Adaptive droplet manipulation in AM-EWOD devices based on test measurements of droplet properties

文档序号：1664210 发布日期：2019-12-31 浏览：24次中文

阅读说明：本技术 基于液滴性质的测试测量的am-ewod器件中的自适应液滴操作 (Adaptive droplet manipulation in AM-EWOD devices based on test measurements of droplet properties ) 是由彼得·马修·福里特斯本杰明·詹姆斯·哈德文彼得·尼尔·泰勒格列高利·盖于 2019-05-28 设计创作，主要内容包括：公开了一种控制方法和相关装置,用于控制被施加到介质上电润湿(EWOD)器件上的元件阵列的阵列元件的致动电压,其中确定测试度量并将其用于优化后续的液滴操纵操作。控制方法包括以下步骤：将液体液滴接收到所述元件阵列上；施加致动电压的电润湿致动图案来致动所述液滴,以将液滴的覆盖区从具有初始覆盖区的第一状态修改为具有修正覆盖区的第二状态；用传感器感测修正覆盖区；基于液体液滴对电润湿致动图案的液滴响应,通过感测指示一个或多个液滴性质的修正覆盖区来确定测试度量；以及基于测试度量来控制被施加到阵列元件的致动电压。测试度量可以包括转变速率和/或与致动图案的一致性。(A control method and related apparatus are disclosed for controlling actuation voltages applied to array elements of an array of elements on an electrowetting on dielectric (EWOD) device, wherein test metrics are determined and used to optimize subsequent droplet manipulation operations. The control method comprises the following steps: receiving a liquid droplet onto the array of elements; applying an electrowetting actuation pattern of actuation voltages to actuate the droplet to modify a footprint of the droplet from a first state having an initial footprint to a second state having a modified footprint; sensing the modified coverage area with a sensor; determining a test metric by sensing a modified footprint indicative of one or more droplet properties based on a droplet response of a liquid droplet to an electrowetting actuation pattern; and controlling actuation voltages applied to the array elements based on the test metrics. The test metrics may include a transition rate and/or consistency with the actuation pattern.)

1. A control method for controlling an actuation voltage applied to an array element of an array of elements on an electrowetting on dielectric (EWOD) device, the control method comprising the steps of:

receiving a liquid droplet onto the array of elements;

applying an electrowetting actuation pattern of actuation voltages to actuate the droplet to modify a footprint of the droplet from a first state having an initial footprint to a second state having a modified footprint;

sensing the modified coverage area with a sensor;

determining a test metric by sensing the modified footprint indicative of one or more droplet properties based on a droplet response of the liquid droplet to the electrowetting actuation pattern; and

controlling actuation voltages applied to the array elements based on the test metric.

2. The control method of claim 1, wherein the test metric comprises a rate of transition from the first state to the second state.

3. The control method according to claim 2, wherein the liquid droplet has a first shape in the first state, has a second shape different from the first shape in the second state, and has the same centroid in the first state and the second state.

4. The control method according to claim 2, wherein the liquid droplet has a first centroid in the first state, has a second centroid different from the first centroid in the second state, and has the same shape in the first state and the second state.

5. The control method according to claim 2, wherein the liquid droplet has a first shape in the first state and a second shape different from the first shape in the second state, and the liquid droplet has a first centroid in the first state and a second centroid different from the first centroid in the second state.

6. A control method according to any one of claims 1 to 5, wherein the test metric comprises a degree of conformance of the droplet with an electrowetting actuation pattern having one recess.

7. A control method according to claim 6, wherein the electrowetting actuation pattern comprises two or more recesses.

8. The control method of claim 6, wherein the electrowetting actuation pattern is a divided actuation pattern that is divided into a first actuation section and a second actuation section spaced apart from the first actuation section.

9. A control method according to any one of claims 1 to 8, wherein the test metric comprises a measure of the voltage drop across the droplet.

10. The control method of any one of claims 1 to 9, wherein the electrowetting actuation pattern is applied at a plurality of electrowetting voltage amplitudes and the test metric is determined based on a droplet response of the droplets at different electrowetting voltage amplitudes.

11. The control method of any one of claims 1 to 10, wherein the actuation pattern is applied at a plurality of electrowetting voltage AC frequencies and the test metric is determined based on a droplet response of the droplets at different electrowetting voltage AC frequencies.

12. The control method according to any one of claims 1 to 11, further comprising: varying a temperature of the EWOD device and applying the actuation pattern at a plurality of temperatures, and determining the test metric based on a drop response of the drop at the different temperatures.

13. The control method of any of claims 1 to 12, wherein said controlling actuation voltages applied to the array elements based on the test metric comprises:

determining a droplet manipulation operation based on the test metric; and

controlling the actuation voltage to perform the determined droplet manipulation operation on one or more droplets applied to the array of elements.

14. The control method of claim 13, wherein said determining a droplet manipulation operation based on said test metric comprises: the test metric is compared to a threshold value, and the droplet manipulation operation is selected from predefined options stored in memory based on the comparison.

15. The control method according to any one of claims 13 to 14, wherein the droplet manipulation operation includes: applying one or more droplets from a liquid reservoir onto the array of elements; and at least one of: separating a droplet into two or more droplets, merging multiple droplets, agitating a droplet to mix the droplets, maintaining a droplet position, or moving a droplet to another position on the array of elements.

16. The control method of any one of claims 1 to 15, wherein said controlling actuation voltages applied to the array elements based on the test metric comprises:

determining whether a fault condition corresponding to droplet non-actuation exists; and

outputting an error message from the EWOD device to notify a user when a fault condition exists.

17. The control method of claim 16, wherein the determining whether a fault condition exists comprises: determining whether a combination of the metrics of the droplets is suitable or unsuitable for performing a desired droplet manipulation operation.

18. A microfluidic system, comprising:

an electrowetting-on-dielectric (EWOD) device comprising an array of elements configured to receive one or more droplets of liquid, the array of elements comprising a plurality of individual array elements;

a control system configured to control actuation voltages applied to the array of elements to perform a manipulation operation with respect to the liquid droplet; and

a sensor for sensing a state of the liquid droplet;

wherein the control system is configured to perform the steps of the control method according to any one of claims 1 to 17.

19. The microfluidic system of claim 18, wherein the sensor is an optical sensor external to the EWOD device and/or a sensor circuit integrated into an array element circuit of each individual array element.

20. A non-transitory computer readable medium storing program code for execution by a processing device for controlling actuation voltages applied to array elements of an array of elements of an electrowetting-on-media, EWOD, device for performing droplet manipulation on droplets on the array of elements, the program code executable by the processing device to perform the steps of:

applying an electrowetting actuation pattern of actuation voltages to actuate a liquid droplet applied to the array of elements to modify a footprint of the droplet from a first state having an initial footprint to a second state having a modified footprint;

sensing the modified coverage area with a sensor;

determining a test metric by sensing the modified footprint indicative of one or more droplet properties based on a droplet response of the liquid droplet to the electrowetting actuation pattern; and

controlling actuation voltages applied to the array elements based on the test metric.

Technical Field

The present invention relates to droplet microfluidic devices, and more particularly to an active matrix medium electrowetting on (AM-EWOD) device and control method for actuating (actuating) device elements.

Background

Active matrix EWOD (AM-EWOD) refers to the implementation of EWOD in an active matrix array containing transistors, for example by using Thin Film Transistors (TFTs). The introduction of the basic principle of this technology can be found in "Digital microfluidics: is a true lab-on-a-chip-capable?", R.B.Fair, microfluidic Nanofluid (2007) 3: 245-.

Fig. 1 shows a portion of a conventional EWOD device in cross-section. The device includes a lower substrate 10, the uppermost layer of the lower substrate 10 being formed of a conductive material that is patterned so as to implement a plurality of array element electrodes 12 (e.g., 12A and 12B in fig. 1). The electrodes of a given array element may be referred to as element electrodes 12. A liquid droplet 14 comprising a polar material (also typically aqueous and/or ionic) is confined in a plane between the lower substrate 10 and the top substrate 16. A suitable gap between the two substrates may be achieved by means of the spacers 18 and a non-polar fluid 20 (e.g. oil) may be used to occupy the volume not occupied by the liquid droplets 14. An insulator layer 22 disposed on the lower substrate 10 separates the conductive element electrodes 12A, 12B from a first hydrophobic coating 24, on which the liquid droplet 14 is positioned at a contact angle 26, denoted θ, on the first hydrophobic coating 16. The hydrophobic coating is formed from a hydrophobic material, typically but not necessarily a fluoropolymer.

On the top substrate 16 is a second hydrophobic coating 28, and the liquid droplet 14 may be in contact with the second hydrophobic coating 28. A reference electrode 30 is interposed between the top substrate 16 and the second hydrophobic coating 28.

The contact angle theta is defined as shown in fig. 1 and is passed through a solid liquid (gamma)_SL) Liquid gas (gamma)_LG) And a non-ionic fluid (gamma)_SG) The balance of the surface tension components between the interfaces is determined and young's law is satisfied without applying a voltage, and the equation is given by:

in operation, one may refer to as the EW drive voltage (e.g., V in FIG. 1)_T、V₀And V₀₀) Is externally applied to different electrodes (e.g., to the reference electrode 30, the element electrodes 12, 12A, and 12B, respectively). The resulting established electric force effectively controls the hydrophobicity of the hydrophobic coating 24. By arranging different EW drive voltages (e.g., V)₀And V₀₀) Applied to the different element electrodes (e.g., 12A and 12B), the liquid droplet 14 may move in a transverse plane between the two substrates 10 and 16.

Example configurations and operations of EWOD devices are described below. US 6911132(Pamula et al, published 6/28/2005) discloses a two-dimensional EWOD array for controlling the position and movement of droplets in two dimensions. US6565727(Shenderov, published 5/20/2003) also discloses methods for other droplet operations, including splitting and merging of droplets, and mixing droplets of different materials together. US 7163612(Sterling et al, published 16.1.2007) describes how TFT-based thin film electronics can be used to control the addressing of voltage pulses to an EWOD array by using a circuit arrangement very similar to that employed in AM display technology.

The method of US 7163612 may be referred to as "electrowetting on active matrix medium" (AM-EWOD). The use of TFT-based thin film electronics to control EWOD arrays has several advantages, namely:

the electronic driving circuit may be integrated on the lower substrate 10.

TFT-based thin film electronics are well suited for AM-EWOD applications. The cost of producing TFT-based thin film electronic devices is low, so that relatively large substrate areas can be produced at relatively low cost.

TFTs fabricated in standard processes can be designed to operate at much higher voltages than transistors fabricated in standard CMOS processes. This is important because many EWOD technologies require the application of electrowetting voltages in excess of 20V.

Various methods of controlling the AM-EWOD device to sense the droplet and perform the desired droplet manipulation have been described. For example, US 2010/0096266(Kim et al, published 22/4/2010) describes the use of capacitive sensing as real-time feedback to control the volume of a droplet dispensed or disrupted from a liquid reservoir (liquid reservoir). US 2010/0194408a1(Sturmer et al, published 5.8.2010) describes the use of capacitive sensing as real-time feedback to determine whether a droplet operation has been successful. US 2017/0056887 (published by Hadwen et al, 3.2017 and 2.d.) describes the use of capacitive detection to sense dynamic properties of reagents as a means for determining assay output.

A problem with conventional AM-EWOD devices is that different liquids have different physical properties (e.g., viscosity, conductivity, surface tension, etc.), and these physical properties affect how the droplets actuate in response to electrowetting forces. These physical properties of a given liquid may also vary with environmental conditions, such as temperature, pressure, and humidity levels (where temperature is particularly significant). The differences in liquid properties and environmental conditions make it difficult to achieve a completely versatile definition of droplet operations, i.e., operations that work reliably for each size of droplet, environmental condition, and droplet configuration.

In general, droplet operations (in particular splitting and dispensing droplets from a liquid reservoir) have to comprise liquid-dependent and/or condition-dependent parameters that have to be predefined by a user. It is difficult and time consuming for a user to predefine the operating parameters for droplet manipulation and device performance can be compromised if the operating parameters are incorrectly predefined. This inability to automatically optimize device operation is one of the reasons for the significant inefficiency of AM-EWOD devices, which has not been adequately considered in conventional configurations.

Disclosure of Invention

The present invention relates to enhanced control systems and methods for actuating array elements in EWOD devices, in particular AM-EWOD devices. The control system automatically selects liquid-dependent and condition-dependent parameters of the droplet manipulation operation in order to reduce or eliminate inefficiencies in the conventional devices described above, and in so doing effectively account for variations in liquid properties and environmental conditions. In this way, the performance efficiency and reliability of droplet manipulation operations on an AM-EWOD device are improved.

In an exemplary embodiment, to perform a desired droplet manipulation operation, automated test measurements are performed to determine one or more metrics indicative of a response of a liquid droplet to electrowetting actuation. For example, the one or more metrics may be indicative of a physical property of the liquid and/or the oil in which the liquid is immersed, and/or an ambient operating condition (e.g., temperature). The measured metrics can typically be stored by the AM-EWOD system and used later in the system operation to further decide how the droplet manipulation operation should be performed. Appropriate droplet operations may then be selected from a library of stored operations based on the measured test metrics, or otherwise determined or calculated, in order to optimize the desired droplet manipulation operation for the particular liquid properties and environmental conditions.

To perform the test measurements, an actuation pattern is applied to the droplets. The actuation pattern may have a different shape, a different size, depression, etc. than the droplet when the actuation pattern is not applied. The level of conformity of the droplets to the actuation pattern and/or the rate of transition from the unactuated state will vary depending on the actuation potential and frequency of the applied actuation voltage, the physical properties of the liquid, and/or the environmental conditions of operation. Once the droplet reaches a static or equilibrium state, a sensor measurement is taken. The consistency of the liquid droplet with the actuation pattern and/or the time response of the transition to the equilibrium state is measured and recorded as a metric describing the response of the droplet to the electrowetting actuation voltage. This metric is then used to design an optimal droplet manipulation algorithm. The droplet manipulation algorithm may be calculated by the system or selected from a library of predefined droplet manipulation operations stored in system memory.

Differences between variations of droplet operations encoded in the calculated parameters or stored library may include, for example:

(a) a variation of a constant rate electrowetting actuation sequence;

(b) a change in time between frames of an electrowetting actuation sequence;

(c) variations on the adaptive electrowetting pattern scheme, e.g., selecting the actuation pattern itself from the drop response, thereby selecting the pattern in response to the sensor measurements;

(d) a change in electrowetting actuation voltage amplitude or voltage AC operating frequency; and

(e) variations in device temperature, for example, can heat the system to make the desired droplet manipulation easier to perform.

Accordingly, one aspect of the present invention provides a control method for controlling actuation voltages applied to array elements of an array of elements on an electrowetting on dielectric (EWOD) device, in which test metrics are determined and used to optimize subsequent droplet manipulation operations. In an exemplary embodiment, the control method includes the steps of: receiving a liquid droplet onto an array of elements; applying an electrowetting actuation pattern of actuation voltages to actuate the droplet to modify a footprint of the droplet from a first state having an initial footprint to a second state having a modified footprint; sensing the modified coverage area with a sensor; determining a test metric by sensing a modified footprint indicative of one or more droplet properties based on a droplet response of a liquid droplet to an electrowetting actuation pattern; and controlling actuation voltages applied to the array elements based on the test metrics.

In an exemplary embodiment, the test metric may include a rate of transition from the first state to the second state, and/or a degree of conformance of the second footprint of the droplet with the electrowetting actuation pattern. The test measurements may be repeated for a plurality of different electrowetting voltage amplitudes, for a plurality of different electrowetting voltage AC frequencies and/or at different temperatures. A test metric may then be determined based on the drop response of the drop at different electrowetting voltage amplitudes, electrowetting voltage AC frequencies, and/or temperatures.

Another aspect of the invention provides a microfluidic system comprising: an electrowetting on dielectric (EWOD) device comprising an array of elements configured to receive one or more droplets of liquid, the array of elements comprising a plurality of individual array elements; a control system configured to control actuation voltages applied to the array of elements to perform a manipulation operation with respect to the liquid droplet; and a sensor for sensing a state of the liquid droplet. The control system is configured to perform the steps of the control method according to any of the embodiments. In an exemplary embodiment, the sensor is an optical sensor external to the EWOD device and/or a sensor circuit integrated into the array element circuit of each individual array element. The control method may be performed by the control system executing program code stored on a non-transitory computer readable medium.

These and further features of the present invention will be apparent with reference to the following description and attached drawings. In the description and drawings, particular embodiments of the invention have been disclosed in detail as being indicative of some of the ways in which the principles of the invention may be employed, but it is understood that the invention is not limited correspondingly in scope. On the contrary, the invention includes all changes, modifications and equivalents coming within the spirit and terms of the claims appended hereto. Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

Drawings

Fig. 1 is a diagram depicting a conventional EWOD device in cross-section.

Fig. 2 is a diagram depicting an exemplary EWOD-based microfluidic system.

Fig. 3 is a diagram depicting an exemplary AM-EWOD device in a schematic perspective view.

Fig. 4 is a diagram depicting a cross-section through some of the array elements of the exemplary AM-EWOD device of fig. 3.

Fig. 5A is a diagram depicting an electrical circuit representation of an electrical load presented at an element electrode when a liquid droplet is present.

Fig. 5B is a diagram depicting an electrical circuit representation of an electrical load presented at an element electrode when no liquid droplet is present.

Fig. 6 is a diagram depicting an exemplary arrangement of thin film electronics in the exemplary AM-EWOD device of fig. 3.

Fig. 7 is a diagram depicting an exemplary arrangement of an array element circuit of the array element.

Fig. 8A, 8B, and 8C are diagrams depicting an exemplary embodiment of measuring drop response to an actuation pattern (actuation pattern) suitable for measuring a drop time response metric.

Fig. 9 is a graph depicting a transition rate versus electrowetting voltage amplitude for an example transition in movement of a droplet of a given shape.

Fig. 10 is a graph depicting the transition rate versus electrowetting voltage AC frequency for an example transition in movement of a droplet of a given shape.

11A, 11B, and 11C are graphs depicting exemplary embodiments of measuring drop responses to an actuation pattern suitable for measuring a measure of the conformance of a drop to a particular shaped actuation pattern.

Fig. 12 is a graph depicting different degrees of conformity as measured for the actuation patterns in fig. 11A-11C.

Fig. 13 is a graph depicting actuation consistency versus electrowetting voltage amplitude for an actuation pattern in the example shape shown in fig. 11A.

Fig. 14 is a graph depicting the actuation consistency versus electrowetting voltage AC frequency also for the example shaped actuation pattern shown in fig. 11A.

Fig. 15 is a diagram depicting a variation of the EWOD-based microfluidic system of fig. 2, wherein the external sensor is an optical sensor disposed over the device.

Fig. 16 is a diagram depicting a variation of the EWOD-based microfluidic system of fig. 15 in which optical sensors are mounted to the sides of the device to measure the side profile of a droplet.

FIG. 17 is a diagram depicting an algorithm for determining a fault condition.

Detailed Description

Embodiments of the present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. It should be understood that the drawings are not necessarily to scale.

Fig. 2 is a diagram depicting an exemplary EWOD-based microfluidic system. In the example of fig. 2, the measurement system includes a reader 32 and a cassette 34. The cartridge 34 may contain microfluidic devices, such as EWOD or AM-EWOD devices 36, as well as conventional fluid input ports and electrical connections (not shown) into the device. The fluid input port may perform the function of inputting fluid into the AM-EWOD device 36 and generating droplets within the device (e.g., by dispensing from an input reservoir as controlled by electrowetting). As described in further detail below, the microfluidic device includes an electrode array configured to receive an input fluid droplet.

The microfluidic system may further comprise a control system configured to control actuation voltages applied to the electrode array of the microfluidic device to perform manipulation operations on the fluid droplets. For example, reader 32 may include such a control system configured to control electronics 38 and a memory device 40, and memory device 40 may store any application software and any data associated with the system. The control electronics 38 may include suitable circuitry and/or processing devices, such as a CPU, microcontroller, or microprocessor, configured to perform various control operations related to the control of the AM-EWOD device 36.

In their function, to implement the features of the present invention, the control electronics may comprise a portion of an overall control system that may execute program code embodied as a control application within the memory device 40. It will be apparent to a person having ordinary skill in the art of computer programming, and specifically in application programming for electronic control devices, how to program a control system to operate and carry out logical functions associated with a stored control application. Accordingly, details as to the specific programming code have been left out for the sake of brevity. Storage device 40 may be configured as a non-transitory computer-readable medium such as a Random Access Memory (RAM), a Read Only Memory (ROM), an erasable programmable read only memory (EPROM or flash memory), or any other suitable medium. Further, while the code may be executed by the control electronics 38 according to an exemplary embodiment, such control system functions could also be carried out via dedicated hardware, firmware, software, or combinations thereof, without departing from the scope of the invention.

The control system may be configured to perform some or all of the following functions:

define the appropriate timing signals to manipulate the liquid droplets on the AM-EWOD device 36.

Interpreting input data representing sensor information measured by a sensor or sensor circuit associated with the AM-EWOD device 36, including calculating the location, size, center of mass, and perimeter of a liquid drop on the AM-EWOD device 36.

Use the calculated sensor data to define appropriate timing signals to manipulate the liquid droplet on the AM-EWOD device 36, i.e. act in a feedback mode.

An implementation that provides a Graphical User Interface (GUI) whereby a user can program commands such as droplet operations (e.g., moving droplets), assay operations (e.g., performing assays), and the GUI can report the results of these operations and other system information to the user.

In the example of fig. 2, an external sensor module 35 is provided for sensing droplet properties. For example, an optical sensor known in the art may be used as an external sensor for sensing properties of the liquid droplet. Suitable optical sensors include camera devices, light sensors, Charge Coupled Devices (CCDs), and similar image sensors, among others. As described in further detail below, the sensors may alternatively be configured as internal sensor circuitry that is included as part of the drive circuitry in each array element. Such sensor circuitry may sense droplet properties by detecting electrical properties (e.g., impedance or capacitance) at the array elements.

A control system, such as via control electronics 38, can provide and control actuation voltages (e.g., desired voltages and timing signals) applied to the electrode array of the microfluidic device 36 to perform droplet manipulation operations and sense liquid droplets on the AM-EWOD device 36. The control electronics can also execute application software to generate and output control voltages for droplet sensing and performing sensing operations. The reader 32 and the cassette 34 may be electrically connected together in use (e.g., by a cable connecting the wires 42), but various other methods of providing electrical communication may be used, as known to those of ordinary skill in the art.

Fig. 3 is a diagram depicting additional details of an exemplary AM-EWOD device 36 in a schematic perspective view. The AM-EWOD device 36 has a lower substrate 44 with thin film electronics 46 disposed on the lower substrate 44. The thin film electronics 46 are arranged to drive the array element electrodes 48. The plurality of array element electrodes 48 are arranged in an electrode or element array 50, the electrode or element array 50 having X by Y array elements, where X and Y may be any integer. A liquid droplet 52, which may comprise any polar liquid and may typically be aqueous, is enclosed between the lower and top substrates 44, 54 separated by a spacer 56, although it will be understood that there may be a plurality of liquid droplets 52.

Fig. 4 is a diagram depicting a cross-section through some of the array elements of the example AM-EWOD device 36 of fig. 3. In the portion of the AM-EWOD device depicted in fig. 4, the device includes a pair of array element electrodes 48A and 48B shown in cross-section, which may be used at the electrode or element array 50 of the AM-EWOD device 36 of fig. 3. The device configuration is similar to the conventional configuration shown in fig. 1, wherein the AM-EWOD device 36 further includes thin film electronics 46 disposed on the lower substrate 44, the lower substrate 44 being separated from the top substrate 54 by spacers 56. The uppermost layer of lower substrate 44 (which may be considered to be part of thin-film electronic device layer 46) is patterned to implement a plurality of array element electrodes 48 (e.g., a specific example of an array element electrode is 48A and 48B in fig. 4). The term element electrode 48 may be understood in the following to refer to the physical electrode structure 48 associated with a particular array element, as well as the nodes of the circuitry directly connected to that physical structure. Reference electrode 58 is shown in fig. 4 as being disposed on top substrate 54, but the reference electrode may alternatively be disposed on lower substrate 44 to achieve an in-plane reference electrode geometry. The term reference electrode 58 may also be understood in the following to refer to either or both of a physical electrode structure and a node of an electrical circuit directly connected to the physical structure.

Further, similar to the conventional structure of fig. 1, in the AM-EWOD device 36, a non-polar fluid 60 (e.g., oil) may be used to occupy the volume not occupied by the liquid droplets 52. An insulator layer 62 may be disposed on the lower substrate 44, the insulator layer 62 separating the conductive element electrodes 48A and 48B from the first hydrophobic coating 64, the liquid droplet 52 being positioned on the first hydrophobic coating 64 at a contact angle 66, denoted θ. The hydrophobic coating is formed from a hydrophobic material, typically but not necessarily a fluoropolymer. On top substrate 54 is a second hydrophobic coating 68, and liquid droplet 52 may be in contact with second hydrophobic coating 68. The reference electrode 58 is interposed between the top substrate 54 and the second hydrophobic coating 68.

Fig. 5A shows a circuit representation of an electrical load 70A between element electrode 48 and reference electrode 58 in the presence of liquid droplet 52. Liquid drop 52 can be generally modeled as a resistor and a capacitor in parallel. Typically, the resistance of the droplet will be relatively low (e.g., if the droplet contains ions) and the capacitance of the droplet will be relatively high (e.g., because the relative permittivity of polar liquids is relatively high, e.g., if the liquid droplet is aqueous, the relative permittivity is about 80). In many cases, the drop resistance is relatively small, such that at the frequency of interest for electrowetting, the liquid drop 52 can effectively function as an electrical short. The hydrophobic coatings 64 and 68 have electrical characteristics that can be modeled as capacitors, and the insulator 62 can also be modeled as a capacitor. The total impedance between element electrode 48 and reference electrode 58 may be approximated by a capacitor whose value is generally dominated by the contribution of insulator 62 and the contributions of hydrophobic coatings 64 and 68, and which may be picofarad in value for typical layer thicknesses and materials.

Fig. 5B shows a circuit representation of an electrical load 70B between the element electrode 48 and the reference electrode 58 in the absence of a liquid droplet. In this case, the liquid droplet assembly is replaced by a capacitor representing the capacitance of the non-polar fluid 60 occupying the space between the top and lower substrates. In this case, the total impedance between element electrode 48 and reference electrode 58 may be approximated by a capacitor whose value is dominated by the capacitance of the non-polar fluid, and is typically small, on the order of femtofarads.

For purposes of driving and sensing the array elements, the electrical loads 70A/70B generally function as capacitors in effect, with values dependent on whether a liquid droplet 52 is present at a given element electrode 48. In the presence of a droplet, the capacitance is relatively high (typically on the order of picofarads), whereas if no liquid droplet is present, the capacitance is low (typically on the order of femtofarads). If a droplet partially covers a given electrode 48, the capacitance may approximately represent the degree of coverage of the element electrode 48 by the liquid droplet 52.

Fig. 6 is a diagram depicting an exemplary arrangement of thin-film electronics 46 in the exemplary AM-EWOD device 36 of fig. 3. Thin film electronics 46 are located on lower substrate 44. Each array element 51 of the element array 50 includes an array element circuit 72 for controlling the electrode potential of the corresponding element electrode 48. Integrated row 74 and column 76 driver circuitry is also implemented in the thin film electronics 46 to provide control signals to the array element circuitry 72. The array element circuitry 72 may also include sensing capabilities for detecting the presence or absence of liquid droplets in the locations of the array elements. Integrated sensor row addressing 78 and column sensing circuitry 80 may also be implemented in the thin film electronics for addressing and readout of the sensor circuitry in each array element.

A serial interface 82 may also be provided to process the serial input data stream and facilitate programming of the desired voltages to the element electrodes 48 in the array 50. The voltage source interface 84 provides the corresponding supply voltage, top substrate drive voltage, and other necessary voltage inputs as further described herein. Even for large array sizes, the number of connections 86 between lower substrate 44 and external control electronics, power supplies, and any other components may be relatively small. Alternatively, the serial data input may be partially parallelized. For example, if two data input lines are used, the first data input line may provide data for columns 1 to X/2, and the second data input line may provide data for columns (1+ X/2) to M with minor modifications to the column driver circuit 76. In this way, the rate at which data can be programmed into the array is increased, which is a standard technique used in liquid crystal display driver circuits.

In general, the exemplary AM-EWOD device 36 including the thin film electronics 46 may be configured as follows. The AM-EWOD device 36 includes the above-mentioned reference electrode 58 (which may alternatively be an in-plane reference electrode) and a plurality of individual array elements 51 on the element array 50, each array element 51 including an array element electrode 48 and an array element circuit 72. Relatedly, the AM-EWOD device 36 may be configured to perform a method of actuating the array elements to manipulate liquid droplets on the array by controlling electrowetting voltages applied to the plurality of array elements. The applied voltage may be provided by operation of a control system as described with respect to fig. 2, including control electronics 38 and applications and data stored on memory device 40. The electrowetting voltage at each array element 51 is defined by the potential difference between the array element electrode 48 and the reference electrode 58. The method of controlling the electrowetting voltage at a given array element generally includes the step of supplying a voltage to the array element electrodes 48 and a voltage to the reference electrode 58 by operation of the control system.

Fig. 7 is a diagram depicting an exemplary arrangement of the array element circuit 72 present in each array element 51. The array element circuit 72 may include an actuation circuit 88, the actuation circuit 88 having inputs ENABLE, DATA, and activate and an output connected to the element electrode 48. The array element circuitry 72 may also contain drop sensing circuitry 90, which may be in electrical communication with the element electrodes 48. In general, the readout of the drop sensing circuit 90 can be controlled by one or more addressing lines (e.g., RW) that can be common to elements in the same row of the array, and can also have one or more outputs (e.g., OUT) that can be common to all elements in the same column of the array.

The array element circuitry 72 may generally perform the following functions:

(i) the element electrodes 48 are selectively actuated by applying voltages to the array element electrodes. Thus, any liquid droplet present at the array element 51 may be actuated or de-actuated by the electrowetting effect.

(ii) The presence or absence of a liquid droplet at the location of the sensing array element 51. The means of sensing may be capacitive, optical, thermal or some other means. Capacitive sensing can be conveniently and efficiently performed using impedance sensor circuitry as part of the array element circuitry.

Exemplary configurations of array element circuit 72 including impedance or capacitance sensor circuits are known in the art and are described in detail, for example, in commonly assigned US 8653832 (published 2014-18/2) and in commonly assigned uk application GB1500261.1, both of which are incorporated herein by reference. These patent documents include a description of how a droplet can be actuated by means of electrowetting and how a droplet can be sensed by capacitive or resistive sensing means. In general, capacitive and impedance sensing can be analog, and can be performed at or near the same time at each element in the array. By processing the information returned from such sensors (e.g., in application software in the memory device 40 of the reader 32), the control system described above can determine the location, size, centroid and perimeter of each liquid drop present in the array of elements 50 in real time or near real time. As mentioned in connection with fig. 2, an alternative to the sensor circuit is to provide an external sensor (e.g. sensor 35), e.g. an optical sensor that can be used to sense properties of the droplets.

With this device configuration, droplet operations can be performed using a time-sequential actuation pattern written to the electrowetting array to perform desired droplet manipulation operations. Examples of basic droplet operations with associated droplet manipulation responses include moving a droplet, merging multiple droplets, splitting a droplet, dispensing a droplet from a larger liquid reservoir, mixing multiple droplets, and the like. More complex droplet operations may involve a combination of basic operations for dilution, washing, elution (elute), and the like. An actuation pattern is defined as a data pattern written to an array of electrowetting devices, typically digital (although in principle analog) and comprising an array element written as a "1" for electrowetting actuation and as a "0" for non-actuation. During the actuated or "1" state, the surface of a given array element corresponds to a surface that is controlled to be hydrophilic for the electrowetting effect, and during the non-actuated or "0" state, the surface of a given array element corresponds to a surface that is controlled to be hydrophobic. Methods of applying various actuation patterns to AM-EWOD are known, such as described in the applicant's commonly owned application serial No. 15/475,410 filed 5/31 in 2017.

According to embodiments of the present disclosure, test measurements are performed to measure drop response to an exemplary actuation pattern. In response to applying the actuation pattern, physical properties of the liquid or liquid droplet may be measured, including, for example, speed of movement, electrowetting strength (as indicated by the ability of the droplet contact line to deform into a curved shape under electrowetting actuation), conductivity, contact angle, and viscosity. The actuation pattern may be selected from a library of actuation patterns designed to measure each desired physical property, and each actuation pattern may differ in actuation voltage amplitude, actuation voltage AC frequency, and operating temperature. The measured response of the drop to the actuation pattern constitutes an automatic test measurement, and the response may be measured using any suitable sensor technology to measure the drop footprint (fotopprint) in response to electrowetting actuation. Suitable sensing technologies may include sensor circuitry integrated into the AM-EWOD device, such as capacitive or impedance sensing, or external sensing (e.g., optical image sensing by using a CCD camera or similar device). As described in further detail below, the results of the test measurements provide metrics for optimizing subsequent droplet manipulation operations.

To perform the test measurements, an actuation pattern is applied to the droplets. The actuation pattern may have a different shape, a different size, depression, etc. than the droplet when the actuation pattern is not applied. The level of conformity of the droplets to the actuation pattern and/or the rate of transition from the unactuated state or other previous state will vary depending on the actuation potential and frequency of the applied actuation voltage, the physical properties of the liquid, and/or the environmental conditions of operation. Once the droplet reaches a static or equilibrium state, a sensor measurement is taken. The consistency of the liquid droplet with the actuation pattern and/or the time response of the transition to the equilibrium state is measured and recorded as a metric describing the response of the droplet to the electrowetting actuation voltage. This metric is then used to design an optimal droplet manipulation algorithm. The droplet manipulation algorithm may be calculated by the system or selected from a library of predefined droplet manipulation operations stored in system memory.

Differences between variations of droplet operations encoded in the calculated parameters or stored library may include, for example:

(a) a variation of a constant rate electrowetting actuation sequence;

(b) a change in time between frames of an electrowetting actuation sequence;

(d) a change in electrowetting actuation voltage amplitude or voltage AC operating frequency; and

(e) variations in device temperature, for example, can heat the system to make the desired droplet manipulation easier to perform.

Embodiments of the present disclosure are superior to conventional configurations by performing test measurements and optimizing subsequent droplet manipulation operations, thus improving device performance such as operational reproducibility, execution speed, and reliability. The enhanced performance is significant because optimal droplet operation will be very dependent on the characteristics of the liquid and the environmental conditions, which may be variable in the field. For example, a liquid that is not well-conformed will require droplet operations with a simpler actuation pattern than a well-conformed droplet. Reagents from different batches or user-added samples may have different physical characteristics, which require different operations to perform the same action. Alternatively, environmental characteristics (e.g., temperature of the user's laboratory) may vary significantly, particularly if the device is used at a particular point of demand that may not be optimally located. The described systems and methods implement this optimization in a fully automated manner such that the user need not take any action (or even must be aware that such optimization is needed and has been achieved).

Fig. 8A-8C are graphs depicting exemplary embodiments of measuring drop responses to an actuation pattern suitable for measuring a drop time response metric. In these examples, the first actuation pattern is applied until the droplet reaches a first stable state in which the droplet has an initial footprint, wherein the footprint corresponds to the shape of the liquid droplet and the location of the centroid. Once the first stable state is reached, a second actuation pattern is applied to change the drop to a second stable state having a modified footprint different from the initial footprint. The time for the drop to transition from the first stable state to the second stable state is recorded. In these figures, the hashed portion represents a drop as configured to be in a first stable state of a first actuation pattern (denoted as a starting drop 100x), and the shaded portion represents a drop as configured to be in a second stable state of a second actuation pattern (denoted as an ending drop 102 x). The rate of droplet transition between steady states is used as a metric for detecting differences between liquids of different characteristics and/or subjected to different environmental conditions to determine the selection of a droplet manipulation operation.

In the example of fig. 8A, the transition from the first stable state to the second stable state constitutes a change in the shape of the droplet while maintaining the centroid (i.e., center of mass) of the droplet. For example, actuating the starting droplet 100a using a square actuation pattern produces a square shape as a first stable state, and effecting the transition by applying a rectangular actuation pattern produces the ending droplet 102a for a second stable state, i.e., the droplet shape is different in the second state relative to the first state. The centroid 104a of the droplet is the same in the first state and the second state, i.e., the centroid remains at a constant position during the transition. In the example of fig. 8B, the transition from the first stable state to the second stable state constitutes a change in the location of the centroid of the droplet while maintaining the same droplet shape in the first state and the second state. This can be performed by using a time-series actuation pattern that gradually repositions the centroid of the drop. For example, starting droplet 100b is actuated again using a square actuation pattern, and the transition is achieved by gradually applying the square actuation pattern in adjacent positions to move the droplet, resulting in ending droplet 102b in a second stable state having a different centroid position 104 b. In the example of fig. 8C, the two transitions are combined in a single operation. The transition from the first stable state to the second stable state constitutes a change in the shape of the droplet and the position of the centroid of the droplet. For example, again actuating the starting drop 100c using a square actuation pattern, and the starting drop 100c corresponding to the first centroid position 104a, the transition is achieved by applying the rectangular actuation pattern at progressively different positions, resulting in an ending drop 102c having a rectangular shape and a different centroid position 104c in the second stable state.

In each example, a transition rate from a first stable state to a second stable state is measured, and the transition rate is used to provide a metric for detecting differences between liquids of different characteristics to select an appropriate droplet manipulation operation. Further, the transition measurement may include measuring a time to achieve the first stable state at the very beginning and to transition from the first stable state to the second stable state. The transition may also be repeated for a plurality of different electrowetting voltage amplitudes, where the transition time is measured at each voltage amplitude. The transition may also be repeated for a plurality of different electrowetting voltage AC frequencies, wherein the transition time is measured at each voltage AC frequency. The transition can also be repeated at different temperatures, by heating the EWOD device and applying the actuation pattern at multiple temperatures. The transition rate test metric may then be determined based on the drop response of the drop at different electrowetting voltage amplitudes, electrowetting voltage AC frequencies, and/or temperatures.

For example, fig. 9 is a graph depicting a transition rate versus electrowetting voltage amplitude for an example transition in movement of a droplet of a given shape as shown in fig. 8B. Thus, the speed of movement is plotted against the electrowetting voltage amplitude. As can be seen from this figure, the electrowetting voltage amplitude increases up to a turning point 106, the turning point 106 corresponding to the minimum actuation voltage for effective droplet movement. The speed of movement increases with the voltage amplitude until a plateau is reached at the turning point 108.

As another example, fig. 10 is a graph depicting a transition rate versus electrowetting voltage AC frequency for an example transition also for movement of a droplet of a given shape as shown in fig. 8B. Therefore, the moving speed is plotted against the AC frequency. It can be seen from this figure that the speed of movement decreases with frequency, from a plateau at break-over point 120 to break-over point 122, which break-over point 122 corresponds to the maximum AC frequency at which the droplet can move effectively.

11A-11C are diagrams depicting exemplary embodiments of measuring drop responses to an actuation pattern suitable for measuring the conformance of a drop to a particular shaped actuation pattern. In these examples, the actuation pattern is applied to change the droplet shape from an original shape (typically an ellipsoid) having a first non-actuated state of initial footprint to a non-standard shape (non-ellipsoid) having a second actuated state of modified footprint different from the initial footprint. Likewise, in the context of the present disclosure, the footprint or coverage area of a droplet may be understood as the contact area of the droplet with the lower or top substrate (typically the lower substrate comprising a patterned array of electrodes). Further, when drop uniformity is a suitable metric, the actuation pattern has a coverage area that is similar to or greater than the coverage area of the drops. More specific features or steps of such generalized operations are described with respect to the accompanying figures.

In these figures, the hashed portion represents the actuation pattern 124, which actuation pattern 124 is overlaid on the shaded portion corresponding to the actual drop 126 shaped in response to the actuation pattern. For example, in FIG. 11A, the drop is formed into a non-standard shape using a stop or similar structure in an actuation pattern that is substantially tear-drop shaped with wedge-shaped cutouts 128. The degree of conformity of the drop contact line of the second footprint with the actuation pattern in the second state is used as a metric for detecting differences between liquids of different characteristics and/or subjected to different environmental conditions to determine the selection of a drop manipulation operation.

The inventors have found that an actuation pattern comprising two or more recesses has shown to be particularly suitable for measuring a drop consistency metric for detecting differences between liquids of different characteristics and/or different environmental conditions. An example of this is shown in fig. 11B, where the actuation pattern is cross-shaped to form four recesses 130, where the cross-section centers intersect. As another example, fig. 11C depicts an actuation pattern that is a divided actuation pattern that is divided into a first actuation portion 132 and a second actuation portion 134 that is spaced apart from the first actuation portion 132. The degree of conformity with the divided actuation pattern may also be used as a measure for detecting differences between liquids of different characteristics and/or subjected to different environmental conditions.

In each example, the degree of conformance of the droplet contact line with the actuation pattern is measured, and this degree of conformance is used to provide another metric for detecting differences between liquids of different characteristics and/or subjected to different environmental conditions to select an appropriate droplet manipulation operation. Similar to the above-described measurement transition rates, the consistency measurement may be repeated for a plurality of different electrowetting voltage amplitudes, with the degree of consistency being measured at each voltage. The consistency measurement may also be repeated for a plurality of different electrowetting voltage AC frequencies, wherein the degree of consistency is measured at each AC frequency. The consistency measurement can also be repeated at different temperatures by heating the EWOD device and applying the actuation pattern at multiple temperatures. The degree of conformance test metric may then be determined based on the drop response of the drop at different electrowetting voltage amplitudes, electrowetting voltage AC frequencies, and/or temperatures.

Thus, fig. 12 depicts a graph of different degrees of conformance as measured for the actuation patterns of fig. 11A-11C. In particular, column A corresponds to a low degree of consistency, column B corresponds to a medium degree of consistency, and column C corresponds to a high degree of consistency. As described above, the degree of uniformity may vary with actuation voltage amplitude, AC frequency, or temperature.

For example, fig. 13 is a graph depicting actuation consistency versus electrowetting voltage amplitude for an actuation pattern in the example shape shown in fig. 11A. Thus, actuation uniformity is plotted against electrowetting voltage amplitude, with the corresponding uniformity progression depicted above the graph. As can be seen from this figure, the electrowetting voltage amplitude increases up to a turning point 136, the turning point 136 corresponding to the minimum actuation voltage for effective droplet shape change. The degree of consistency increases until a plateau is reached at inflection point 138, where inflection point 138 indicates maximum consistency. In this way, the relationship between the degree of conformity and the actuation voltage amplitude is comparable to the relationship between the transition rate and the actuation voltage amplitude shown in fig. 9.

The strength of the electrowetting force and the corresponding correspondence of the droplet contact line with the actuation pattern is described by the known Lippmann-Young equation, which relates the contact angle to the actuation voltage. The strength of an electrowetting actuation is described by the ratio of the square of the voltage to the surface tension at the interface between the liquid droplet and the surrounding medium (typically oil). The surface tension may vary depending on the composition of the droplets or oil, particularly in relation to the composition and concentration of any surfactant species present in either medium. Typically, one or more surfactants are included to reduce surface tension. The surface tension may also depend on environmental variables, such as in particular the operating temperature.

According to this embodiment, the conformity with the actuation pattern is measured for a plurality of voltage amplitudes and an optimized actuation voltage amplitude is determined from the result. In addition to selecting an actuation voltage amplitude large enough to ensure proper consistency, there is also an incentive to make the actuation voltage amplitude not too large. Operating at too large an actuation voltage amplitude can reduce the reliability of droplet manipulation because applying too much energy to the droplet contact line can destabilize the contact line. Furthermore, operating at actuation voltage amplitudes greater than required can compromise the reliability of the device itself, for example by applying a higher than required electric field through the insulator layer and the hydrophobic coating. Actuation voltage amplitudes higher than necessary also consume power unnecessarily. This balance between the positive and detrimental effects of larger actuation voltage amplitudes is also applicable to optimized voltage selection with respect to transition rate (speed of movement) as described in connection with fig. 9.

As another example, fig. 14 is a graph depicting actuation consistency versus electrowetting voltage AC frequency also for an exemplary shaped actuation pattern as shown in fig. 11A. Thus, the degree of consistency is plotted against the AC frequency, with the corresponding progress of consistency being depicted above the graph. As can be seen from this figure, the degree of conformity decreases with decreasing frequency from the plateau at break-over point 140 to break-over point 142, break-over point 142 corresponding to the maximum AC frequency for effectively effecting the change in droplet shape. In this way, the relationship between the degree of conformity and the actuation voltage AC frequency is comparable to the relationship between the transition rate and the AC frequency as shown in fig. 10. The frequency response of the conformance to the actuation pattern is a function of the drop conductivity. For example, if the ion concentration of the droplets is less than 1 μ M, the decrease in uniformity will be significant at AC frequencies less than 1 kHz. Similarly, if the ion concentration is about 10 μ M, the critical AC frequency will be about 10kHz, and if the ion concentration is about 100 μ M, the critical AC frequency will be about 100 kHz.

Thus, fig. 8-14 illustrate how test metrics may facilitate selection of parameters for subsequent droplet manipulation operations. For example, according to the test measurements performed in the above illustration, for an applicable liquid, what level of electrowetting voltage amplitude and AC frequency will be optimal to achieve a desired transition rate or consistency for any given droplet manipulation operation to be performed. In this way device performance is improved. Similar test measurements may be performed with respect to other drop properties and environmental conditions to determine comparable metrics.

According to any embodiment, the drop response may be measured in any suitable manner when the actuation pattern is applied. For example, an integrated sensor such as impedance/capacitor sensor circuit 90 (FIG. 7) may be used to determine the properties of a droplet including the droplet footprint. Additionally or alternatively, external optical sensors, such as CCD cameras, may be used to measure properties of the droplets including the droplet footprint. For example, fig. 15 is a diagram depicting a variation of the AM-EWOD microfluidic system of fig. 2, wherein the external sensor is an optical sensor 135 placed above (or below) the device. Additionally or alternatively, fig. 16 is a diagram depicting a variation of the AM-EWOD microfluidic system of fig. 15, wherein optical sensors 135 are mounted to the sides of the device to measure the side profile of the droplet. An example optical measurement taken from the side and recorded as a metric is the contact angle 66 of the droplet 52 on the hydrophobic surface 64 (see also fig. 4). As another example, referring back to fig. 5A and 5B, a sensor measurement may be made to determine the voltage drop across the droplet 52 compared to the voltage drop across the electrowetting element without a droplet (modeled as a capacitor 60) to measure the conductivity of the liquid. All of these measurements (including, for example, droplet footprint, contact angle, conductivity, etc.) may be used to determine droplet response metrics for detecting differences between liquids of different characteristics and/or subjected to different environmental conditions to select an appropriate droplet manipulation operation.

The test measurements described in the above embodiments may be used for subsequent automatic selection of a droplet manipulation operation to be performed by the AM-EWOD device. In this way, the test measurements provide feedback results to detect specific characteristics of the liquid from which additional droplets are to be dispensed, taking into account the liquid composition and environmental conditions that can affect how the droplets will respond to actuation of the array elements. Therefore, the control method includes: controlling actuation voltages applied to the array elements based on the test metrics by: determining a droplet manipulation operation based on the test metric; and controlling the actuation voltage to perform the determined droplet manipulation operation on one or more droplets applied to the array of elements.

The feedback results provided by the previous test measurements may be used in various ways. For example, the feedback result may determine a selection of an analog value of the steering parameter, such as an actuation voltage AC frequency or an actuation voltage amplitude. These values can be achieved by simple scaling based on the drop response in the test measurements, or by calculation from predefined equations (e.g., look-up polynomials) implemented in software.

An additional method of using the feedback results is to select a droplet manipulation operation from two or more options as an option based on the results of the test measurements. For example, if the number of test measurements is "x", the droplet manipulation operation may have multiple options, in this particular example three options: operation A, operation B, and operation C. Any suitable number of options may be used. The appropriate droplet manipulation operation may be selected based on a comparison of the measured value "x" from the test measurement to one or more preprogrammed thresholds (in this example, two preprogrammed thresholds "a" and "b"), the resulting selection of operations being illustrated by the following table. Similar to the above, any suitable number of pre-programmed thresholds may be employed.

x＜a	Selection operation A
		a＜x＜b	Selection operation B
b＜x	Selection operation C

For the present example, the generally measured value "x" may relate to one or more of the above-referenced test metrics corresponding to drop response to the applied actuation pattern. For example, the value of "x" may be a transition rate, such as a speed of movement or a transition rate from a first stable state to a second stable state, or may be a degree of conformance with an actuation pattern. As described above, measurements for obtaining the metric may be made at multiple actuation voltage amplitudes, AC frequencies, and/or temperatures, where the drop response is measured and stored by the device control system. Different predefined operations A, B and C may correspond to different possible selections of actuation patterns for performing a droplet manipulation operation, where each actuation pattern corresponds to a series of array elements to be actuated, and actuation voltage parameters (e.g., amplitude and AC frequency). Thus, for the present example, if the measured value "x" is less than the pre-programmed threshold "a", then operation a is selected; if the measured value "x" is between the preprogrammed thresholds "a" and "B", then operation B is selected; and if the measured value "x" is greater than the preprogrammed threshold "b", then operation C is selected. A plurality of test metrics and preprogrammed thresholds may be grouped and analyzed for selecting an optimal droplet manipulation operation.

In a generalized illustration, a more viscous and conductive liquid droplet at a relatively low temperature will have a different measure of response than a less viscous and less conductive liquid droplet at a relatively high temperature. The measured "x" values will be different in terms of system operation, which may result in different selections of droplet manipulation operations, either by calculation or by selection from predefined operations in a look-up table. Even liquids that are generally considered "the same" may vary within tolerances, and environmental conditions may differ, so the system may select an optimal operational actuation pattern to perform a given droplet manipulation operation.

An example of this operation may be in the selection of a droplet manipulation operation, including a sequence of actuation patterns for dispensing droplets from a larger liquid reservoir. An exemplary test metric may be a degree of conformance determined using the measurements described in accordance with fig. 11-14. Based on the drop response metric from the conformance measurement, a series of actuation patterns for dispensing drops can be calculated or selected from among a plurality of predefined operations stored in a look-up table to perform a dispense operation in a manner that requires a lower or higher conformance of the drops to the actuation patterns for successful performance of the dispense operation. For example, the dispensing operation a may require a high consistency with the actuation pattern to perform reliably, but if this is assumed to be the case, the volume reproducibility of the dispensed droplets may be very high. In contrast, operation C may be performed more reliably than operation a in cases where the consistency of the droplets with the actuation pattern is low. The increased reliability for poor actuating liquids may make operation C a preferred droplet application operation, even if it takes longer to perform or has lower volume reproducibility than operation a.

The principles described above may be applied to any suitable droplet manipulation operation. Examples include using metrics to determine or select a droplet operations algorithm from a predefined library to break a droplet into two or more droplets, merge multiple droplets, agitate droplets to mix droplets, hold droplet position, move droplets to another position on an array of elements, and so forth. More complex droplet manipulation operations may involve a combination of these basic operations for dilution, washing, elution, and the like. Furthermore, many examples have been described with respect to selecting alternative droplet manipulation operations from predefined libraries stored in the system, but this need not be the case. Alternatively, the droplet operations may be determined by calculations performed by the system without reference to any predefined library. An advantage of this approach is that for some types of liquids, the droplet manipulation operations required for other liquids may not need to occur. Additional examples may include using the metric to change the order of two or more droplet operations.

In another example, the metric is used to determine whether a fault condition corresponding to liquid droplet non-actuation exists, which may include notifying a user of an error message output by the EWOD device. FIG. 17 is a diagram depicting an algorithm for determining a fault condition. In this example, the speed of movement is plotted against actuation consistency as a test measure. A first region 150 (denoted as "pass-through region") in the figure represents a combination of movement speed and actuation consistency suitable for performing a desired droplet manipulation operation. In contrast, a second region 152 (denoted as a "failed region") in the figure represents a combination of movement speed and actuation consistency that is not suitable for performing a desired droplet manipulation operation. If the test metric for drop response falls within failure region 152, the system may output an error message to notify the user. In some cases, the cause of the malfunction may be diagnosed (e.g., a particular liquid is out of specification) and the user prompted to take corrective action (e.g., remove the cartridge and begin using the liquid within the new cartridge and specification again). The fault system is advantageously: if the reagent does not function in an appropriate manner under the corresponding environmental conditions, the droplet manipulation sequence is allowed to stop. Although the speed of movement and the degree of consistency are the metrics used in this example, more generally, determining a fault condition may include determining whether any combined metric of droplets is suitable or unsuitable for performing the desired droplet manipulation operation.

The system is also fully automated. In an exemplary embodiment, the control system may execute any number of test measurement protocols of executable program code that is part of the control application, which may be stored in memory device 40 and executed by a processor device of control electronics 38 (see fig. 2, 16, and 17). The control system may also receive drop response measurements based on the sensor measurements and determine resulting test metrics, which may also be stored in a system memory device. Using such test metrics, the control system may also perform the necessary calculations and/or select from a stored look-up table of specific operable actuation patterns to perform a droplet manipulation operation. In this manner, the device user may simply initiate any desired operational protocol, which may include one or a series of droplet manipulation operations selected by the user through the interface device of the control electronics, or automatically selected in other ways as part of the control application. The AM-EWOD system can then automatically perform any suitable test operations and proceed to determine and select the optimal droplet manipulation operation without further additional input from the user.

Embodiments of the present disclosure are superior to conventional configurations by executing a test protocol and optimizing subsequent droplet manipulation operations based on metrics corresponding to droplet responses to an actuation pattern applied during the test protocol. This improves device performance including operational reproducibility, execution speed, and reliability. Thus, the described method takes into account differences in droplet response that may vary according to the characteristics of the liquid and/or environmental conditions (which may be variable in the field) to optimize droplet manipulation operations. The described systems and methods implement this optimization in a fully automated manner such that the user need not take any action (or even must be aware that such optimization is needed and has been achieved).

In an exemplary embodiment of the control method, the test metric comprises a rate of transition from the first state to the second state.

In an exemplary embodiment of the control method, the droplet has a first shape in the first state, has a second shape different from the first shape in the second state, and has the same centroid in the first state and the second state.

In an exemplary embodiment of the control method, the droplet has a first centroid in the first state and a second centroid different from the first centroid in the second state, and the droplet has the same shape in the first state and the second state.

In an exemplary embodiment of the control method, the droplet has a first shape in the first state and a second shape different from the first shape in the second state, and the droplet has a first centroid in the first state and a second centroid different from the first centroid in the second state.

In an exemplary embodiment of the control method, the test metric comprises a degree of conformance of the droplet with an electrowetting actuation pattern having one recess.

In an exemplary embodiment of the control method, the electrowetting actuation pattern comprises two or more recesses.

In an exemplary embodiment of the control method, the electrowetting actuation pattern is a divided actuation pattern, which is divided into a first actuation section and a second actuation section spaced apart from the first actuation section.

In an exemplary embodiment of the control method, the test metric comprises a measurement of a voltage drop across the droplet.

In an exemplary embodiment of the control method, the electrowetting actuation pattern is applied at a plurality of electrowetting voltage amplitudes and the test metric is determined based on droplet responses of the droplets at different electrowetting voltage amplitudes.

In an exemplary embodiment of the control method, the actuation pattern is applied at a plurality of electrowetting voltage AC frequencies and the test metric is determined based on the drop response of the drop at different electrowetting voltage AC frequencies.

In an exemplary embodiment of the control method, the method further comprises varying a temperature of the EWOD device and applying the actuation pattern at a plurality of temperatures, and determining the test metric based on drop responses of the drops at the different temperatures.

In an exemplary embodiment of the control method, controlling the actuation voltages applied to the array elements based on the test metrics comprises: determining a droplet manipulation operation based on the test metric; and controlling the actuation voltage to perform the determined droplet manipulation operation on one or more droplets applied to the array of elements.

In an exemplary embodiment of the control method, determining the droplet manipulation operation based on the test metric comprises comparing the test metric to a threshold value, and selecting the droplet manipulation operation from predefined options stored in a memory based on the comparison.

In an exemplary embodiment of the control method, the droplet manipulation operation comprises dispensing one or more droplets from a liquid reservoir onto the array of elements, and at least one of: separating the droplet into two or more droplets, merging multiple droplets, agitating the droplets to mix the droplets, maintaining the position of the droplets, or moving the droplets to another location on the array of elements.

In an exemplary embodiment of the control method, controlling the actuation voltages applied to the array elements based on the test metrics comprises: determining whether a fault condition corresponding to droplet non-actuation exists; and outputting an error message from the EWOD device to notify a user when a fault condition exists.

In an exemplary embodiment of the control method, determining whether a fault condition exists includes determining whether a combination of the drop metrics is suitable or unsuitable for performing a desired drop manipulation operation.

Although the invention has been shown and described with respect to one or more particular embodiments, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a "means") used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.

Industrial applicability

The described embodiments may be used to provide enhanced AM-EWOD devices. The AM-EWOD device may form part of a lab-on-a-chip system. Such devices may be used to manipulate, react and sense chemical, biochemical or physiological materials. Applications include medical diagnostic tests, materials testing, chemical or biochemical materials synthesis, proteomics, tools for research in life science and forensic medicine.

List of reference numerals

10-lower substrate

12-array element electrode

12A-array element electrode

12B-array element electrode

14-liquid droplet

16-top substrate

18-spacer

20-nonpolar fluids

22-insulator layer

24-first hydrophobic coating

26-contact Angle

28-second hydrophobic coating

30-reference electrode

32-reader

34-box

35-external sensor module

36-AM-EWOD device

38-control electronics

40-memory device

42-connecting line

44-lower substrate

46-thin film electronic device

48-array element electrode

48A-array element electrode

48B-array element electrode

50-element array

51-array element

52-liquid droplet

54-top substrate

56-spacer

58-reference electrode

60-capacitor

62-insulator layer

64-first hydrophobic coating

66-contact Angle

68-second hydrophobic coating

70A-Electrical Loading in the Presence of liquid droplets

70B-Electrical Loading without droplet Presence

72-array element circuit

74-Integrated Row driver

76-column driver

78-Integrated sensor Row addressing

80-column detection circuit

82-serial interface

84-Voltage Source interface

86-connecting line

88-actuation circuit

90-droplet sensing circuit

100 a-starting droplet

100 b-starting droplet

100 c-starting droplet

102 a-end droplet

102 b-end droplet

102 c-end droplet

104 a-first centroid position

104 b-different centroid positions

104 c-different centroid positions

106-turning point

108-turning point

120-turning point

122-turning point

124-actuation pattern

126-droplet

128-wedge cut

130-four depressions

132-first actuating part

134-second actuating part

135-optical sensor

136-turning point

138-turning point

140-turning point

142-turning point

150-first region

152-second region.

38页详细技术资料下载

Adaptive droplet manipulation in AM-EWOD devices based on test measurements of droplet properties

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