Directing motion of droplets using differential wetting
Inventors
Assignees
Publication Number
US-11123729-B2
Publication Date
2021-09-21
Expiration Date
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Abstract
Apparatus for controlling motion of liquid droplets. A set of electrode pads is arranged to define one or more tracks over which liquid droplets may be induced to move over a sequence of 5 the electrode pads. A surface over the electrode pads is dielectric, smooth, and slippery to the droplets. In some cases, the smooth surface is formed as a thin layer of a second liquid that is immiscible with the liquid of the droplets. The surface has wetting affinity to the liquid that can be individually varied in a controlled manner by application of voltage to respective electrode pads. A control is designed to alter the wetting characteristic of varying-wettability portions of 10 the surface over respective electrode pads to effect induced motion of the droplets over the surface. The apparatus is designed with the smooth hydrophobic surface open, with no overlying or facing electrode or plate above the droplets.
Core Innovation
The invention features apparatus for controlling motion of liquid droplets in which a set of electrode pads is arranged in an array or in paths defining one or more tracks over which liquid droplets may be induced to move over a sequence of the electrode pads. A surface over the electrode pads is dielectric, smooth to within 2 μm, has a slide angle for a 5 μl droplet of the liquid of no more than 5 degrees, and has a wetting affinity to the liquid that can be altered by application of voltage to the electrode pads, and a control is designed to alter the wetting characteristic of portions of the surface over respective electrode pads to effect induced motion of the droplets by controlling charging and discharging of the electrode pads in a desired sequence.
Alternative aspects include a smooth, hydrophobic surface having portions with wetting affinity that can be varied in a controlled manner and a solid surface textured to hold a thin layer of a second liquid that is immiscible with the liquid of the droplets, an upper surface of the second liquid forming a liquid-liquid surface that is slippery with respect to the liquid droplets; in these aspects the varying-wettability portions are arranged in an array or in paths defining one or more tracks and a control is designed to vary the wetting characteristic of the varying-wettability portions to effect induced motion of the droplets. In several aspects the smooth hydrophobic surface is open, with no overlying or facing electrode or plate above the droplets.
The background identifies a need to prepare a surface that has low adhesion with water to allow droplets to be moved along the surface by small forces generated by gradients in electric field and surface tension, and to reduce droplet pinning, contact angle hysteresis, trails left behind by droplets, droplet cross contamination, and sample loss during droplet movement. The description states that smoothing and creating a hydrophobic or slippery surface can reduce pinning and contact angle hysteresis and permit lower actuation voltages and repeatable behavior of droplet motion.
Claims Coverage
Two independent claims are identified and nine inventive features are extracted from those claims.
Electrode arrays with first and second plurality of electrodes
An array comprising a first plurality of electrodes and a second plurality of electrodes configured on a substrate.
Liquid coating filling gaps between adjacent electrodes
A liquid coating filling in gaps between adjacent electrodes of the first plurality of electrodes and the second plurality of electrodes.
Dielectric disposed over electrodes and liquid coating
A dielectric disposed over the first plurality of electrodes, the second plurality of electrodes, and the liquid coating filling in gaps between adjacent electrodes.
Liquid layer supporting a droplet and immiscible with the droplet
A liquid layer disposed over the dielectric that is configured to support a droplet on a surface of the liquid layer, wherein the liquid layer comprises a liquid that has a wetting affinity characteristic for the dielectric and is immiscible with the droplet.
Electrodes supply electric field to induce droplet motion
The first plurality of electrodes and the second plurality of electrodes are configured to supply an electric field to induce the droplet to motion along a surface of the liquid layer.
Controller alters wetting characteristic of liquid layer surface
A controller operatively coupled to the first plurality of electrodes and the second plurality of electrodes, configured to direct at least a subset of electrodes to supply an electric field to alter a wetting characteristic of the surface of the liquid layer to thereby induce the droplet to motion along the surface of the liquid layer.
Providing an array with electrodes, liquid coating, dielectric, and liquid layer
A method step providing an array comprising the first plurality of electrodes, the second plurality of electrodes, the liquid coating filling gaps, the dielectric disposed over them, and the liquid layer disposed over the dielectric configured to support a droplet.
Introducing a droplet on the surface of the liquid layer
A method step introducing a droplet comprising a sample on the surface of the liquid layer disposed over the dielectric.
Directing electrodes to alter wetting characteristic to induce motion
A method step directing at least a subset of the first plurality of electrodes and the second plurality of electrodes to supply an electric field to alter a wetting characteristic of the surface of the liquid layer, to thereby induce the droplet to motion along the surface of the liquid layer.
The independent claims cover systems and methods that combine electrode arrays, a liquid coating filling gaps, a dielectric over the electrodes and coating, and a liquid layer that supports droplets and is immiscible with the droplets, together with control of electric fields by a controller to alter wetting characteristics of the liquid layer surface and thereby induce droplet motion.
Stated Advantages
Low actuation voltage for droplet motion.
Reduced droplet pinning and reduced contact angle hysteresis enabling lower voltages and repeatable behavior of droplet motion.
Reduced trail left behind by droplets, reduced droplet cross contamination, and reduced sample loss during droplet movement.
Cleaning by washing an LLEW device surface and replenishment of lubricating oil to reduce cross contamination.
Ability to operate an arbitrarily-large open face allowing actuation of droplets of volumes between 1 nanoliter and 1 milliliter.
Documented Applications
Droplet transport, droplet merging, droplet mixing, droplet splitting, droplet dispensing, and droplet shape change for microfluidic droplet actuation.
A 'lab-in-a-box' desktop digital wetlab to automate biological protocols, assays, and tests including PCR amplification, DNA assembly, molecular cloning, DNA sequencing, single cell sorting, cell incubation, cell culture, cell lysing, DNA extraction, protein extraction, RNA extraction, and RNA and cell-free protein expression.
Process stations including mixing stations, incubation stations, magnetic bead stations for nucleic acid and protein isolation and purification, nucleic acid delivery stations, optical inspection stations, and loading/unloading stations via acoustic liquid handlers or microdiaphragm based pump dispensers.
Arbitrarily-large open face electrowetting for multi-scale fluid manipulation across two-dimensional arrays to run multiple droplets in parallel and to reduce cross-contamination.
Use with acoustic droplet ejection, microdiaphragm pumps, inkjet nozzles, syringe pumps, capillary tubes, or pipettes to introduce or inject liquid droplets onto the electrowetting device.
Two-plate (sandwiched) and single-plate (open surface) electrowetting configurations for droplet manipulation and processing.
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