mixing

Abstract

a b s t r a c tThe use of capacitance measurements to identify the composition of droplets and monitor mixing in electrowetting on dielectric devices is examined here. Measurements were repeatable at each addressable location, with standard deviations on the order of 0.1 pF and a two-point calibration allowed repeatable differentiation of water-methanol solutions as the capacitance was linear with concentration. Capacitance at addressable locations was monitored throughout the mixing of water-methanol solutions. It was shown analytically and experimentally that the dimensionless capacitance is approximately equal to the dimensionless dielectric constant for practical EWOD applications. The number of cycles required for complete mixing remained constant for periods of actuation between 400 and 1000 ms and applied voltages between 90 and 110 V RMS . Although minimizing actuation period and maximizing droplet velocity decreases mixing time, these parameters have little affect on the number of cycles necessary to achieve mixing in EWOD devices. This shows mixing efficiency in EWOD devices is better described by the number of cycles, not the time, required for full mixing.

Emerging Technologies for Decentralized Production of PET Tracers

“…Liquid manipulation is performed electronically, eliminating the need for moving parts such as pumps and valves (inherently increasing reliability), and simplifying the chip and the external control system. Furthermore, it is possible to integrate additional electronically controlled functions into the chip such as sensors to monitor liquid volumes (Gong and Kim 2008) and composition (Schertzer et al 2010) (Sadeghi et al Submitted) as well as heaters and temperature sensors for heating liquid droplets or evaporating solvent (Nelson et al 2010). EWOD devices have the additional advantage of digitally-programmable fluid pathways that could readily be configured for a wide variety of microscale batch organic syntheses, optimization, or screening studies for diverse tracers.…”

Dimensionless model for impedimetric sensing of particle laden droplets in digital microfluidic devices

“…This signal is generally detected using external or imbedded fluorescence imaging, electrochemiluminescence, or chemoreceptive neuron MOS transistors (Shen et al 2004;Endo et al 2005;Satoh et al 2005;Luan et al 2008;Miller and Wheeler 2008;Miller et al 2011). Real-time capacitive monitoring of droplet composition and mixing of inert droplets in DMFs has been validated analytically and experimentally (Schertzer et al 2010a). This technique was enhanced by including resistive and capacitive components of impedance to measure the presence and composition of particle free droplets in DMF devices (Lederer et al 2012;Sadeghi et al 2012).…”

A Low-Cost and High-Resolution Droplet Position Detector for an Intelligent Electrowetting on Dielectric Device

“…Another capacitive-sensing method uses conventional bench single-channel capacitance meters (which are large in size) for testing the capacitance of a single electrode pair, 7,8 but they suffer from several limitations, such as low 566940J LAXXX10.1177/2211068214566940Journal of Laboratory AutomationLi et al resolution, uncontrollable outputs, physical size, and a mono-channel output. With the advances in IC design, capacitance data can be directly read out of a serial communication port from an all-in-one IC preforming a capacitance-todigital conversion.…”