Patent Application
20190331638
The current invention relates to a cartridge, in particular a disposable cartridge for use in an electrowetting sample processing system an electrowetting sample processing system and a method for operating such a cartridge or system.
The document WO 2014/108186 A1 describes a cartridge with a waste zone, such that the cartridge together with the waste is discarded after process completion.
It is a task of the current invention to provide a cartridge that allows for a precise and versatile processing of microfluidic droplets.
This task is solved by a cartridge with the features of claim 1. Further embodiments of the cartridge, an electrowetting sample processing system with or without such a cartridge, as well as a method for operating such a cartridge or system are defined by the features of further claims.
A cartridge according to the invention, in particular a cartridge for use in an electrowetting sample processing system, comprises one or more inlet ports for introducing an input liquid into an internal gap of the cartridge. The gap comprises at least one hydrophobic surface for enabling an electrowetting induced movement of multiple microfluidic droplets separated from the input liquid. The cartridge further comprises at least one outlet port that is operably connected to the inlet port for providing a liquid flow through the cartridge, if a liquid driving force, in particular an electrowetting force or a pressure force, is applied to at least a part of the input liquid.
In an embodiment, the cartridge comprises a first part with the inlet port and a second part attached to the first part, such that the gap is formed between the first part and the second part.
In a further embodiment, the first part comprises a rigid body and/or the second part comprises or is an electrode support element or a flexible film, in particular a polymer film and/or an electrically isolating film. In particular, the second part is attached to a peripheral side structure of the first part.
In a further embodiment, the gap is defined by a spacer that is arranged between the first part and the second part and/or by the shape of at least one of the two parts of the cartridge, in particular by a flexible part or a rigid part of the cartridge.
In a further embodiment, one or more of the following comprise an outlet port: the first part, the second part, the spacer, the peripheral side structure of the first part.
In a further embodiment, the cartridge is configured to provide the flow through the cartridge as a continuous flow and/or to substantially maintain a volume equilibrium in the cartridge. The continuous flow may include periods of unbalanced pressure, for example an under-pressure or an over-pressure, which may result from differences of flow between the input flow and the output flow, i.e. differences in the pumping characteristic. In one example, the maximum length of the period of unbalanced pressure is 1 second, in particular 0.25 seconds.
In a further embodiment, the cartridge comprises a plurality of electrodes, in particular an electrode array, for applying an electrowetting force to the microfluidic droplets.
In an embodiment, the second part of the cartridge, in particular the electrode support element or the flexible film or the membrane, is reversibly attachable to the electrodes of the electrowetting sample processing system.
In a further embodiment, at least two of the electrodes are connected to an electrical interface, in particular to an electrical connector or contact field.
In a further embodiment, the cartridge comprises the inlet port as a single inlet port.
In a further embodiment, the cartridge is configured as a disposable cartridge and/or as cartridge that is removably attachable to an electrowetting sample processing system.
In a further embodiment, the input liquid comprises a carrier liquid and/or an electrowetting filler liquid, further in particular a silicone oil.
In a further embodiment, the input liquid comprises a processing liquid that comprises at least one of:
In a further embodiment, the cartridge comprises at least one liquid removal element, in particular a line removal and/or a removal zone, that is operably connected to the outlet port.
In a further embodiment, the cartridge comprises a pressure compensation outlet and/or an air ventilation outlet for providing a fluid output arranged separate from the outlet port, in particular gas exhaust.
The features of the above-mentioned embodiments of the cartridge can be used in any combination, unless they contradict each other.
An electrowetting sample processing system according to the present invention, in particular a biological sample processing system, comprises a cartridge according to anyone of the above-mentioned embodiments.
An electrowetting sample processing system according to the invention comprises an internal gap and one or more inlet ports for introducing an input liquid into the internal gap. The gap comprises at least one hydrophobic surface for enabling an electrowetting induced movement of multiple microfluidic droplets separated from the input liquid. The internal gap further comprises at least one outlet port that is in operable connection with the inlet port for providing a liquid flow through the internal gap, if a liquid driving force, in particular an electrowetting force or a pressure force, is applied to at least a part of the input liquid.
In an embodiment, the electrowetting sample processing system comprises a plurality of electrodes for applying an electrowetting force to the microfluidic droplets, in particular an electrode array, further in particular a two-dimensional electrode array.
In an embodiment, at least two of the electrodes are connected to an electrical interface, in particular to an electrical connector or contact field.
In an embodiment, the electrowetting sample processing system comprises a cartridge, which is reversibly attachable to the electrodes of the electrowetting sample processing system, wherein in particular the cartridge comprises a electrode support element or a flexible second part, further in particular a flexible film or the membrane.
In an embodiment, the electrowetting sample processing system or the cartridge comprises a processing zone, which is configured for processing samples, in particular for processing biological sample, and/or which is operably connected to the delivery zone.
In an embodiment, the processing zone is configured for processing least one of:
In an embodiment, the processing zone is configured for processing a PCR (Polymerase chain reaction) process and/or a hybridization.
In an embodiment, the electrowetting sample processing system comprises a liquid feeder operably connected to the inlet port by a tube, in particular a flexible tube, for feeding the input liquid to the inlet port.
In an embodiment, the liquid feeder is configured to provide the input liquid as sequential feed and/or alternating feed of a processing liquid and a carrier liquid.
In an embodiment, the liquid feeder is configured to provide the input liquid as feed of at least two processing liquids of different compositions separated by an carrier liquid.
In an embodiment, the liquid feeder comprises a T-shaped junction and/or a multi-port valve for providing the input liquid.
In an embodiment, the liquid feeder comprises a bypass that is controllable for flushing a tube of the feeder and/or for removing an access liquid from a feeding liquid and to providing the remaining part of the feeding liquid as the input liquid.
In an embodiment, the liquid feeder comprises a control element, in particular a pump and/or a multi-port valve, for introducing the input liquid into the internal gap and/or for removing an output liquid from the internal gap.
In an embodiment, the liquid feeder is configured to operate independently and/or asynchronously from the operation of electrodes used for electrowetting.
In an embodiment, the input liquid comprises at least one of:
In an embodiment, the electrowetting sample processing system comprises a reagent detector for indicating the presence of processing liquid in the input liquid and/or for monitoring the amount of processing liquid in the input liquid, in particular in relation to a predetermined value.
The features of the above-mentioned embodiments of the electrowetting sample processing system can be used in any combination, unless they contradict each other.
The invention further concerns a method for operating the cartridge according to the invention or the sample processing system according to the invention.
The invention further concerns a method for operating a cartridge according to the invention or a sample processing system according to the invention that comprises an internal gap, which comprises one or more inlet ports, an outlet port and at least one hydrophobic surface enabling an electrowetting induced movement of microfluidic droplets separated from the input liquid. The method comprises:
In an embodiment, the driving force is provided by a plurality of electrodes, in particular by an electrode array, further in particular by a two-dimensional electrode array.
In an embodiment, the step of providing the flow through the internal gap as a substantially continuous flow and/or maintaining a volume equilibrium.
In an embodiment, the method comprises inducing a movement of multiple microfluidic droplets by operating a plurality of electrodes, in particular an electrode array (9), for applying the electrowetting force to the microfluidic droplets.
In an embodiment, the input liquid comprises a carrier liquid and/or an electrowetting filler liquid, in particular a silicone oil. In a further embodiment, the input liquid comprises a processing liquid that comprises at least one of:
The features of the above-mentioned embodiments of the method can be used in any combination, unless they contradict each other.
Embodiments of the current invention are described in more detail in the following with reference to the figures. These are for illustrative purposes only and are not to be construed as limiting. It shows
The
The digital microfluidics system 1 comprises a base unit 7 with at least one cartridge accommodation site 8 that is configured for taking up a disposable cartridge 2. The digital microfluidics system 1 can be a standalone and immobile unit, on which a number of operators are working with cartridges 2 that they bring along. The digital microfluidics system 1 thus may comprise a number of cartridge accommodation sites 8 and a number of electrode arrays 9 at least some of which are located on electrode boards 41.
It may be preferred to integrate the digital microfluidics system 1 into a liquid handling workstation or into a Freedom EVO® robotic workstation, so that a pipetting robot can be utilized to transfer liquid portions and/or sample containing liquids to and from the cartridges 2. Alternatively, the system 1 can be can be configured as a hand-held unit which only comprises and is able to work with a low number, e.g. a single disposable cartridge 2. Every person of skill will understand that intermediate solutions that are situated in-between the two extremes just mentioned will also operate and work within the gist of the present invention.
According to the present invention, the digital microfluidics system 1 also comprises at least one board accommodation site 40 for taking up an electrode board 41 which comprises an electrode array 9 that substantially extends in a first plane and that comprises a number of electrodes 10. Such an electrode board 41 preferably is located at each one of said cartridge accommodation sites 8 of the base unit 7. Preferably each electrode array 9 is supported by a bottom substrate 11. It is noted that the expressions “electrode array”, “electrode layout”, and “printed circuit board (PCB)” are utilized herein as synonyms.
The digital microfluidics system 1 may also comprise at least one cover plate 12 with a top substrate; though providing of such cover plates 12 is particularly preferred, at least some of the cover plates may be dispensed with or may be re-placed by an alternative cover for holding a disposable cartridge 2 in place inside the base unit of the microfluidics system 1. Thus, at least one cover plate 12 may be located at one of said cartridge accommodation site 8. The cover plate 12 and the bottom substrate 11 with the electrode array 9 or PCB define a space or cartridge accommodation site 8 respectively. In a first variant (see the two cartridge accommodation sites 8 in the middle of the base unit 7, the cartridge accommodation sites 8 are configured for receiving a slidingly inserted disposable cartridge 2 that is movable in a direction substantially parallel with respect to the electrode array 9 of the respective cartridge accommodating site 8. Such front- or top-loading can be supported by a drawing-in automatism that, following a partial insertion of a disposable cartridge 2, transports the cartridge 2 to its final destination within the cartridge accommodation site 8, where the cartridge 2 is precisely seated. Preferably, these cartridge accommodation sites 8 do not comprise a movable cover plate 12. After carrying out all intended manipulations to the samples in liquid droplets, the used cartridges 2 can be ejected by the drawing in automatism and transported to an analysis station or discarded.
In a second variant (see the two cartridge accommodation sites 8 on the right and left of the base unit 7), the cartridge accommodation sites 8 comprise a cover plate 12 that is configured to be movable with respect to the electrode array 9 of the respective cartridge accommodating site 8. The cover plate 12 preferably is configured to be movable about one or more hinges 16 and/or in a direction that is substantially normal to the electrode array 9.
Similar to the possibilities for inserting a disposable cartridge 2 into a cartridge accommodation site 8, possibilities for inserting the electrode board 41 into a board accommodation site 40 comprise the following alternatives:
(a) vertically lowering the electrode board 41 through the respective cartridge accommodation site 8 and into the board accommodation site 40;
(b) horizontally sliding the electrode board 41 below the respective cartridge accommodation site 8 and into the board accommodation site 40;
(c) horizontally sliding the electrode board 41 below the respective cartridge accommodation site 8 and substantially vertically lifting into the board accommodation site 40.
In
The digital microfluidics system 1 also comprises a central control unit 14 for controlling the selection of the individual electrodes 10 of said at least one electrode array 9 and for providing these electrodes 10 with individual voltage pulses for manipulating liquid droplets within said cartridges 2 by electrowetting. As partly indicated in
The at least one cover plate 12 preferably comprises an electrically conductive material that extends in a second plane and substantially parallel to the electrode array 9 of the cartridge accommodation site 8 the at least one cover plate 12 is assigned to. It is particularly preferred that this electrically conductive material of the cover plate 12 is configured to be not connected to a source of an electrical ground potential. The cover plate 12 can be configured to be movable in any arbitrary direction and no electrical contacts have to be taken in into consideration when selecting a particularly preferred movement of the cover plate 12. Thus, the cover plate 12 may be configured to be also movable in a direction substantially parallel to the electrode array 9 and for carrying out a linear, circular or any arbitrary movement with respect to the respective electrode array 9 of the base unit 7.
The
The cover plate 12 is mechanically connected with the base unit 7 of the digital microfluidics system 1 via a hinge 16; thus, the cover plate 12 can swing open and a disposable cartridge 2 can be placed on the cartridge accommodation site 8 via top-entry loading (see
The cover plate 12 is configured to apply a force to a disposable cartridge 2 that is accommodated at the cartridge accommodation site 8 of the base unit 7. This force urges the disposable cartridge 2 against the electrode array 9 in order to position the bottom layer 3 of the cartridge as close as possible to the surface of the electrode array 9. This force also urges the disposable cartridge 2 into the perfect position on the electrode array 9 with respect to an optional piercing facility 18 of the cover plate 12. This piercing facility 18 is configured for introducing sample droplets into the gap 6 of the cartridge 2. The piercing facility 18 is configured as a through hole 19 that leads across the entire cover plate 12 and that enables a piercing pipette tip 20 to be pushed through and pierce the top layer 4 of the cartridge 2. The piercing pipette tip 20 may be a part of a handheld pipette (not shown) or of a pipetting robot (not shown).
In the case shown in
The electrode array 9 is located on an immovably fixed bottom substrate 11. The digital microfluidics system 1 is configured for manipulating samples in liquid droplets 23 within disposable cartridges 2 that contain a gap 6. Accordingly, the samples in liquid droplets 23 are manipulated in the gap 6 of the disposable cartridge 2. The disposable cartridge 2 comprises the bottom layer 3, the top layer 4, and the spacer 5 that defines the gap 6 between the bottom and top layers 3,4 for manipulating samples in liquid droplets 23 in this gap 6. The bottom layer 3 and the top layer 4 comprise a hydrophobic surface 17 that is exposed to the gap 6 of the cartridge 2. The bottom layer 3 and the top layer 4 of the cartridge 2 are entirely hydrophobic films or at least comprise a hydrophobic surface that is exposed to the gap 6 of the cartridge 2. It is clear from this
Further the cartridge 2 comprises an upper part 4, a spacer 5, a hydrophobic layer 3″, a support element 11′ for the electrode array 9′, an optional through hole 19, a liquid input port 19′ and electrically conductive material. The upper part 4 and the spacer 5 may be provided as separate parts or in form of a single piece. The hydrophobic layer 3″, the electrode array 9′ and the support element 11′ form the lower part of the cartridge. The electrode array 9′ is arranged between the hydrophobic layer 3″ and the support element 11′ and the gap is formed between the upper part 4 and the hydrophobic layer 3″. Further, the hydrophobic layer 3″ is attached to a peripheral side structure of the upper part 4 resp. to the spacer 5. The support element 11′ further comprises electrical connectors 14′, which are connected via multiple electrical wires to the electrode array 9′. In turn, the electrical connectors 14′ provide for a connection to a central control unit 14 such that the electrical connectors 14′ implement an electrical interface between cartridge 2 and the digital microfluidics system 1. The electrical interface can also be implemented by a contact field, i.e. a plurality of electrically conductive, mutually insulated contact areas.
Preferably, the flexible bottom layer 3 is reversibly attached to the electrodes 10 in an electrowetting sample processing system 1. The spacer 5 may be a part of the cartridge 2 or a part of the electrowetting sample processing system 1. In one example, the spacer 5 comprises stainless steel, aluminum, hard plastic, in particular COP or ceramic. The spacer 5 may be designed to define the height of the gap 6. The spacer 5 may additionally serve as a gasket for sealing the gap 6.
Preferred dimensions and materials are pointed to in table 1. These indications of materials and dimensions serve as preferred examples without limiting the scope of the present invention.
An inlet port 19′ for introducing a liquid 60,61 into the gap 6 is provided in the top layer 4 of the cartridge 2. In addition, an outlet port 80 is provided for removing liquid from the gap 6 of the cartridge 2. The outlet port 80 is arranged in this case also in the top layer 4 of the cartridge 2. Preferably, the top layer 4 comprises a rigid body when the inlet port 19′ and/or an outlet port 80 are arranged within the top layer 4, to provide a certain stability to the ports 19′,80. Stability is desired to ensure a sufficiently tight connection of tubes 87 of an outer liquid circuit to the ports, so that the liquid does not leak at the connection between the port(s) 19′,80 of the cartridge 2 and the tubes 87.
Preferably, the inlet port 19′ and the outlet port 80 are operably connected. By this, a liquid flow is provided through the cartridge 2 if a liquid driving force is applied to at least a part of the input liquid 105. A liquid driving force may be a pressure force applied to at least a part of the input liquid 105 and/or an electrowetting force for example applied to at least a part of the input liquid 105 when it has been moved into the gap 6 of the cartridge 2.
In addition, a vacuum supply line 92 is exemplarily shown in
An inlet port 19′ is provided again in the top layer 4 of the cartridge 2. By means of the inlet port 19′, an input liquid 60,61 can be introduced into the cartridge 2. An inlet port 19′ may also be arranged in the side structures of the cartridge 2, for example in a spacer 5 or in peripheral side structures 82 of the top layer 4, depending on the chosen structure of the cartridge 2. In one example, the inlet port 19′ is located on the bottom layer and enters the spacer 5 and—after a 90 degree turn—enters into the side of the cartridge 2. In another example the gap spacer that enables the liquid connection is located in the middle or a center part of the cartridge 2.
In the embodiment of
The number of outlet ports 80 provided by a cartridge 2 may depend on the application for which the cartridge 2 is designed. According to the invention, at least one inlet port 19′ and at least one outlet port 80 are provided, to enable a liquid flow throughout the cartridge 2. In another example multiple inlet ports 19′ are used, which in particular provide input for different reagents or different classes of reagents, for example at least one bulk reagent via a first inlet port and at least one stoichiometric reagent via a second inlet port. In another example, the multiple inlet ports 19′ are individually connected to a control element, in particular to a multi-port valve 90 and/or to a pump, to an individual input syringe pump 99 and/or an individual T-shaped junction 88.
In
Alternatively, an inlet port 19′ and/or an outlet port 80 may be a simple passage opening into which a tube of an outer liquid circuit may be mounted. Preferably, the passage opening comprises a seal 81 for a tight connection.
By the operational connection of the inlet port 19′ and the outlet ports 80, a liquid flow through the cartridge 2 is provided, if a liquid driving force is applied to at least a part of the input liquid 105. The input liquid 105 may comprise a carrier liquid 60 and/or a processing liquid 61.
A particular suitable carrier liquid 60 is an electrowetting filler liquid, for example a silicone oil. In an embodiment, an additional carrier liquid, for example a silicone oil may be used. An electrowetting filler liquid may be used for filling the gap 6, while a carrier liquid may be used to a liquid which segments droplets in the droplet generator. In one embodiment, the electrowetting filler liquid and the carrier liquid may be the same liquid. In a further embodiment, the electrowetting filler liquid is a different liquid, for example a different oil than the liquid used as a carrier liquid.
A processing liquid 61 can be any kind of liquid or liquid composition which is used for example in assay reactions or for analysis purposes or other applications carried out in the cartridge 2. Such a processing liquid 61 may be for example buffers, reaction liquids which comprise reactants required for a defined application, sample liquids which comprise a sample to be analyzed, diluent liquids, elution liquids, etc. Samples are for example DNA (Desoxyribonucleic acid), RNA (Ribonucleic Acid), derivatives thereof, proteins, cells, or other biologically or biochemically derived molecules or combinations thereof. The processing liquid 61 may in an embodiment comprise magnetic beads, to which for example one or more samples are bound.
Applications which may be carried out using a cartridge 2 and an electrowetting sample processing system 1 are for example at least one of chemical reactions, washing processes, heating processes, polymerase chain reaction (PCR) processes, hybridization processes, mixing processes, dilution processes, and NGS (next-generation sequencing) library prep assays.
The liquid flow through the cartridge 2 is realized by removing an amount of liquid as an output liquid 102 from the cartridge 2 via the outlet port 80 which is equivalent to the amount of input liquid 105 introduced into the cartridge 2. This operational linkage allows for example to maintain the level of liquid in the cartridge 2. Additionally, droplets of a determined volume may be generated outside the gap 6 of the cartridge 2, which allows a more precise volume control. This further allows storage of input liquids outside the cartridge 2, which removes requirements on the design of the gap 6 and the electrode array concerning for example the temperature of delicate liquids or volume requirements for bulk amounts of liquid. By removing such requirements from the cartridge 2, the design of the cartridge is more flexible, which allows the integration of more and/or more complex applications within one cartridge 2. The output liquid 102 may comprise at least a part of carrier liquid 60, processing liquid 61, sample containing liquid or any combinations thereof. The output liquid 102 may be treated as a waste liquid, which is discarded, or may be used for further processing.
Preferably, the delivery of the input liquid 105 through a liquid inlet port 19′ into the gap 6 for an electrowetting induced movement is synchronized with the electrowetting control, to ensure a proper hand-off of droplets 23. However, other processes outside the cartridge 2 required beforehand of the delivery may be carried out independently from the operations of electrodes 10 used for electrowetting. Though some processes may be synchronized, others may be carried out asynchronously from the operation of the electrodes 10, as described in the following.
Possible liquid operations in connection with the liquid inlet port 19′ and the outlet port(s) 80 are shown exemplarily in
The liquid feeder 86 comprises a multi-port valve 90 which allows for the movement of liquids 60,61 within the tubes 87 for introducing into the internal gap 6 of the cartridge 2, wherein in particular, the liquid feeder 86 comprises a liquid selector valve, for example a multiport valve, that works with an input syringe pump 99 for providing the liquid movement within the tubes. Because the inlet port 19′ and the outlet ports 80 are connected operationally, liquid may additionally be removed from the gap 6 of the cartridge 2 by means of a further pump or the waste pump 103. Liquid 60,61 which has been removed from the cartridge 2 via the outlet port 80 is transported via tubes 87 for example to a waste collecting place. Tubes 87 which are involved in the removal of waste liquids are shown in light grey, the direction of liquid movement within the tubes 87 is indicated by dashed arrows.
The movement of liquids within the tubes 87 may be supported by providing one or more additional pumps 99,103 operably connected to the tube(s) 87, e.g. via a bypass 97. In the embodiment of the electrowetting sample processing system 1 shown in
Waste management may further be supported by providing a removal line 91 within the cartridge 2. Such a removal line 91 is typically formed by a specific array of electrodes which guide input liquid 60,61 immediately from the inlet port 19′ to an outlet port 80. This allows the immediate removal for example of wash fluid from the inlet port 19′. As shown in
The liquid feeder 86 of the embodiment of the electrowetting sample processing system 1 shown in
At the T-shaped junction 88 the cross-flow is used for generating droplets of a defined volume. In particular, an carrier liquid 60 is pumped towards the T-shaped junction 88 by the left syringe pump 99 in alternating coordination with a processing liquid 61 from the direction of the liquid feeder 86, which is pumped into the T-shaped junction 88 in a cross-flow direction. By alternating flows of processing liquid 61 and carrier liquid 60, droplets of processing liquid 61 of controlled volume, separated by the carrier liquid 60, are generated.
Two different processing liquids 61 of a defined volume are generated by the T-shaped junction 88, indicated by white and black droplets, and are transported towards the liquid inlet port 19′. The distinct volumes of processing liquid 61 are separated by specific volumes of carrier liquid 60, so that the processing liquids 61 may be fed to the inlet port 19′ alternatingly with the carrier liquid 60. Depending on the flow of the carrier liquid 60 towards the T-shaped junction 88 and the feeding of different processing liquids 61 into the tube towards that junction 88, it is also possible to provide the input liquid 105 as a sequential feed of a single type of processing liquid 61 or a sequential feed of two or more processing liquids 61, which differ in their composition.
The liquid feeder 86 comprises a multi-port valve 90 and four separate storage tubes 98, which are in fluid connection with the multi-port valve 90, wherein in each storage tube 98 stores a different processing liquid 61. In another example, up to 8, in particular up to 20, separate storage tubes 98 with different processing liquids are in fluid connection with the multi-port valve 90. Preferably, at least one storage tube 98 is provided and connected to the multi-port valve 90, however, multiple storage tubes 98 are preferred to provide sufficient storage space for different processing liquids 61.
In addition to the processing liquid 61, the carrier liquid 60 may be in fluid connection to the liquid feeder as well, as indicated for the supply tube 87 on the rightmost side of the multi-port valve 90.
In the present embodiment, the carrier liquid 60 comprises the same material composition as the electrowetting filler liquid, namely a silicon oil. In another example, the carrier liquid 60 and the electrowetting filler liquid 60 may be different, e.g. silicon oil with different viscosities.
The liquid feeder 86 additionally comprises a bypass 97 for removing access liquid from liquids which are to be provided as input liquid 105. Other liquids such as liquids for flushing one or more tubes 87 of the liquid feeder 86 may also be removed from the tubular connection with the inlet port 19′ by using the bypass 87.
In this example, the cartridge 2 further comprises an air ventilation outlet 85 for providing a fluid output that is arranged separate from the outlet port. Here, the air ventilation outlet 85 serves as gas exhaust, in another example, the pressure cartridge comprises a compensation outlet such as a liquid overflow.
In this embodiment, the electrowetting sample processing system 1 comprises a reagent detector 104 for indicating the presence of reagent liquid in the input liquid, for example by detecting at least one characteristic of the reagent liquid, in particular an optical characteristic such as transmissivity (resp. absorbance) or refraction index or an electrical characteristic such as resistance (resp. conductivity) or capacity.
As shown in situation A, a bulk droplet of processing liquid 61 is pumped into the T-shaped junction 88, and an initial volume of liquid 61 crosses the shear location. By starting the flow of the carrier liquid 60 towards the shear point in the T-shaped junction 88, an initial droplet of processing liquid 61 is sheared of the bulk droplet at the shear point. The initial droplet of processing liquid 61 is discarded and may be pumped, for example by means of separate pump like a syringe pump 99, into a waste path for removal. The new leading edge of the bulk droplet of processing liquid 61 is now at a defined position within the T-shaped junction 88 (situation B), so that the following droplets may be generated under controlled conditions. The residual bulk droplet (situation C) is discarded as well to ensure that the last droplet is created by shearing on both ends.
An example of moving liquid towards a waste removal processing is shown for the situations D and E. This process may be used when for example an air gap is located within the processing liquid 61 and the carrier liquid 60. Using a syringe pump, reagents are pumped into the valve 89 with the air gap between the silicone oil and the processing liquid (situation D). Then, the valve is switched to a tube 87 which is connected with the waste removal system, and the air is pumped to the waste removal processing place.
3′
11′
14′
19′
