Droplet-based microfluidics with nonaqueous solvents and solutions

Chatterjee, Debalina; Hetayothin, Boonta; Wheeler, Aaron R.; King, Daniel J.; Garrell, Robin L.

doi:10.1039/b515566e

Cited by 218 publications

(196 citation statements)

References 53 publications

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“…9 is always positive since the electrowetted contact angle ⎝ e is always lower than ⎝ n and both are <180 o . The sum of first two terms is negative, but for a wide range of dimensions typically used in EWOD devices and empirically observed contact angles from literature (at no applied potential [9] and at EWOD potential [10] for device geometry close to our conditions), the third term dominates. Thus, higher surface tension increases the splitting pressure, p n --p e .…”

Section: Splitting Pressure: Influence Of Liquid Properties and Geometrymentioning

confidence: 72%

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On-demand droplet loading for automated organic chemistry on digital microfluidics

et al. 2013

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Organic chemistry applications on digital microfluidic devices often involve reagents that are volatile or sensitive and must be introduced to the chip immediately before use. We present a new technique for automated, on--demand loading of 1 µL droplets from large (~1 mL), sealed off--chip reservoirs to a digital microfluidic chip in order to address this challenge. Unlike aqueous liquids which generally are non--wetting to the hydrophobic surface and must be actively drawn into the electrowetting--on--dielectric (EWOD) chip by electrode activation, organic liquids tend to be wetting and can spontaneously flood the chip, and hence require a retracting force for controlled liquid delivery. Using a combination of compressed inert gas and gravity to exert driving and retracting forces on the liquid, the simple loading technique enables precise loading of droplets of both wetting and non--wetting liquids in a reliable manner. A key feature from a practical point of view is that all of the wetted parts are inexpensive and potentially disposable, thus avoiding cross--contamination in chemical and biochemical applications. We provide a theoretical treatment of the underlying physics, discuss the effect of geometry and liquid properties on its performance, and show repeatable reagent loading using the technique. Its versatility is demonstrated with the loading of several aqueous and non--aqueous liquids on an EWOD digital microfluidic device.

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Section: Splitting Pressure: Influence Of Liquid Properties and Geometrymentioning

confidence: 72%

“…The specimen liquids used in this work span a wide range of properties, most importantly surface tension and density. Thus, we anticipate that the technique presented here can be extended to many other solvents and reagents used in organic chemistry, provided that they can be actuated using EWOD digital microfluidics [10].…”

Section: Discussionmentioning

confidence: 99%

On-demand droplet loading for automated organic chemistry on digital microfluidics

et al. 2013

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“…This leads to a decrease in the driving force, and the droplet quickly comes to rest as the forces equilibrate. Solving Equation (10) shows that for a droplet volume <0.65 µL and a channel diameter of 1.1 mm, the capillary forces exceed the insertion forces ( Figure 5). Indeed, our experiments showed that with these volumes and dimensions, vertical functionality could only be obtained with hydrophilic walls.…”

Section: Characterization Of Droplet Forces and Design Parametersmentioning

confidence: 99%

“…To move the droplets, an electrical potential is applied to electrodes adjacent to the target liquid droplet. The resulting electromechanical force drives droplet translation through a combination of electrowetting and dielectrophoretic (DEP) mechanisms, depending on the liquid and the applied frequency [8,10,11]. Translation by electrowetting can be analyzed in terms of an electrostatic force, a surface tension force, and a pressure force [8].…”

Section: Introductionmentioning

confidence: 99%

Digital Microfluidic System with Vertical Functionality

Bender

Garrell

2015

Micromachines

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Digital (droplet) microfluidics (DµF) is a powerful platform for automated lab-on-a-chip procedures, ranging from quantitative bioassays such as RT-qPCR to complete mammalian cell culturing. The simple MEMS processing protocols typically employed to fabricate DµF devices limit their functionality to two dimensions, and hence constrain the applications for which these devices can be used. This paper describes the integration of vertical functionality into a DµF platform by stacking two planar digital microfluidic devices, altering the electrode fabrication process, and incorporating channels for reversibly translating droplets between layers. Vertical droplet movement was modeled to advance the device design, and three applications that were previously unachievable using a conventional format are demonstrated: (1) solutions of calcium dichloride and sodium alginate were vertically mixed to produce a hydrogel with a radially symmetric gradient in crosslink density; (2) a calcium alginate hydrogel was formed within the through-well to create a particle sieve for filtering suspensions passed from one layer to the next; and (3) a cell spheroid formed using an on-chip hanging-drop was retrieved for use in downstream processing. The general capability of vertically delivering droplets between multiple stacked levels represents a processing innovation that increases DµF functionality and has many potential applications.

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“…However, the relatively complex circuitry and the high sampling rates required in this measurement approach limit the applicability in low cost and point of care devices; in addition, this approach is limited to detect capacitance change when the EWOD device is being operated under DC voltage conditions. DC operation severely limits the variety of liquids that can be actuated 22 and increases the chance of dielectric breakdown in the device 23 , which may cause irreversible reactions and oxidation in the chip 24 . Furthermore, the accuracy and the resolution are fundamentally limited by the magnitude of the induced frequency shift and ability of the system to resolve high frequency modulations.…”

Section: Introductionmentioning

confidence: 99%

On Chip Droplet Characterization: A Practical, High-Sensitivity Measurement of Droplet Impedance in Digital Microfluidics

et al. 2012

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We demonstrate a new approach to impedance measurement on digital microfluidics chips for the purpose of simple, sensitive, and accurate volume and liquid composition measurement. Adding only a single series resistor to existing AC droplet actuation circuits, the platform is simple to implement and has negligible effect on actuation voltage. To accurately measure the complex voltage across the resistor (and hence current through the device and droplet), the designed system is based on software-implemented lock-in amplification detection of the voltage drop across the resistor which filters out noise, enabling high-resolution and low-limit signal recovery. We observe picoliter sensitivity with linear correlation of voltage to volume extending to the microliter volumes that can be handled by digital microfluidic devices. Due to the minimal hardware, the system is robust and measurements are highly repeatable. The detection technique provides both phase and magnitude information of the real-time current flowing through the droplet for a full impedance measurement. The sensitivity and resolution of this platform enables it to distinguish between various liquids which, as demonstrated in this paper, could potentially be extended to quantify solute concentrations, liquid mixtures, and presence of analytes.

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Droplet-based microfluidics with nonaqueous solvents and solutions

Cited by 218 publications

References 53 publications

On-demand droplet loading for automated organic chemistry on digital microfluidics

On-demand droplet loading for automated organic chemistry on digital microfluidics

Digital Microfluidic System with Vertical Functionality

On Chip Droplet Characterization: A Practical, High-Sensitivity Measurement of Droplet Impedance in Digital Microfluidics

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