Spatial and temporal pinching for robust multi-size dispensing of liquids on high electrode density electrowetting arrays

Abstract

A digital microfluidics system comprising: (a) a bottom plate comprising an electrode array, the electrode array comprising a plurality of digital microfluidics propulsion electrodes; (b) a top plate comprising a common top electrode; (c) a controller coupled to the processing unit, common top electrode and bottom electrode array; and (d) a processing unit operably programmed to: receive input instructions relating to a droplet diameter and aspect ratio; calculate actuation parameters comprising: a length of an actuation hold, a length of an actuation neck and a height of an actuation head for dispensing a droplet having the diameter and aspect ratio of the input instructions; output electrode actuation instructions to the controller, the electrode actuation instructions relating to a dispensing drive sequence for implementing the calculated actuation parameters to dispense a droplet having the input diameter and aspect ratio; wherein the electrodes have a size that is less than the droplet diameter.

Description

[0001] background

[0002] Digital microfluidic devices utilize independent electrodes to advance, split, and combine droplets in confined environments, thus providing a “lab-on-a-chip” experience. Digital microfluidic devices are alternatively referred to as electrowetting on dielectrics, or “EWoD,” to further distinguish this approach from competing microfluidic systems that rely on electrophoretic flow and / or micropumps. Wheeler provides a 2012 review of electrowetting techniques in “Digital Microfluidics,” Annu. Rev. Anal. Chem. 2012, 5:413-40, which is incorporated herein by reference in its entirety. This technique allows for sample preparation, assaying, and synthetic chemistry using both minute amounts of sample and minute amounts of reagents. In recent years, controlled droplet manipulation using electrowetting in microfluidic units has become commercially viable, and products are now available from large life science companies such as Oxford Nanopore.

[0003] Most literature on EWoDs reports concern so-called “passive matrix” devices (also known as “segmented” devices), where ten to twenty electrodes are directly driven by a controller. While segmented devices are easy to manufacture, the number of electrodes is limited by space and driving constraints. Therefore, it is not possible to perform a large number of parallel measurements, reactions, etc., in passive matrix devices. In contrast, “active matrix” devices (also known as active matrix EWoDs, or AM-EWoDs) can have thousands, hundreds of thousands, or even millions of addressable electrodes. The electrodes are typically switched via thin-film transistors (TFTs), and the droplet movement is programmable, allowing AM-EWoD arrays to be used as general-purpose devices, enabling a great deal of freedom in controlling multiple droplets and performing simultaneous analytical processes.

[0004] Digital microfluidic systems are designed for biological or chemical applications. These often require introducing large volumes of liquid as reservoirs into the device, followed by dispensing smaller amounts for reactions or other functions. Traditionally, dispensing is achieved by having large, segmented reservoirs and then using a series of steps to dispense droplets along a single-sized path. The basic procedure for dispensing typically begins by extending a line of liquid from the reservoir. A narrow neck is then formed between the reservoir and the initial droplet, and the reservoir and droplet move in opposite directions. This method is useful, but it is often compromised in reproducibility due to the large variation in reservoir volume, and it is limited to dispensing droplets of only a single size due to the structure of the rest of the array. For example, International Publication WO 2008 / 124846 describes a common method for extending a drop of fluid to a neck and then splitting it into sub-droplets. Its system relies on a segmented array, where there is no choice regarding the size of the resulting droplets. A multi-segmented structure is used for the reservoir region, but only a single-segment-wide channel is used for dispensing the droplets. Nikapitiya et al. (Micro and Nano Syst Lett (2017) 5:24) developed a method using a special structure to achieve a coefficient of variation (CV) of less than 1%. The innovation lies in how the neck is formed and how the droplet is cleaved (along the diagonal), resulting in cleaner, repeatable symmetry for cleaving. However, the design is segmented and limited to a fixed droplet size.

[0005] Cho et al. (Journal of Microelectromechanical Systems, Volume: 12, Issue: 1, Feb. 2003) provide a physical analysis of how basic droplet operations occur on an electrowetting device, and define which parameters need to be tuned to maximize efficiency for each operation using physical parameters of the electrowetting system such as dielectric constant, voltage, and thickness. Specifically, this reference describes the requirements and several parameters for neck formation associated with splitting electrodes. U.S. Patent No. 8,936,708 describes a method for smaller droplets to split from larger droplets. This reference primarily relates to defining prototypes of pixels with different geometries such as hexagons, and how to split droplets on such pixels. However, no precise method is provided for systematically distributing droplets of different sizes. U.S. Patent No. 8,834,695 discusses the possibility of using small electrodes to formulate larger patterns that can be used as distribution reservoirs. This method for size control utilizes the aggregation of small droplets into larger droplets, but does not provide a system and efficient distribution of droplets with variable sizes, nor does it address any concerns regarding methods for improving CV. Invention Overview

[0007] In a first aspect, this application addresses the shortcomings of the prior art by providing an alternative method for distributing droplets on a digital microfluidic system, the system comprising: (a) a substrate including: a bottom electrode array including a plurality of digital microfluidic propulsion electrodes; and a first dielectric layer covering the bottom electrode array; (b) a top plate including: a common top electrode; and a second dielectric layer covering the common top electrode; (c) a processing unit operatively programmable to perform a microfluidic actuation method; and; and (d) a controller operatively coupled to the processing unit, the common top electrode, and the bottom electrode array, wherein the controller is configured to provide a propulsion voltage between the common top electrode and the substrate propulsion electrodes. The method includes: receiving an input command in the processing unit, the input command being related to a droplet diameter and aspect ratio; calculating actuation parameters in the processing unit, the actuation parameters including: the length of an actuation retainer, the length of an actuation neck, and the height of an actuation head, for distributing a droplet having the diameter and aspect ratio of the input command; outputting an electrode actuation command from the processing unit to the controller, the electrode actuation command being related to a distribution drive sequence for implementing the calculated actuation parameters; executing the distribution drive sequence on the propulsion electrode to: shape fluid in a reservoir to form an actuation retainer and an actuation neck; split the droplet from the head of the neck; and return the neck fluid to the reservoir, wherein the electrode has a dimension smaller than the droplet diameter.

[0008] In a second aspect, this application provides a novel digital microfluidic system comprising: (a) a substrate including: a bottom electrode array including a plurality of digital microfluidic propulsion electrodes; and a first dielectric layer covering the bottom electrode array; (b) a top plate including: a common top electrode; and a second dielectric layer covering the common top electrode; (c) a processing unit; and (d) a controller operatively coupled to the processing unit, the common top electrode, and the bottom electrode array, wherein the controller is configured to provide a propulsion voltage between the common top electrode and the substrate propulsion electrodes. The processing unit is operatively programmed to: receive an input command related to a droplet diameter and aspect ratio; calculate actuation parameters including: a length of an actuation holding portion, a length of an actuation neck, and a height of an actuation head, for distributing droplets having the diameter and aspect ratio of the input command; and output electrode actuation to the controller, the electrode actuation command being associated with a distribution drive sequence for implementing the calculated actuation parameters to distribute droplets having the input diameter and aspect ratio; wherein the size of the electrodes is smaller than the diameter of the droplets.

[0009] In a third aspect, this paper provides an improved method for dispensing droplets on a digital microfluidic system, the method comprising extending a liquid line from a reservoir, forming an actuation neck between the reservoir and the initial droplet, and cleaving the droplet from an actuation head of the neck, the improvement comprising increasing the height of the actuation head to the forward cleaving height before cleaving the droplet from the head. Brief description of the attached diagram

[0011] Figure 1 A conventional microfluidic device including a common top electrode is shown.

[0012] Figure 2 This is a schematic diagram of the TFT structure of multiple propulsion electrodes used in an EWoD device.

[0013] Figure 3 This is a schematic diagram of a portion of a substrate TFT array, which includes a propulsion electrode, a thin-film transistor, a storage capacitor, a dielectric layer, and a hydrophobic layer.

[0014] Figure 4 This is a schematic top view of a memory defined by a high-density electrode grid.

[0015] Figure 5A and Figure 5B yes Figure 4 A top view of the memory, with the electrode grid no longer shown for clarity. Figure 5A and Figure 5B This illustrates the actuation of the neck at different heights.

[0016] Figure 6 yes Figure 4 A top view of the storage, in which the actuation parameters used to implement the allocation drive sequence are identified.

[0017] Figure 7 This is a flowchart illustrating an exemplary droplet distribution process according to this application.

[0018] Figure 8 This is a schematic diagram illustrating the droplet distribution pattern.

[0019] Figure 9 This schematically illustrates the operation of centering the fluid in the reservoir.

[0020] Figure 10 This explains the formation of the head and neck.

[0021] Figure 11 This indicates that the droplet splits open at the neck.

[0022] Figure 12A This illustrates the changes as the droplets split, forming an elongated "time neck". Figure 12B It is the effect of timed necking on the negative radius of curvature at the clamping point.

[0023] Figure 13A It is a change in the splitting of small droplets, in which the head height increases to a larger forward head height. Figure 13B This demonstrates the effect of the head height advancing at the clamping point on the radius of curvature.

[0024] Figure 14 This explains the mechanism by which the droplet is cut off from the actuating neck.

[0025] Figure 15A Explain the voltage mode on the active pixel electrode. Figure 15B Explain the voltage mode on the passive pixel electrode.

[0026] definition

[0027] Unless otherwise stated, the following terms have the meanings indicated.

[0028] "Actuation" of one or more electrodes refers to the realization of a change in the electrical state of one or more electrodes, which, in the presence of a droplet, results in the manipulation of the droplet.

[0029] A "droplet" refers to a volume of liquid that electrowets a hydrophobic surface and is at least partially surrounded by a carrier liquid. For example, a droplet may be completely surrounded by the carrier liquid or may be surrounded by the carrier liquid and one or more surfaces of the EWoD device. Droplets can take various shapes; non-limiting examples typically include disc-shaped, strip-shaped, truncated spheres, ellipsoids, spheres, partially compressed spheres, hemispheres, ovoids, cylindrical shapes, and various shapes formed during droplet operation such as merging or splitting, or due to contact between such shapes and one or more working surfaces of the EWoD device; droplets may include generally polar fluids such as water, in the case of aqueous or non-aqueous compositions, or may be mixtures or emulsions comprising aqueous and non-aqueous components. The specific composition of the droplet is not particularly relevant, as long as it electrowets the hydrophobic working surface. In various implementations, droplets may include biological samples such as whole blood, lymph, serum, plasma, sweat, tears, saliva, sputum, cerebrospinal fluid, amniotic fluid, semen, vaginal secretions, serous fluid, synovial fluid, pericardial fluid, peritoneal fluid, pleural fluid, exudate, exudate, cystic fluid, bile, urine, gastric juice, intestinal juice, fecal samples, liquids containing single or multiple cells, liquids containing organelles, fluidized tissues, fluidized organisms, liquids containing multicellular organisms, biological swabs, and biological washes. Furthermore, droplets may include one or more reagents such as water, deionized water, saline solutions, acidic solutions, alkaline solutions, detergent solutions, and / or buffer solutions. Other examples of droplet contents include reagents used in biochemical protocols, nucleic acid amplification protocols, affinity-based assay protocols, enzyme assay protocols, gene sequencing protocols, protein sequencing protocols, and / or protocols for analyzing biological fluids. Further examples of reagents include those used in biochemical synthetic methods, such as reagents for synthesizing oligonucleotides and / or more than one nucleic acid molecule that have been found to have applications in molecular biology and medicine. Oligonucleotides may contain natural or chemically modified bases and are most commonly used as antisense oligonucleotides, small interfering therapeutic RNA (siRNA) and their bioactive conjugates, primers for DNA sequencing and amplification, probes for detecting complementary DNA or RNA via molecular hybridization, tools for targeting the introduction of mutations and restriction sites in the context of gene editing technologies such as CRISPR-Cas9, and tools for synthesizing artificial genes by “synthesizing and splicing” DNA fragments.

[0030] "Droplet manipulation" refers to any manipulation of one or more droplets on a microfluidic device. For example, droplet manipulation may include: loading droplets into a microfluidic device; dispensing one or more droplets from a source droplet; splitting, separating, or dividing a droplet into two or more droplets; transporting a droplet from one location to another in any direction; merging or combining two or more droplets into a single droplet; diluting droplets; mixing droplets; agitating droplets; deforming droplets; holding droplets in place; cultivating droplets; heating droplets; evaporating droplets; cooling droplets; processing droplets; delivering droplets out of the microfluidic device; other droplet manipulations described herein; and / or any combination of the foregoing. The terms "merge," "merging," "combine," "combining," etc., are used to describe the generation of a single droplet from two or more droplets. It should be understood that when such terms are used with respect to two or more droplets, any combination of droplet manipulations sufficient to result in the combination of two or more droplet groups into a single droplet may be used. For example, “merging droplet A with droplet B” can be achieved by delivering droplet A to contact with stationary droplet B, delivering droplet B to contact with stationary droplet A, or delivering droplets A and B to contact each other. The terms “split,” “separate,” and “divide” are not intended to imply any particular result regarding the volume of the resulting droplets (i.e., the volumes of the resulting droplets can be the same or different) or the number of resulting droplets (the number of resulting droplets can be 2, 3, 4, 5, or more). The term “mixing” refers to droplet manipulation that results in a more uniform distribution of one or more components within the droplet. Examples of “loading” droplet manipulation include microdialysis loading, pressure-assisted loading, robotic loading, passive loading, and pipette loading. Droplet manipulation can be electrode-mediated. In some cases, droplet manipulation is further facilitated by using hydrophilic and / or hydrophobic regions on the surface and / or by physical barriers.

[0031] "Diameter," when used in relation to droplets, is intended to identify the longest straight line segment between two points on the surface of the droplet.

[0032] A "gate driver" is a power amplifier that receives a low-power input from a controller, such as a microcontroller integrated circuit (IC), and generates a high-current drive input for the gate of a high-power transistor, such as a TFT. A "source driver" is a power amplifier that generates a high-current drive input for the source of a high-power transistor. A "top electrode driver" is a power amplifier that generates a drive input for the top-plane electrode of an EWoD device.

[0033] "Nucleic acid molecules" are a collective term for single-stranded or double-stranded, sense or antisense DNA or RNA. These molecules are composed of nucleotides, which are monomers consisting of three parts: a pentose sugar, a phosphate group, and a nitrogenous base. If the sugar is ribose, the polymer is RNA (ribonucleic acid); if the sugar is derived from ribose as deoxyribose, the polymer is DNA (deoxyribonucleic acid). Nucleic acid molecules vary in length, from common oligonucleotides of about 10 to 25 nucleotides used for gene detection, research, and forensics to relatively long or very long prokaryotic and eukaryotic genes with sequences of about 1,000, 10,000 nucleotides or more. Their nucleotide residues can be entirely naturally occurring or at least partially chemically modified, for example, to slow down degradation in vivo. The molecular backbone can be modified, for example, by introducing nucleoside organothiophosphate (PS) nucleotide residues. Another modification used for the medical application of nucleic acid molecules is 2' sugar modification. Modifying the 2' sugar is thought to increase the effectiveness of therapeutic oligonucleotides by enhancing their target binding ability, especially in antisense oligonucleotide therapies. The two most commonly used modifications are 2'-O-methyl and 2'-fluoro.

[0034] When a liquid in any form (such as droplets or a continuous body, whether moving or stationary) is described as being "on", "at", or "above" an electrode, array, matrix, or surface, such liquid may be in direct contact with the electrode / array / matrix / surface, or may be in contact with one or more layers or films interposed between the liquid and the electrode / array / matrix / surface.

[0035] When a droplet is described as being “on” or “loaded” on a microfluidic device, it should be understood that the droplet is arranged on the device in a manner that facilitates one or more droplet operations on the droplet using the device, the droplet is arranged on the device in a manner that facilitates sensing the properties of the droplet or signals from the droplet, and / or the droplet has already undergone droplet operations on a droplet actuator.

[0036] The word "each," when used with respect to multiple items, is intended to identify a single item in a set, but does not necessarily refer to every item in the set. Exceptions may occur if explicitly stated otherwise or clearly specified in the context.

[0037] Throughout this specification, regardless of whether the terms "exemplary" or "non-exclusive" precede the term "implementation," references to "an embodiment," "some embodiments," "one or more embodiments," or "implementation" mean that a particular feature, structure, material, step, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. Therefore, phrases such as "in one or more embodiments," "in some embodiments," "in one embodiment," or "in an embodiment" appearing in various places throughout this specification do not necessarily refer to the same embodiment of the invention. Furthermore, specific features, structures, materials, steps, or characteristics can be combined in one or more embodiments in any suitable manner.

[0038] In the context of microfluidic devices, the use of "top" and "bottom" is merely conventional because the positions of the top and bottom plates can be switched, and the device can be oriented in various ways. For example, the top and bottom plates can be substantially parallel, while the entire device is oriented such that the plates are perpendicular to the working surface (as opposed to being parallel to the working surface as shown in the figure). The top or bottom plate may include additional functionality, such as heating via commercially available microheaters and thermocouples integrated with the microfluidic platform and / or temperature sensing.

[0039] Detailed Explanation

[0040] Precise control of fluid volume for efficient and varied droplet distribution is highly beneficial. This capability also enables the execution of complex droplet operations involving a large number of droplets carrying reactants, often combined in the context of methods characterized by parallel reactions. Furthermore, high repeatability and minimal size variation across all droplet sizes are important. Liquids can also have varying viscosities and variable surface tensions, which can greatly benefit from highly tunable distribution patterns. This invention provides a method for distributing droplets with high precision and repeatability at variable sizes using a high-density electrode system, such as a thin-electrode transistor (TFT) array. Importantly, this robust distribution strategy is applicable to reservoirs that can cover droplet volumes of several orders of magnitude, particularly down to very small droplets.

[0041] As discussed in the background, the basic procedure for dispensing remains similar in some respects to those reported in the literature: First, a liquid line extends from the reservoir. Then, a narrow neck is formed between the reservoir and the initial droplet, and the reservoir and droplet move in opposite directions. Conventional methods are primarily based on segmented arrays with limited control over the dispensing volume and CV. The low density of the storage electrodes allows for a limited degree of control over the stored fluid. Since the electrode size is on the order of the droplet diameter, the ability to control the necking properties in more than one dimension is also limited. Therefore, it is almost impossible to dispense fluids of different viscosities with variable droplet sizes.

[0042] In contrast, this application defines a reservoir and dispensing pattern that relies on multiple actuation parameters, which can be dynamically adjusted based on variables such as droplet size, viscosity, and surface tension. The pattern relies on a high-density electrode array, thereby eliminating problems generally associated with fixed segmented structures and ensuring uniformity of dispensing across a variety of droplet sizes, while allowing dynamic accounting of residual liquid in the reservoir. The reservoir and neck are shaped to define the desired droplet size and achieve clean dispensing with high accuracy and repeatability. After neck formation, several strategies can be used for splitting, depending on the droplet properties.

[0043] The dispensing method of this application reduces the failure rate in multi-step droplet operations, such as in complex assays, thereby increasing the reliability of the EWoD microfluidic cartridge. The range of reagents that can be used on the digital microfluidic device is also increased, thus improving the scope of feasible applications. High reproducibility of parallel assays at various volume scales is also ensured, improving the parallelization capability of the device, especially at low liquid volumes.

[0044] In a representative embodiment, the backplane of the microfluidic device includes an active matrix dielectric-on-electrowetting (AM-EWoD) array characterized by multiple elements, each array element including a push electrode; however, other configurations for driving the backplane electrodes are also considered. The AM-EWoD matrix can be in the form of a transistor active matrix backplane, such as a thin-film transistor (TFT) backplane, where each push electrode is operatively connected to a transistor and a capacitor that effectively maintain electrode states while electrodes of other array elements are addressed. The top electrode circuitry can independently drive the top plate electrode.

[0045] The propulsion voltage can be defined by the voltage difference between the array electrodes and the top electrode across the microfluidic region. By adjusting the signal frequency and amplitude driving the array electrodes and the top electrode, the propulsion voltage of each pixel in the array can be controlled to operate the AM-EWoD device in different operating modes according to the different droplet manipulation operations to be performed. In one embodiment, the TFT array can be implemented using amorphous silicon (a-Si), thereby reducing production costs to the point that the device can be disposable.

[0046] Basic operation of general EWoD devices Figure 1 The cross-sectional view illustrates that the EWoD 100 includes a microfluidic region filled with a filling fluid 102 and at least one aqueous droplet 104. Generally, a nonpolar filling fluid is used for manipulating the aqueous droplet. The nonpolar fluid can be a hydrocarbon such as dodecane, silicone oil, or other nonpolar long-chain organic fluids. The gap between the microfluidic regions depends on the size of the droplet being processed and is typically in the range of 50 to 200 µm, but can be larger. Figure 1 In the basic configuration, multiple propulsion electrodes 105 are disposed on a substrate, and a common top electrode 106 is disposed on opposing surfaces. The device further includes a hydrophobic coating 107 on the surface in contact with the oil layer, and a dielectric layer 108 between the propulsion electrodes 105 and the hydrophobic coating 107. (The upper substrate may also include a dielectric layer, but...) Figure 1 (Not shown in the image). The hydrophobic layer prevents droplets from wetting the surface. When no voltage difference is applied between adjacent electrodes, the droplets will remain spherical to minimize contact with the hydrophobic surface (oil and hydrophobic layer). Because the droplets do not wet the surface, they are unlikely to contaminate the surface or interact with other droplets unless such behavior is desired.

[0047] While a single layer can be used for both dielectric and hydrophobic functions, such a layer typically requires a thick inorganic layer (to prevent pinholes), resulting in a low dielectric constant and thus requiring voltages greater than 100V for droplet movement. For low-voltage propulsion, it is often better to have a thin, pinhole-free inorganic layer for high capacitance, topped with a thin organic hydrophobic layer. Using this combination, electrowetting operation can be achieved with voltages ranging from + / -10 to + / -50V, within the range available from conventional TFT arrays.

[0048] Hydrophobic layers can be manufactured by depositing hydrophobic materials onto a surface as a coating via suitable techniques. Exemplary deposition techniques include spin coating, molecular vapor deposition, and chemical vapor deposition, depending on the hydrophobic material to be applied. Hydrophobic layers can be more or less wettable, which is typically defined by their respective contact angles. Unless otherwise stated, angles herein are measured in degrees (°) or radians (rad), depending on the context. For the purpose of measuring the hydrophobicity of a surface, the term “contact angle” should be understood as referring to the contact angle of the surface relative to deionized (DI) water. A surface is classified as hydrophilic if water has a contact angle of 0° < θ < 90°, while a surface producing a contact angle of 90° < θ < 180° is considered hydrophobic. Generally, moderate contact angles are considered to fall in the range of about 90° to about 120°, while high contact angles are generally considered to fall in the range of about 120° to about 150°. In the case of a contact angle of 150° < θ, the surface is often referred to as superhydrophobic or extreme hydrophobic. Surface wettability can be measured using analytical methods known in the art, such as by distributing droplets onto the surface and measuring the contact angle using a contact angle goniometer. Anisotropic hydrophobicity can be verified by tilting a substrate with gradient surface wettability along the transverse axis of the pattern and examining the minimum tilt angle at which the droplets can move.

[0049] Hydrophobic layers with medium contact angles typically include one or blends of fluoropolymers such as PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene propylene), PVF (polyvinylidene fluoride), PVDF (polyvinylidene fluoride), PCTFE (polytrifluoroethylene chloride), PFA (perfluoroalkoxy polymer), FEP (fluorinated ethylene propylene), ETFE (polyethylene tetrafluoroethylene), and ECTFE (polyethylene trifluorochloroethylene). Commercially available fluoropolymers include Cytop. ® (AGC Chemicals, Exton, PA), Teflon ® AF (Chemours, Wilmington, DE) and FluoroPel from Cytonix (Beltsville, MD) TM Coatings. The advantage of fluoropolymer films is that they can be highly inert and retain their hydrophobicity even after exposure to oxidative treatments such as corona treatment and plasma oxidation.

[0050] Also Figure 1As illustrated, when a voltage difference is applied between adjacent electrodes, the voltage on one electrode attracts the opposite charge in the droplet at the dielectric-to-droplet interface, and the droplet moves toward that electrode. The voltage required for acceptable droplet propulsion depends on the properties of the dielectric and hydrophobic layers. AC drive is used to reduce the degradation of the droplet, dielectric, and electrode due to various electrochemical processes. The operating frequency for EWoD can range from 100 Hz to 1 MHz, but for use with TFTs having limited operating speeds, a lower frequency of 1 kHz or lower is preferred.

[0051] Back Figure 1 The top electrode 106 is a single conductive layer normally set to zero volts or a common voltage value (VCOM) to account for the offset voltage on the advance electrode 105 due to capacitive backlash from the TFT used to switch the voltage on the electrode (see [link]). Figure 3 The top electrode can also have a square wave applied to increase the voltage across the liquid. This arrangement allows a lower push voltage to be used for the push electrode 105 of the TFT connection, since the top plate voltage 106 is added to the voltage supplied through the TFT.

[0052] like Figure 2 As illustrated, the active matrix of the push electrodes can be arranged to be driven by data and gate (select) lines, much like the active matrix in a liquid crystal display. The scan gate (select) lines are used for addressing one row at a time, while the data lines carry the voltage to be transmitted to the push electrodes for electrowetting operations. If no movement is required, or if the droplet is intended to move away from the push electrode, 0V is applied to that (non-target) push electrode. If the droplet is intended to move towards the push electrode, an AC voltage is applied to that (target) push electrode.

[0053] Figure 3 The diagram illustrates the structure of amorphous silicon, a TFT switch, and a drive electrode. The dielectric layer 308 must be sufficiently thin and have a dielectric constant compatible with low-voltage AC drive, such as that obtained from conventional image controllers used in LCD displays. For example, the dielectric layer may comprise a layer of about 20-40 nm SiO2 coated with 200-400 nm of plasma-deposited silicon nitride. Alternatively, the dielectric may comprise 2 to 100 nm thick, preferably 20 to 60 nm thick, Al2O3 deposited atomically. TFTs can be constructed using methods known to those skilled in the art by forming alternating layers of differently doped a-Si structures along various electrode lines. The hydrophobic layer 307 may be made of materials such as Teflon. ® AF and FlurorPel TM The materials listed above are used to construct the material, which can be spin-coated onto the dielectric layer 308.

[0054] Circuitry for connecting and / or controlling the voltage of the top and bottom electrodes can be housed within the top plate itself, the bottom plate (e.g., at the edge of the electrode array), or elsewhere in the device as required and constrained by the intended application. As described above, Cho et al. (Journal of Microelectromechanical Systems, Volume: 12, Issue: 1, Feb. 2003) provide a physical analysis of how basic droplet operation occurs on conventional electrowetting devices.

[0055] Figure 14 This diagram schematically illustrates how a droplet can be selectively cleaved via EWoD electrodes. When cleaving is ready, by actuating the electrodes on both sides while keeping the middle electrode de-energized, the head of the neck is clamped longitudinally, thus clamping it in the middle. During clamping, the left and right electrodes are energized, causing their contact angles to decrease, resulting in an increase in the radius of curvature R1. Simultaneously, the electrodes (multiple cells) at the clamping point float or ground, keeping the middle portion hydrophobic. As a result, the meniscus on the middle electrode begins to contract to maintain a constant overall volume of the neck. In other words, cleaving is achieved by elongating the droplet longitudinally and necking it in the middle (negative radius of curvature R1). Figure 14 (As shown in the figure) Let's begin. It can be proven that the ratio of the radii of curvature R and R1 follows equation (1):

[0056]

[0057] in It is the dielectric constant of vacuum. The dielectric constant of the dielectric layer, t is the thickness of the dielectric layer, and V is the dielectric constant. d Applied voltage, height of the microfluidic region gap, Surface tension between the droplet and the filling fluid (see Cho et al.)

[0058] As also described above, the allocation drive sequence according to this application utilizes a high-density electrode array. Figure 4This is a schematic top view of a storage unit 400 defined by a high-density electrode grid 402. For example, an area with a base electrode density resolution of 1 square inch and 100 pixels / inch would include 100 advance electrodes. The same area at a higher resolution, such as 200 pixels / inch or higher, would result in an area with 200 or more advance electrodes. It can be seen that the density of the electrode grid allows its pixels to have dimensions such as width, height, or diagonal smaller than the droplet diameter, which allows for the distribution of droplets of different sizes and aspect ratios. For example, droplet 404 is equal in width and height to a square formed by four electrodes, droplet 406 is larger and equal to eight electrodes, and droplet 408 has the same height as droplet 406 but twice the width, resulting in a rectangular shape with an aspect ratio of 2:1. However, embodiments featuring single-electrode droplets are also conceivable.

[0059] Figure 5A and Figure 5B Show Figure 4 The same memory is used, but the electrode grid is no longer shown for clarity. The dashed lines represent the areas where the electrodes are actuated. It can be seen that... Figure 5A and Figure 5B The difference lies in the height of the actuated neck, i.e., the long extension. The reservoir area where electrode actuation occurs is defined as the "holding section," which is necessary to prevent the aqueous fluid from moving uncontrollably out of the reservoir area. A portion of the fluid is driven to the outside of the reservoir to form the actuated "neck," i.e., the extension terminating at the "head," which is the leading edge of the fluid. It can be seen that "dikes" are formed on both sides of the neck because no excessive fluid is included in the dispensing pattern. Ideally, the goal would be to minimize the formation of the dikes while allowing the neck to extend freely and the droplets to separate from the head.

[0060] Actuation parameters

[0061] include Figure 6 The actuation parameters described herein can be used to plan and implement electrode drive sequences for dispensing droplets with desired dimensions and aspect ratios. The value of each parameter can be calculated to describe the shape and other characteristics of the reservoir, droplet, neck, and holder. Each of these characteristics and its associated parameters is examined sequentially.

[0062] Storage: The storage is specified to have a length equal to the storage's length (L). R ) multiplied by width (L) R ·W R The area of ​​the storage (W) RThe dispensing direction is parallel to the dispensing direction. The reservoir fluid will generally be aqueous and will contain surfactants, buffers, proteins such as enzymes, nucleic acid molecules, or other compounds. By precisely adjusting the parameters disclosed herein, dispensing is not limited to aqueous fluids but can also include other solvents and solutes such as alcohols, ethers, ketones, and aldehydes.

[0063] Droplet Size: The size of the droplet can be provided based on either its volume or diameter. Alternatively, it can be specified based on the pixel area covered by the droplet on the device surface, for example, by multiplying the length of the area by its height. In one implementation, the user can input a specific droplet volume into the device programmed to calculate its corresponding area. Where a square coverage area is desired, the area can be calculated using the following algorithm:

[0064]

[0065] Neck parameters: In addition to the head height s, the neck is defined by the neck length "n", which can be set by the user or calculated by the device. The value of n should be kept within a reasonable range so as not to exceed the volume limit of the storage unit. Generally, the product n · s should not exceed, for example, 80% or less of a threshold percentage of the storage unit volume. The parameter "g*" marks the starting position of the neck relative to the length of the gap between the edges of the retaining part, and in principle can be zero or negative, such that the neck begins at the edge of the retaining part or even after the edge of the retaining part.

[0066] Retaining part parameters: The retaining part length "h" should be set with the volume of the storage device in mind. Generally, when the retaining part extends across the entire vertical dimension L... R At this time, h is equal to approximately 10%-20% of the area occupied by the fluid in the reservoir. The length h of the retaining section can vary to account for changes in the volume of the fluid in the reservoir, and the size of the retaining section is also controlled based on the droplet size. In one embodiment, h is related to 1 / D 2 Scale proportionally to tighten the dike when distributing smaller droplets, where D is the droplet diameter.

[0067] The parameter "g" defines the adjustment gap used for the retainer, which adjusts the amount of fluid reduction in the reservoir and holds the retainer in the position where the remaining fluid is. For example, if g is always equal to zero, it will eventually become impossible to hold the reservoir fluid in the proper position. The parameter "h*" is defined in its place, different from L. RThe height of the retainer is maintained. Due to the reduction in overall fluid volume, the value of h* may need to be reduced at the start of the dispensing drive sequence. This will allow the fluid to be centered around the intended location for forming the neck. This height h* can also be changed when the droplets are pinched and / or split, and can be increased above its dispensing value according to equation (1). The gap between the retainer and the neck g* can be varied to handle more viscous or problematic fluids, resulting in less restrictive actuation across the reservoir. In one non-limiting embodiment, the length n of the neck is scaled proportionally to 1 / D to enable improved droplet dispensing at smaller sizes. In another non-limiting embodiment, the head height s is scaled proportionally to D to enable dispensing of droplets of different sizes.

[0068] Size Range and Limitations: Generally, electrowetting arrays are characterized by a grid of square pixels spaced by a regular pattern. However, the methods disclosed in this application can be implemented on grid patterns of electrodes and / or pixels based on different geometries, such as triangles, rectangles, or hexagons, and of different sizes, as long as the spatial and temporal necking disclosed herein remains feasible. For TFT structures, pixel sizes can vary, but there are no fundamental limitations to ensuring memory operation. Typical pixel values ​​range from 100 micrometers to 1 mm pixel length, but can be extended beyond this range. Similarly, the array can consist of variable resolution regions to ensure finer dimensions (such as finer cleaved regions to induce necking separation from droplets via parameters similar to s*, as described below).

[0069] The dimensions of the reservoir, holder, neck, and droplet can be specified based on the surface area measured in pixels. The droplet volume should generally not exceed approximately 30% of the reservoir volume, as dispensing at larger volumes may prove problematic. Preferably, the temperature should not exceed the array's operating temperature range. Similarly, it is preferable not to exceed the freezing and boiling points of the liquid. Aqueous formulations typically range from 4°C to 95°C.

[0070] The processing unit can calculate each actuation parameter by applying user input to a reference correlation stored in the storage unit. For example, in an embodiment where the actuation neck length n is scaled proportionally to 1 / D, the processing unit of the device can apply a reference correlation in the form of equation (2):

[0071]

[0072] Where a and b are reference-dependent constants that can vary depending on the type of fluid used and other characteristics of the upcoming application, such as the temperature being measured or the surface tension. In some cases, the equation may include terms proportional to other powers of D, such as 1 / D. 2 Or D 1 / 2And / or additional terms depending on other application-specific variables. Similar considerations apply to the algorithmic steps used to calculate the length of the actuation retainer and the height of the actuation neck.

[0073] Generate an image and output it to the electrode.

[0074] The image corresponding to the memory allocation event can be generated in a manner similar to an animation consisting of consecutive steps, as an implementation of user input and calculated actuation parameters. In one implementation, codes are assigned to active pixels and passive pixels. Passive pixels will ultimately not receive voltage pulses, while active pixels will receive a set of voltage pulses for each output image, referred to herein as a "waveform". The image is then transmitted to the controller in the form of a waveform specifying the voltage pulses applied to the active pixels.

[0075] In an active matrix device, the controller uses an active matrix scan to drive pixels to their respective voltages. Each image corresponds to a single step in the memory allocation procedure. This route can continue for multiple steps / images until a droplet is allocated. Each image is implemented via multiple voltage pulses or "frames," in which active pixels are driven to a set voltage, while passive pixels are generally held at 0V. The voltage pulses can span a given positive or negative range, typically within ±30V or ±40V on a TFT array. Figure 15A As explained, the driving sequence can include both positive and negative voltage pulses. The frequency of the voltage pulse is defined by the duration of the voltage pulse with specific voltage and polarity received by the active pixel. Example

[0076] Figure 7 The flowchart illustrates an exemplary droplet dispensing process 700, thereby enabling the calculation and implementation of electrode drive sequences for specific top and bottom plate electrodes based on the diameter and aspect ratio of the droplets to be dispensed in the microfluidic system. In step 702, the user inputs the desired droplet diameter and aspect ratio in the form of instructions stored in a computer-readable medium accessible through the processing unit of the device. The user may also input other relevant variables, such as the viscosity and surface tension of the aqueous fluid in the droplets, that affect the actuation parameters.

[0077] The instructions instruct the processing unit to execute an algorithm stored in a computer-readable medium and to calculate actuation parameters specific to the characteristics of the desired droplet, including neck and retainer parameters such as the width of the retainer, the length of the neck, and the height of the head (step 704). Each parameter can be calculated as a function of one or more reference correlations as input variables, which can be stored in a storage location under the control of the processing unit or input by the user at some point before or during the dispensing process.

[0078] The processing unit then generates an image corresponding to the allocation (step 706) and calculates the polarity, frequency, and amplitude of each pulse of the corresponding waveform (step 707). The processing unit then outputs the waveform to the controller (step 708), and the controller outputs a signal to the driver of the push electrode (step 710). In the case where the substrate includes a TFT electrode array, the controller outputs a gate line signal to the gate line driver and a data line signal to the data line driver, thereby driving the desired push electrode. The selected push electrode is then driven to perform a drive sequence for distributing droplets (step 712).

[0079] Figure 8 This is a schematic illustration of an exemplary distribution pattern starting with configuration A, where fluid is collected vertically toward the center. In optional configuration B... * In configuration B, the fluid moves to the front of the reservoir and forms a retainer and neck. Then, in configuration C, the splitting of the droplets begins from the head. In optional configuration D... * In configuration D, before the neck is pulled back into the reservoir, the droplet is given an additional step to remove it from the head, referred to here as the "timing neck" stage. Finally, in configuration D, the reservoir reforms, and the droplet moves further.

[0080] Figure 9-1 3. Explanation Figure 8 The various stages of the distribution pattern. Figure 9 The diagram illustrates stage 1, which involves several operations to center the fluid in the reservoir. This can be achieved by centering it vertically (A), then collecting any liquid from the rear (B) and moving it to the front (C). Typically, the liquid located in front of the designated reservoir area is the preferred starting point for the dispensing operation. The dimensions of the centering pattern (shown in magenta) generally extend the full length or width of at least one reservoir area, with other dimensions proportional to the remaining volume of the reservoir and large enough to extend at least 20% beyond the liquid edge in the cases of B and C. For vertical centering (or a direction orthogonal to dispensing), the centering pattern covers approximately 50% of the reservoir's length (horizontally) and vertical space. Note that the reservoir can be positioned for both vertical and horizontal dispensing, so these definitions can vary depending on orientation.

[0081] Figure 10 Phase 2 is described, in which a retainer and a neck are created, followed by stretching of the neck. As disclosed above, several actuation parameters are associated with the retainer and the neck. The neck begins short (approximately the size of the target droplet) and then extends outward in the dispensing direction until it reaches the specified neck length. The neck is centered around the vertical direction, and as described above, parameter g... *The value of this value allows the neck to begin precisely at the edge of the retaining portion. Generally, the distance the neck extends in the dispensing direction is approximately half the desired droplet diameter. However, this value can be as small as a single pixel electrode.

[0082] Figure 11 Phase 3, where the splitting of the droplet begins once the neck is fully extended, is described. The area designated for separating the reservoir liquid from the desired droplet is deactivated, shown in red. To initiate splitting, the area (A) is deactivated by floating or grounding the electrodes (multiple electrodes) in region (A), and the droplet continues to move to the right in a minimum step of generally one pixel, where the typical step is half the pixel size in the dispensing direction (B). The final step retracts the reservoir by driving a region equal to the fluid retained in the neck, which completely crosses the direction orthogonal to the dispensing direction. Simultaneously, the droplet moves further away from the reservoir (C).

[0083] In such Figure 12A In the variation of stage 3 described, step B adds several steps, and the droplet moves further away before being pulled back into the reservoir, thus forming an extended "timing neck." Through this strategy, the negative radius of curvature R increases to R0. * This helps to split the droplets ( Figure 12B The parameter "t" defines the number of additional steps that can be used for droplet dispensing before pulling the neck back into the reservoir.

[0084] In further variations of stage 3, such as Figure 13A As explained, the two-dimensional necking capability provided by the high-density electrodes can be used to achieve improved control of the droplet splitting step. Specifically, by actuating the electrodes on both sides of the neck, the head height s, i.e., the size of the advancing neck orthogonal to the advancing direction of the neck, can be increased to a new "advancing splitting height" s* greater than the original. As shown in equation (1), in order to split the neck, R should gradually become negative, so a larger R1 (provided by increasing s to s*) is desired to obtain a more efficient splitting ( Figure 13B The parameter “s*” can be referred to as the new height of the side of the neck orthogonal to the assignment direction. The degree to which s* is greater than s can be specified based on the pixel electrode or as a percentage of the original head height s.

[0085] It will be apparent to those skilled in the art that various changes and modifications can be made to the specific embodiments described above without departing from the scope of the invention. Therefore, the entire foregoing description should be interpreted in an illustrative rather than restrictive sense.

[0086] All contents of the aforementioned patents and applications are incorporated herein by reference in their entirety. In the event of any inconsistency between the contents of this application and any patents and applications incorporated herein by reference, the contents of this application shall be controlled to the extent necessary to resolve such inconsistency.

Claims

1. A method for distributing droplets on a digital microfluidic system, The system includes: (a) A base plate, said base plate comprising: A bottom electrode array, comprising a plurality of digital microfluidic propulsion electrodes; and A first dielectric layer covering the bottom electrode array; (b) A top plate, said top plate comprising: Common top electrode; and A second dielectric layer covering the common top electrode; (c) A processing unit operablely programmable for microfluidic actuation methods; and (d) A controller operatively coupled to the processing unit, the common top electrode and the bottom electrode array, wherein the controller is configured to provide a propulsion voltage between the common top electrode and the bottom plate propulsion electrode; The microfluidic actuation method includes: The processing unit receives input instructions related to the droplet diameter and aspect ratio. The processing unit calculates actuation parameters, including the length of the actuation holding part, the length of the actuation neck, and the height of the actuation head, for dispensing droplets with the diameter and aspect ratio of the input command. The processing unit outputs an electrode actuation command to the controller, the electrode actuation command being associated with an allocation drive sequence of actuation parameters used to perform the calculation; The distribution drive sequence is executed on the propulsion electrode to: The fluid in the reservoir is shaped to form the actuation retainer and the actuation neck; Split the droplets from the head at the neck; and Allow the fluid in the neck to return to the reservoir. The electrodes of the bottom electrode array have a size smaller than the droplet diameter.

2. The method for distributing droplets according to claim 1, wherein the length of the actuation retainer is calculated according to an equation that is at least responsive to the input droplet diameter and associates the droplet diameter with the length of the actuation retainer.

3. The method for distributing droplets according to claim 1, wherein the length of the actuating neck is calculated according to an equation that is at least responsive to the input droplet diameter and correlates the droplet diameter with the length of the actuating neck.

4. The method of distributing droplets according to claim 1, wherein the height of the actuating head is calculated according to an equation that is at least responsive to the input droplet diameter and correlates the droplet diameter with the height of the actuating neck.

5. The method for distributing droplets according to claim 1, wherein, The actuation parameters also include one or more of the following: reservoir height, adjustment space for the retaining part, length of the actuation retaining part, height of the actuation neck, retaining gap, amount of remaining fluid in the reservoir, and length of the gap between the actuation retaining part and the actuation neck.

6. The method of dispensing droplets according to claim 1, further comprising forming a timing neck to give the droplets additional time to be removed from the neck.

7. The method of dispensing droplets according to claim 1, further comprising increasing the height of the actuating head to the forward splitting height before splitting the droplets from the head of the neck.

8. The method for dispensing droplets according to claim 1, further comprising lowering the height of the retaining portion to center the fluid around the location forming the neck.

9. A digital microfluidic system, comprising: (a) A base plate, said base plate comprising: A bottom electrode array, comprising a plurality of digital microfluidic propulsion electrodes; and A first dielectric layer covering the bottom electrode array; (b) A top plate, said top plate comprising: Common top electrode; and A second dielectric layer covering the common top electrode; (c) Processing unit; (d) A controller operatively coupled to a processing unit, a common top electrode, and a bottom electrode array, wherein the controller is configured to provide a propulsion voltage between the common top electrode and the bottom plate propulsion electrode; and The processing unit is operatively programmed to: Receive input instructions, which are related to the droplet diameter and aspect ratio; Calculate actuation parameters, including the length of the actuation holding part, the length of the actuation neck, and the height of the actuation head, for distributing droplets with the diameter and aspect ratio of the input command; Electrode actuation commands are output to the controller. These commands are associated with a distribution drive sequence used to implement the calculated actuation parameters in order to distribute droplets with input diameter and aspect ratio. The electrodes of the bottom electrode array have a size smaller than the droplet diameter.

10. The digital microfluidic system of claim 9, wherein the processing unit is operatively programmed to calculate the length of the actuation retainer according to an equation that is at least responsive to the input droplet diameter and correlates the droplet diameter with the length of the actuation retainer.

11. The digital microfluidic system of claim 9, wherein the processing unit is operatively programmed to calculate the length of the actuation neck according to an equation that is at least responsive to the input droplet diameter and relates the droplet diameter to the length of the actuation neck.

12. The digital microfluidic system of claim 9, wherein the processing unit is operatively programmed to calculate the height of the actuation head using an equation that is at least responsive to the input droplet diameter and correlates the droplet diameter with the height of the actuation head.

13. The digital microfluidic system of claim 9, wherein the actuation parameters further include one or more of the following: reservoir height, adjustment space for the retainer, length of the actuation retainer, height of the actuation neck, retaining gap, amount of remaining fluid in the reservoir, and length of the gap between the actuation retainer and the actuation neck.

14. The digital microfluidic system of claim 9, wherein the processing unit is also operatively programmed to form a timing neck to provide additional time for the droplet to be removed from the neck.

15. The digital microfluidic system of claim 9, wherein the processing unit is also operablely programmed to increase the height of the actuating head to the forward slicing height before slicing the droplet from the head of the neck.

16. The digital microfluidic system of claim 9, wherein the processing unit is also operablely programmed to reduce the height of the retaining portion so that the fluid is centered around the location forming the neck.

17. The digital microfluidic system of claim 9, wherein the baseplate further comprises a transistor active matrix backplane, each transistor of the backplane being operatively connected to a gate driver, a data line driver, and a push electrode.

18. The digital microfluidic system of claim 17, wherein, The transistors on the backplane are thin-film transistors (TFTs).

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