Capacitive liquid volume measurement

Abstract

A laboratory automation device with a liquid volume measurement function includes a table, a pipettor including a pipetting head having an electrode that provides a reference electrode for a capacitive sensor. The robotic arm is configured to move the pipette head over the table. The processor is operatively coupled to the robotic arm, the pipettor, and the electrode by electronic circuitry. The capillary tube is located on a table having an opening for receiving a target amount of liquid from the pipettor to form a gas-liquid meniscus in the capillary tube. The robotic arm is configured to hover the electrode over the capillary to detect a change in capacitance associated with a position of the meniscus, and the processor is configured to calculate a transfer amount of the liquid based on the position of the meniscus in the capillary.

Description

TECHNICAL FIELD

[0001] The present invention relates to a laboratory automation device with a liquid volume measurement function based on a capacitive measurement. Another aspect relates to a method for determining the volumetric performance of a laboratory automation device using a capacitive measurement and a computer program for performing the method. BACKGROUND

[0002] Automation of diagnostic or clinical laboratory workflows is of paramount importance as the number of samples significantly increases, requiring faster turnaround times, and thus certain operations need laboratory automation devices to accomplish tasks that were previously performed manually. For example, laboratory automation devices have facilitated the rapid development of high-speed testing methods that can test very high numbers of samples at relatively low cost during the COVID pandemic. Laboratory automation devices include i) robotic arms for moving or manipulating laboratory instrument components on a worktable of the laboratory automation device, and ii) pipettes for aspirating and / or dispensing liquids in laboratory instrument components, which can include multiple (e.g., eight) pipette tips coupled to the robotic arms, which can be separate from another robotic arm for manipulating laboratory instrument components; iii) sample processing devices such as stirrers, heaters, coolers, thermal cyclers, analytical testing devices such as microplate readers, DNA preparation devices, DNA sequencers including microfluidic chips, etc.

[0003] The space of the worktable of the laboratory automation device is limited, leading to a narrow arrangement of laboratory instrument components and laboratory instruments with miniaturized dimensions. This requires precise positioning of laboratory instrument components and liquid pipettes, and precise movements of the robotic arms.

[0004] Sample volumes can be in the range of picoliters or sub-picoliters, and thus accurate aspiration and dispensing of small volumes is of paramount importance for reliable and robust operation of the laboratory automation device. Regular functional checks by a user of the device or quality control (QC) checks and / or calibration of dispensed volumes by a field service engineer can be required. Some testing methods are standardized and contained in the ISO 23783-2 standard: “Automatic liquid handling systems - Determination of volumetric performance procedure”.

[0005] The dispensed volume can be measured gravimetrically, requiring a high-precision microbalance, which is expensive and special precautions must be taken to prevent evaporation of the sample. For example, the precision and delicate calibration standards used can be damaged during transport. Alternatively, an absorbance system based on a photometer and a liquid containing a dye of known concentration is used, which requires additional dye solution and an expensive photometer. The ISO 23783-2 standard summarizes the single-dye, double-dye, and fluorescent dye methods.

[0006] US20140150522A1 discloses a measuring device comprising one or more capillary tubes to measure the volume of dispensed fluid. The fluid is manually pipetted and sucked into the fine capillary tube, the position of the meniscus (air-liquid phase boundary) is detected using a viewing window, which together with the dimensions of the capillary tube determines the dispensed volume. The position of the meniscus can be determined by the person observing the capillary tube or by a separate dedicated sensor.

[0007] US20080233009A1 discloses volume calibration using capillary tubes based on visual detection of the meniscus using a scale. A robotic arm of an automated workstation moves the liquid volume for calibration into the opening of the capillary tube.

[0008] DE102020103211A1 discloses a device with multiple capillary tubes for volume calibration, the meniscus position of each capillary tube is detected with a digital camera or flatbed scanner. Detailed information on deriving the exact position of the fluid front from the pixelated image and calculating the volumetric performance of the automated liquid handler can be found in ISO 23783-2.

[0009] US20240217102A1 discloses a method for precisely positioning a robotic arm on a worktable of a laboratory automation device. The robotic arm comprises a first electrode, the arm scans over a capacitive reference object which provides a measurement capacitor with the first electrode. The reference object is located at a known position on the worktable, has a specific three-dimensional shape, e.g. a concave triangle, defines different heights for the dielectric (air). The detection of the shape of the reference object is used to precisely position the robotic arm.

[0010] US20160356737A1 discloses an electronic circuit for detecting a change in capacitance in a measurement capacitor formed between an electrode (pipette tip) and a worktable to detect the liquid level in a test tube and to distinguish between the presence of liquid or foam in the test tube. The electronic circuit comprises at least one comparator unit which detects the charging time of the measurement capacitor in response to a supply voltage directed to the electrode. SUMMARY

[0011] The pipetting volume of an automated liquid handler has to be measured accurately for quality control (QC) and periodic function tests. Current methods require external and expensive devices like a balance and a photometer, which are inconvenient to transport and / or require a trained field service engineer (FSE) for quality checks. There is a need for an automated and reliable method to detect the dispensed volume integrated in a laboratory automation device, which can easily be used for periodic function or quality checks made by the device user or a field service engineer.

[0012] It is an object of the present invention to overcome the drawbacks of the prior art and to provide a laboratory automation apparatus with a volume calibration function using a capillary without the need to add an external analytical testing device. It is an object to provide a simple method for measuring the dispensed volume of a laboratory automation apparatus based on a capacitive volume measurement of a liquid dispensed in a capillary. It is a further object to provide a computer program for performing the method.

[0013] The independent claims solve these objects, further exemplary embodiments are apparent from the dependent claims and the following description including the drawings.

[0014] One aspect of the present invention relates to a laboratory automation apparatus or laboratory system with a liquid volume measurement function. The laboratory automation apparatus comprises a worktable defining an x-y plane and an automated liquid handler with a pipette comprising a pipette head or pipette channel with an electrode. The electrode in combination with a reference electrode provides a capacitive sensor or measurement capacitor. A robot arm is configured to move the pipette head with the electrode in a space above the worktable. A processor is operatively coupled to the robot arm, the pipette and the electrode by electronic circuitry. A capillary or microfluidic chip is located on the worktable at a defined x-y position, at least a portion of the capillary (or chip) is oriented substantially parallel to the worktable. The capillary comprises an opening for receiving a target amount of liquid from the pipette and is further configured to draw the liquid from the opening into the capillary to form a gas-liquid meniscus. The robot arm is configured to hover the electrode of the pipette head above the capillary to detect a change in capacitance of the measurement capacitor related to the position of the meniscus, the processor is configured to calculate the amount of liquid received in the capillary from the position of the meniscus.

[0015] The pipette is part of a liquid handling device which can comprise a positive displacement pipette, a system liquid filling pipette and / or an air displacement pipette for aspirating and / or dispensing liquid. The liquid handling device can comprise a piezoelectric or acoustic dispenser and other types of dispensers. The pipette can comprise a pipette tip fixed to a pipette head or a disposable tip which can be releasably connectable to a pipette head.

[0016] The electrode can comprise a disc, plate, pipette tip or needle or can be integrated into other features of the pipette. The electrode in combination with a reference electrode is part of the measurement capacitor; the reference electrode can comprise the worktable or comprise a dedicated reference electrode. The reference electrode can comprise a plurality of electrically conductive portions surrounding the electrode of the pipette head. The electrode or at least a portion of the electrode can be oriented parallel to the reference electrode, e.g. parallel to the worktable.

[0017] The capillary or microfluidic chip can be located in the capacitive sensor between the electrode and the reference electrode for detecting the position of the meniscus.

[0018] The robot arm is configured to move the pipette tip in a space above the worktable, and the robot arm can move the pipette tip in x-y-z directions. The pipette tip is preferably oriented along the z-axis perpendicular to the worktable, and the robot arm preferably moves the pipette tip orthogonally such that the pipette tip remains vertically oriented during the movement, thereby maintaining the orientation of the electrode relative to the reference electrode.

[0019] The processor in the electronic circuit also enables control of the movement of the robot arm, the control of the pipette (e.g. the control of an air displacement pump in the pipette), etc. The processor processes the signals received from the measurement capacitor and is able to measure the properties of the measurement capacitor consisting of the pipette tip and its environment including the reference electrode. The electronic circuit can comprise a pulse generator for generating electrical pulses to the electrode or the reference electrode.

[0020] The capillary can be a glass capillary or a plastic capillary. The plastic capillary can be manufactured by embossing a fluid guiding path in a polymer material, whereafter the guiding path is covered by a sheet. Alternatively, the fluid guiding path is made by injection molding, laser cutting, nano-imprint technology. The path of the capillary can have a linear shape, a curved shape or can be bent by back and forth meandering. The width and depth (cross-sectional area) of the capillary is preferably constant along the fluid guiding path. The capillary channel can be opened or closed to prevent evaporation. The capillary surface for liquid contact can be treated to form a hydrophilic surface, thereby facilitating the fluid migration within the capillary. The capillary can be comprised in a labware component, which can be a consumable, and thus the capillary is used only once. The labware component can be a reusable product, where the capillary is emptied (e.g. liquid is sucked out of the capillary) or replaced after use. Alternatively, both the capillary comprising the holding member and the inlet section are designed as disposable products. The labware component can be a microfluidic chip comprising a plurality of capillaries, each capillary having a detection zone for detecting an amount of liquid.

[0021] The capillary can be oriented substantially horizontally on the worktable, and the electrode or the distal end of the electrode can also be oriented parallel to the worktable. The pipette tip is moved with the robot arm such that the end of the electrode remains parallel to the worktable. The robot arm can tilt or rotate the pipette tip with the electrode such that the capillary in a tilted or even vertical position on the worktable can be accurately measured.

[0022] Each end of the capillary can have two openings for connecting the capillary to the environment. One end of the capillary can be connected to an opening configured to receive liquid from a pipette. The opening configured to receive liquid can have a conical or cylindrical shape. The size of the opening provides an entry section for insertion of a pipette tip of a manual pipette or an automated pipette using a laboratory automation device. A target volume can be aspirated by the pipette, for example, by controlling the plunger motion in an air displacement pipette. The target volume can be selected based on the pipette tip used and can be included in a factory setting. The received volume in the capillary refers to the volume of liquid that will be checked against the target volume in a routine check or for quality control purposes to determine if the pipette delivered the expected amount of liquid accurately.

[0023] A gas-liquid meniscus / boundary can form at the fluid front towards the end in the capillary and / or towards the opening of the capillary, and one or both menisci can be used to detect the amount of liquid received in the capillary. The entry section of the capillary or the opening on the entry section can be designed to draw all the liquid into the capillary. For example, the opening can have a hydrophobic surface for facilitating the flow of liquid from the entry into the hydrophilic capillary.

[0024] The defined position of the capillary in the x-y plane can be checked by a lab automation device, which can use a capacitive sensor as disclosed in US20240217102A1 for example. The defined position in the z direction can be detected using a force controlled motion, which lowers the pipetting head until it abuts against the top surface of the holding piece holding the capillary or the top surface of an assembly holding multiple capillaries. The capillary axis can be aligned with the electrode scan axis by a capacitive scan of a calibration structure (triangular recess or channel) or directly using a capillary filled with a filling liquid. In the latter case, a scan orthogonal to the capillary axis can be used to determine the translational and rotational shift of the capillary axis relative to the electrode scan axis. Subsequently, the robot arm with the electrode is raised, creating a z-directional offset between the electrode and the capillary, generating a defined air gap between the top surface of the capillary and the electrode. The robot arm is moved in the x direction, the y direction or both x and y directions for scanning the surface of the capillary, hovering above the capillary. The robot arm can first reach the defined x-y position and perform a linear scan to hover along the direction of the fluid path of a single capillary or to hover above the detection section of multiple capillaries. Once the electrode reaches the fluid front in the capillary, a sudden change from a capillary filled with a filling liquid to a capillary filled with air is provided. This changes the dielectric medium and the impedance of the measuring capacitor. The change in capacitance is detected and this is used to determine the position of the meniscus in the fluid path. The dimensions of the capillary are known and can be stored in a storage unit of the processor for calculating the volume of liquid received in the capillary. The dimensions of the capillary can be computer- readable encoded for example by a 2D barcode or an RFID tag on the labware product containing the capillary.

[0025] Alternatively, for a lab chip having a channel providing a fluid path for a liquid to be processed, the position of the meniscus in the fluid path is determined. Such a chip can comprise a DNA sequencing chip, in which DNA fragments are dissolved in a sample liquid, which is guided through a path in the chip. Detecting the meniscus at the liquid front can help to detect whether the chip is ready for use, as the liquid path can need to be prepared or wetted with a conditioning liquid or a washing liquid or the position of the meniscus can indicate that a certain processing step has been completed or even to detect the end of life of the chip.

[0026] Capacitive measuring units can be included in laboratory automation devices for liquid level detection (see e.g. US20160356737A1), whereby the pipette is brought into vertical proximity and contact with a horizontally oriented meniscus in a test tube. Capacitive measuring units are exclusively used in the present disclosure for detecting a vertically oriented meniscus within a capillary tube, the position of which is used to measure the volume of liquid dispensed into the capillary tube. The measurement does not require liquid contact or additional analytical test devices like a photometer or a precise balance, the laboratory automation device thus provides a simple and reliable verification method that can be applied by the device's daily user and / or a field service engineer.

[0027] The electrode can be attached to the distal end of a pipetting tip of a pipetting head of the pipette. The pipetting head can be a fixed pipetting tip permanently coupled to the pipetting head of the pipette. Alternatively, the pipetting tip is a disposable pipetting tip releasably connected to the pipetting head. Whether reusable or disposable, the pipetting tip is at least partially electrically conductive. The pipetting tip can be made of metal, paper (cellulose) or plastic. The surface of the pipetting tip can be at least partially covered with an electrically conductive coating or electrically conductive strips are integrated into the wall of the pipetting tip. The plastic material can be carbon-filled, for example a graphite-filled polymer selected from, for example, polyethylene, polypropylene, polystyrene, polymethyl methacrylate or polycarbonate. The end of the tip surrounding the liquid outlet can provide the electrode.

[0028] The disposable pipetting tip used as an electrode can be used beforehand with the pipette for dispensing a target volume of liquid into the capillary tube, or the disposable pipetting tip can be used only as an electrode.

[0029] Alternatively, a dedicated electrode is attached to the distal end of the pipetting head. The dedicated electrode can be permanently coupled or integrated into the pipetting head or can be releasably attached to the distal end of the pipetting head. The dedicated electrode can have a tip with narrow dimensional tolerances, for example a sharp pin.

[0030] Alternatively, the distal end of the pipetting head can provide the electrode, which can include a coupling unit or a cone for connection to a pipetting tip.

[0031] The volume of liquid received or transferred can be calculated by multiplying the cross-sectional area of ​​the capillary by the length of the liquid-filling path defined by the detection positions of the capillary inlet and the meniscus. The dimensions of the capillary and the shape of the fluid path can be stored in a storage device for calculating the received volume. The capillary dimensions can be in the micrometer range and can depend on the target volume. For example, a height and width of less than 500 micrometers can be selected, preferably less than 100 micrometers, and more preferably less than 50 micrometers. The capillary can have a circular or semi-circular cross-section with a diameter less than 500 micrometers, preferably less than 100 micrometers, and more preferably less than 50 micrometers. The capillary can have a rectangular, V-shaped, T-shaped, or U-shaped cross-section with an upper width of less than 500 micrometers, preferably less than 200 micrometers, and more preferably less than 100 micrometers. The lateral dimensions of the capillary along the flow path can be constant, or the width / height or diameter of the capillary can vary. Very narrow channels (e.g., below 20 micrometers) can lead to inaccurate measurements because at some point the resistive part of the complex permittivity becomes increasingly important.

[0032] The capillary may include a flow restrictor. The capillary may include a defined reservoir in the flow path for absorbing a large portion (e.g., 80%) of the target volume. The capillary is fluidly coupled to the reservoir for absorbing, for example, 30% of the target volume. The capillary may include a venting capillary or an venting membrane to prevent cavitation or bubbles from forming in the capillary. In another aspect, a method for measuring the dispensing volume of a laboratory automation device is disclosed. The laboratory automation device includes:

[0033] - The worktable, which defines the x-y plane;

[0034] - A robotic arm configured to move a pipette, including a pipette tip, in the space above the worktable;

[0035] - An electrode, which is connected to the pipette tip or serves as the distal end of the pipette tip, provides a reference electrode for the capacitive sensor;

[0036] - A processor that is operatively connected to the robotic arm, pipette, and electrodes via electronic circuitry;

[0037] - A capillary tube located at a defined x-y position on the stage, between the electrode and the reference electrode, at least a portion of the capillary tube being oriented substantially parallel to the stage, and the capillary tube having an opening for receiving liquid.

[0038] The method includes the following steps:

[0039] - Aspirate a certain amount of liquid using a pipette;

[0040] - Guide the robotic arm, including the pipette, to the opening of the capillary;

[0041] - dispensing a target amount of liquid into the opening, thereby drawing the liquid into the capillary to form a gas-liquid meniscus or a gas-liquid phase boundary, wherein the target amount of liquid can be less than the amount of liquid aspirated by the pipette;

[0042] - hovering the electrode over the capillary with the robotic arm;

[0043] - detecting a change in capacitance of the capacitive sensor, which change in capacitance is indicative of the position of the meniscus in the capillary;

[0044] - calculating the amount of liquid received or transferred in the capillary using the detected position of the meniscus and the dimensions of the capillary.

[0045] The robotic arm can move the pipette tip of the pipette along the x-axis, y-axis and z-axis. The reference electrode can comprise a worktable. The x-y position of the pipette can first be checked using a dedicated topography on the worktable in combination with a capacitive measurement unit, for example as shown in US20240217102A1.

[0046] Subsequently, the robotic arm with the pipette can approach the position of the capillary (defining the x-y position). The topography can be comprised in a holder for the capillary, in a labware product comprising the capillary or in the worktable.

[0047] z-position check: the pipette, with or without pipette tip, can be lowered in force-controlled manner, and once the pipette tip or pipette tip contacts the top surface of the capillary or the top surface of the holder holding the capillary, the pipette can stop. The force-controlled measurement can be repeated, for example on each corner of the holder or on each corner of the top surface of the capillary assembly. A reference z-height can be defined, or an average reference z-height can be defined from the force-controlled measurements. An offset z-height or hover height is added to the reference height in order to hover the pipette tip over the capillary. The pipette tip is preferably maintained at a constant hover height. Alternatively, the hover height varies with the x-position or y-position, for example when the capillary has been tilted.

[0048] As mentioned above, the capillary for receiving the liquid can have an inlet section which can have a hydrophobic surface, while the capillary can have a hydrophilic surface. The target volume can be aspirated by a controlled displacement of an air displacement unit connected to the pipette tip, and the target volume can be dispensed into the opening of the capillary using the air displacement unit.

[0049] The target amount can be dispensed using a free or contact dispensing technique.

[0050] The volume quantity can be calculated from the distance of the fluid path between the opening and the position of the meniscus detected at the liquid front. Alternatively, the positions of the starting meniscus and the ending meniscus in the capillary are detected and used to calculate the received liquid quantity.

[0051] The method can be used by an operator of the laboratory automation device for a routine check of the volume dispensed by the pipette, or the method can be used by a field service engineer providing service to the laboratory automation device for quality control purposes. Alternatively, the method is used for factory calibration of the pipette in the laboratory automation device. The method can be used without the need for external and expensive external analytical test devices such as a photometer and / or a balance.

[0052] In one embodiment, the method can comprise additional steps, for example, comparing the received volume (V r ) of liquid to a target volume (V t ), and recalibrating the pipette or sending an alarm signal to the user if there is a difference between the received volume and the target volume. The target volume is preferably stored in a memory unit of the electronic circuit, and before the alarm signal is released or before the pipette needs to be recalibrated, a difference D = (V t -V r ) / V t * 100% is calculated between the two values. The difference D can be greater than 1%, or greater than 5%, or greater than 10%, or greater than 20%.

[0053] The automatic recognition of the deviation of the pipette between the target volume and the dispensed volume can increase the reliability of the device and prevent the use of imprecise laboratory automation devices in combination with expensive process liquids or sample liquids.

[0054] In another embodiment, when the method is performed, the electrically conductive pipetting tip is attached or attachable to the pipetting head of the pipette, and the distal end of the electrically conductive pipetting tip provides the electrode. The electrode can be provided by the distal surface surrounding the opening or separate from the distal surface. The electrically conductive pipetting tip can be a reusable pipetting tip or a disposable pipetting tip.

[0055] The same electrically conductive pipetting tip can be used to dispense the target volume of liquid into the opening of the capillary and hover over the capillary. Alternatively, the electrically conductive pipetting tip is only used to scan the capillary, which has been filled with liquid by another pipetting tip beforehand. The electrically conductive pipetting tip can be used to scan or hover over the capillary filled with liquid by another pipetting tip beforehand, or the same electrically conductive pipetting tip is used both to dispense the target volume of liquid into the capillary and to hover over the capillary to detect the meniscus.

[0056] Scanning with a separate unused pipette tip can prevent contamination of the electrodes with droplets attached to the distal end of the tip in previous aspiration / dispensing steps.

[0057] The electrical impedance measurement is used to detect the position of the meniscus or phase boundary in the capillary. The change in electrical impedance can be detected as a change in the absolute or relative capacitance of the capacitive sensor when hovering over the meniscus. For example, a supply voltage can be applied between the electrode and the reference electrode and the change in dielectric medium from air to water is detected when crossing the meniscus or air-liquid phase boundary. Alternatively, the change in capacitance is detected by electronic circuitry using charge-based or oscillation-based measurement techniques. For charge-based techniques, the charging or discharging of the capacitor can provide a feedback signal in response to an input signal (supply voltage) directed to the electrode. The input signal can be directed to the electrode, or to the reference electrode, or to both the electrode and the reference electrode. The input signal or supply voltage can be modulated and have different waveforms, such as sinusoidal, square, triangular, sawtooth or pulse-shaped waveforms. The change in charging time can be detected using a dedicated sensor included in the electronic circuitry. The input signal is preferably modulated in the kilohertz frequency range.

[0058] Optionally, a reference scan is performed in which the electrode hovers over an empty capillary to determine the parasitic capacitance around the facility in the laboratory automation device. The change in capacitance in the reference scan can be subtracted from the detection scan in which the electrode hovers over a capillary filled with liquid. Alternatively, the scan can be repeated back and forth over a section with a meniscus on the region of interest and the multiple scans can be averaged.

[0059] The input signal can be a pulse width modulated (PWM) signal and the electronic circuitry can comprise at least one time-to-digital converter (TDC) or comparator unit for detecting the time required for the feedback signal to reach a threshold voltage defining the charging time of the capacitor. Alternatively, the circuit comprises two or more comparator units for detecting, for example, a lower threshold voltage and an upper threshold voltage for detecting the charging time of the capacitor.

[0060] The received amount of liquid can be calculated with the cross-sectional area of the capillary multiplied with the liquid fill length in the capillary. The fill length can be defined by the position of the meniscus detected at the liquid front or by the half-moon detected at the beginning and end of the liquid fill fluid path.

[0061] The liquid used in the method for measuring the dispense volume of a laboratory automation device can be water, deionized water or ionized water, for example a salt solution, such as a saline solution. Alternatively, an organic solvent is used. The liquid used can additionally be colored with a dye for optical monitoring of the filling of the fluid path.

[0062] The capillary used in the method or used in the laboratory automation device can be composed of a plastic material received in a carrier which can be located in a defined x-y position. An additional metal plate or metal rack can be stacked between the worktable and the holder. The additional metal plate serves as a low impedance ground, which can be integrated into the holder of the capillary or even provide the holder for the capillary. The capillary can be imprinted on a flat piece of polymer material, which can subsequently be closed with a plastic cover, sealing the top surface. Alternatively, the topography of the channel is built by injection molding of a plastic sheet, which is closed by a cover. As another alternative sheet molding process, a laser ablation or micro-embossing process is used to generate the channel.

[0063] In another aspect, a computer program for measuring the dispense volume of a laboratory automation device is presented and the computer program is adapted to perform the steps of the method when executed by a processor. The processor can be part of the laboratory automation device or a separate processor.

[0064] Another aspect relates to a computer readable medium storing a computer program. The computer readable medium can be an optical disc, a USB stick or a hard drive. The computer readable medium can be part of a cloud solution.

[0065] These and other aspects of the present application will become apparent from the embodiments described hereinafter, from the attached claims as well as from the embodiments itself, the realization of which constitutes the technical solution of the present application. Embodiments can be combined or individual aspects of embodiments can be combined. BRIEF DESCRIPTION OF DRAWINGS

[0066] Embodiments of the present application are described in more detail with reference to the accompanying drawings, in which:

[0067] Figure 1 A perspective view of a laboratory automation device with two pipetting heads for accommodating disposable pipette tips is shown;

[0068] Figure 2 A perspective view of a laboratory automation device with a pipette having a fixed, reusable pipette tip is shown;

[0069] Figure 3 A schematic view of a laboratory automation device is shown, in which a pipette tip approaches an empty capillary on a worktable;

[0070] Figure 4 A schematic view of a laboratory automation device is shown, in which a pipette tip scans a capillary filled with liquid;

[0071] Figure 5 A schematic view of a capillary filled with liquid scanned by a pipette tip is shown;

[0072] Figure 6The charging time of the capacitor detected in the feedback signal in response to the PWM input signal is shown;

[0073] Figure 7 The schematic layout for measuring the capacitance C is shown;

[0074] Figure 8 An example of the capacitor impedance versus position along the x-axis is shown;

[0075] Figure 9 The derivative of the impedance detected in the feedback signal in response to the PWM input signal is shown versus the position on the x-axis; Figure 8

[0076] Figure 10 A block diagram showing the steps of a method for measuring the dispensed volume of a laboratory automation device is shown. DETAILED DESCRIPTION

[0077] Definitions: distal or distal direction is defined by the direction of flow of the liquid, thus the distal tip of the pipette is defined by the outlet of the pipette tip, proximal is opposite to distal. The indefinite article "a" or "an" does not exclude a plurality. For example "a pipette tip" does not exclude the fact that there can be two pipette tips functionally or structurally implementing the purpose of "a pipette tip". Meniscus can mean that there is a front and back meniscus in the fluid path. In the claims the word "comprising" does not exclude other elements or steps. Another expression for pipette tip is pipette channel or tip adapter. The term "meniscus" is used throughout the disclosure for the gas-liquid phase boundary oriented essentially perpendicular to the capillary axis.

[0078] Figure 1 ​A perspective view of a laboratory automation device 1 comprising a worktable 2 is shown. The worktable 2 defines an x-y plane, the beam 26 holding the robot arm 6 is axially offset in z-direction and is supported by two side columns 27. A space is left between the worktable 2 and the beam 26 for moving a pipette 3 by the robot arm 6. By using the same robot arm 6, laboratory instrument parts can be placed and moved on the worktable, whereby the pipette 3 has been replaced by a gripper for gripping laboratory instrument parts, or the laboratory automation device 1 comprises a second robot arm with a gripping unit dedicated for moving and manipulating laboratory instrument parts on the worktable 2. Laboratory instrument parts can include microplate, tray, dish, pipette tip holder, sample container, liquid supply, sample or process liquid holder, waste container, etc. Sample testing and manipulation devices such as a shaker, thermal cycler, mixing device, microplate reader or microfluidic chip can be on the worktable. The pipette 3 is attached to an air displacement unit 28 or to a system liquid filling line which is connected to a syringe pump which can provide under- or overpressure to a pipetting head or pipetting channel 4 comprised in the pipette 3. An electrode 5 can be attached to the pipetting head 4. The electrode 5 can be part of the pipetting head 4. In Figure 1 In an example, two pipetting heads are shown, one without attached pipette tip, one with attached tip. Either the distal end of the pipetting head itself or the distal end of a pipette tip attached to the pipetting head 4 can act as the electrode 5. Alternatively, a separate electrode 5, e.g. a metal needle, is attached to the pipetting head 4.

[0079] Figure 1 The electrode 5 in can be releasably attached to the pipetting head 4. A pipette tip 9 can be attached to the distal end of the pipetting head 4 and separate from the electrode 5, and the pipette tip can be used to aspirate liquid from a sample container using the air displacement unit 28 which creates underpressure in the pipette tip. The sample liquid can be dispensed by applying overpressure in the pipette tip using the air displacement unit 28. The pipette 3 comprises a capacitive sensor 14 which can be used to detect a change in capacitance indicative of contacting the liquid in the sample container before starting to aspirate liquid. The pipette tip 9 can serve a dual purpose in that it provides the electrode 5 for both the sensor and the liquid manipulation feature. For example, the distal end 10 of the pipette tip 9 can provide the electrode 5 for the capacitive sensor 14. The capacitive sensor 14 can comprise a reference electrode comprising the worktable 2 or a low impedance ground plate. The capacitive sensor 14 can further comprise the electrode 5 and a plurality of surrounding electrodes which can even provide parasitic capacitances which need to be cancelled out to reduce noise in the detection signal. The electrode 5 of the capacitive sensor can be charged by a charging unit or signal generator which will be explained in detail below. Figure 1The shown laboratory automation device 1 comprises two separate pipetting heads or two channels, each channel being equipped with a pipetting head 4 and an electrode 5. A multi-channel pipette with two, four, eight or sixteen channels can be designed without deviating from the working principle of the laboratory automation device, and each channel can be equipped with a capacitive sensor 14. The laboratory automation device comprises a processor or processing unit 12 for controlling the device and signal processing of signals received from the capacitive sensor 14.

[0080] Another example of a laboratory automation device 1 is shown in Figure 2 which is essentially the same as the device in Figure 1 . The device comprises a single-channel pipette 3, the pipetting tip 9 being fixedly attached to the pipetting head 4. The pipette 3 can comprise a separate electrode 5, or the distal end 10 of the pipetting tip 9 can provide the electrode 5 for the capacitive sensor.

[0081] The accuracy of the aspirated and dispensed volume of liquid is a primary feature of a laboratory automation device, which is checked as a factory parameter during quality control tests before delivery to the customer, or as a regular control check by the device operator or field service engineer after regular maintenance. The operator or field service engineer can use a separate balance to gravimetrically measure the liquid dispensed volume, or the absorbance measurement of a photometer. Both methods require additional external facilities and a trained operator.

[0082] In the present disclosure, the capillary 7 is combined with a capacitive measurement for checking the volume dispensed from the pipette 3, as shown in Figure 3 and Figure 4 . The capillary 7 is located on the worktable 2, the axis of the capillary 7 being oriented horizontally. Alternatively, the axis can be oriented vertically, or at any angle between zero and ninety degrees to the worktable 2. A target volume of liquid is pipetted into the opening 8 of the capillary, the liquid migrating into the capillary 7 towards the outlet 13. The length and dimensions of the liquid-filled path define the volume of liquid received in the capillary 7. The capacitive sensor is used to determine the length of the liquid-filled path when the capillary is located between the electrode 5 and the worktable 2 as part of the reference electrode.

[0083] The robot arm 6 is coupled by electronic circuitry to a processor 12, which controls the movement of the robot arm 6, which holds the pipette 3, to which the electrode 5 is attached to the pipette tip 4. The pipette tip 9 is attached to the pipette tip 4, for example by picking it up from a labware component such as a tray holding disposable pipette tips. The picking up can be an automated pick up, whereby the robot arm 6 moves to a tray holding pipettes, the pipette tip 4 is lowered to engage a collar of the pipette tip to the pipette tip 4. The pipette 3 is then moved to a liquid container in a labware component located on the worktable 2 and lowered until the liquid level is detected. The processor 12 controls the air displacement unit 28 of the pipette 3 and a target amount of liquid is aspirated into the pipette tip 9. This is followed by the robot arm 6 moving to the opening 8 of the capillary 7 and dispensing the target amount of liquid into the opening 8. The dispensing step can be with contact between the distal end of the pipette tip 9 and the opening 8 or there can be an air gap during so-called free dispensing. The opening 8 can be conical in shape and the distal end of the pipette tip 9 can slide over the cone towards the center of the cone before starting the contact dispensing. The liquid used for determining the dispensed volume can be water, deionized water or an ionic solution such as a saline solution. The liquid can be colorless or colored using a dye such as methyl orange or crystal violet.

[0084] As explained in US20240217102A1, the position of the tray holding the disposable tips in the x-y plane, the position of the opening 8 of the capillary 7, or the position of the holder 19 holding the capillary 7 can be checked separately using capacitive sensor measurements with dedicated topographies.

[0085] The liquid is sucked into the capillary 7 and the liquid front with the meniscus 11 or air / liquid phase boundary migrates to the outlet 13 of the capillary 7, see Figure 4 The electrode 5 and / or the pipette tip 9 are moved to a z-position with a defined distance from the top surface of the capillary 7, which defines the hover height, and the distal end 10 of the electrode 5 and / or the pipette tip is moved over the surface of the capillary 7 to identify the position of the meniscus 11 using capacitive sensors, as will be explained below.

[0086] A schematic view of the capillary 7 is shown in Figure 5 The capillary has a known and calibrated geometry. The capillary can be inserted in a separate housing 30 or the capillary 7 is integrated in the housing 30. The capillary can be included in a disposable labware component. A target amount of liquid has been pipetted into the opening 8 of the capillary, the distance travelled by the liquid 20 depends on the surface properties of the capillary 7, the surface properties of the opening 8, the geometry of the capillary and the surface tension of the selected liquid. In Figure 5In the illustrated example, all liquid is drawn into the capillary tube, and the capacitive sensor can detect both the front end air / liquid phase boundary (meniscus) and the rear end air / liquid phase boundary (meniscus). Alternatively, a small amount of liquid remains attached to the capillary tube inlet section 8 at a known location. In this case, only the front end meniscus 11 needs to be detected to determine the length of the liquid fill path. The front end meniscus 11 migrates towards the area of interest section 29, where the liquid front is expected to stop when the target amount of liquid is drawn into the capillary tube. The area of interest 29 can be a transparent section in the capillary tube and / or the housing 30 holding the capillary tube, or the entire housing can be transparent. The area of interest 29 can include a scale for optically identifying the front end of the liquid. The length of the path multiplied by the cross-sectional area of the capillary tube defines the amount of liquid received in the capillary tube, which can be compared to the target amount after automatically calculating the received amount of liquid by the operator, field service engineer, or processor. The received amount can be compared to the target amount stored in a memory unit.

[0087] The pipette tip 9 used to draw and dispense the target amount into the capillary tube 7 can then be used as the electrode 5 of the capacitive sensor. Alternatively, the pipette tip 9 used to dispense into the capillary tube is discarded and a new, unused pipette tip is used as the electrode 5. As a further alternative, no pipette tip is attached, but the distal end (cone) of the pipette 4 is used as the electrode 5, or a separate, dedicated electrode 5 is attached to the pipette 4. The dedicated electrode 5 can be a metal pin with a well-defined tip geometry. Using the pipette tip 9 as the electrode 5 requires that the pipette tip be at least partially electrically conductive. The pipette tip can be made of a carbon-filled polymer such as polypropylene.

[0088] The electrode 5 or the distal end 10 of the pipette tip 9 hovers or scans over the capillary tube 7 as indicated by the arrow in Figure 5 The electrode 5 or the distal end 10 of the pipette tip can perform multiple scans, for example from left to right or from right to left. The scans are preferably linear scans along the x-axis or along the y-axis. Alternatively, scans along the diagonals can also be performed by simultaneously moving the robot arm along the x-axis and the y-axis. The scan speed can vary between 0.5 mm / s and 100 mm / s, preferably between 5 mm / s and 50 mm / s, and more preferably between 10 mm / s and 30 mm / s.

[0089] A reference scan of an empty capillary can be performed before scanning a filled capillary. Multiple scans can be used to average the signal from the capacitive sensor to reduce noise, or the reference scan can be subtracted to reduce the effect of parasitic capacitance around the capillary. A signal generator or charging unit is connected to the processor 12 and electronic circuit, and an input signal (power supply voltage) is directed to the electrode 5 or pipette tip 9. The input signal can be a modulated signal, and can represent a switch in the electronic circuit, such that the electrode 5 is charged when the switch is closed, and discharged when the switch is open. Alternatively, the signal generator or charging unit is operated in an oscillating mode, whereby the capacitive sensor is partially charged and discharged. The charging and discharging of the capacitor is detected in the feedback signal, and the speed of the charging and discharging depends on the impedance of the capacitor. When the distal end 10 of the electrode 5 or tip is moved across the meniscus, the dielectric medium locally changes from liquid to air as it passes the phase boundary, and this change results in a change in impedance, resulting in a different charging time of the capacitive sensor.

[0090] For example, as Figure 6 depicted, a pulse width modulated (PWM) signal 17 is directed to the electrode, for charging and discharging the capacitive sensor. The voltage is increased / decreased stepwise, and the feedback signal 18 (capacitor voltage) increases and levels off towards the power supply voltage. The frequency of the PWM signal can be in the kilohertz range, for example between 0.1 kHz and 10 kHz, preferably between 1 kHz and 5 kHz, so that the capacitor is not fully charged. The charging time 16 of the capacitive sensor is defined by the time required to reach a threshold voltage 21. Within each cycle of the PWM signal, the charging time τ i 16 can be detected, and an average can be calculated.

[0091] Figure 7 A schematic of the capacitive sensor 14 is given in Fig. 1, together with a cross-sectional view of the capillary 7. In this example, the capillary is a groove or trench 24 imprinted on a plastic sheet, which is closed by a cover sheet 25 to form the capillary 7. Alternatively, the trench 24 is made by injection molding of a polymer using a mold with positive ribs extending from a flat surface. The trench presented in this example is a rectangular trench, and the dimensions of the trench are preferably in the micrometer range. The width and height can be larger than 5 micrometers, preferably larger than 10 micrometers, preferably larger than 20 micrometers, preferably larger than 30 micrometers, preferably larger than 50 micrometers, or preferably larger than 100 micrometers.

[0092] The capacitance C1 depends on the cumulative size A1, thickness d1 and dielectric constant ε1 of the material stacked between the bottom of the capillary 7 and the worktable 2. The capacitance C2 depends on the cumulative size A2, thickness d2 and dielectric constant ε2 of the material present in the air gap between the channel, the cover sheet 25 and the tip of the electrode 5 and the cover sheet. The dielectric constant ε2 depends on whether air or liquid is present in the capillary, resulting in different capacitances C2. In the current embodiment, a comparator C15 is included in the electronic circuit for detecting changes in the capacitance C2 by measuring the charging time 16 of the capacitive sensor 14. Other means for measuring capacitance can use so-called capacitive-to-digital chips.

[0093] Figure 8 An example of the detected impedance versus position x along the capillary is shown. When the distal end of the electrode 5 or pipette tip hovers over the region of interest in the capillary with a liquid-air meniscus, the charging time t decreases. The curve changes from convex to concave with an inflection point in between. Figure 8 The derivative of the sinusoidal curve has been shown as an example to derive the curve inflection point position representative of the meniscus position. Figure 9 A threshold 22 is indicated in the graph which defines a cut-off 23 as a means to limit the meniscus position. Other mathematical models can be used to derive the position of the inflection point along the x-axis.

[0094] The method steps of measuring the dispensed volume of a laboratory automation device are as Figure 10 depicted:

[0095] a) aspirating a volume of liquid by a pipette (3);

[0096] b) guiding a robot arm (6) comprising the pipette (3) to an opening (8) of a capillary (7);

[0097] c) dispensing a target volume of liquid into the opening (8), whereby the liquid is sucked into the capillary (7) to form an air-liquid meniscus (11), whereby the target volume is lower than the aspirated volume;

[0098] d) hovering an electrode (5) over the capillary (7) using the robot arm (6);

[0099] e) detecting a change in capacitance of a capacitive sensor (14) indicating the position of the meniscus (11) in the capillary (7);

[0100] f) calculating the received volume of liquid in the capillary using the detected meniscus position and the dimensions of the capillary, or by using the front and back meniscus and the cross-sectional dimensions of the capillary.

[0101] Optionally, the method comprises a step g):

[0102] g) comparing the received amount to the target amount and recalibrating the pipette (3) or sending an alarm signal if there is a difference between the received amount and the target amount.

[0103] List of reference signs

[0104] 1 laboratory automation device

[0105] 2 worktable

[0106] 3 pipette

[0107] 4 pipetting head, pipetting channel

[0108] 5 electrode

[0109] 6 robot arm

[0110] 7 capillary

[0111] 8 opening

[0112] 9 pipetting tip

[0113] 10 distal pipetting tip

[0114] 11 meniscus

[0115] 12 processor

[0116] 13 outlet

[0117] 14 capacitive sensor

[0118] 15 comparator C

[0119] 16 charging time

[0120] 17 input signal, supply voltage

[0121] 18 feedback signal

[0122] 19 holding piece

[0123] 20 liquid

[0124] 21 threshold feedback signal

[0125] 22 threshold derivative

[0126] 23 cut-off value

[0127] 24 embossed groove

[0128] 25 cover sheet

[0129] 26 beam

[0130] 27 column

[0131] 28 air displacement unit or syringe pump

[0132] 29 region of interest

[0133] 30 housing

Claims

1. A laboratory automation device (1) with liquid volume measurement function, comprising: - Workbench (2), the workbench defining the x-y plane; - A pipette (3), the pipette including a pipette tip (4) having an electrode (5) which provides a reference electrode for a capacitive sensor (14); - A robotic arm (6) configured to move the pipette head (4) above the worktable (2); - Processor (12), which is operatively connected to the robotic arm (6), the pipette (3) and the electrode (5) via electronic circuitry; - A capillary tube (7) located at a defined x-y position on the worktable, at least a portion of which is oriented substantially parallel to the worktable (2), the capillary tube (7) having an opening (8) for receiving a target amount of liquid from the pipette (3) and configured to draw the liquid from the opening (8) into the capillary tube (7) to form a gas-liquid meniscus (11). Its features are, The robotic arm (6) is configured to suspend a pipette head (4) with electrodes (5) above the capillary (7) to detect capacitance changes related to the position of the meniscus (11), wherein the processor (12) is configured to calculate the amount of liquid received in the capillary (7) based on the position of the meniscus.

2. The laboratory automation equipment according to claim 1, characterized in that, The electrode (5) is the distal end of the pipette tip (4), or the distal end (10) of the pipette tip (4) attached to the pipette (3), or the distal end of a dedicated electrode attached to the pipette tip.

3. The laboratory automation equipment according to claim 2, characterized in that, The pipette tip (9) is a disposable pipette tip that can be releasably connected to the pipette head (4), and the pipette tip (9) is at least partially conductive.

4. The laboratory automation equipment according to any one of claims 1 to 3, characterized in that, The amount of liquid received is calculated by multiplying the cross-sectional area of ​​the capillary (7) by the length of the liquid filling path defined by the detected position of the meniscus (11).

5. A method for measuring the dispensing volume of a laboratory automation device, the laboratory automation device (1) comprising: - Workbench (2), the workbench defining the x-y plane; - A robotic arm (6) configured to move a pipette (3) including a pipette tip (4) above the worktable (2); - Electrode (5), which is connected to the pipette tip and provides a reference electrode for the capacitive sensor (14); - Processor (12), which is operatively connected to the robotic arm (6), the pipette (3) and the electrode (5) via electronic circuitry; - Capillary (7), the capillary is located at a defined x-y position on the worktable (2), at least a portion of the capillary is oriented substantially parallel to the worktable (2), the capillary (7) has an opening (8) for receiving liquid; The method includes the following steps: - A certain amount of liquid is drawn up using the pipette (3); - Guide the robotic arm (6) including the pipette (3) to the opening (8) of the capillary (7); - Distribute the target amount of liquid into the opening (8), thereby drawing the liquid into the capillary (7) to form a gas-liquid meniscus (11); - Use the robotic arm (6) to suspend the electrode (5) above the capillary (7); - Detect the capacitance change of the capacitive sensor (14), the capacitance change indicating the position of the meniscus (11) in the capillary (7); - Calculate the amount of liquid received in the capillary using the detection position of the meniscus and the size of the capillary.

6. The method according to claim 5, characterized in that, The electrode (5) is the distal end of the pipette tip (4), or the distal end (10) of the pipette tip (4) attached to the pipette (3), or the distal end of a dedicated electrode attached to the pipette tip.

7. The method according to claim 6, characterized in that, At least a partially conductive pipetting tip (9) is attached to or can be attached to the pipetting tip (4) of the pipette (3), wherein the distal end (10) of the conductive pipetting tip (9) provides the electrode (5).

8. The method according to claim 7, characterized in that, It also includes the following steps: - Compare the received amount with the target amount and recalibrate the pipette (3), or send an alarm signal if there is a difference between the received amount and the target amount.

9. The method according to any one of claims 5 to 8, characterized in that, The change in capacitance is the change in the charging time (16) of the capacitive sensor detected from the feedback signal (17) of the electrode in response to the input signal (18).

10. The method according to claim 9, characterized in that, The input signal (18) is a pulse width modulation signal, wherein the electronic circuit includes at least one comparator unit (15) for detecting the time required for the feedback signal (17) to reach a threshold voltage that defines the charging time (16) of the capacitive sensor.

11. The method according to any one of claims 5 to 8, characterized in that, The amount of liquid received is calculated by multiplying the cross-sectional area of ​​the capillary by the filling length defined by the detected position of the meniscus.

12. The method according to claim 11, characterized in that, The liquid is a salt solution.

13. The method according to any one of claims 5 to 8, characterized in that, The capillary is made of plastic material received in a carrier, wherein the carrier is located at the defined x-y position, and wherein an additional metal plate or conductive frame is positioned between the worktable and the holder.

14. A computer-readable medium storing a computer program for measuring the dispensing volume of a laboratory automation device, which, when executed by a processor, is adapted to perform the steps of the method according to any one of claims 5 to 13.

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