GB2455506A - Detectors for microfluidic systems - Google Patents

Abstract

A method for detecting and measuring samples in the form of liquid droplets or slugs in a carrier liquid comprises providing a microfluidic device with conduits and at least one detector, moving a carrier liquid containing the liquid droplets or slugs through the microfluidic device until a first droplet or slug comes into contact with the at least one detector, measuring at least one property of the liquid droplet or slug with the detector, removing the sample, flushing the detector with a flushing liquid and then repeating the detection sequence. A device for carrying out the method comprises a first conduit, 12 a detector 10 and a second conduit 14 in liquid communication with the first conduit.

Description

Detectors for microfluidic systems

TECHNICAL FIELD

This invention relates to detectors for use with microfluidic systems, and in particular to detectors for use with systems for mixing discrete volumes of chemical and biological solutions and suspensions in an accurate, versatile and predetermined manner.

BACKGROUND OF THE INVENTION

Microfluidic systems have the advantages of using very small volumes, consuming small amounts of samples and reagents, and compact size.

In 1957 Leonard Skeggs invented a special flow analysis technique named "continuous flow analysis" (CFA) that was commercialized by Technicon Corporation. This method is disclosed by Skeggs in US patent number 2797149, issued in 1959. Originally CFA used air to segment the flow of reagents and samples, but the air was later replaced by an immiscible carrier liquid as disclosed by Smytle and Morris in e.g. US3479141, issued in 1969. As long as the droplets and carrier fluid are moving, a film of carrier fluid can be maintained on the walls of the conduits. Thus the carrier liquid can prevent the sample and reagent droplets from touching the walls of the conduit system through which they pass, preventing contamination of the walls and the subsequent samples. US3479 141 also teaches the injection of solution into droplets at a T-junction. which is a useful technique for modern microfluidic applications. Figure 3 of US3479 141 indicates the injection of copper neocuproine solution into droplets to assay glucose in the droplets. Note, however, that droplets are here treated as a Continuous stream. Also, samples are distributed over several droplets. Therefore droplets are not individually treated or manipulated.

A similar approach was developed by the inventor of the present invention in GB patent 2097692B in 1982. Here samples etc. are dispensed into oil in a conduit system as individual droplets. Liquids can be added to samples, which can be heated, incubated, analyzed etc. Each droplet is equivalent to a test-tube and it is dealt with individually. Also, GB2097692B teaches miniaturization and the construction of conduits by forming depressions in the surface of one or more sheets and bringing these sheets into face-to-face contact. Improved methods for dispensing, priming and calibrating a microfluidic device, and also novel hardware were later disclosed by the present inventor in patent application GB0704786.3.

These methods have a disadvantage in that they are difficult to use with solid phase detectors because of the presence of the oil, and because it is difficult to remove a sample in order to measure a subsequent sample. For example, if a pH meter were placed in a conduit, with suitable geometry it would be possible to make a droplet in oil adhere to the meter. If the oil in the conduit is moved it is possible to detach part of the droplet from the meter and move it away from the meter, but some of the droplet would remain adhering to the meter. If a subsequent sample (i.e. a subsequent droplet) were brought into contact with the meter the subsequent sample would become contaminated by the original sample.

A need therefore exists for a method and apparatus that allows a plurality of samples in droplets in oil (or another carrier liquid) to be measured with solid phase detectors.

There are many inacroscale detectors that are used with microfluidic devices, or could be scaled down and used with them. Such detectors include pH meters, ion-selective electrodes, refractometers, conductivity detectors, fiber optic detectors. biosensors, etc. Microscale detectors are also well-known, such as MEMS detectors, and these are particularly suitable for use with microfluidics because they are small and cheap.

The objective of the present invention is to provide a method and apparatus that allows solid-phase detectors to be used with droplet-based microfluidic systems. A second objective is to prevent the carrier liquid used from interfering with the detector.

BRIEF SUMMARY OF THE INVENTION

One aspect of the invention is a means of analyzing samples in droplets within a droplet-based microfluidic system.

A second aspect is a method of flushing and cleaning a detector in a droplet-based microfluidic system.

A third aspect is an apparatus that provides one or more conduits for the introduction of at least one liquid that can flush etc. a detector. Advantageously, some or all of the flushing liquids can be miscible with the samples and reagents, or with the carrier liquid, or with both.

A similar approach can advantageously be used to remove bound and unbound analyte from the detector, and to prime said detector so that it can be reused.

The method of the invention comprises providing a detector in a conduit, moving a carrier liquid until a first droplet containing a sample coalesces with said detector, using the detector to analyze the sample, removing the sample after analysis by flushing the detector with a flushing liquid, optionally cleaning and priming the detector for reuse, reintroducing said carrier liquid into said conduit, and repeating the forgoing cycle to measure one or more other samples in droplets.

In one variation of the invention a flushing liquid is used that is miscible with aqueous liquids, with the carrier liquid, or with both. Said flushing liquid can be used advantageously both before and after cleaning and/or priming the detector.

A second variation of the invention uses a series of tiushing liquids where early members of the series can dissolve carrier liquid but not samples, while later members of the series can dissolve samples but not the carrier liquid. In such a series, each liquid should be miscible with the next member of the series.

The apparatus comprises a device with conduits that is suitable for use as a droplet-based microfluidic system, which possesses one or more detectors located in at least one conduit. In addition, the apparatus possesses at least one conduit that can provide liquids to flush said detector or detectors. Additional conduits can be used to introduce cleaning liquids and priming liquids to prime said detector prior to reuse.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a cut-away view of a simple microfluidic device with a detector that can carry out the method of the invention.

Figures 2a to 2e show the steps of a method of flushing and reusing a detector using a liquid (or liquids) that is miscible with both the sample and the carrier liquid.

Figures 3a to 3f show the steps of a method for flushing and reusing a detector using a hydrophilic barrier around the detector to prevent carrier liquid from coming into contact with the detector.

Figure 4 shows an alternative configuration where the sensitive surface of the detector (10) is set back from the side-wall (44) of the conduit (12) in an indentation (46) or blind hole.

Figure 5a shows that samples may not coalesce with the detector. Figure 5b shows that after an electric potential is applied to the barrier (or to the detector) coalescence is achieved.

Figure 6 shows one of many possible designs of a microfluidic device with several secondary conduits for introducing a plurality of liquids for flushing, cleaning, priming etc. a detector.

Figure 7 shows that a single conduit of a microfluidic device can be connected to a valve that allows the introduction of a plurality of liquids for flushing, cleaning, priming etc. a detector.

Figure 8 shows an apparatus that is similar to the apparatus of any previous figure, which has in addition a set of conduits for dispensing and mixing solutions such that they form droplets or slugs in an immiscible liquid.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in detail, with reference to the accompanying drawings.

In the accompanying drawings, like features are denoted by like numerals.

Figure lshows a 3-dimensional cut-away view of a microfluidic device. Figures 2a to 2e, 3a to 31, 4a and 4b, and figure 5 show schematic cross-sections of a microfluidic conduit. Figures 6. 7 and 8 show schematic plan views of various devices.

Figure 1 shows a cut-away view of a simple microfluidic device with a detector that can carry out the method of the invention. A detector (10) is positioned in a conduit (12). The conduit is filled with a carrier liquid. For a system that can handle aqueous samples, the carrier liquid could be a paraffin oil.

silicone oil. halogenated oil etc. Fluorinated oils are important examples of halogenated oils that can advantageously be used. A side-arm (14) is provided for introducing liquids for flushing, cleaning, priming etc. the detector.

The device is suitable for moving sample droplets in the carrier liquid along the conduit until the droplets come into contact with and adhere to the detector.

Figures 2a to 2e show the steps of a method of flushing and reusing a detector using a liquid (or liquids) that is miscible with both the sample and the carrier liquid. Figure 2a, shows a cross-section of a conduit (12) which possesses a detector (10) embedded into one wall. In figure 2b, a sample has been introduced into the conduit in the form of a droplet (20). The droplet (20) is moved along the conduit by moving the carrier liquid. In Figure 2c the droplet (22) has come into contact with the detector and is adhering to it.

A measurement of the droplet is now taken. In figure 2d, an intermediate liquid (24) that is miscible with both the carrier liquid and the sample droplet is introduced into the conduit. When the intermediate liquid is introduced, part of the droplet (26) may leave the detector, while part of the droplet (28) adheres to the detector. The intermediate liquid removes the last part of the sample from the detector. In figure 2e. all samples and intermediate liquids have been removed from the conduit near the detector (12) and carrier liquid is reintroduced into this region of the conduit. The system is now ready to measure a new droplet, and for another cycle of detection.

Many possibilities exist for the choice of the intermediate liquid of figures 2a to 2e. For example, if aqueous samples are used, and if the carrier liquid is paraffin oil, then the intermediate liquid could be an alcohol such as butanol or an acetone. These liquids are at least partially miscible with both aqueous liquids and with paraffin. In some cases it may be necessary to use a series of liquids where the miscibility with carrier liquid slowly increases or decreases as one moves through the series. For example, the conduit could be filled first with pentanol, then butanol. then ethanol etc. This may be advantageous when the samples contain solutes or solvents that are not readily miscible with a single intermediate liquid. Another example is the series aqueous, ethanol, silicone fluid, paraffin oil. Each liquid is fully miscible with the next in the series, but if a member of the series is skipped, the resulting combination of liquids is not fully miscible. After cleaning the detector etc. the series can advantageously be used in reverse order to reinstate the carrier liquid.

Figures 3a to 3f show the steps of a method for flushing and reusing a detector using a hydrophilic barrier around the detector that prevents carrier liquid from coining into contact with the detector. A hydrophilic barrier is used for aqueous samples, but the same principle could be applied using barriers with other properties in combination with samples that are not aqueous. In figure 3a, a droplet (20) approaches a detector that has a barrier (30) around it. This barrier advantageously has a surface that has a high affinity to the sample droplets. For example if the droplets are aqueous, barriers with hydrophilic surfaces can advantageously be used. This ensures that a volume of e.g. aqueous liquid (32) is retained which covers the detector (10). In figure 3b, the droplet (33) has come into contact with the barrier, and adheres to the barrier and to the detector. A measurement of the droplet is now taken. In figure 3c, a liquid that is miscible with the droplet (34) is introduced into the conduit. The current produced may cause part of the droplet (26) to leave the detector, although part (24) will remain in contact with it. In figure 3d, the liquid that is miscible with the samples completely fills the conduit, although drops of carrier liquid that adhere to the walls of the conduit (38) may remain. In figure 3e, carrier liquid (39) is reintroduced into the conduit. In figure 3f the conduit is completely full of carrier liquid, except for liquid that is miscible with the samples (32), which remains in contact with the detector. The system is now ready for a new droplet, and another cycle of detection.

Figure 4 shows an alternative configuration where the sensitive surface of the detector (10) is set back from the side-wall (44) of the conduit (12) in an indentation (46). The indentation can also be described as a short or very short blind hole, with the detector at the end of it. The side-walls of the indentation (48) can advantageously be constructed from a material that has a high affinity for the sample droplets. The analyte may come into contact with the detector by convection, diffusion, viscous flow etc. The steps shown in figures 2a -2e, 3a -3f and 4a -4b can obviously be used with the device of figure 4.

Figure 5a shows that samples may not coalesce with the detector. This may be because a film of carrier liquid (42) remains between the detector and the sample. Figure 5b shows that after an electric potential is applied to the barrier (or to the detector) coalescence is achieved. The electric potential causes the sample droplet (33) to come into contact with the detector. A similar method can be used with other designs, such as the detectors shown in figures 2a to 2e, and in figure 4. Note that droplet-based and slug-based microfluidic devices sometimes use liquids that contain surface-active agents, lipids or detergents.

These ingredients may decrease the tendency for droplets or slugs to adhere to the walls of the conduit.

However, these ingredients may also increase the tendency for droplets or slugs to remain uncoalesced with detectors. Therefore the method described of applying an electric potential may be particularly helpful when surface-active agents, lipids and detergents etc. are present.

An alternative method of causing a sample droplet to come into contact with the detector is to energize the system with ultrasound.

Figure 6 shows one of many possible designs of a microfluidic device with several secondary conduits for introducing a plurality of liquids for flushing, cleaning, priming etc. a detector. As before, a side-arm or arm (14) joins a conduit (12) that possesses a detector (10). This side-arm is in communication with a plurality of secondary conduits (50). For example, one conduit could advantageously contain a liquid, such as water or buffer, for flushing the detector. Another could advantageously contain a liquid for cleaning a detector such as detergent, acid or base. A third could advantageously contain a liquid for derivatizing the active parts of the detector. A forth conduit could advantageously contain a molecule such as a protein or nucleic acid that interacts specifically with the analyte that is to be detected in the samples. This molecule could advantageously be immobilized on the surface of the detector. Also, solutions with intermediate miscibility, as were described with reference to figures 2a to 2e, could be introduced via secondary conduits. Each of the conduits for introducing liquids possesses a means for moving liquids, although these means are not shown in figure 5.

Figure 7 shows that a single conduit of a microfluidic device can be connected to a valve that allows the introduction of a plurality of liquids for flushing, cleaning, priming etc. a detector. The detector is in a rnicrofluidic device (60). This microfluidic device possesses an arm (14) that is connected to a valve (62) with a plurality of conduits for introducing liquids (64). A rotary valve is shown, hut clearly many different styles of valves could be used including slide-valves, needle valves, diaphragm valves, solenoid valves and pinch valves. In addition, liquid can be moved in said secondary conduit or conduits by means of one or more gear pumps, piston pumps, syringe pumps, centrifugal pumps or peristaltic pumps.

Figure 8 shows an apparatus that is similar to the apparatus of any previous figure, which has in addition a set of special conduits for dispensing and mixing solutions such that they form droplets or slugs in an immiscible liquid. As before, it possesses a conduit (12), with a detector (10), and a side-arm or arm (14).

it also possesses one or more special conduits (70) for introducing samples and reagents, in the form of droplets or slugs, into carrier liquid in said conduit. This aspect of the device is similar to the inventions disclosed in patents US3479141, GB2097692B. and patent application GB0704786.3 described above. Detectors for microfluidic systems

TECHNICAL FIELD

This invention relates to detectors for use with microfluidic systems, and in particular to detectors for use with systems for mixing discrete volumes of chemical and biological solutions and suspensions in an accurate, versatile and predetermined manner.

BACKGROUND OF THE INVENTION

Microfluidic systems have the advantages of using very small volumes, consuming small amounts of samples and reagents, and compact size.

In 1957 Leonard Skeggs invented a special flow analysis technique named "continuous flow analysis" (CFA) that was commercialized by Technicon Corporation. This method is disclosed by Skeggs in US patent number 2797149, issued in 1959. Originally CFA used air to segment the flow of reagents and samples, but the air was later replaced by an immiscible carrier liquid as disclosed by Smytle and Morris in e.g. US3479141, issued in 1969. As long as the droplets and carrier fluid are moving, a film of carrier fluid can be maintained on the walls of the conduits. Thus the carrier liquid can prevent the sample and reagent droplets from touching the walls of the conduit system through which they pass, preventing contamination of the walls and the subsequent samples. US3479 141 also teaches the injection of solution into droplets at a T-junction. which is a useful technique for modern microfluidic applications. Figure 3 of US3479 141 indicates the injection of copper neocuproine solution into droplets to assay glucose in the droplets. Note, however, that droplets are here treated as a Continuous stream. Also, samples are distributed over several droplets. Therefore droplets are not individually treated or manipulated.

A similar approach was developed by the inventor of the present invention in GB patent 2097692B in 1982. Here samples etc. are dispensed into oil in a conduit system as individual droplets. Liquids can be added to samples, which can be heated, incubated, analyzed etc. Each droplet is equivalent to a test-tube and it is dealt with individually. Also, GB2097692B teaches miniaturization and the construction of conduits by forming depressions in the surface of one or more sheets and bringing these sheets into face-to-face contact. Improved methods for dispensing, priming and calibrating a microfluidic device, and also novel hardware were later disclosed by the present inventor in patent application GB0704786.3.

These methods have a disadvantage in that they are difficult to use with solid phase detectors because of the presence of the oil, and because it is difficult to remove a sample in order to measure a subsequent sample. For example, if a pH meter were placed in a conduit, with suitable geometry it would be possible to make a droplet in oil adhere to the meter. If the oil in the conduit is moved it is possible to detach part of the droplet from the meter and move it away from the meter, but some of the droplet would remain adhering to the meter. If a subsequent sample (i.e. a subsequent droplet) were brought into contact with the meter the subsequent sample would become contaminated by the original sample.

A need therefore exists for a method and apparatus that allows a plurality of samples in droplets in oil (or another carrier liquid) to be measured with solid phase detectors.

There are many inacroscale detectors that are used with microfluidic devices, or could be scaled down and used with them. Such detectors include pH meters, ion-selective electrodes, refractometers, conductivity detectors, fiber optic detectors. biosensors, etc. Microscale detectors are also well-known, such as MEMS detectors, and these are particularly suitable for use with microfluidics because they are small and cheap.

The objective of the present invention is to provide a method and apparatus that allows solid-phase detectors to be used with droplet-based microfluidic systems. A second objective is to prevent the carrier liquid used from interfering with the detector.

BRIEF SUMMARY OF THE INVENTION

One aspect of the invention is a means of analyzing samples in droplets within a droplet-based microfluidic system.

A second aspect is a method of flushing and cleaning a detector in a droplet-based microfluidic system.

A third aspect is an apparatus that provides one or more conduits for the introduction of at least one liquid that can flush etc. a detector. Advantageously, some or all of the flushing liquids can be miscible with the samples and reagents, or with the carrier liquid, or with both.

A similar approach can advantageously be used to remove bound and unbound analyte from the detector, and to prime said detector so that it can be reused.

The method of the invention comprises providing a detector in a conduit, moving a carrier liquid until a first droplet containing a sample coalesces with said detector, using the detector to analyze the sample, removing the sample after analysis by flushing the detector with a flushing liquid, optionally cleaning and priming the detector for reuse, reintroducing said carrier liquid into said conduit, and repeating the forgoing cycle to measure one or more other samples in droplets.

In one variation of the invention a flushing liquid is used that is miscible with aqueous liquids, with the carrier liquid, or with both. Said flushing liquid can be used advantageously both before and after cleaning and/or priming the detector.

A second variation of the invention uses a series of tiushing liquids where early members of the series can dissolve carrier liquid but not samples, while later members of the series can dissolve samples but not the carrier liquid. In such a series, each liquid should be miscible with the next member of the series.

The apparatus comprises a device with conduits that is suitable for use as a droplet-based microfluidic system, which possesses one or more detectors located in at least one conduit. In addition, the apparatus possesses at least one conduit that can provide liquids to flush said detector or detectors. Additional conduits can be used to introduce cleaning liquids and priming liquids to prime said detector prior to reuse.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a cut-away view of a simple microfluidic device with a detector that can carry out the method of the invention.

Figures 2a to 2e show the steps of a method of flushing and reusing a detector using a liquid (or liquids) that is miscible with both the sample and the carrier liquid.

Figures 3a to 3f show the steps of a method for flushing and reusing a detector using a hydrophilic barrier around the detector to prevent carrier liquid from coming into contact with the detector.

Figure 4 shows an alternative configuration where the sensitive surface of the detector (10) is set back from the side-wall (44) of the conduit (12) in an indentation (46) or blind hole.

Figure 5a shows that samples may not coalesce with the detector. Figure 5b shows that after an electric potential is applied to the barrier (or to the detector) coalescence is achieved.

Figure 6 shows one of many possible designs of a microfluidic device with several secondary conduits for introducing a plurality of liquids for flushing, cleaning, priming etc. a detector.

Figure 7 shows that a single conduit of a microfluidic device can be connected to a valve that allows the introduction of a plurality of liquids for flushing, cleaning, priming etc. a detector.

Figure 8 shows an apparatus that is similar to the apparatus of any previous figure, which has in addition a set of conduits for dispensing and mixing solutions such that they form droplets or slugs in an immiscible liquid.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in detail, with reference to the accompanying drawings.

In the accompanying drawings, like features are denoted by like numerals.

Figure lshows a 3-dimensional cut-away view of a microfluidic device. Figures 2a to 2e, 3a to 31, 4a and 4b, and figure 5 show schematic cross-sections of a microfluidic conduit. Figures 6. 7 and 8 show schematic plan views of various devices.

Figure 1 shows a cut-away view of a simple microfluidic device with a detector that can carry out the method of the invention. A detector (10) is positioned in a conduit (12). The conduit is filled with a carrier liquid. For a system that can handle aqueous samples, the carrier liquid could be a paraffin oil.

silicone oil. halogenated oil etc. Fluorinated oils are important examples of halogenated oils that can advantageously be used. A side-arm (14) is provided for introducing liquids for flushing, cleaning, priming etc. the detector.

The device is suitable for moving sample droplets in the carrier liquid along the conduit until the droplets come into contact with and adhere to the detector.

Figures 2a to 2e show the steps of a method of flushing and reusing a detector using a liquid (or liquids) that is miscible with both the sample and the carrier liquid. Figure 2a, shows a cross-section of a conduit (12) which possesses a detector (10) embedded into one wall. In figure 2b, a sample has been introduced into the conduit in the form of a droplet (20). The droplet (20) is moved along the conduit by moving the carrier liquid. In Figure 2c the droplet (22) has come into contact with the detector and is adhering to it.

A measurement of the droplet is now taken. In figure 2d, an intermediate liquid (24) that is miscible with both the carrier liquid and the sample droplet is introduced into the conduit. When the intermediate liquid is introduced, part of the droplet (26) may leave the detector, while part of the droplet (28) adheres to the detector. The intermediate liquid removes the last part of the sample from the detector. In figure 2e. all samples and intermediate liquids have been removed from the conduit near the detector (12) and carrier liquid is reintroduced into this region of the conduit. The system is now ready to measure a new droplet, and for another cycle of detection.

Many possibilities exist for the choice of the intermediate liquid of figures 2a to 2e. For example, if aqueous samples are used, and if the carrier liquid is paraffin oil, then the intermediate liquid could be an alcohol such as butanol or an acetone. These liquids are at least partially miscible with both aqueous liquids and with paraffin. In some cases it may be necessary to use a series of liquids where the miscibility with carrier liquid slowly increases or decreases as one moves through the series. For example, the conduit could be filled first with pentanol, then butanol. then ethanol etc. This may be advantageous when the samples contain solutes or solvents that are not readily miscible with a single intermediate liquid. Another example is the series aqueous, ethanol, silicone fluid, paraffin oil. Each liquid is fully miscible with the next in the series, but if a member of the series is skipped, the resulting combination of liquids is not fully miscible. After cleaning the detector etc. the series can advantageously be used in reverse order to reinstate the carrier liquid.

Figures 3a to 3f show the steps of a method for flushing and reusing a detector using a hydrophilic barrier around the detector that prevents carrier liquid from coining into contact with the detector. A hydrophilic barrier is used for aqueous samples, but the same principle could be applied using barriers with other properties in combination with samples that are not aqueous. In figure 3a, a droplet (20) approaches a detector that has a barrier (30) around it. This barrier advantageously has a surface that has a high affinity to the sample droplets. For example if the droplets are aqueous, barriers with hydrophilic surfaces can advantageously be used. This ensures that a volume of e.g. aqueous liquid (32) is retained which covers the detector (10). In figure 3b, the droplet (33) has come into contact with the barrier, and adheres to the barrier and to the detector. A measurement of the droplet is now taken. In figure 3c, a liquid that is miscible with the droplet (34) is introduced into the conduit. The current produced may cause part of the droplet (26) to leave the detector, although part (24) will remain in contact with it. In figure 3d, the liquid that is miscible with the samples completely fills the conduit, although drops of carrier liquid that adhere to the walls of the conduit (38) may remain. In figure 3e, carrier liquid (39) is reintroduced into the conduit. In figure 3f the conduit is completely full of carrier liquid, except for liquid that is miscible with the samples (32), which remains in contact with the detector. The system is now ready for a new droplet, and another cycle of detection.

Figure 4 shows an alternative configuration where the sensitive surface of the detector (10) is set back from the side-wall (44) of the conduit (12) in an indentation (46). The indentation can also be described as a short or very short blind hole, with the detector at the end of it. The side-walls of the indentation (48) can advantageously be constructed from a material that has a high affinity for the sample droplets. The analyte may come into contact with the detector by convection, diffusion, viscous flow etc. The steps shown in figures 2a -2e, 3a -3f and 4a -4b can obviously be used with the device of figure 4.

Figure 5a shows that samples may not coalesce with the detector. This may be because a film of carrier liquid (42) remains between the detector and the sample. Figure 5b shows that after an electric potential is applied to the barrier (or to the detector) coalescence is achieved. The electric potential causes the sample droplet (33) to come into contact with the detector. A similar method can be used with other designs, such as the detectors shown in figures 2a to 2e, and in figure 4. Note that droplet-based and slug-based microfluidic devices sometimes use liquids that contain surface-active agents, lipids or detergents.

These ingredients may decrease the tendency for droplets or slugs to adhere to the walls of the conduit.

However, these ingredients may also increase the tendency for droplets or slugs to remain uncoalesced with detectors. Therefore the method described of applying an electric potential may be particularly helpful when surface-active agents, lipids and detergents etc. are present.

An alternative method of causing a sample droplet to come into contact with the detector is to energize the system with ultrasound.

Figure 6 shows one of many possible designs of a microfluidic device with several secondary conduits for introducing a plurality of liquids for flushing, cleaning, priming etc. a detector. As before, a side-arm or arm (14) joins a conduit (12) that possesses a detector (10). This side-arm is in communication with a plurality of secondary conduits (50). For example, one conduit could advantageously contain a liquid, such as water or buffer, for flushing the detector. Another could advantageously contain a liquid for cleaning a detector such as detergent, acid or base. A third could advantageously contain a liquid for derivatizing the active parts of the detector. A forth conduit could advantageously contain a molecule such as a protein or nucleic acid that interacts specifically with the analyte that is to be detected in the samples. This molecule could advantageously be immobilized on the surface of the detector. Also, solutions with intermediate miscibility, as were described with reference to figures 2a to 2e, could be introduced via secondary conduits. Each of the conduits for introducing liquids possesses a means for moving liquids, although these means are not shown in figure 5.

Figure 7 shows that a single conduit of a microfluidic device can be connected to a valve that allows the introduction of a plurality of liquids for flushing, cleaning, priming etc. a detector. The detector is in a rnicrofluidic device (60). This microfluidic device possesses an arm (14) that is connected to a valve (62) with a plurality of conduits for introducing liquids (64). A rotary valve is shown, hut clearly many different styles of valves could be used including slide-valves, needle valves, diaphragm valves, solenoid valves and pinch valves. In addition, liquid can be moved in said secondary conduit or conduits by means of one or more gear pumps, piston pumps, syringe pumps, centrifugal pumps or peristaltic pumps.

Figure 8 shows an apparatus that is similar to the apparatus of any previous figure, which has in addition a set of special conduits for dispensing and mixing solutions such that they form droplets or slugs in an immiscible liquid. As before, it possesses a conduit (12), with a detector (10), and a side-arm or arm (14).

it also possesses one or more special conduits (70) for introducing samples and reagents, in the form of droplets or slugs, into carrier liquid in said conduit. This aspect of the device is similar to the inventions disclosed in patents US3479141, GB2097692B. and patent application GB0704786.3 described above.

Claims (14)

1. What I claim is: I. A method of measuring samples in the form of liquid droplets or slugs in a carrier liquid that is immiscible with said samples, where the method comprises the steps of: (1) providing a microfluidic device with conduits, (2) filling at least some of said conduits with a carrier liquid, (3) introducing samples in the form of liquid droplets or slugs into the carrier liquid, (4) providing at least one detector in said conduits, (5) moving said carrier liquid until a first droplet comes into contact with a detector, (6) using the detector to measure a property or properties of said first droplet, (7) removing the sample after analysis by flushing the detector with a flushing liquid, (8) optionally cleaning, derivatizing, priming the detector for reuse, (9) reintroducing said carrier liquid into said conduit, and (10) repeating steps (3) to (9) to measure one or more other samples in droplets.
2. 2. A method as claimed in claim 1 in which at least one flushing liquid is at least partially miscible either with the carrier liquid, with the samples, or with both.
3. 3. A method as claimed in claim 2 in which a series of flushing liquids is provided, where each member of the series has properties in terms of miscibility that lie between the members before and after it.
4. 4. A method as claimed in claim 3 in which at least one member of the series is miscible with the samples, while at least one member of the series is miscible with the carrier liquid.
5. 5. A method as claimed in claim I in which said detector possesses a barrier around it which prevents carrier liquid from coming into contact with the detector.
6. 6. A method as claimed in claim I in which said detector is placed in an indentation or blind hole, to prevent carrier liquid from coming into contact with the detector.
7. 7. A method as claimed in any previous claim where a liquid droplet or slug is brought into contact with a detector by applying an electric potential to said detector or to a nearby feature such as a barrier around said detector.
8. 8. A method as claimed in any previous claim where a liquid droplet or slug is brought into contact with a detector by energizing the system with ultrasound.
9. 9. A method as claimed iii any previous claim where after flushing the detector the detector is optionally cleaned, optionally reconditioned and optionally primed ready to take another measurement.
10. 10. A device that is suitable for measuring the properties of liquid droplets or slugs that possesses a first conduit, a detector, and at least one other conduit that is in liquid communication with said first conduit.
11. 11. A device as claimed in claim 10 where said other conduit or conduits can be filled with liquids for flushing, cleaning, or priming a detector.
12. 12. A device as claimed in claim 10 where at least one secondary conduit is in fluid communication with said detector by means of one or more rotary valves, slide-valves, needle valves, diaphragm valves, solenoid valves or pinch valves.
13. 13. A device as claimed in any previous claim where at least one secondary conduit is in fluid communication with said detector, and where fluid is moved in said secondary conduit or conduits by means of one or more gear pumps, piston pumps, syringe pumps, centrifugal pumps or peristaltic pumps.
14. 14. A device as claimed in any previous claim which has in addition to the features described in previous claims one or more special conduits from which samples and reagents can be dispensed into a conduit that contains a carrier liquid in order to form droplets or slugs.

    14. A device as claimed in any previous claim which has in addition to the features described in previous claims one or more special conduits from which samples and reagents can be dispensed into a conduit that contains a carrier liquid in order to form droplets or slugs.

    What I claim is: I. A method of measuring samples in the form of liquid droplets or slugs in a carrier liquid that is immiscible with said samples, where the method comprises the steps of: (1) providing a microfluidic device with conduits, (2) filling at least some of said conduits with a carrier liquid, (3) introducing samples in the form of liquid droplets or slugs into the carrier liquid, (4) providing at least one detector in said conduits, (5) moving said carrier liquid until a first droplet comes into contact with a detector, (6) using the detector to measure a property or properties of said first droplet, (7) removing the sample after analysis by flushing the detector with a flushing liquid, (8) optionally cleaning, derivatizing, priming the detector for reuse, (9) reintroducing said carrier liquid into said conduit, and (10) repeating steps (3) to (9) to measure one or more other samples in droplets.

    2. A method as claimed in claim 1 in which at least one flushing liquid is at least partially miscible either with the carrier liquid, with the samples, or with both.

    3. A method as claimed in claim 2 in which a series of flushing liquids is provided, where each member of the series has properties in terms of miscibility that lie between the members before and after it.

    4. A method as claimed in claim 3 in which at least one member of the series is miscible with the samples, while at least one member of the series is miscible with the carrier liquid.

    5. A method as claimed in claim I in which said detector possesses a barrier around it which prevents carrier liquid from coming into contact with the detector.

    6. A method as claimed in claim I in which said detector is placed in an indentation or blind hole, to prevent carrier liquid from coming into contact with the detector.

    7. A method as claimed in any previous claim where a liquid droplet or slug is brought into contact with a detector by applying an electric potential to said detector or to a nearby feature such as a barrier around said detector.

    8. A method as claimed in any previous claim where a liquid droplet or slug is brought into contact with a detector by energizing the system with ultrasound.

    9. A method as claimed iii any previous claim where after flushing the detector the detector is optionally cleaned, optionally reconditioned and optionally primed ready to take another measurement.

    10. A device that is suitable for measuring the properties of liquid droplets or slugs that possesses a first conduit, a detector, and at least one other conduit that is in liquid communication with said first conduit.

    11. A device as claimed in claim 10 where said other conduit or conduits can be filled with liquids for flushing, cleaning, or priming a detector.

    12. A device as claimed in claim 10 where at least one secondary conduit is in fluid communication with said detector by means of one or more rotary valves, slide-valves, needle valves, diaphragm valves, solenoid valves or pinch valves.

    13. A device as claimed in any previous claim where at least one secondary conduit is in fluid communication with said detector, and where fluid is moved in said secondary conduit or conduits by means of one or more gear pumps, piston pumps, syringe pumps, centrifugal pumps or peristaltic pumps.