Microfluidic devices containing reversibly pinned droplet samples and methods
Inventors
Assignees
Publication Number
US-12370550-B2
Publication Date
2025-07-29
Expiration Date
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Abstract
A microfluidic device comprising: (a) a plate comprising a substrate, a plurality of electrodes, and a first layer of hydrophobic material applied over the plurality of electrodes; (b) a processing unit operably programmed to perform a method of pinning an aqueous droplet within the microfluidic device; and (c) a controller operably connected to a power source, the processing unit, and the plurality of electrodes. The method of pinning an aqueous droplet comprises: applying an electric field of a first polarity to an aqueous droplet located on the surface of the layer of hydrophobic material and having a first contact angle, to cause the droplet to maintain a second contact angle in the absence of the electric field, wherein the aqueous droplet contains a surfactant and the second contact angle is less than the first contact angle.
Core Innovation
A microfluidic device comprising a substrate bearing a plurality of electrodes with a first layer of hydrophobic material applied over the plurality of electrodes, a processing unit operably programmed to perform a method of pinning an aqueous droplet within the microfluidic device, and a controller operably connected to a power source, the processing unit, and the plurality of electrodes. The method of pinning an aqueous droplet comprises applying an electric field of a first polarity to an aqueous droplet located on the surface of the layer of hydrophobic material and having a first contact angle, to cause the droplet to maintain a second contact angle in the absence of the electric field, wherein the aqueous droplet contains a surfactant and the second contact angle is less than the first contact angle. The device may be embodied as a single-plate or dual-plate arrangement including a continuous conductor on a top substrate and a gap between hydrophobic layers in which a droplet can be introduced.
The invention addresses the tendency of droplets to drift from their location on electrowetting-on-dielectric (EWoD) arrays when voltage is turned off, a problem that is conventionally mitigated by applying a continuous low voltage holding force. Continuous low addressing voltage is described as potentially degrading the EWoD device or the biological sample present in the droplet and as energy inefficient. Accordingly, the invention provides an improved EWoD device capable of temporarily pinning a droplet in a desired location on the array without requiring a constant application of voltage.
The pinning process is reversible: application of an electric field of the first polarity to a surfactant-containing aqueous droplet causes a reduction in contact angle (or an increase in maximum diameter in dual-plate embodiments) that is maintained in the absence of the electric field, and application of an electric field of opposite polarity causes the contact angle (or maximum diameter) to revert so the droplet is no longer pinned. The processing unit is programmed to calculate polarity, frequency, and amplitude parameters for pulses applied to electrodes and to output instructions to controllers and drivers to effect the pinning pulse sequences. The result is that aqueous droplets resist drift in the absence of an electric field while the pinning process remains reversible.
The described devices and methods explicitly contemplate use of surfactants, including non-ionic surfactants, in the aqueous droplet to achieve the maintained change in contact angle or maximum diameter. The embodiments describe that actuation parameters may account for surfactant content and composition of solvent and solvates, and that AC driving is used to reduce degradation of the droplets, dielectrics, and electrodes. The patent states that pinned aqueous droplets resist drift in the absence of an electric field and therefore may provide devices requiring less power for operation, increase the operational lifetime of the devices, and are less likely to adversely affect biological materials within the droplet samples.
Claims Coverage
The claims include one independent claim. The main inventive features extracted from the independent claim focus on the device structure, the driver architecture, and the method of applying and halting an electric field to a surfactant-containing aqueous droplet resulting in a maintained reduction in contact angle.
First layer of hydrophobic material completely covering the plurality of electrodes
A first layer of hydrophobic material completely covers the plurality of electrodes on a first substrate as recited in the independent claim.
Plurality of gate and data line drivers operationally coupled to the plurality of electrodes
A plurality of gate line drivers and a plurality of data line drivers are operationally coupled to the plurality of electrodes and responsive to one or more signals to control electrode actuation.
Application of a first electric field of a first polarity to a surfactant-containing aqueous droplet to reduce contact angle maintained in absence of field
The plurality of data line drivers and plurality of gate line drivers apply a first electric field of a first polarity to an aqueous droplet containing a surfactant located on the hydrophobic layer, causing the droplet to have a second contact angle less than the first contact angle and to remain at the location on the surface in the absence of the first electric field.
Halting application of the first electric field while maintaining the reduced contact angle
The plurality of data line drivers and plurality of gate line drivers halt application of the first electric field during a second time, with the aqueous droplet remaining at the location on the surface and maintaining the reduced second contact angle in absence of the applied field.
The independent claim covers a device architecture combining a hydrophobic layer fully covering electrodes, driver circuitry (gate and data line drivers) operably coupled to those electrodes, and a method of applying and halting an electric field of a specified polarity to a surfactant-containing aqueous droplet so that the droplet maintains a reduced contact angle and remains pinned in the absence of the field.
Stated Advantages
Reduced power consumption by avoiding continuous application of voltage to hold droplets in place.
Increased operational lifetime of the devices by reducing degradation associated with constant actuation.
Less likely to adversely affect biological materials within the droplet samples.
Documented Applications
Digital microfluidic lab-on-a-chip applications including sample preparation, assays, and synthetic chemistry performed with tiny quantities of samples and reagents.
Use in active matrix EWoD arrays to enable programmable droplet motion for massively parallel assays and simultaneous analytical processes.
Performing analytical procedures on droplet samples including fluorescence observation, absorption measurements in IR/UV/visible wavelengths, and attenuated total-internal reflection spectroscopy through light-transmissive substrates and layers.
A wide range of droplet operations such as loading, dispensing, splitting, transporting, merging, diluting, mixing, agitating, retaining in position, incubating, heating, vaporizing, cooling, disposing of droplets, and transporting droplets out of a microfluidic device.
Biological and biochemical protocols including nucleic acid amplification protocols, affinity-based assays, enzymatic assays, gene sequencing protocols, protein sequencing protocols, analyses of biological fluids, and synthesis of oligonucleotides.
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