GB2597958A

GB2597958A - Droplet generation system

Info

Publication number: GB2597958A
Application number: GB2012504.3A
Authority: GB
Inventors: Keppie Mccluskey Daniel; Marie Coudron Loic; Roger Munro Ian
Original assignee: University of Hertfordshire
Current assignee: University of Hertfordshire
Priority date: 2020-08-11
Filing date: 2020-08-11
Publication date: 2022-02-16
Also published as: GB202012504D0

Abstract

An apparatus 10 for introducing and/or removing a fluid droplet to/from a fluidic system, the apparatus comprising a first substrate 12 and a working surface 14 wherein the first substrate is provided with an aperture 16a, 16b and the droplet is introduced onto/removed from the working surface through the aperture. Ideally, the system is a microfluidic system such as an electrowetting on dielectric system (EWOD) with the aperture being a through hole via (THV) formed in an electrode of the electrode array 14 and the first substrate is a printed circuit board (PCB). Alternatively, the system is a Laplace pressure gradient self-propulsion system (fig 6). Preferably, aperture diameter is smaller than droplet diameter and is configured to allow the droplet to move across the aperture. The working surface may be part of the first substrate or be part of a second substrate. The system may comprise a plurality of apertures for introducing and/or removing droplets. The apparatus further comprises a fluid supply reservoir 20, a removed fluid reservoir 34, means for moving the fluid through the aperture 22, 30 in the form of pressure driven means such as diaphragm pumps or vacuum driven means in the form of reverse syringes, and means to determine the presence of a droplet.

Description

DROPLET GENERATION SYSTEM

FIELD OF THE INVENTION

This invention relates to an apparatus for introducing and/or removing a said fluid droplet from a said surface of a said fluidic system, in particular it relates to an automated droplet introduction and recovery module for a Fluidic System, more particularly for a Micro Fluidic System and even more particularly for a Digital Micro Fluidic System.

BACKGROUND OF THE INVENTION

Following the pioneering work of Bruno Berge and co-workers in developing Electrowetting on Dielectric (EWOD) in the mid-90s, the boost in interest in Electrowetting gave birth to tremendous application prospects in various topical fields such as tuneable lenses, displays and lab-on-a-chip. Electrowetting is the effect by which the contact angle of a droplet can be modulated by an electric field applied to the droplet, an effect that can be enhanced using a dielectric layer to boost charge collection in the case of an EWOD system. In order to optimise the contact angle modulation range, fluoropolymers are used to form a hydrophobic layer at the surface contacting the droplet. Teflon® AF and Cytop® have been the prevailing materials used for the realisation of hydrophobic surfaces in EWOD devices.

Using a 2D network of buried electrodes (pads), digital microfluidic (DMF) devices take advantage of the EWOD principle to accurately and sequentially actuate a droplet in any region of the 2D network (i.e. droplets can be precisely controlled and positioned on any pad constituting the network). Fully automated DMF devices have been successfully demonstrated exploiting EWOD's capability to individually control droplet samples via specific control electrode activation sequences. There are two common configurations of EWOD-based DMF devices: the single-plate (or 'open') and the parallel-plate (or 'closed') configuration. Most reported devices use the parallel-plate configuration, both because it provides reliable droplet volumes by protecting droplets from evaporation and because droplets in parallel-plate devices are less affected by gravity than single-plate devices. In a parallel-plate device, two plates, one containing the electrode network (i.e. base plate) and one ground plate (i.e. the top plate), sandwich the actuation medium, commonly air or a low viscosity oil (e.g. silicon oil or olive oil).

Interfacing the system with the external world (i.e. converting large volume continuous-flow microfluidics to small volume digital microfluidics) is one of the main challenges facing DMF that only few techniques attempt to address. The most common solution for droplet dispensing consists of a large pad serving as an on-chip liquid reservoir from which droplets are delivered onto the smaller actuation pads constituting the DMF pattern. In this method, droplets are pulled and split directly from a main puddle of fluid in the reservoir using EWOD driving forces. Feedback methods, which may be electrical or optical, allow for detection of fluid on the appropriate pad in order to confirm successful formation and detachment of the droplet. In some versions of the method, the interface between the DMF device and the external world is possible via manual pipetting but, in most cases, the fluid is pipetted into the reservoir prior to closing of the device to prevent further fluid being delivered whilst the device is in operation. In any case, this method fails to address the volume discrepancy between continuous and digital flow.

Direct injection of fluid from an external continuous flow device (e.g. syringe-pump) on a bespoke location on the chip via a rigid tubular component (cannula, a capillary or a needle) is a good alternative to the on-chip reservoir dispensing method described above. In the most common approach of this method, a droplet is pumped to the desired location through the tubular component and is monitored, similarly to above, via capacitive detection of the fluid until the desired volume is achieved. Direct injection of fluid can respond to the real-world interface challenges facing DMF, however, in the examples above, the use of rigid, external components pose two main issues. Firstly, the existence of an external, potentially rigid part may cause mechanical degradation (e.g. scratch damage) to the EWOD functionalised surface (hydrophobic and dielectric layers) when aligning the delivery component during assembly of the device. The alignment of the tubular component at the desired location and the related design constraints constitute the second major drawback of this method.

A slight improvement of this method can be found where the droplet is injected into the side of the EWOD sandwich assembly. In the most elaborate version of this technique, a bridging electrode where the droplet can be dispensed is located at the periphery of the device and only partially covered by the top plate, such that the pad's external edge is left exposed and accessible. The bridging droplet formed on the bridging electrode provides the means by which the macroscale (continuous flow device) to microscale (DMF system) transition is achieved in a straightforward fashion (no adhesives, fittings, etc.).

Finally, using a similar approach, a solution can be found where the droplet is injected through a large hole (1mm to 5mm diameter) in the top plate (i.e. the ground plate not comprising the electrode network) into a reservoir comprising or connected to a bridging electrode.

These last two solutions reduce the risk of potential mechanical scratch damage to the plate but don't solve the tedious alignment problem. In addition, in the current state of the last technique, it is unclear that a droplet can be actuated across the significantly large hole in the top plate, hence the region around the hole can only be dedicated to droplet delivery.

Another alternative for droplet introduction is the direct extraction of the droplet from a continuous-flow micro-channel using EWOD forces, example of which is documented in US patent US20120298205. As with previous techniques, control of volume and droplet location can be provided by capacitive detection of the fluid. This method allows direct interface between the external continuous flow environments, allowing continuous flow through of the latter, without the need of any valve element within the digital microfluidic chip. However, as for the tubular injection method, there are design constraints due to spatial occupation of the microchannel.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided an apparatus for introducing and/or removing a said fluid droplet from a said fluidic system wherein the apparatus comprises a first substantially planar substrate and a working surface, wherein the first substantially planar substrate is provided with an aperture and wherein said fluid droplet is introduced onto or removed from the working surface through the aperture.

Preferably the diameter of the aperture is smaller than the diameter of the said fluid droplet.

Preferably the diameter of the aperture is smaller than the diameter of the said fluid droplet once the said fluid droplet has been introduced onto the working surface.

Preferably the diameter of the aperture is smaller than the imprint diameter of the said fluid droplet.

Preferably the diameter of the aperture is less than the diameter of the said fluid droplet.

Preferably the diameter of the aperture is less than the diameter of the said fluid droplet once the said fluid droplet has been introduced onto the working surface.

Preferably the diameter of the aperture is less than the imprint diameter of the said fluid droplet.

Preferably the diameter of the aperture is configured to allow the said fluid droplet to move across the aperture.

Preferably the diameter of the aperture is configured to allow the said fluid droplet to move across the aperture once the said fluid droplet has been introduced onto the working surface.

Compared to prior art, the aperture is small with respect to the said fluid droplet imprint diameter which allows for the said fluid droplet to move across it -which is not possible with the bigger apertures documented in prior art. As such, the invention enables direct feed of the said fluid droplet anywhere onto the working surface which is not possible with prior art being limited by (1) the size of the aperture, which a said fluid droplet cannot cross; (2) physical presence of a tube, which adds a dimensional constraint to the feed location to around the edges of the working surface; or (3) the requirement for a bridging electrode to extract the said fluid droplet from a reservoir/puddle, which again implies design constraints due to spatial occupation of the reservoir.

In one alternative the first substantially planar substrate comprises the working surface.

In one alternative the apparatus further comprises a second substantially planar substrate.

In one alternative the second substantially planar substrate comprises the working surface.

In one alternative the first substantially planar substrate acts as a supporting material base. In another alternative the second substantially planar substrate acts as a supporting material base. Preferably the first and/or second substantially planar substrate has a thickness of between about 0.05mm to about 2.0mm. In one alternative the first and/or second substantially planar substrate comprises a printed circuit board (PCB), preferably with a thickness of between about 0.5mm and about 2.0mm, in another alternative the first and/or second substantially planar substrate comprises a glass plate, preferably with a thickness of between about 0.5mm and about 2.0mm, in yet another alternative the first and/or second substantially planar substrate comprises a polymer or paper sheet, preferably with a thickness of between about 0.05mm and about 1.0mm.

Preferably the working surface is provided with a coating.

In one alternative the coating comprises a hydrophobic layer, preferably the hydrophobic layer is comprises an amorphous fluoropolymer, such as Cytop®.

In another alternative the coating comprises a superhydrophobic layer, preferably the hydrophobic layer comprises a dimethyl silicone polymer with silica nanoparticles, such as 15 NeverWet®.

In another alternative the coating comprises an impermeable dielectric layer and a hydrophobic layer, preferably the dielectric layer comprises Parylene-C, preferably the hydrophobic layer comprises an amorphous fluoropolymer, such as Cytop®.

In another alternative the coating comprises an impermeable dielectric layer surmounted by a hydrophobic layer, preferably the dielectric layer comprises Parylene-C, preferably the hydrophobic layer comprises an amorphous fluoropolymer, such as Cytop®.

In another alternative the coating comprises an impermeable dielectric layer and a superhydrophobic layer, preferably the dielectric layer comprises Parylene-C, preferably the superhydrophobic layer comprises a dimethyl silicone polymer with silica nanoparticles such as NeverWet®.

In another alternative the coating comprises an impermeable dielectric layer surmounted by a superhydrophobic layer, preferably the dielectric layer comprises Parylene-C, preferably the superhydrophobic layer comprises a dimethyl silicone polymer with silica nanoparticles, such as NeverWet®.

Preferably the dielectric layer is between about lpm to about lOpm thick.

Preferably the hydrophobic layer is in the order of lOnm to 200nm thick.

Preferably the diameter of the aperture is between about 0.1mm and about 0.5mm.

Preferably the volume of the said fluid droplet is between about 0.5p1 and about 100p1 preferably between about 0.5p1and about 3.0plin one alterative, preferably between about lpl and about 100p1 in another alternative.

Preferably the apparatus further comprises a fluid reservoir. Preferably the apparatus comprises first and second fluid reservoirs. Preferably the first fluid reservoir retains fluid to be introduced onto the working surface of the first substantially planar substrate and the second reservoir retains fluid removed from the working surface.

Preferably the fluid reservoir is in fluid communication with the aperture.

Preferably the fluid communication between the fluid reservoir and the aperture is provided by a cylindrical tube.

Preferably the first fluid reservoir is in fluid communication with the aperture.

Preferably the fluid communication between the first fluid reservoir and the aperture is provided by a first cylindrical tube.

Preferably the second fluid reservoir is in fluid communication with the aperture.

Preferably the fluid communication between the second fluid reservoir and the aperture is provided by a second cylindrical tube.

In one alternative there may be only one aperture provided, however, in an alternative a plurality of apertures may be provided. Where a plurality of apertures are provided preferably each aperture is in fluid communication with the fluid reservoir(s) and preferably each aperture is in fluid communication with the working surface. Where a plurality of apertures are provided this essentially provides for a plurality of locations for introducing or removing the said fluid droplet from the working surface.

Preferably the apparatus further comprises a means for moving the said fluid droplet through the aperture. The movement through the aperture may be to either introduce the said fluid droplet onto the working surface or to remove the said fluid droplet from the working surface.

In one alternative the means for moving the said fluid droplet through the aperture comprises a pressure driven means, preferably the pressure driven means is selected from a diaphragm pump, a peristaltic pump, an electroosmotic pump, other microfluidic pump, a syringe, an injector or other pumping means.

In one alternative the means for moving the said fluid droplet through the aperture comprises a vacuum driven means, preferably the vacuum driven means is selected from a reverse diaphragm pump, a reverse peristaltic pump, an reverse electroosmotic pump, other microfluidic reverse pump, a reverse syringe, a reverse injector, or other suction means.

In one alternative the means for moving the said fluid droplet through the aperture comprises an electroactive means, preferably the electroactive means is selected from electroosmotic flow, dielectrophoresis, or electrowetting.

In one alternative the means for moving the said fluid droplet through the aperture comprises a passive means, preferably the passive means is selected from wicking, or gravimetric.

Preferably the apparatus further comprises a means to determine the presence of the said fluid droplet and/or control the size of the said fluid droplet and/or control the volume of the said fluid droplet and/or determine the size of the said fluid droplet and/or determine the volume of the said fluid droplet on the working surface.

In one alternative the means comprises a capacitive detection means.

Preferably the capacitive detection means comprises an insulated electrode and a counter electrode, preferably the counter electrode is configured to be in contact with the said fluid droplet.

Alternatively, the means comprises a resistive detection means.

Preferably the resistive detection means comprises an electrode and a counter electrode, preferably the counter electrode is configured to be in contact with the said fluid droplet.

Alternatively, the means comprise an optical detection means.

Alternatively, a fixed volume reservoir is provided to limit and/or define the said fluid droplet size and/or volume.

Preferably the means is configured to interact with the said fluid droplet and the working surface.

In one alternative the means comprises an electrode. The aperture may in one alternative be formed at or within the electrode, in another alternative the aperture is located near (at a distance representing 10% of the fluid droplet radius, typically from tens of micrometres to hundreds of micrometres) to an electrode. Preferably the electrode is configured to create an electric field or current and the said fluid droplet interacts with the electric field or current in a meaningful way, for example, by measurement of charge quantity, residual voltage or frequency.

In one alternative an array of electrodes are provided near the aperture.

In one alternative an array of electrodes are provided wherein each electrode is provided with an aperture.

In one alternative a single electrode is provided with a plurality of apertures.

Where a plurality of apertures are provided the said fluid droplet can be introduced and/or removed through any of the apertures.

In one alternative the said fluid droplet when introduced onto the working surface is constrained between the first substantially planar substrate and a second substantially planar substrate.

In another alternative the said fluid droplet when introduced onto the working surface is open to atmosphere.

According to a second aspect of the present invention there is provided a fluidic system for introducing and/or removing a said fluid droplet from the fluidic system wherein the fluidic system comprises an apparatus as described in relation to the first aspect of the invention.

Preferably the fluidic system comprises a Micro Fluidic System and even more preferably a Digital Micro Fluidic System.

According to a third aspect of the present invention there is provided a method of introducing a said fluid droplet onto a working surface of a fluidic system comprising the steps of: a) providing a fluidic system as described in relation to the second aspect of the present invention; b) introducing the said fluid droplet onto the working surface through the aperture. 15 According to a fourth aspect of the present invention there is provided a method of removing a said fluid droplet from a working surface of a fluidic system comprising the steps of: a) providing a fluidic system as described in relation to the second aspect of the present invention; b) removing the said fluid droplet from the working surface through the aperture.

In introduction mode, a precise amount of fluid is introduced from a fluid reservoir at the desired location through an aperture directly in the substrate in the form of a fluid droplet.

The amount of fluid can be precisely controlled by a detection method as the fluid is detected in the region of the aperture. Detection of fluid can be optical or electrical via an electrode (in close proximity -within a distance corresponding to 10% of the fluid droplet radius, typically hundreds of micrometres -or surrounding the fluid delivery hole). Once the desired volume is reached, a method of moving the fluid droplet away from the introduction aperture is provided preferably by locally controlling physical interaction at the fluid interfaces for example by manipulating local Laplace pressure gradient or electrically modifying the energy balance surrounding the fluid droplet (e.g. using electrowetting) or relying on other physical or mechanical effects (e.g. vibration or magnetic actuation). This actuation method can be used to move the fluid droplet precisely on the working surface of the fist substantially planar substrate while the detection method mentioned previously can be used to track the exact position of the fluid droplet. The actuation method can be used to move the fluid droplet toward an extraction aperture -which can be the same as the introduction aperture. The fluid droplet located at the extraction aperture can be detected by the detection method and then removed through the, for example, extraction aperture into the second fluid reservoir, or waste reservoir.

In the present invention a method is proposed that tackles the limitation found in the prior art methods of only allowing fluid to be dispensed at a specified location of the device instead by preferably using plated Through Hole Vias (THV) which are preferably directly fabricated within the control electrodes as part of the printed circuit board (PCB) EWOD base plate as a route to deliver fluid droplets directly to the region, or regions, of interest. In contrast with previously reported EWOD on PCB devices, the invention utilises a super-planar process that guarantees high level planarity across the whole plate, including at the location of THV for reliable, damage free defect fluid droplet actuation. In one alternative the THV is fabricated in the substrate comprising a glass plate, preferably with a thickness of between about 0.5mm and about 2.0mm, in yet another alternative the THV is fabricated in the substrate comprising a polymer or paper sheet, preferably with a thickness of between about 0.05mm and about 1.0mm. In these alternatives, a conductive electrode can be printed or deposited prior or after the fabrication of the THV.

In addition, the present invention addresses the continuous bulk fluid to digital interface by allowing a fluid droplet to be dispensed or extracted virtually anywhere on a plate preferably due to the direct electronic control of the THV fluidic port and driving electrode. In one alternative, the fluid droplet is actuated by manipulating local Laplace pressure gradient. In another alternative, the fluid droplet is actuated by relying on other physical or mechanical effects (e.g. vibration or magnetic actuation).

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

Figure 1 illustrates an automated fluid droplet introduction and recovery module of the present invention; Figure 2 illustrates a magnified cut away portion of an automated fluid droplet introduction and recovery module of the present invention; Figure 3 illustrates a 2D cross-sectional view of the delivery region in a closed configuration; Figure 4 illustrates a 2D cross-sectional view of the delivery region in an open configuration; Figure 5 illustrates a 2D cross-sectional view of the delivery region though a cover plate rather than a substrate; Figure 6 illustrates a 2D cross-sectional view the of the delivery region in a device using Laplace pressure gradient self-propulsion as droplet actuation mode; Figure 7 illustrates a 2D schematic drawing of a DMF device employing the preferred embodiment of the invention; Figure 8 illustrates a 2D schematic drawing of an inkjet DMF device employing an alternative embodiment of the invention; and Figure 9 illustrates a detailed 2D schematic drawing of a self-propulsion DMF droplet generator employing an alternative embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention comprises a fully automated fluid droplet introduction and recovery module 10 for a fluidic system such as a Digital Microfluidic (DMF) system. Figure 1 illustrates an automated fluid droplet introduction and recovery module 10 of the present invention.

In preferred embodiments of this invention, a substrate 12 is provided comprising a 0.5mm to 2.0mm thick printed circuit board which is provided with an array of electrodes 14 upon which one or more fluid droplets can be actuated. Each electrode 14 is typically a square with side from 1mm to 5mm. Each electrode 14 is typically separated by 0.05mm to 0.10mm spacing.

In another embodiment of this invention the substrate instead comprises a 0.5mm -2.0mm thick glass plate which may in one embodiment be provided with a patterned array of conductive electrodes of the same dimensions and spatial distribution as described above.

In another embodiment, the substrate comprises a 0.05mm to 1.00mm thick polymer sheet or paper sheet, which may in one embodiment be printed (e.g. inkjet-printed) with conductive electrodes of the same dimensions and spatial distribution as described above.

In preferred embodiments of this invention, the substrate is coated with a thin (1pm to 10pm thick) impermeable dielectric layer, such as of Parylene-C, surmounted by a thin (tens or hundreds of nm thick) hydrophobic layer, preferably comprising an amorphous fluoropolymer, such as Cytop® or superhydrophobic layer, preferably comprising a dimethyl silicone polymer with silica nanoparticles, such as NeverWet®.

In other embodiments of this invention, the substrate is simply coated with a thin (tens or hundreds of nm thick) hydrophobic layer, preferably comprising an amorphous fluoropolymer, such as Cytop® or superhydrophobic layer, preferably comprising a dimethyl silicone polymer with silica nanoparticles, such as NeverWet®.

One or more introduction apertures 16a are provided which extend through the substrate 12 at an introduction electrode 18a, next to the array of electrodes 14. An introduction aperture of between about 0.1 mm and about 0.5 mm diameter allows for a between about 0.5p1 and about 3.0p1 fluid droplet to be introduced through the introduction aperture 16a.

Once the fluid droplet has been introduced it can then be subsequently actuated, on the hydrophobic layer, away from the delivery site.

The delivered fluid droplet can be actuated across the array of electrodes 14 to an extraction electrode 18b which may be provided with one or more extraction apertures 16b. A capacitive sensing method is used to monitor the movement of the fluid droplet from the introduction electrode 18a to the extraction electrode 16b. Once the fluid droplet is located at the extraction electrode 18b, the fluid droplet can then be extracted through extraction aperture 16b.

In one embodiment of the invention illustrated in Figure 3, the fluid droplet is moved across the array of electrodes 114 by employing an electrowetting-on-dielectric (EWOD) based actuation. In this embodiment of this invention, the EWOD base actuation is performed in ambient air with the fluid droplet sandwiched between the actuation region of the substrate 112 and a so-called cover plate 136, which is another hydrophobic, flat, conductive, preferably electrically grounded surface in this so-called EWOD parallel plate configuration.

In another embodiment of the invention illustrated in Figure 4 a between about 1p1 and about 100p1 fluid droplet can be actuated using the so-called single plate EWOD configuration were the fluid droplet is supported only on the substrate 212 without a second plate.

In another embodiment of this invention illustrated in Figure 5, the array of electrodes 314 comprises a unique introduction electrode 318a which covers the entire surface of the substrate 312. In this embodiment the substrate 312 is also positioned as a cover plate 336 in the so-called EWOD parallel plate configuration. A fluid droplet is introduced from the cover plate 336 through introduction aperture 316a and actuated on a facing EWOD substrate 340 comprising actuation electrodes 344.

In yet another embodiment of this invention illustrated in Figure 6, the array of electrodes 414 comprises a unique introduction electrode 18a covering the entire surface of the substrate 412. In this embodiment of the invention, the fluid droplet is sandwiched between the substrate 412 and an actuatable, superhydrophobic, flat, surface 436, and the fluid droplet is actuated and detached from the introduction aperture 416a via a self-propulsion mechanism originating from a Laplace pressure gradient.

The fluid to be introduced is stored in a reservoir 20. During the introduction process, employing a micro pump 22 the fluid is pumped from the reservoir 20 through the tubing connection 24 connected to the introduction aperture 16a by the interface with the fluidic system 26 seen in Figure 2. The fluid being transported inside the tubing 24 is detected by an optical sensor 28 which is configured to reduce the pace or speed of fluid being transported for volume control. The control of the volume of the fluid droplet can be performed by simple timing of the fluid being transported once detected by the optical sensor 28 or it can be coupled with the capacitive detection of fluid at the introduction electrode 18a for improved accuracy of the volume of the fluid droplet being delivered.

The extraction of a fluid droplet from the substrate 12 is performed as follows: once a fluid droplet is detected at the target extraction electrode 18b, the extraction micropump 30 is operated to pump out the droplet through the extraction aperture 16b via the tubing connection 32 of the fluidic system to the dispense reservoir 34 or into any other fluidic component.

It can be noted that, depending on the application the proposed method allows for * Multiple fluid introduction apertures 16a and/or extraction apertures 16b to be used within an array of electrodes * Multiple fluid introduction apertures 16a and/or extraction apertures 16b to exist on a single electrode * Fluid to be introduced or extracted through any introduction apertures 16a or extraction apertures 16b. i.e. an extraction aperture 16b can play the role of an introduction aperture 16a and vice-versa.

In some embodiments of the invention, the introduction/extraction tubing connections 24, 32 are precisely aligned with the introduction/extraction apertures 16a, 16b and are simply pressure-connected and pressure-sealed against the introduction/extraction apertures 16a, 16b at the back of the substrate 12, hence constituting the interface of the fluidic system 26 and allowing for easy removal and replacement of the first planar substrate 12.

In some embodiments of the invention, the substrate comprises an integrated, electrically connected and functionalised printed circuit board (PCB) which is configured to encompass the electrode array which allows for the local control of the electric field used for droplet actuation. The substrate is electrically connected to a bespoke drive electronics allowing control of the electric field of each of the electrodes of the array. The system is completed by a ground electrode parallel to the actuation region of the substrate and separated from it by a working gap allowing for a squeezed droplet to be introduced and actuated.

The invention preferably automatically produces and dispenses a fluid droplet of controlled volume from a continuous microfluidic element (e.g. pump) through an aperture onto the working surface of the first planar substrate such as an electrode array of the fluidic system. Once the fluid droplet has been delivered and detected it can then be actuated, preferably by Electrowetting-on-Dielectric (EWOD) or alternatively by manipulating local Laplace pressure gradient or relying on other physical or mechanical effects (e.g. vibration or magnetic actuation). The fluid droplet is transported and delivered onto the working surface of the first planar substrate, preferably a PCB or alternatively a glass-based or polymer-based encompassing an array of electrodes (with a number of electrode varying from zero to several hundreds) through an aperture such as a through hole via (THV) disposed on the electrodes of the array (potentially every electrode can be addressed by a THV). An integrated electronics capacitive detection module or optical detection module is preferably used to confirm the presence of the fluid droplet at the delivery region and allows precise control of the volume of the fluid droplet. Recovery of the fluid droplet can be achieved by removal of the fluid droplet through the same THV after the fluid droplet has been detected at the extraction location using for example a capacitive or optical detection method.

Figure 7 illustrates an embodiment of the invention comprising an EWOD PCB system. In this embodiment introduction of the fluid droplet to the PCB EWOD plate is via a 0.3mm diameter aperture 516a through the PCB EWOD plate 512. Fluid is delivered to the underside of the PCB EWOD plate via a 0.19mm ID lsmatec Lab PVC tube 524 (116- 0549-02-CP). The tube 524 forms a fluidic seal 526 against the PCB EWOD plate 512 via compression. The seal 526 does not need to work at significant pressure as the increase in diameter of the tube 524 from 0.19mm to 0.3mm at the joint interface in conjunction with the 1.6mm thickness PCB EWOD plate 512 means that fluid pressure in the delivery tube 524 will tend to dissipate via moving fluid through the aperture 516a in the PCB EWOD plate 512 rather than breaking the butt seal between the tube 524 and the PCB EWOD plate 512. The tube 524 has a moulded stop 550 on it. A PMMA plate 560 at the bottom of the assembly acts as a back stop to apply pressure. The length of the tube 424 is arranged such that it compresses by approximately 0.2mm when forming the fluidic seal 526 with the PCB EWOD plate 512. Lateral alignment is achieved by sprung pins 570 that are a push fit into the PMMA plates 560 that hold the fluid tube in position. The sprung pins 570 mate with matching holes 572 in the PCB EWOD plate 512. This method of fluidic joining to the PCB EWOD plate 512 is preferred element of the present invention.

The actuation of droplet is performed via EWOD in a parallel plate device. The EWOD plate 512 is coated with 6pm of Parylene-C 580 surmounted with a thin layer (20nm) of an amorphous fluoropolymer, such as spin-coated Cytop® 590a. The cover plate 536 is made of ITO-coated glass surmounted with a thin layer (20nm) of an amorphous fluoropolymer, such as spin-coated Cytope 590b.

Each of the electrodes 518 of the PCB EWOD plate 512 are electrically connected to the electronic system allowing for capacitive detection of fluid and actuation signal (sinusoidal, 150 V RMS, 1kHz) to be addressed. Once introduced and detected, the fluid droplet is moved using EWOD from the introduction electrode 518a to the next electrode on the array 514 by energising the latter with the actuation signal while the introduction electrode 518a is left grounded. In a similar fashion, the now delivered and detached fluid droplet can be moved from one electrode to the next using EWOD.

Figure 8 illustrates another embodiment of the invention comprising an inkjet printed on polymer EWOD device. In this embodiment droplet introduction to the Inkjet printed EWOD device is via a 0.3mm diameter aperture 616a through the 2.5mm thick cover plate 636 of the parallel plate Inkjet printed EWOD device. The cover plate 636 is made of a 0.5mm thick conductive triple-layer polymer sheet glued on its backside to a 2mm thick PMMA plate 642. The triple-layer polymer is composed of a PET sheet 646 spin-coated on its front side with conductive, transparent polymer PEDOT:PSS 638 surmounted by a hydrophobic layer preferably comprising an amorphous fluoropolymer, such as Cytop® 690b. The apertures 616, 676 are preferably laser-cut through both the PMMA plate 642 and the triple layer polymer sheet 638, 646, 690b. In the same fashion as described in relation to Figure 7 above, fluid is delivered to the backside of the cover plate 636 via a 0.19mm ID Ismatec Lab PVC tube 624 (116-0549-02-CP). The tube 624 forms a fluidic seal 626 against the back of the cover plate 636 via compression. The seal does not need to work at significant pressure as the increase in diameter from 0.19mm to 0.3mm at the joint interface in conjunction with the 2.5mm thickness cover plate 636 means that fluid pressure in the delivery tube 624 will tend to dissipate via moving fluid through the PMMA plate 642 and the triple-layer polymer sheet 638, 646, 690b rather than breaking the butt seal between the tube 624 and the PMMA plate 642 (back of the cover plate). The tube 624 has a moulded stop 650 on it. Another PMMA plate 660 at the bottom of the assembly acts as a back stop to apply pressure. The length of the tube 624 is arranged such that it compresses by approximately 0.2mm when in contact 626 with the PMMA plate 642 (back of the cover plate 636). Lateral alignment of the fluidic connection is achieved by sprung pins 670 that are a push fit into the PMMA plates 660 that hold the fluid tube in position. The sprung loaded pins mate with matching holes 676 in the cover plate 636. This method of fluidic joining to the cover plate 636 is a preferred element of the present invention.

Opposite the cover plate 636, which comprises the droplet delivery system, sits an EWOD plate 612. The EWOD plate 648 comprises an array of PEDOT:PSS electrodes 614 inkjet printed on a 0.5mm thick PET polymer sheet 612 glued onto a 4mm thick PMMA plate 672. The EWOD plate 648 is coated with 6 kirn of Parylene-C 680 surmounted with a thin layer (20nm) of an amorphous fluoropolymer, such as Cytop® 690a. The cover plate 636 is aligned with the EWOD plate 648 by mating the matching holes 676 of the cover plate 636 with pins 670 push-fitted into the previously laser etched EWOD plate 648 clamped with sprung loaded copper connectors connected to each of the electrical lines addressing the EWOD electrodes of the array. This way, each of the electrodes in the array 614 of the EWOD plate is electrically connected to the electronic system allowing for capacitive detection of fluid and actuation signal (sinusoidal, 150 V RMS, 1kHz) to be addressed.

Once introduced and detected, the fluid droplet is moved using EWOD from the introduction electrode 618a to the next electrode on the array 614 by energising the latter with the actuation signal while the introduction electrode 618a is left grounded. In a similar fashion, the now delivered and detached fluid droplet can be moved from one electrode to the next using EWOD.

Figure 9 illustrates another embodiment of the invention comprising a self-propulsion droplet generator. In this embodiment fluid droplets are generated via a 0.3mm diameter aperture 716a through a 2 mm delivery plate 736. The delivery plate 736 comprises a PMMA plate 712 coated with a 100nm chromium layer 714 surmounted with a thin superhydrophobic topcoat layer preferably comprising a dimethyl silicone polymer with silica nanoparticles, such as NeverWet® 790a. The fluid is delivered via a silicon tube 722 connected to the substrate by a glued 1/16' PEEK tubing 724 and connected on the other to a pump allowing constant flow rate of liquid to be supplied.

A top plate 742 comprising a glass/ITO slide 742 coated with a 6pm Parylene-C layer 780 surmounted with superhydrophobic coating, preferably comprising a dimethyl silicone polymer with silica nanoparticles, such as NeverWet® 790b is positioned, tilted at a small angle (1 °), opposite the delivery plate 736. Upon delivery, fluid (which may be detected by capacitive detection) will naturally form a fluid droplet as it is squeezed between the delivery plate 736 and the tapered surface of the top plate 742. Due to the local geometry around the squeezed fluid droplet, a Laplace pressure gradient is formed leading to self-propulsion of the fluid droplet. It is expected that a 6 degree of freedom stage actuator will allow full control of the tilt of the top plate 742 and distance from the substrate coupled with electrowetfing for tailoring the surface tension can be used for complete control of the motion of the fluid droplet.

Claims

CLAIMS1. An apparatus for introducing and/or removing a said fluid droplet from a said fluidic system wherein the apparatus comprises a first substantially planar substrate and a working surface, wherein the first substantially planar substrate is provided with an aperture and wherein said fluid droplet is introduced onto or removed from the working surface through the aperture.
2. An apparatus as claimed in Claim 1 wherein the diameter of the aperture is smaller than the diameter of the said fluid droplet.
3. An apparatus as claimed in Claim 1 or Claim 2 wherein the diameter of the aperture is configured to allow the said fluid droplet to move across the aperture.
4. An apparatus as claimed any preceding claim wherein the first substantially planar substrate comprises the working surface.
5. An apparatus as claimed in any preceding claim further comprising a second substantially planar substrate.
6. An apparatus as claimed in Claim 5 wherein the second substantially planar substrate comprises the working surface.
7. An apparatus as claimed in any preceding claim wherein the first and/or second substantially planar substrate has a thickness of between about 0.05mm to about 2.0mm.
8. An apparatus as claimed in any preceding claim wherein the first and/or second substantially planar substrate comprises a printed circuit board (PCB), preferably with a thickness of between about 0.5mm and about 2.0mm.
9. An apparatus as claimed in any of claims 1 to 7 wherein the first and/or second substantially planar substrate comprise a glass plate, preferably with a thickness of between about 0.5mm and about 2.0mm.
10. An apparatus as claimed in any of claims 1 to 7 wherein the first and/or second substantially planar substrate comprises a polymer or paper sheet, preferably with a thickness of between about 0.05mm and about 1.0mm.
11. An apparatus as claimed in any preceding claim wherein the working surface is provided with a coating.
12. An apparatus as claimed in any preceding claim wherein the diameter of the aperture is between about 0.1mm and about 0.5mm.
13. An apparatus as claimed in any preceding claim wherein the volume of the said fluid droplet is between about 0.5p1 and about 100p1 preferably between about 0.5p1 and about 3.0p1 in one alterative, preferably between about 1p1 and about 100p1 in another alternative.
14. An apparatus as claimed in any preceding claim wherein the apparatus further comprises a fluid reservoir.
15. An apparatus as claimed in Claim 14 wherein the apparatus comprises first and second fluid reservoirs.
16. An apparatus as claimed in Claim 15 wherein the first fluid reservoir retains fluid to be introduced onto the working surface of the first substantially planar substrate and the second reservoir retains fluid removed from the working surface of the first substantially planar substrate.
17. An apparatus as claimed in any of claims 14 to 16 wherein the fluid reservoir is in fluid communication with the aperture.
18. An apparatus as claimed in any preceding claim wherein a plurality of apertures are provided.
19. An apparatus as claimed in Claim 18 wherein each aperture is in fluid communication with the fluid reservoir(s) and preferably each aperture is in fluid communication with the working surface.
20. An apparatus as claimed in any preceding claim wherein the apparatus further comprises a means for moving the said fluid droplet through the aperture.
21. An apparatus as claimed in Claim 20 wherein the means for moving the said fluid droplet through the aperture comprises a pressure driven means, preferably the pressure driven means is selected from a diaphragm pump, a peristaltic pump, an electroosmotic pump, other microfluidic pump, a syringe, an injector or other pumping means.
22. An apparatus as claimed in Claim 20 wherein the means for moving the said fluid droplet through the aperture comprises a vacuum driven means, preferably the vacuum driven means is selected from a reverse diaphragm pump, a reverse peristaltic pump, an reverse electroosmotic pump, other microfluidic reverse pump, a reverse syringe, a reverse injector, or other suction means.
23. An apparatus as claimed in Claim 20 wherein the means for moving the said fluid droplet through the aperture comprises a electroactive means, preferably the electroactive means is selected from electroosmotic flow, dielectrophoresis, electrowetting.
24. An apparatus as claimed in Claim 20 wherein the means for moving the said fluid droplet through the aperture comprises a passive means, preferably the passive means is selected from wicking, gravimetric.
25. An apparatus as claimed in any preceding claim wherein the apparatus further comprises a means to determine the presence of the said fluid droplet and/or control the size of the said fluid droplet and/or control the volume of the said fluid droplet and/or determine the size of the said fluid droplet and/or determine the volume of the said fluid droplet on the working surface.
26. An apparatus as claimed in Claim 25 wherein the means comprises a capacitive detection means preferably the capacitive detection means comprises an insulated electrode and a counter electrode, preferably the counter electrode is configured to be in contact with the said fluid droplet.
27. An apparatus as claimed in Claim 25 wherein the means comprises a resistive detection means preferably the resistive detection means comprises an electrode and a counter electrode, preferably the counter electrode is configured to be in contact with the said fluid droplet.
28. An apparatus as claimed in Claim 25 wherein the means comprises an optical detection means.
29. An apparatus as claimed in Claim 25 wherein the means comprises a fixed volume reservoir to limit and/or define the said fluid droplet size and/or volume.
30. An apparatus as claimed in Claim 25 wherein the means is configured to interact with the said fluid droplet and the working surface of the first substantially planar substrate.
31. An apparatus as claimed in Claim 25 or Claim 30 wherein the means comprises an electrode.
32. An apparatus as claimed in Claim 31 wherein the aperture is formed at or within the electrode.
33. An apparatus as claimed in Claim 31 or Claim 32 wherein the electrode is configured to create an electric field and the said fluid droplet interacts with the electricfield in a measurable way.
34. An apparatus as claimed in any of claims 31 to 33 wherein an array of electrodes are provided near the aperture.
35. An apparatus as claimed in Claim 34 wherein each electrode is provided with an aperture.
36. An apparatus as claimed in any of claims 31 to 33 wherein a single electrode is provided with a plurality of apertures.
37. An apparatus as claimed in any preceding claim when dependent on Claim 18 and/or Claim 36 wherein the said fluid droplet can be introduced and/or removed through any of the apertures.
38. An apparatus as claimed in any preceding claim when dependent on Claim 5 wherein the said fluid droplet when introduced onto the working surface is constrained between the first substantially planar substrate and the second substantially planar substrate.
39. An apparatus as claimed in any of claims 1 to 37 wherein the said fluid droplet when introduced onto the working surface is open to atmosphere.
40. A fluidic system for introducing and/or removing a said fluid droplet from the fluidic system wherein the fluidic system comprises an apparatus as claimed in any of claims 1 to 39.
41. A fluidic system as claimed in Clam 40 wherein the fluidic system comprises a Micro Fluidic System and even more preferably a Digital Micro Fluidic System.
42. A method of introducing a fluid droplet onto a working surface of a fluidic system comprising the steps of: a) providing a fluidic system as claimed in Claim 40 or Claim 41; b) introducing a fluid droplet onto the working surface through the aperture.
43. A method of removing a fluid droplet from a working surface of a fluidic system comprising the steps of: a) providing a fluidic system as claimed in Claim 40 or Claim 41; b) removing a fluid droplet from the working surface through the aperture.