HK1120861A

HK1120861A - Electrical drop surveillance

Info

Publication number: HK1120861A
Application number: HK08112532.2A
Authority: HK
Inventors: Wenzig Peter; Ziegler Guenter
Original assignee: F. Hoffmann-La Roche Ag
Priority date: 2005-11-15
Filing date: 2008-11-14
Publication date: 2009-04-09

Description

Electronic drop monitoring

Technical Field

The present invention provides a method, apparatus and computer program for detecting a liquid leak of a liquid transfer device.

Background

The increasing degree of automation and parallelization of industrial and scientific methods places high demands on the precision and reliability of the robot, especially when optimizing sample volumes and time-to-result relationships based on operational needs.

For the pharmaceutical industry and diagnostic applications, the automation and parallelization involves processing liquids like biological samples or reagents. A prominent example in this respect is the parallelization of PCR amplification in the form of microwells with e.g. 386 or even 1536 individual reactions. In order to process such multiple tests within a reasonable period of time, automation is necessary to transfer reagents and samples to microplates.

Each PCR amplification involves a number of individual preparation steps, such as cell lysis, digestion, isolation and purification. Each individual preparation step must be controlled to avoid end result errors. For handling liquids it is important to control the volume of aspirated sample to detect leakage from the transfer device and completion of the dispensing process.

In particular, leakage control of the transfer device is important not only because the amount of liquid being transferred must be accurate, but also because of the risk of liquid leakage creating cross-contamination during the transfer process.

In the state of the art, drip monitoring and aspiration/dispense control are primarily performed by pressure monitoring of the liquid transfer device. WO 96/41200 discloses an automatic pipetting instrument with a leak detection function based on a pressure sensor connected to the pipetting system to measure the change of the internal pressure in the pipetting system over time. US 5,503,036 discloses a device and method for determining whether a sample probe of an automated fluid sample aspirating/dispensing device is blocked by measuring the pressure within the sample probe. EP 1066532 discloses a method and apparatus for drawing a biological sample using a manual or automatic suction and discharge device including means for detecting pressure changes, while pressure monitoring is used for Liquid Level Detection (LLD) to minimize the penetration depth of the device and corresponding wetting of the outer walls of the device. WO 01/88549 claims a method for determining the performance of an aspiration process comprising recording a pressure curve. US 2001/14477 claims a system for dispensing precise amounts of transfer liquid comprising the step of sensing pressure changes to measure the volume of transfer liquid. WO 02/73215 discloses recording state variables of a liquid during aspiration and/or dispensing to show the results of an evaluation of the liquid dispensing process.

Furthermore, the liquid treatment can be monitored by electronic means. US 2001/49148 discloses a method of sampling a compound comprising the step of sensing an electrical signal indicative of contact between a dissolved fluid within a capillary and a compound reversibly immobilised on a surface. JP 2003-172744 discloses a method of placing a liquid from a nozzle of a dropping section on a surface of a substrate, wherein the electrostatic capacity between the substrate and the nozzle of the dropping section is measured to ensure that only a droplet generated at the nozzle of the dropping section is in contact with the surface of the substrate.

In the state of the art for liquid handling at present, electronics are also used for Liquid Level Detection (LLD) prior to the pumping process, and there are mainly two different methods, resistance LLD (rlld) and capacitance LLD (clld). When performing rLLD, the resistance between the liquid transfer device and e.g. an electrode connected to the outside of the liquid transfer device is simply measured and when this liquid level is reached the resistance will drop significantly (e.g. US 3,754,444). In performing the cLLD, an alternating voltage source is used to monitor changes in capacitance between the liquid transfer device and the container containing the liquid. There are different alternative embodiments of such a mechanism (setup), for example, the liquid transfer device itself is configured as a first electrode, while the liquid-containing reservoir to be aspirated forms a second electrode. When the liquid transfer means approaches the liquid level in said container, the capacitance will change (EP164679, EP 355791, US 4,818,492). A more sophisticated method for cLLD is disclosed in EP 555710, wherein both electrodes belong to the liquid transfer device.

Disclosure of Invention

The invention discloses a method, an apparatus and a computer program for detecting liquid leakage of a liquid transfer device by electronic equipment. There are many methods for detecting liquid leakage from liquid transfer devices based on pressure monitoring known to those skilled in the art. It is an object of the present invention to provide an alternative to the drop monitoring technical problem, which results in improved performance with respect to sample diversity. More particularly, the present invention discloses a method, apparatus and computer program for electronic drop monitoring of a liquid transfer device.

One subject of the invention is a method for detecting a liquid leak of a liquid transfer device, comprising the steps of:

a) using the liquid transfer device, aspirating liquid from a liquid-containing vessel,

b) moving the liquid transfer device to a position in the container a distance d above the liquid level,

c) measuring an electrical signal between the liquid transfer device and the liquid remaining in the container for a time deltat,

wherein a liquid leak of the liquid transfer device is detected if the electrical signal measured in step c) changes within the measurement time Δ t.

In the present invention, a liquid transfer device is any device adapted to aspirate a quantity of liquid at a first location and to dispense said quantity of liquid at a later time in one other location in one whole or in several parts at several other locations. However, if the liquid transfer device loses part of the sucked liquid over time, or if a droplet forms at the liquid transfer device, this is called a liquid leak within the scope of the present application.

In the present invention, the liquid to be aspirated will be provided in a container that in most cases contains more liquid than is required for a single aspiration process. Thus, a certain amount of liquid will remain in the container after the pumping process. The contact surface between the remaining liquid in the container and the ambient air is referred to as the liquid level in the container. The distance d of the liquid transfer device above said liquid level is defined as the vertical distance relative to the liquid-air contact surface. Thus, for the liquid level, all positions having a certain distance d represent a virtual plane above the liquid-air contact surface within the container.

In the present invention, electronic technology is used to detect liquid leakage from a liquid transfer device. If electrical excitation is applied to a medium, the medium will respond with an electrical signal, which is a measure of the electrical properties of the medium. Thus, if the electrical signal changes over time without altering the electrical excitation, this indicates that the electrical properties of the medium have changed.

Another aspect of the invention is a liquid transfer instrument with electronic leak detection, comprising:

a) suction means for sucking liquid from a container having liquid transfer means,

b) a moving means for placing said liquid transfer means containing liquid at a distance d above the liquid level in said container,

c) an electronic mechanism for detecting a liquid leak of the liquid transfer device, and

d) an electronic clock for controlling the liquid leakage detection time deltat,

wherein the electronic mechanism is capable of detecting a liquid leak of the liquid transfer device by exciting and measuring an electrical signal between the liquid transfer device and the remaining liquid in the container when the liquid transfer device is placed at the time at above the liquid level in the container by the distance d.

The phrase "suction device" covers all devices capable of sucking a controlled amount of liquid from a container containing said liquid using a liquid transfer device. Typically, such a suction device will operate using low pressure.

In the present invention, the moving means is a means capable of moving the liquid transfer means both vertically and parallel to the liquid level in the container.

In the present invention, the phrase "electronic mechanism" is intended to encompass a variety of electronic devices suitable for applying electrical excitation as well as measuring the electrical response of a medium. It is possible to use a single electronic mechanism having both features, or two separate electronic mechanisms, each having one feature.

The liquid transfer apparatus according to the invention comprises an electronic clock for controlling the time at of the detection of a liquid leak. In the present invention, the process of measuring an electrical signal while placing a liquid transfer device at a distance d above the liquid level in the container is referred to as liquid leak detection. The time Δ t of the liquid leakage detection is controlled by an electronic clock, and various electronic clocks are suitable in the present invention as long as they have sufficient accuracy.

A further aspect of the invention is a computer program executable by a liquid transfer apparatus according to the invention for detecting liquid leakage from a liquid transfer device, comprising the steps of:

a) defining an allowable liquid leakage rate V of the liquid transfer device as a function of the measurement time Deltat and the distance d of the liquid transfer device above the liquid level in the container_L，

b) Moving a liquid-containing liquid transfer device to a position above the liquid level in the container by the predetermined distance d, and

c) measuring an electrical signal between the liquid transfer device and the liquid in the container during the defined measurement time at,

wherein the leakage rate V of the detected leakage is determined if the electrical signal varies within the defined measurement time Deltat_LGreater than (4/3. pi. (d/2)³/Δt)。

The requirements of the liquid transfer means in terms of tightness vary depending on the time period required for carrying out the liquid transfer of the invention and the risk of cross-contamination. Thus, depending on the application of the liquid transfer device, different allowable liquid leakage rates V may be defined_L。

Drawings

FIG. 1: the liquid transfer device is placed above the liquid level in two steps (a) and three steps (b).

FIG. 2: a droplet is formed at the nozzle of the liquid transfer device.

FIG. 3: electrode means for measuring current or capacitance.

FIG. 4: schematic (a) of the tubular system of disposable and gripper and schematic electronic mechanism (b) to effect the inspection of the resistive droplets.

FIG. 5: electrical signal for positive drop inspection.

FIG. 6: an example of a drop check for an unacceptable electrical signal.

FIG. 7: an example of a drop check for an unacceptable electrical signal.

FIG. 8: an example of a drop check for an unacceptable electrical signal.

Detailed Description

b) moving the liquid transfer device to a position in the container a distance d above the liquid level, and

In the present invention, a liquid transfer device is any device adapted to aspirate a quantity of liquid at a first location and to dispense said quantity of liquid at a later time in one other location in one whole or in several parts at several other locations. The liquid transfer process must be controlled so as not to cause erroneous results, in particular for detecting any possible leakage of the transfer device. However, aspiration sample volume and completion of the dispensing process are also sources of liquid transfer process error.

Leakage control of liquid transfer devices is important not only because the amount of liquid being transferred must be accurate, but also because of the risk of liquid leakage creating cross-contamination during the transfer process. Depending on the design of the experimental setup, the liquid transfer device will follow its path across some part of the setup to the dispensing position, and the loss of droplets leads to contamination of the setup. Using a mechanism with, for example, a microplate, the liquid transfer device will span a certain number of wells during the transfer process, and loss of droplets can lead to cross-contamination of the sample.

Obviously, the requirements for the liquid transfer device with respect to contamination by liquid leakage depend on the design of the experimental setup. For liquid transfer processes that take a long time, acceptable liquid leakage will be small, and where the liquid transfer device spans a large number of other containers.

In the present invention, electronic technology is used to detect liquid leakage from a liquid transfer device. If electrical excitation is applied to a medium, the medium will respond with an electrical signal, which is a measure of the properties of the medium. Thus, if the electrical signal changes over time without altering the electrical excitation, this indicates that the electrical properties of the medium have changed. For example, if the gap between the two electrodes is filled with air, the current response to the applied potential will be negligible because of the extremely high resistance of air. However, if the voids are now filled with electrolyte due to the formation of droplets, the current response to the same applied potential will increase significantly due to the smaller resistance of the electrolyte.

The electronic technique of the present invention has at least its advantages independent of sample density compared to pressure monitoring techniques well known to those skilled in the art. If pressure measurements are used to detect leaks, the technician has to consider that the pressure curve depends on the density of the sample fluid. In other words, due to the density difference, the pressure curves of the two samples may be different and thus may hinder the detection of a leak.

The distribution of sample density (e.g., almost 10% of the blood sample) has no effect on the performance of the electronic drop monitoring technique. The present invention is based in part on the following findings: the effect of sample density on leak detection can be eliminated by using an electronic drop monitoring technique.

It is noted that a falling droplet having a diameter smaller than the distance d between the liquid transfer device and the liquid level cannot be detected by the mechanism of the present invention. It is essential that the liquid droplets formed at the nozzle of the liquid transfer device establish a liquid connection bridge between the liquid transfer device and the liquid level, wherein said liquid connection bridge can be periodic (liquid droplets are formed periodically) or continuous (stationary flow).

This is another difference compared to pressure monitoring techniques, since here the pipette position is arbitrary. In other words, to implement the electronic drop monitoring technique of the present invention, a thorough understanding of drop formation and pipette position is a prerequisite.

Theoretically, if a capacitance measurement is made which is sensitive enough to detect such small changes in the dielectric environment of such a liquid transfer device, it is of course possible to detect the formation of droplets as well without a liquid connection bridge between the liquid transfer device and the liquid level. Thus, if such sensitive measurements are made within the scope of the present invention, the requirement to place the liquid transfer device at a certain distance d above the liquid level in the container is no longer necessary.

In a preferred method according to the invention, said suction step a) is carried out using a device for generating a depression, preferably an air pump or a hose system filled with water.

For the aspiration of the liquid, the liquid transfer device must be partially immersed in the liquid in the container. Because the liquid transfer device is in contact with the liquid within the sample with a risk of contamination and because the liquid will wet the surface of the liquid transfer device, it is preferred to have the immersion depth of the liquid transfer device as small as possible. It is noted that it is possible that liquid outside the liquid transfer device may merge and drip at some later time.

Since the liquid level in the container will vary during the pumping process, the position of the liquid transfer device must be continuously adjusted. To ensure a sufficient immersion depth of the liquid transfer device throughout the aspiration process, it may be necessary to increase the immersion depth of the liquid transfer device above the required minimum.

As the liquid transfer device is immersed in the liquid in the container, suction may be applied by applying a low pressure, preferably using an air pump, such as a standard syringe. Also preferred is a hose system filled with system fluid, such as a suction pump.

In another preferred method according to the invention, the liquid transfer device is a pipette tip.

In the present invention, the phrase "pipette tip" is intended to cover all kinds of hollow objects having two openings, one for connecting to the device for generating low pressure and the other for aspirating liquids. Disposable pipette tips are preferably used in order to avoid sample contamination and therefore the connection between the device for generating low pressure and the pipette tip must be reversible. Since the pipette tip is preferably disposable, it is intended to use plastic tips. On the other hand, for certain embodiments, it is preferred to provide a pipette tip that is electrically conductive to use the pipette tip as an electrode for the electronic mechanism. It is also preferred that the pipette tips are equipped with filters to avoid contamination of the device for generating the low pressure.

In a more preferred method according to the invention, the pipette tip has a capacity of 0.1 ml to 100 ml, mainly preferably 1ml to 10 ml. The pipette tip preferably has an opening with a diameter of 0.1 mm to 10 mm.

In a further preferred method according to the invention, the liquid transfer device in step b) is first moved to a second position, which is located a second distance d above the liquid level in the container, before the liquid transfer device is placed in the container at the position a distance d above the liquid level in the container₂And then moved closer to the liquid.

If the level detection is not possible or only possible by mistake during the removal of the liquid transfer deviceSuch an embodiment of the invention can be used. In other words, the liquid transfer device is first moved to a distance d above the liquid level₂Thereafter, the liquid transfer device is brought into proximity or contact with the liquid level to detect the liquid level. After said level detection, the liquid transfer device is placed at its final distance d (see fig. 1 b).

Furthermore, due to the viscosity of the liquid, the contact between the liquid transfer device and the liquid in the container will not be interrupted until a certain distance d' above the liquid level of the liquid transfer device is reached. Thus, if the distance d is less than the distance d', in certain embodiments, the liquid transfer device must first be moved to a second distance d greater than the distance d₂And then the liquid transfer device can be placed at its final distance d (see fig. 1 b).

It is noted that if the leakage rate is too high, it will prevent the liquid transfer device from being positioned exactly at the distance d according to the procedure shown in fig. 1a and 1 b. In positioning the liquid transfer device, positioning will be inaccurate or even impossible if the liquid drain has formed a droplet.

In another preferred embodiment of the method according to the invention, said distance d of said liquid level in said container from said liquid transfer means will be less than a volume V_dOf the liquid droplet (which may form at the liquid transfer device).

As previously mentioned, in most cases, electronic liquid leak detection requires a liquid connection bridge between the liquid transfer device and the liquid in the container (see fig. 2). If the distance d between the liquid transfer device and the liquid in the container is too large, drops of liquid formed at the nozzle of the liquid transfer device will fall due to gravity before the liquid bridge is formed. It is therefore important to adjust the distance d with respect to the viscosity of the liquid and the geometry of the liquid transfer device to create a liquid connecting bridge before the drop lands. Theoretically, if a capacitance measurement is made which is sensitive enough to detect such small changes in the dielectric environment of such a liquid transfer device, the formation of droplets can also be detected without a liquid connection bridge between the liquid transfer device and the liquid level.

In a further preferred embodiment of the method according to the invention, the volume V of the droplets_dPredetermined by the geometry of the liquid transfer device and the surface tension of the liquid.

The surface tension at the liquid-air interface defines the maximum droplet size that can be formed at a given nozzle geometry before gravity causes the droplets to drop. Without wishing to be bound by theory, according to V_d(2 · pi · a · σ)/(g · ρ), volume V of the droplet_dIt will be larger for fluids with high surface tension and low density, whereas a is the opening diameter of the liquid transfer device, σ is the surface tension and ρ is the density of the fluid.

In a more preferred embodiment of the method according to the invention, the volume V of said droplets_dIs 1. mu.l to 1ml, preferably 3. mu.l to 300. mu.l.

The use of pipette tips with an opening diameter of about 0.7mm for processing e.g. plasma will form droplets with a volume of 4 to 30 μ l. With aqueous reagents or larger opening diameters, the drop volume will increase according to the above formula.

In a preferred embodiment of the method according to the invention, said distance d between said liquid transfer device and said liquid level in said container will be from 1mm to 15mm, preferably from 2mm to 4 mm.

It is noted that for most embodiments the distance d between the liquid transfer device and the liquid level in the container must be slightly smaller than the diameter of the droplet to form a liquid connecting bridge before the droplet lands. The distance d between the liquid transfer device and the liquid level in the container may also be larger than the droplet diameter if a capacitance measurement is made which is sensitive enough to even detect droplet formation.

A preferred method according to the invention is a method wherein said electrical signal measured in step c) is the electrical current between said liquid transfer device and said remaining liquid in said container.

In order to measure the current between the liquid transfer device and the liquid in the container, an electrical potential has to be applied between the two electrodes. Preferably, the liquid transfer device itself is one of the two desired electrodes (fig. 3b and 3 c). For this purpose, it is of course necessary to use electrically conductive liquid transfer means. But it is also possible to use an insulated liquid transfer device and a single electrode within the liquid transfer device (fig. 3 a).

For the second desired electrode there are mainly two (to) possible embodiments. In one embodiment, a single electrode is immersed in a container containing the liquid to be transferred (see fig. 3a and 3 b). In another preferred embodiment, the container containing the liquid to be transferred represents the second electrode itself and therefore needs to be electrically conductive (fig. 3 c).

Another preferred method according to the invention is a method wherein said electrical signal measured in step c) is a capacitance dependent on the dielectric environment of the liquid transfer device.

To measure the capacitance between the liquid transfer device and the liquid-containing vessel, an alternating voltage is applied. The capacitance C between the two electrodes depends on the dielectric constant ε of the connecting materials and their distance d, in terms of C- ε/d. Thus, if the space between the liquid transfer device and the container is gradually filled with liquid, the capacitance will increase due to the higher dielectric constant of the liquid (air ∈ 1, water ∈ 80).

As described for current measurement, there are also different possible electrode mechanisms for capacitance measurement. The liquid transfer device itself may be configured as a first electrode, while the container containing the liquid to be aspirated may form a second electrode. A more sophisticated method for cLLD is disclosed in EP 555710, wherein both electrodes belong to the liquid transfer device.

Yet another preferred method according to the invention is a method wherein said capacitance is measured by an electromagnetic field generated by said liquid transfer device.

Without intending to be bound by theory, the electromagnetic field created by the liquid transfer device is dependent on the dielectric environment. Thus, if the dielectric properties between the liquid transfer device and another remote electrode change over time, the electromagnetic signal measured at the remote electrode will change.

The frequency of the electromagnetic field should be rather high in order to increase the measured voltage difference when the dielectric environment changes, since the voltage difference depends on the ac resistance of the capacitance (which is inversely proportional to the ac frequency). On the other hand, at high frequencies, problems caused by radiation occur and expensive equipment becomes necessary. Therefore, the frequency must be optimized. In a preferred method according to the invention, the frequency applied is 50 kHz.

In a more preferred method according to the invention, the liquid transfer device generates an electromagnetic field and measures an electromagnetic signal.

In this preferred embodiment, the liquid transfer device not only generates an electromagnetic field, but also serves as a second electrode which measures an electromagnetic signal dependent on the dielectric environment of the liquid transfer device. Such an electrode mechanism is illustrated in fig. 3e), wherein the container is grounded. It is clear that the liquid transfer device must be electrically conductive in order to achieve the mechanism described above.

Such a preferred liquid transfer device suitable for the electrode mechanism described in fig. 3e) is for example described in US 5,304,347. Here, the liquid transfer needle forms a coaxial electrode array with two surrounding coaxial electrodes, both of which are electrically insulated from the needle and from each other. This application also discloses a suitable detection circuit for the coaxial electrode array, which uses an ac power supply with a relatively high frequency (about 50 kHz).

In a preferred embodiment of the method according to the invention, the measurement time Δ t of the electrical signal is at least 1 second, preferably 1 to 4 seconds.

The time taken for measuring the electrical signal depends on the permitted leakage rate V_L. If no electrical signal is detected for the measurement time Δ t, the leak rate V_LLess than (4/3. pi. (d/2)³,/Δ t). In other words, increasing the time without any electrical signal passing through the liquid transfer device as required will reduce the leakage rate allowed by the device. Furthermore, the rate of liquid leakage allowed by the device depends on the transfer time t required to move the liquid transfer device from the aspirating position to another position for dispensing, since no droplet formation can occur during this time.

Another preferred embodiment of the method according to the invention comprises the following further steps:

d) drawing in a quantity of air V_A，

e) Moving the liquid transfer device to a remote location, and

f) the liquid is dispensed in a manner such that,

provided that the electrical signal measured in step c) does not change during said measurement time Δ t.

In this embodiment of the method according to the invention, after the liquid transfer device has passed the liquid leak test of step c), a certain amount of air V is drawn in by suction_AAn additional amount of security is obtained. This amount of air sucked up will increase the time until droplet formation becomes possible and thus reduce the risk of liquid leakage during the movement of the liquid transfer device to a remote location where all or part of the sucked up liquid should be dispensed.

In another preferred embodiment of the method according to the invention, the suction of air is performed using a device that generates a depression.

As previously mentioned, the low pressure is preferably generated using an air pump, such as a standard syringe, or a system of hoses filled with system fluid, such as a suction pump.

In a further preferred embodiment of the method according to the invention, the amount of air V_AGreater than (V)_dT, wherein it takes time t to move the liquid transfer device to the remote location.

The amount of air drawn depends on the liquid leakage rate V of the liquid transfer device_L＝(V_dAt) and the time t required to move the liquid transfer device to the remote dispensing position. If no electrical signal is detected in step c), it will be known that the leakage is below V_L. Therefore, if the amount of air V sucked is_AGreater than (V)_dT, no droplet formation will occur for time t.

In a more preferred embodiment of the process according to the invention, said amount of air V_AAt least 3. mu.l, preferably 5 to 500. mu.l.

It is noted that the maximum amount of air that can be sucked up depends on the geometry of the liquid transfer device. If the amount of air being sucked is too large, the air will enter the liquid transfer device in the form of bubbles.

For the dispensing step f), the liquid is dispensed by relieving the depression applied for aspiration. Alternatively, the dispensing process may be performed by applying high pressure.

In a further preferred embodiment of the method according to the invention, the distance d between the liquid transfer device and the liquid level in the container is adjusted based on a Liquid Level Detection (LLD), preferably by electronic measurement.

For carrying out the method according to the invention it is important to place the liquid transfer device at a known distance d from the liquid level in the container, since the liquid leakage rate of the liquid transfer device can only be determined if the distance is accurately known. It is therefore necessary to detect the level of liquid in the container before positioning the liquid transfer device. In the present invention, detecting the liquid level in the container is referred to as Liquid Level Detection (LLD).

The level of liquid in the container after the suction can be detected during withdrawal (fig. 1a) or by subsequent access to a liquid transfer device (fig. 1 b). As mentioned before, the procedure of fig. 1b can be used if no level detection or only a false detection can be performed during the removal of the liquid transfer device, e.g. when the liquid tends to form a meniscus before the liquid connection bridge is broken.

For the method according to the present invention, it is preferred that the electronic LLD comprises measuring a current between the liquid transfer device and the liquid inside the container or measuring a capacitance depending on the dielectric environment of the liquid transfer device.

As mentioned before, if the leakage rate is too high, it will prevent the liquid transfer device from being positioned exactly at the distance d according to the procedure shown in fig. 1a and 1 b. In positioning the liquid transfer device, positioning will be inaccurate or even impossible if the liquid drain has formed a droplet.

In a preferred embodiment of the method according to the invention, the liquid comprises a biological sample, nucleotides, enzymes and/or buffer solutions.

The method of the present invention is suitable for various applications requiring liquid treatment. Without limiting the scope of the invention, a reasonable application is high throughput analysis of biological samples, such as blood screening applications. Another example is the preparation of multiplex PCR amplifications in the form of microplates, where various reagents such as nucleotides, enzymes and buffer solutions must be prepared.

d) an electronic clock for controlling the time deltat of the liquid leakage detection,

The liquid transfer apparatus according to the present invention is capable of detecting a liquid leak of the liquid transfer device with electronic means. In order to achieve the performance of its intended use, the liquid transfer device must be positioned a certain distance d above the liquid level in the container before the electronic measurement of the electronic mechanism, since only an accurate knowledge of the distance is possible to determine the liquid leakage rate of the liquid transfer device.

Furthermore, in order to accurately determine the liquid leakage rate of the liquid transfer device, it is also necessary to accurately monitor the time Δ t of liquid leakage detection by the electronic mechanism. Therefore, the liquid transfer apparatus according to the invention must comprise an electronic clock for controlling said time Δ t of the liquid leakage detection.

In a preferred embodiment of the liquid transfer apparatus according to the invention, the liquid transfer device is a pipette tip.

The meaning of the phrase "pipette tip" has been explained above and preferably the pipette tip is electrically conductive in order to simplify the electronic mechanism of the liquid transfer instrument.

In another preferred embodiment of the liquid transfer apparatus according to the invention, the suction device is a device for generating low pressure.

In the present invention, the suction device for sucking liquid from a container with a liquid transfer device is a device for applying low pressure, preferably an air pump such as a standard syringe or a system of hoses filled with system fluid such as a suction pump.

In a further preferred embodiment of the liquid transfer apparatus according to the invention, the suction device is a device which is also used to suck air.

Aspirating a quantity of air after aspirating the liquid will reduce the liquid leakage rate of the liquid transfer device and can avoid the formation of droplets in the time required to move the liquid transfer device to its dispensing position. It is noted that bubble formation will limit the suction of air as previously described.

The phrase "electronic device" encompasses various devices capable of generating DC (direct current) or AC (alternating current) excitation and measuring the electrical response of the excited system.

In a further preferred embodiment of the liquid transfer apparatus according to the invention, the electronic mechanism is capable of detecting a liquid leakage of the liquid transfer device by exciting and measuring an electrical signal between the liquid transfer device and the remaining liquid in the container, and if the electrical signal changes within the measurement time Δ t, the liquid leakage of the liquid transfer device is detected.

In a further preferred embodiment of the liquid transfer apparatus according to the invention, the liquid leakage of the liquid transfer device is detected if the electrical signal changes within the measurement time Δ t.

In other words, the detection of a liquid leak of the liquid transfer apparatus according to the invention is based on a change in electrical signal between the liquid transfer device and the liquid remaining in the container during the measurement time Δ t.

As previously mentioned, a liquid leak of the liquid transfer device will change the dielectric environment of the liquid transfer device and may form a conductive liquid connection bridge to the remaining liquid in the container. Monitoring the electrical properties of the space between the liquid transfer device and the remaining liquid in the container for a certain time deltat provides the opportunity to detect the presence of a liquid leak and to estimate the value of the liquid leak.

In a further preferred embodiment of the liquid transfer apparatus according to the invention, the electronic means is capable of measuring a current between the liquid transfer device and the remaining liquid in the container or measuring a capacitance dependent on the dielectric environment of the liquid transfer device.

In the case of a DC measurement, a periodic or constant liquid connection bridge between the liquid transfer device and the remaining liquid in the container can be detected upon a sudden increase in current. In making the AC measurement, the capacitance between the liquid transfer device and the remaining liquid in the container may be measured.

There are several different electrode mechanisms to perform the two types of measurements possible within the scope of the invention. Preferably, the liquid transfer device itself is one of the two desired electrodes (fig. 3b and 3 c). For this purpose, it is of course necessary to use electrically conductive liquid transfer means. But it is also possible to use an insulated liquid transfer device and a single electrode within the liquid transfer device (fig. 3a and 3 d).

In another preferred embodiment of the liquid transfer apparatus according to the invention, the electronic mechanism comprises a second electrode to measure an electrical signal between the liquid transfer device and the second electrode.

In a more preferred embodiment of the liquid transfer apparatus according to the invention, the second electrode is a reservoir.

There are mainly two possible embodiments for the second desired electrode. In one embodiment, a single electrode is immersed in a container containing the liquid to be transferred (see fig. 3 b). In another preferred embodiment, the container containing the liquid to be transferred represents the second electrode itself and therefore needs to be electrically conductive (fig. 3 c).

In a further preferred embodiment of the liquid transfer apparatus according to the invention, the liquid transfer device is capable of generating an electromagnetic field and measuring an electromagnetic signal dependent on the dielectric environment of the liquid transfer device, while the container is grounded.

If capacitance is measured, the liquid transfer device may be configured such that the generated electromagnetic field is distributed into the dielectric environment of the liquid transfer device. In addition, the liquid transfer device may be configured such that it can also measure electromagnetic signals from the dielectric environment. In this case it is preferred that the container is grounded and that an electrical potential is applied between the liquid transfer device and said ground (fig. 3 e).

In a further preferred embodiment of the liquid transfer apparatus according to the invention, the distance d between the liquid transfer device and the liquid level in the container is smaller than a droplet diameter at which the droplet can be formed, and the diameter of the droplet is predetermined by the geometrical dimensions of the liquid transfer device and the viscosity of the liquid.

The distance d between the liquid transfer device and the liquid level in the container depends on the diameter of the liquid droplet, which can form at the liquid transfer device. The diameter itself depends on the surface tension of the liquid used and the geometry of the opening of the liquid transfer device. These correlations have been elucidated in detail above.

Another preferred embodiment of the liquid transfer apparatus according to the present invention further comprises a Liquid Level Detection (LLD) to adjust said distance d between said liquid transfer device and said liquid level in said container, preferably said LLD is an electronic LLD.

In a more preferred embodiment of the liquid transfer apparatus according to the present invention, said electronic LLD comprises means for measuring a current between said liquid transfer device and said liquid in said container or measuring a capacitance dependent on the dielectric environment of the liquid transfer device.

A liquid transfer apparatus can only correctly determine the leakage rate of a liquid transfer device if the distance d between said liquid transfer device and said liquid level in said container is accurately adjusted. It is therefore necessary to detect the level of liquid in the container and then to position the liquid transfer device, and this is preferably done using electronic measurement means.

Before the computer program according to the invention can be run, it is necessary to define the permitted leakage rate V of the liquid transfer device on the basis of the measurement time at and the distance d of the liquid transfer device above the liquid level in the container_L. Allowable liquid leakage rate V_LDepending on the time required to move the liquid transfer device to the dispensing position, the required dispensing accuracy and the risk of sample contamination.

If no change in the electrical signal measured in step c) is detected within the measurement time Δ t, the liquid leakage rate V_LLess than (4/3. pi. (d/2)³,/Δ t). If the size of a droplet that can be formed at the liquid transfer device is identified using information about the geometry of the liquid transfer device and the surface tension of the liquid, then a distance d of the liquid transfer device above the liquid level in the container can be defined.

In a preferred embodiment of the computer program according to the invention, the electrical signal is a current between the liquid transfer device and the remaining liquid in the container or a capacitance depending on the dielectric environment of the liquid transfer device.

In another preferred embodiment of the computer program according to the invention said distance d between the liquid transfer device and the liquid level in said container is smaller than the volume V_dThe droplet being formable at the liquid transfer device and having a volume V_dPredetermined by the geometry of the liquid transfer device and the surface tension of the liquid.

In yet another preferred embodiment of the computer program according to the invention the distance d between the liquid transfer device and the liquid level in the container is adjusted based on a Liquid Level Detection (LLD), preferably the LLD is performed by electronic measurement.

In yet another preferred embodiment of the computer program according to the present invention said LLD is performed by measuring a current between said liquid transfer device and said liquid in said container or by measuring a capacitance depending on the dielectric environment of the liquid transfer device.

The following examples and figures are provided to aid the understanding of the present invention, the true scope of which is set forth in the appended claims. It will be understood that various modifications can be made in the procedures set forth without departing from the spirit of the invention.

Examples

In the drop inspection measurements of the liquid transfer instrument according to the invention, the potential-time graphs of fig. 5 to 8 were recorded.

The liquid transfer apparatus used was a self-made prototype equipped with a piston driven air pump 1 (see fig. 4a, discharge capacity of about 5 ml) connected via a plastic tube 2 (see fig. 4a, internal diameter 1.6 mm) to a gripper unit 3 (see fig. 4a), said gripper unit 3 being able to retrieve disposable plastic nozzles 4. The entire pipetting system (also called pipettor, including air pump, connecting tube and gripper) is arranged on an x, y, z movable table, so that the disposable nozzle can be moved to a container to aspirate a certain amount of sample, checked for droplet loss according to the invention, and then transferred to another container, which is located at a desired position accessible to any pipettor.

In the present invention, a disposable nozzle having the following features is used: a maximum suction volume of 3.5ml, equipped with a filter 5 (see fig. 4a) to avoid clarification of the holder (pore size 30-80 microns), made of conductive plastic (mainly polypropylene), nozzle opening diameter 0.8 mm and total length 104 mm.

The container containing the sample to be aspirated (for this example) has the following features: a standard 10 ml sample tube (Becton Dickinson), such as those commonly used for blood screening applications, is made of conductive polypropylene, has a cylindrical shape, and has a diameter of 13.3 millimeters.

The experiments were performed with negative human plasma in EDTA (from endogenous sources) on a home-made instrument with the following mechanical functional parts: a pipetting robot capable of moving the disposable nozzle in x, y, z, an apparatus for aspirating/dispensing sample volumes at a controllable pipetting rate, and a gripper comprising a retrieval of the disposable prior to aspiration and a disposal of the disposable after aspiration. Furthermore, the instrument used is equipped with capacitance and resistance measuring devices to perform electronic drop monitoring according to the invention.

Using conductive disposables, the liquid transfer instrument is able to generate an electromagnetic field at the pipette tip and measure an electrical signal that is dependent on the dielectric environment, enabling capacitive liquid level detection (cLLD) without the need for an additional second electrode. However, the instrument is equipped with a second electrode (see fig. 4b, made of copper) immersed in the sample in the container, enabling additional resistive liquid level detection (rLLD), wherein the current is measured between the second electrode and the pipette tip.

Using an instrument according to the invention with cLLD and resistive droplet detection, an exemplary pumping process for droplet inspection measurements comprises the following steps:

1. moving gripper units onto disposable item guides

2. Retrieving disposable items with a gripper unit

3. Moving a gripper (pipette) with a disposable to a sample rail

4. Accessing samples with activated cLLD

5. After the liquid level was detected, the sample was pierced by 1.5 mm

6. Aspirate 850 microliter sample

7. Remove pipette from sample (raise pipette above sample, not contact liquid- > cLLD Low)

8. Activating the rLLD and monitoring the rLLD signal current

9. Access to sample liquid with cLLD set in working condition

10. When the liquid level is found (cLLD high), withdraw the pipette a full 2mm from the cLLD position

11. Obtaining a rLLD signal for at least 3 seconds to check the sealability of the disposable nozzle

It is noted that basically, the instrument according to the invention does not require two different methods for level detection, it being sufficient to be able to realize one of the capacitive or resistive detections. However, implementing both techniques provides enhanced flexibility in the design of suitable measurement programs.

The experimental data of fig. 5 shows rLLD data obtained in a typical drop inspection measurement. rLLD monitoring begins at step 8 of the process described above, just after aspiration of the nominal volume, when the pipette is brought close to the liquid level for a second time. The contact surface causes the rLLD signal to produce a sudden decrease in signal voltage (indicated by a "1" in fig. 5). After this rLLD detection, the pipettor is automatically withdrawn from the surface and positioned 2mm above the liquid level. During this movement, the negative rLLD signal undergoes an exponential decrease, and at this point, when the physical contact between the disposable and the sample is broken, the rLLD signal jumps back to its "non-contact level" (at time t 500 milliseconds, indicated by "2" in fig. 5). During the subsequent 5.5 second hold period, there was no change in the rLLD signal, confirming that the gap between the liquid level and the disposable nozzle was maintained, which means that the results of the drop check were positive. At time "3", the pipette is moved to the destination container for dispensing.

Fig. 6 to 8 show the case of a drop check failure, in which the rate of leakage of the disposable is sufficiently large to be detectable with the method according to the invention.

In fig. 6, in addition to the ramps denoted by "1", "2" and "3" already explained in accordance with fig. 5 in the drop inspection program, two signal spikes (denoted by "4") also occur in the rLLD signal. Both of these spikes indicate droplets formed during the hold period, allowing a brief contact between the disposable and the sample liquid. Between two droplets there is no contact between the disposable and the sample liquid once the droplet landing signal switches back to a non-contact level.

Fig. 7 shows another rLLD signal recorded during the drop check procedure, which indicates an intensely dripping disposable that formed 9 drops during the same hold time as fig. 6.

Fig. 8 shows another type of drop check failure detected by recording the rLLD signal. Here, after the formation of two droplets (represented by the spikes as depicted in fig. 6 and 7), the disposable experienced a constant flow pattern of liquid leakage (starting at about 3000 milliseconds).

The all unsealed or drip disposable of this example was prepared by scoring the interface between the disposable and the disposable controller.

Claims

1. A method for detecting a liquid leak of a liquid transfer device, comprising the steps of:

a) using the liquid transfer device, withdrawing liquid from a liquid-containing vessel,

2. Method according to claim 1, wherein prior to placing said liquid transfer device in said position in said container at a distance d above said liquid level in said container in step b), the liquid transfer device is first moved to a second position which is located at a second distance d above said liquid level in said container₂And then moved closer to the liquid.

3. Method according to claims 1-2, wherein the distance d between the liquid level in the container and the liquid transfer device is less than a volume V_dWherein the droplet is likely to form at the liquid transfer device.

4. A method according to claims 1-3, wherein said electrical signal measured in step c) is the current between said liquid transfer device and said remaining liquid in said container.

5. Method according to claims 1-4, wherein the electrical signal measured in step c) is a capacitance dependent on the dielectric environment of the liquid transfer device.

6. The method according to claims 1-5, comprising the further steps of:

d) drawing a certain amount of air V_A，

e) Moving said liquid transfer device to a remote location, and

f) the liquid is dispensed in a manner such that,

7. Method according to claims 1-6, wherein the distance d between the liquid transfer device and the liquid level in the container is adjusted based on Liquid Level Detection (LLD), preferably the LLD is performed by electronic measurement.

8. A liquid transfer instrument with electronic liquid leak detection, comprising:

9. A liquid transfer apparatus according to claim 8, wherein said liquid leak of said liquid transfer device is detected if said electrical signal changes within a measurement time Δ t.

10. A liquid transfer apparatus according to claim 9, wherein the electronic means is capable of measuring a current between the liquid transfer device and the remaining liquid in the container or measuring a capacitance dependent on the dielectric environment of the liquid transfer device.

11. A liquid transfer apparatus according to claims 8-10, wherein the distance d between the liquid transfer device and the liquid level in the container is smaller than a droplet diameter at which the droplet can be formed, and wherein the diameter of the droplet is predetermined by the geometry of the liquid transfer device and the surface tension of the liquid.

12. Liquid transfer apparatus according to claims 8-11, further comprising a Liquid Level Detection (LLD) to adjust the distance d between the liquid transfer device and the liquid level in the container, preferably the LLD is an electronic LLD.

13. A computer program executable by a liquid transfer apparatus according to claims 8-12 for detecting liquid leakage of a liquid transfer device, comprising the steps of:

14. A computer program according to claim 13, wherein the electrical signal is a current between the liquid transfer device and the remaining liquid in the container or a capacitance dependent on a dielectric environment of the liquid transfer device.

15. A computer program according to claims 13-14, wherein said distance d between the liquid transfer device and the liquid level in said container is less than V_dWherein the droplet can be formed at the liquid transfer device, and wherein the volume V of the droplet_dFrom said liquidThe geometry of the body transfer device and the surface tension of the liquid are predetermined.

16. Computer program according to claim 13-15, wherein the distance d between the liquid transfer device and the liquid level in the container is adjusted based on Liquid Level Detection (LLD), preferably by electronic measurement.