Liquid handling system and method for analyzing tip status

Abstract

According to an exemplary aspect of the present invention, a liquid handling system for dispensing a liquid sample from a pipette tip is provided. The system includes a light source configured to project a first light beam via a first light path that interacts with the pipette tip or its contents, and further configured to guide a second light beam via a second light path that does not interact with the pipette tip and its contents; a first detector configured to detect the first light beam; a second detector configured to detect the second light beam; an analysis unit configured to analyze a state of the pipette tip based on signals obtained from the first and second detectors; wherein the second detector is a normalized detector configured to measure the intensity of the light source.

Description

Technical Field

[0001] The present invention relates to liquid handling systems and, more particularly, to optical and photometric methods for monitoring and analyzing the status of tips used in such systems. Background Art

[0002] In handheld pipettes and automated liquid handling devices (liquid handling robots), precise pipetting requires a reliable method for detecting and monitoring the state of the tip that is to aspirate the liquid. First, the tip needs to be immersed to a certain depth in the liquid to be aspirated. Then, a precise volume of liquid is aspirated while lowering the tip so that the lower end of the tip remains below the surface of the liquid. Finally, the tip is transferred above a holding container and part or all of the liquid is dispensed into the container.

[0003] It is known to use, for example, pressure measurement or capacitance methods for detecting the liquid level in pipette tips. These methods have a number of disadvantages. For high viscosity fluids, the liquid level changes more slowly than the pressure, which reduces the accuracy of pressure-based level monitoring. Pressure measurement cannot reliably detect partial blockages of the tip in cases where air can still flow through the blockage. In addition, both ambient pressure and altitude affect the measured pressure value.

[0004] EP 1756587 B1 discloses a pipette system comprising a pipette body component having a fluid channel extending therein and first and second optical conductors configured to receive and / or transmit light therethrough. A controller detects contact of the pipette tip with a fluid based on a level of light received from the pipette tip by at least one of the first and second optical conductors, and when contact of the pipette tip with the fluid is detected, determines a liquid level based on a position of the pipette body component.

[0005] Photometric methods are already used to some extent in automated analyzers:

[0006] US 8203721 B2 discloses a photometric method for detecting liquid-gas interfaces in the wells of a microtiter plate in an automated liquid handling device. Light is directed simultaneously to a plurality of illumination points which are located in a flat, convex or concave plane corresponding to the actual shape of the liquid interface to be detected.

[0007] EP 1756587 B1 discloses an optical liquid detection method for an automated pipette system. In the method, a pipette tip having discontinuities of varying outer diameter is used. Light is passed through the tip material. Contact between the tip and the fluid is optically detected by detecting changes in light reflected from the outer surface of the tip when the discontinuities come into contact with the fluid.

[0008] The following publications disclose the use of special tips for photometric detection of liquid levels in handheld pipettes:

[0009] FI 120336B describes an optical method for analyzing liquid in a pipette tip. The tip includes a grating structure and light is conducted to the liquid via the tip material and the grating. The light source and detector are located in the pipette body.

[0010] US 5844686 describes the incorporation of mirrors and windows into pipette tips for the purpose of performing photometric measurements.

[0011] There is a need to develop an accurate, improved tip monitoring and liquid level detection method that is independent of ambient conditions and liquid properties and can be successfully used with handheld pipettes and automated pipetting systems, as well as conventional disposable tips, over their entire range of dispense volumes.

[0012] At least some embodiments of the present invention are directed to overcoming at least some of the above-mentioned disadvantages and limitations of known methods for analyzing and monitoring tips and their contents in liquid handling devices. Summary of the invention

[0013] According to a first aspect of the present invention, there is provided a liquid handling system for dispensing a liquid sample from a tip, the system comprising: a light source configured to project a first light beam via a first light path that interacts with the tip or its contents, and further configured to guide a second light beam via a second light path that does not interact with the tip and its contents; a first detector configured to detect the first light beam; a second detector configured to detect the second light beam; an analysis unit configured to analyze a state of the tip based on signals obtained from the first and second detectors; wherein the second detector is a normalization detector configured to measure the intensity of the light source.

[0014] Various embodiments of the first aspect may include at least one feature from the following list:

[0015] • The first and second detectors and the light source are located within a barrel of a liquid handling system, and the liquid handling system is a handheld pipette.

[0016] • The first and second detectors are located within a cylinder of the liquid handling system, and the light source is located outside the cylinder.

[0017] • The first and second detectors and the light source are located outside the cylinder of the liquid handling system.

[0018] The light source is located above an upper edge of the tip and is configured to project light into the material of the tip.

[0019] The light source is located on a side of the tip and is configured to project light toward the tip, and the liquid handling system is an automated liquid handling station.

[0020] The barrel of the liquid handling system is configured to direct light from the light source through the material of the barrel to the interior of the tip, preferably to the surface of the liquid.

[0021] • The system comprises a time-of-flight assembly comprising a light source and a first detector.

[0022] • The system includes a time-of-flight assembly located within a cylinder of a liquid handling system.

[0023] • The system includes a time-of-flight assembly, and the light source in the time-of-flight assembly is located outside the cylinder of the liquid handling system, and the first detector in the time-of-flight assembly is located inside the cylinder of the liquid handling system.

[0024] The system comprises an optical fiber extending from a light source to an interior of the tip, preferably towards a surface of a liquid in the tip, and configured to direct a first light beam from the light source to the surface of the liquid.

[0025] The system comprises an optical element, such as a lens or a cone, located in front of the first detector and configured to focus a first light beam coming from the interior of the tip, preferably from a surface of a liquid inside the tip, onto the first detector.

[0026] The lower edge of the barrel of the liquid handling system is lens-shaped and the barrel is configured to conduct light from the light source through the material of the barrel and said lens-shaped lower edge to the interior of the tip, preferably to the liquid surface, and wherein the barrel is further configured to collect light that has interacted with the tip or its contents, in particular the liquid surface, to the first detector.

[0027] The system comprises an optical assembly, and the optical assembly is a detachable lens system connecting a barrel of the liquid handling system to the tip and attached to an outer surface of the barrel and an inner surface of the tip, wherein the lens system is configured to direct light from a light source to an interior of the tip, in particular to a liquid surface, and wherein the lens system is further configured to collect light that has interacted with the tip or its contents, in particular with the liquid surface, to a first detector.

[0028] • The system comprises a support arm movable around and along the suction head, and the first detector, and preferably also the second detector, are attached to the support arm.

[0029] The first detector, and preferably also the second detector, are formed as line sensors.

[0030] • The system includes a support arm movable around and along the suction head, and a light source is attached to the support arm.

[0031] The light source is located inside the cylinder of the liquid handling system.

[0032] • The system comprises two support arms on opposite sides of the pipette head, and a light source is attached to one of the support arms and a first detector is attached to the other of the support arms, the support arms being movable around the pipette head.

[0033] According to a second aspect of the present invention, there is provided a method for analyzing the state of a disposable tip for aspirating and dispensing liquids used in a liquid handling system, the method comprising the steps of: directing a first light beam from a light source to a first detector via a first light path that interacts with the tip or its contents; and measuring the quantity; directing a second light beam from the light source to a second detector via a second light path that does not interact with the tip and its contents; and measuring the intensity of the light source, and analyzing the state of the disposable tip based on the measured quantity and the measured intensity of the light source; wherein the second detector is a normalized detector.

[0034] Various embodiments of the second aspect may include at least one feature from the following list of items:

[0035] The first light beam interacts with the material of the tip or the liquid in the tip or both.

[0036] The analyzing comprises one or more of: determining a liquid level in the tip, determining a liquid volume in the tip, determining contact between the tip and a liquid surface, determining contact between the tip and an external container, and determining movement of the tip.

[0037] • The analysis step involves determining the level or volume of liquid in the tip, and that quantity is the reflectance.

[0038] • The analysis step involves determining the level or volume of liquid in the tip, and this quantity is the absorbance.

[0039] • The liquid handling system is a system according to the first aspect of the invention.

[0040] At least some embodiments of the present invention provide significant advantages over known methods for liquid level detection and tip monitoring in liquid handling devices. The present method can accurately measure the liquid level even for high viscosity fluids, the method is independent of ambient pressure conditions, and the method can reliably detect any blockage of the tip.

[0041] At least some embodiments of the present invention provide a general optical approach that can be easily implemented for tip monitoring in handheld and automated liquid handling devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 illustrates the principle of relative measurement using two detectors according to at least some embodiments of the present invention;

[0043] Figure 2 An embodiment is shown in which the primary interaction between light and the liquid in the tip is reflectivity;

[0044] Figure 3 and 4 An embodiment is shown in which the primary interaction between light and the liquid in the tip is absorbance;

[0045] Figure 5 and 6 Additional embodiments are shown where the primary interaction between light and the liquid in the tip is absorbance;

[0046] Figure 7 and 8 Additional embodiments are shown where the primary interaction between light and liquid in the tip is reflectivity;

[0047] Fig. 9 and 10 Additional embodiments are shown where the primary interaction between light and liquid in the tip is reflectivity;

[0048] Fig.11 and 12 A detachable module for photometric measurement according to at least some embodiments of the present invention is shown;

[0049] Fig.13 An embodiment is shown where the light source and detector are movable around the tip.

[0050] Fig.14 An embodiment is shown in which the detector is movable around the tip.

[0051] Fig.15 An embodiment is shown where the light source and detector are movable around the tip.

[0052] Fig.16An embodiment utilizing a time-of-flight assembly located within a cylinder is shown.

[0053] Fig.17 and 18 An embodiment utilizing a time-of-flight assembly partially within a cylinder is shown.

[0054] Fig.19 An experimental set-up for photometric measurement according to an embodiment of the present invention is shown.

[0055] Fig. 20 is a diagram showing a measurement signal as a function of aspirated liquid volume according to an embodiment of the present invention. DETAILED DESCRIPTION

[0056] definition

[0057] In the context of this article, the term "liquid handling system" includes handheld pipettes and automated liquid handling stations or robots. These systems can be manual, electronic or electromechanical.

[0058] In the context of this document, the term "tip" includes disposable and non-disposable tips that are removable and used in handheld pipettes or automated liquid handling stations or robots to hold liquid samples to be dispensed into containers, microplates, etc. Such tips may be custom made or mass produced and made of any suitable material, preferably a plastic material. In a preferred embodiment, the tip is a disposable tip.

[0059] In liquid handling systems such as pipettes, linear actuators are present for driving a plunger longitudinally in a barrel to draw fluid into and dispense fluid from a pipette tip.

[0060] We have observed that optical measurements can be successfully applied to detect and monitor different states of the tip during liquid handling or dispensing activities. In the context of this article, "state of the tip" refers to, for example, the liquid level or liquid volume in a pipette tip, the stability of the tip, the contact between the tip and an external liquid container, or the contact between the tip and the liquid surface in the container. The method is based on performing relative measurements using two detectors. The use of this principle enables the design of a surprisingly large number of working measurement geometries.

[0061] The optical method can be based on the time-of-flight principle or on photometry. In photometry, the intensity of light is the measured quantity.

[0062] In some embodiments of the present invention, light passes through or enters the tip via a specific optical path so that the light interacts with the tip and / or its contents in various ways. After the interaction, the light is collected and characterized at a detector to analyze the state of the tip and any changes therein.

[0063] The present method makes it possible to detect the liquid level in the tip, the stability of the tip, the volume of liquid in the tip, and the contact between the tip and the surface of the liquid in the container by using optical measurements.

[0064] The geometric arrangement of the measurement determines the type of interaction that occurs between the light and the tip or the liquid in the tip. The interaction can be, for example, reflection, absorption, refraction, scattering or interference. Preferably, the interaction is reflection or absorption. Factors that affect the measurement dynamics include the incident direction and angle of the light, the position of the detector, the geometry of the tip, and the wavelength of the light.

[0065] In a preferred embodiment, the light from the light source is split into two beams, which are transmitted via two different light paths. "Different light paths" refers to paths that pass at least partially through different parts or interfaces of the material of the tip, the barrel of the liquid handling system, or the liquid / airspace within the tip; and / or the lengths of the paths are at least partially different and / or the angles of incidence are different. One or both light paths can pass through the airspace of the tip. One or both light paths can pass through the tip material or the barrel material.

[0066] Preferably, the optical measurement is performed by using infrared, ultraviolet or visible light or a combination thereof.

[0067] In photometric methods, the light source is preferably an LED or a laser.

[0068] Figure 1 The principle of relative measurement by using two optical detectors 11, 12 is shown. In this embodiment, the light from the LED 10 is split into two optical paths. The first optical path (measurement path) is configured for interaction with the suction head 13, and the second optical path is configured for directly measuring the intensity of the light source 10. By measuring the relative value between the two detectors, the instability of the light source is compensated.

[0069] In the first optical path, the interaction between the light and the liquid to be measured is mainly the reflection of the light from the liquid surface. A relative reflectivity measurement is performed. The following equation 1 defines the relative reflectivity R as a function of the detector blank and the time-dependent voltage signal:

[0070]

[0071] When V NB ≈V NK hour.

[0072] In Equation 1, V MB is the voltage of the measuring detector 11 in a blank measurement when the tip is empty, and V NB is the normalized detector 12 voltage in a blank measurement when the tip is empty. V MK is the time t when the tip contains liquid K The voltage of the measuring detector at the NK is the time t at which the tip contains liquid K The normalized detector voltage at .

[0073] exist Figures 2 to 18 In the figure, the second optical path and the normalized detector are not shown for clarity. Figures 2 to 18 In the embodiment shown in , the second optical path is configured for directly measuring the intensity of the light source.

[0074] exist Figure 2 In the embodiment, both the light source 20 and the measurement detector 23 are located in the barrel 22 of the pipette. The main interaction between the light transmitted via the measurement path and the liquid to be measured is reflection from the liquid surface 21. The relative reflectivity is measured.

[0075] exist Figure 3 and 4 In the embodiment of the present invention, light is transmitted into the tip material and is reflected from the lower edge 31, 41 of the tip 33, 43. The tip has a shape suitable for optical measurement so that light is transmitted from the tip to the liquid. The main interaction between the light transmitted via the measurement path and the liquid 32, 42 to be measured is the absorption of the light when it passes through the liquid in the tip. The light source is indicated by reference numerals 30, 40 and the measurement detector is indicated by reference numerals 34, 44.

[0076] We have observed Figure 2 and 4 The geometry shown in is particularly reliable and effective.

[0077] Figure 3 The embodiment is particularly suitable for use in automated liquid handling stations because the illumination and detection geometry is approximately vertical in the sense that the light source 30 and the detector 34 are located above the pipette tip 33.

[0078] If the tip touches the surface of the liquid in the external container, a decrease in the measurement signal can be observed, because the proportion of light reflected from the lower edge of the tip decreases relative to the amount of light that passes through the lower edge. This is based on the fact that the refractive indices of the tip material and the liquid are similar and they differ from the refractive index of air.

[0079] exist Figure 5 and 6In the embodiment of the present invention, the tip is illuminated from the outside by a light source 50, 60 and the light is reflected from the tip surface to a detector 51, 61. The response of the liquid to be measured is based on the absorption of the light when it passes through the liquid and on other optical phenomena.

[0080] exist Figure 3 , 4 In the embodiments shown in FIGS. 5 and 6 , it is possible to detect contact between the tip and the external container.

[0081] exist Figure 7 and 8 In the embodiment, the tip is illuminated from the outside by a light source 70, 80, and the light is reflected from the tip and the liquid surface to the detector 71, 81. The response of the liquid to be measured is based on reflections from the liquid surface 72, 82 and other optical phenomena.

[0082] Figures 5 to 7 The embodiment shown in provides a variety of measurement possibilities. By changing the angle of incidence, it is possible to measure various reflections of light: directly from the liquid surface; from an optical discontinuity between the liquid and the plastic tip material; or to observe changes in the optical conductivity of the plastic tip material.

[0083] Figures 5 to 8 The embodiment shown in is particularly suitable for use in an automated liquid handling station. In such a station, the position and orientation of the light source can be chosen very freely, and it is possible to illuminate the pipette tip from the side, for example.

[0084] exist Fig. 9 and 10 In the embodiment of the present invention, light is transmitted into the material of the cylinder 91, from which the light is refracted from the lower edge 92 of the cylinder toward the liquid surface 93. The lower edge 92 has an inclined surface or a lens shape. The response of the liquid to be measured is based on reflection from the liquid surface and other optical phenomena. The light source is indicated by reference numeral 90, and the measurement detector is indicated by reference numeral 94.

[0085] Fig. 9 Embodiments of can be applied to both handheld pipettes and automated liquid handling stations. The measuring geometry enables a compact structure.

[0086] exist Fig.10 In the embodiment of the invention, the light reflected from the liquid surface 101 is collected over a maximum area by using the lower edge 102 of the cylinder which has been shaped as a lens with a large diameter. The body 103 of the cylinder acts as a light conductor, inside which the light stays due to total internal reflection. Total internal reflection occurs because the material of the cylinder has a much greater refractive index than the air surrounding it. The light source is indicated by reference numeral 100, and the measurement detector is indicated by reference numeral 104. Fig.10 Embodiments of the invention are suitable for both automated liquid handling stations and handheld pipettes.

[0087] exist Fig.11 and 12 In this method, a removable measuring module in the form of a lens system is used, which is fixed to the inner or outer surface of the cylinder.

[0088] exist Fig.11 In the embodiment, the module 111 is sealed against the outer surface 112 of the cylinder. The body of the module acts as a light conductor and the lower surface 113 of the module acts as a lens. The suction head is sealed against the outer surface 114 of the module body. The light source is indicated by reference numeral 110 and the measurement detector is indicated by reference numeral 116.

[0089] Fig.11 Embodiments of the invention are particularly suitable for use in automated liquid handling stations.

[0090] exist Fig.12 In the embodiment, the module 121 is sealed against the inner surface 122 of the cylinder. The light source 120 and the detector 126 are located inside the module: in one embodiment, they are encased. In another embodiment, they have been cast in the light conductor forming the module. The lower surface 124 of the module forms a surface that reflects light, so that the light becomes reflected towards the liquid surface. Alternatively, small-sized components can be directed towards the liquid surface inside the module.

[0091] By using a photoconductor, this can be achieved by moving the light source and detector to the desired location, such as close to the pipette body. Figures 1 to 11 The geometric arrangement of .

[0092] exist Fig.13 In the embodiment, a light source 130 and a detector 133 are located on opposite sides of the tip and are fixed to a movable support frame 131. The frame can be formed as two support arms. The tip is scanned by rotating the frame and moving it in a vertical direction. The tip and its contents can be scanned very accurately. Based on the measurement data, it is possible to observe the straightness of the tip, the volume of liquid, the mixing of different liquids, and the airspace between two liquids in the dilution mode of the pipette.

[0093] exist Fig.14 In the embodiment of the present invention, a high-resolution line sensor 142 is used as a detector. The sensor is fixed to a movable support arm 141. By moving and rotating the support arm, the sensor is rotated around the tip. In this way, the tip and its contents can be scanned quickly and accurately. The uppermost pixel of the sensor can be used as a reference in the measurement, so that a separate reference detector is no longer needed for obtaining relative measurements. A two-dimensional image sensor can also be used instead of a line sensor.

[0094] exist Fig.15, the light source 150 is located at the lower end of the support arm 152, below the line sensor 151. A portion of the light that has passed through the outer surface of the suction head at a right angle is reflected upward from the opposite outer surface of the suction head toward the line sensor.

[0095] Figures 13 to 15 The embodiment shown in FIG. 1 is particularly suitable for use in liquid level detection in an automated liquid handling station.

[0096] In photometric measurements, the light source can generate different wavelengths that alternate frequently according to the time division principle. The parallel measurement data obtained in this way can be used to improve the measurement accuracy of liquids with different colors. It becomes possible to analyze the mixture of different liquids in the tip. By using the same light source assembly, different wavelengths can be easily generated, for example by using RGB LEDs.

[0097] In photometric measurements, signal processing can be performed by utilizing the phase-sensitive detection principle or a lock-in amplifier. The input signal to be measured modulates a carrier signal that has been formed by chopping the light source. In this way, the input signal is shifted to a suitable higher frequency, where it is not affected by low-frequency noise. Before sampling is performed by an AD converter, the signal is filtered by an analog anti-aliasing low-pass filter. After demodulation, the signal is filtered using a steep narrow-band digital low-pass filter, which can separate the input signal from the noise.

[0098] In addition to conventional photometric measurements, it is also possible to use modern and integrated time-of-flight components for monitoring the movement of pipette tips and determining the volume of liquid contained in the tip. Time-of-flight components measure the flight time of a light signal. The light transmitted by the component is reflected from the liquid surface to a detector located at the opposite edge of the component, whereby the component calculates the distance to the liquid surface based on the flight time of the light. The advantage of the time-of-flight measurement is that it is independent of the reflected light intensity, provided that the intensity exceeds a certain minimum level.

[0099] exist Fig.16 In FIG. 1 , the time-of-flight assembly 160 is completely located within the pipette barrel 161 .

[0100] exist Fig.17In the embodiment of the invention, the time of flight assembly 170 is only partially located inside the pipette barrel 171. The emitter side of the assembly is located outside the barrel. The light generated by the emitter is guided into the barrel via a multimode optical fiber 172. One end of the optical fiber is formed as a lens that guides the light toward the liquid surface 173. The light reflected from the liquid surface is collected over a maximum area using a lens 174, which focuses the collected light onto a detector of the measuring assembly. By using an optical fiber, the incident light is guided past or through the lens that collects the reflected light to avoid the incident light being reflected directly from the lens onto the detector. In this way, the measurement result is as accurate as possible. The lens can be a Fresnel lens, which allows it to be thin and light.

[0101] exist Fig.18 In, use Fig.17 A similar time of flight assembly 180 is shown in FIG. 1 . The lens that collects the reflected light has been replaced by a cone 182 that collects the light reflected from the liquid surface. The inner surface of the cone is reflective, whereby the cone effectively focuses the collected light onto a detector that measures the time of flight assembly. Instead of a cone, the collector can be shaped as a parabola.

[0102] Figures 16 to 18 The embodiments shown in FIG. 4 can be applied in both handheld pipettes and automated liquid handling stations.

[0103] In some embodiments of the present invention, light is conducted and directed toward the liquid surface or toward the pipette tip by using optical fibers or photoconductors.

[0104] In some embodiments of the present invention, light is conducted and directed toward a detector through the use of optical fibers or photoconductors.

[0105] The use of optical fibers provides flexibility in positioning the light source and / or detector in a liquid handling system, particularly in a handheld pipette, where the space available for adding additional components is limited.

[0106] When the pipette tip is illuminated from the outside, it is possible to detect contact of the pipette tip with a liquid surface in a container which is separate from the pipette and which serves, for example, as a liquid source or as a holding container for dispensing liquid.

[0107] In some embodiments, by utilizing a photoconductor, the light source and detector may be positioned close to the body of the pipette.

[0108] In one embodiment, infrared light is used in the measurement. The IR light source and / or the IR detector can be integrated into, for example, the lower part of the tip ejection sleeve of the liquid handling system.

[0109] In some embodiments, light is projected (reflected) to the measurement detector via two alternative paths: 1) through the tip material, or 2) through the airspace within the tip. The invention enables optimization of signal strength and accuracy with respect to the volume of liquid to be analyzed: for large liquid volumes (e.g. greater than 0.5 ml, preferably greater than 1 ml), path 2 is used. For small volumes (e.g. less than 1 ml, preferably less than 0.5 ml), path 1 is used. It is also possible to use two paths with different weights.

[0110] Preferably, the method is suitable for analyzing liquid volumes from 1 μl to about 10 ml, more preferably from 10 μl to 5 ml, such as from 10 μl to 200 μl.

[0111] The hysteresis phenomenon can be applied to analyze whether the tapered lower end of the tip contains liquid.

[0112] One advantage is that conventional disposable tips can be used. The tips do not need to contain any special components for conducting or directing the light, such as gratings, lenses or custom shapes.

[0113] In some embodiments, the tip includes vertically protruding channels on opposite sides thereof. The channels are preferably made of the same material as the rest of the tip, and they are configured to conduct light from the light source to the detector. Light is conducted downward from the light source via one channel and upward to the measurement detector via another channel.

[0114] The method can be applied to handheld pipettes or to automated liquid handling stations. In liquid handling stations, two independent methods for analyzing the liquid level in the tip can be used, such as the optical method and the method based on pressure measurement.

[0115] This method can accurately measure liquid volumes in the μl range.

[0116] The present invention overcomes several disadvantages of pressure-based liquid level detection methods: The present invention is not affected by ambient pressure or altitude above sea level. The present invention is able to detect clogging of the tip. In addition, the present method is suitable for detecting liquids with high viscosity. The movement of such liquids is delayed with respect to pressure changes within the tip. The optical measurement according to the present invention enables immediate and real-time detection of the volume of liquid contained in the tip.

[0117] In the following, we describe in more detail the electronics and signal processing according to some embodiments.

[0118] Relative measurement

[0119] By performing a relative measurement between two detectors, the instability of the light source (e.g., LED or laser) and its power supply is compensated. The light emitted from the light source is split into two optical paths. One optical path interacts with the pipette tip, while the other optical path is configured to measure the intensity of the light source directly or with a constant attenuation without any interaction with the pipette tip. The two detectors do not have to be identical, as long as they are used within their linear range. The accuracy of the measurement is based on the linear response of the detectors.

[0120] Noise Source

[0121] The term "noise" refers to everything that affects the measurement result but is not a function of the parameter to be measured. In optical measurements of pipette tips and the liquid volume inside them, the most significant noise is the noise in the optical signal. Scattered light from the environment and the dark current of the detector are observed as DC components in the measured signal, and room lighting can produce a 100 Hz component. Optical and electronic measuring devices also include 1 / f noise, white noise, and 50 Hz and 150 Hz components of the mains frequency. Apart from white noise, the most important noise sources have frequencies of less than 175 Hz.

[0122] Modulation and Sampling

[0123] In modulation, the input signal is shifted to a suitable higher frequency, where it is no longer affected by low-frequency noise. The signal generated by the detector is modulated to a frequency corresponding to the LED chopping. In the sampling performed by the AD converter, each on / off state of the LED forms a digital value. The sampling frequency (FS) is therefore doubled with respect to the modulation frequency. The input signal is transmitted as an amplitude modulated signal relative to the sampling frequency at the so-called Nyquist frequency (FS / 2).

[0124] Analog anti-aliasing filtering

[0125] Before sampling is performed by the AD converter, the signal is filtered by an analog low-pass filter. The so-called anti-aliasing low-pass filter limits the frequencies exceeding half the sampling frequency (FS / 2) to be folded into the sampled signal during sampling. The sampling of the AD converter is synchronized with the modulation, which means that the signal with a frequency of FS / 2 must pass through an analog low-pass filter whose cut-off frequency (-3dB) is set to FS / 2 plus a reasonable threshold.

[0126] Demodulation and filtering

[0127] When an amplitude modulated input signal at the Nyquist frequency is multiplied by a cosine signal of the Nyquist frequency of the form [1, -1, 1, -1 ...], it is demodulated, i.e. shifted to zero frequency. In the case of amplitude modulation, the spectrum of the modulated signal is shifted around the carrier signal. In order to detect the pipette tip and the liquid volume inside the tip, the intensity of the signal at zero frequency is of interest. After demodulation, the input signal is contained in the DC component and the remaining AC content is considered as noise about the measurement. As a result of the demodulation, the maximum noise power located near the zero frequency is shifted around the Nyquist frequency. After demodulation, the signal is filtered by a maximally steep and narrowband low-pass filter to prevent the input signal from being corrupted by noise or interference. In this way, the principle of phase-sensitive detection or lock-in amplifier is implemented.

[0128] Example

[0129] Fig.19 The measurement system built into a handheld mechanical pipette (Tacta model from Sartorius) is shown. The system is based on photometric measurement. In this test system, no normalized detector was used. In all other respects, the system uses Figure 2 The measurement geometry shown in . During the measurement, a 1000-μl pipette tip was used and the dispense volume was set to 1000 μl. The detector signal was recorded during the liquid aspiration. Digital low-pass filtering was performed by averaging the instantaneous AD converter results obtained by polling from the measurement system. The results are in Fig. 20 A graph of the measured signal intensity versus the volume of liquid in the tip is shown in . The results show that the system can reliably detect the presence of liquid in the tip and successfully pick up the tip.

[0130] It should be understood that the disclosed embodiments of the invention are not limited to the specific structures, process steps or materials disclosed herein, but extend to their equivalents, as will be recognized by those skilled in the relevant art. It should also be understood that the terminology employed herein is only used for the purpose of describing specific embodiments and is not intended to be limiting.

[0131] References throughout this specification to an embodiment or embodiments mean that the particular features, structures, or characteristics described in conjunction with the embodiment are included in at least one embodiment of the invention. Thus, the phrases "in one embodiment" or "in an embodiment" appearing in various places throughout this specification do not necessarily all refer to the same embodiment. Where values ​​are referenced using the terms such as, about, or substantially, the exact value is also disclosed.

[0132] As used herein, for convenience, multiple items, structural elements, constituent elements and / or materials may be presented in a common list. However, these lists should be interpreted as each component in the list being individually identified as a separate and unique component. Therefore, any individual component in such a list should not be interpreted as being in fact equivalent to any other component in the same list based solely on their presentation in a common group without an indication to the contrary. In addition, the various embodiments and examples herein may be mentioned together with alternatives to their various components. It should be understood that these embodiments, examples and alternatives should not be interpreted as in fact equivalents to each other, but should be regarded as separate and autonomous representations of the present invention.

[0133] In addition, the described features, structures or characteristics can be combined in any suitable manner in one or more embodiments. In this specification, many specific details, such as examples of length, width, shape, etc., are provided to provide a thorough understanding of embodiments of the present invention. However, those skilled in the relevant art will recognize that the present invention can be practiced without one or more specific details or by using other methods, components, materials, etc. In other cases, known structures, materials or operations are not shown or described in detail to avoid making various aspects of the present invention vague.

[0134] Although the foregoing examples illustrate the principles of the present invention in one or more specific applications, it is obvious to those skilled in the art that various modifications may be made in form, use and implementation details without implementing the inventive capability and without departing from the principles and concepts of the present invention. Therefore, the embodiments of the present invention are merely exemplary and are not intended to limit the present invention.

[0135] The verbs "comprise" and "include" are used herein as open-ended limitations, which neither exclude nor require the presence of unrecorded features. Unless expressly stated otherwise, the various embodiments of the embodiments of the present disclosure may be freely combined with each other. Furthermore, it should be understood that the use of "a" or "an", i.e., the singular form, throughout this document does not exclude a plurality.

[0136] Industrial Applicability

[0137] At least some embodiments of the present invention find industrial application in handheld pipettes and automated liquid handling stations.

[0138] Reference List

[0139] Patent Literature

[0140] EP 1756587 B1

[0141] US 8203721 B2

[0142] EP 1756587 B1

[0143] FI 120336 B

[0144] US 5844686

Claims

1. A liquid handling system for dispensing a liquid sample from a pipette tip, characterized in that It includes: - a light source configured to project a first light beam via a first light path that interacts with the pipette tip or its contents, and further configured to direct a second light beam via a second light path that does not interact with the pipette tip and its contents; - a first detector configured to detect a first light beam; - a second detector configured to detect the second light beam; - an analyzing unit configured to analyze the state of the tip based on the signals obtained from the first and second detectors; wherein the second detector is a normalized detector configured to measure the intensity of the light source; The liquid handling system includes a time-of-flight component including the light source and the first detector and configured to calculate a distance from the time-of-flight component to a surface of a liquid in a tip.

2. The system of claim 1, wherein the first and second detectors and the light source are located within a barrel of the liquid handling system, and wherein the liquid handling system is a handheld pipette.

3. The system of claim 1, wherein the first and second detectors are located within a cylinder of the liquid handling system and the light source is located outside of the cylinder.

4. The system of claim 1, wherein the first and second detectors and the light source are located outside a cylinder of the liquid handling system.

5. The system of claim 1, wherein the light source is located above an upper edge of the tip and is configured to project light into a material of the tip.

6. The system of claim 1, wherein the light source is located on a side of the tip and is configured to project light toward the tip, and wherein the liquid handling system is an automated liquid handling station.

7. The system of claim 1, wherein the barrel of the liquid handling system is configured to conduct light from the light source through a material of the barrel to an interior of the tip.

8. The system of claim 1, wherein the time-of-flight component is located within a barrel of the liquid handling system; and the liquid handling system is a handheld pipette.

9. The system according to claim 1, wherein: The light source in the time-of-flight assembly is located outside the cylinder of the liquid handling system, and the first detector in the time-of-flight assembly is located within the cylinder of the liquid handling system.

10. The system according to any one of claims 1-9, further comprising an optical fiber extending from the light source to the interior of the tip and configured to direct the first light beam from the light source to the liquid surface.

11. The system according to any one of claims 1-9, further comprising an optical assembly located in front of the first detector and configured to focus the first light beam from the interior of the tip onto the first detector.

12. The system of claim 7, wherein the lower edge of the cylinder of the liquid handling system is lens-shaped, and wherein the cylinder is configured to conduct light from the light source through the material of the cylinder and the lower edge of the lens shape to the interior of the nozzle, and in, The barrel is further configured to collect light interacting with the tip or its contents, in particular light interacting with the liquid surface, to the first detector.

13. A method for analyzing the status of a tip for aspirating and dispensing liquids used in a liquid handling system, characterized in that The following steps are involved: - directing a first light beam from a light source to a first detector via a first light path interacting with the tip or its contents; and measuring the amount of the first light beam; - directing a second light beam from the light source to a second detector via a second light path that does not interact with the tip and its contents; and measuring the intensity of the light source, and - analyzing the state of the disposable tip based on the measured quantity and the measured intensity of the light source; wherein the second detector is a normalized detector; The liquid handling system includes a time-of-flight component including the light source and the first detector and configured to calculate a distance from the time-of-flight component to a surface of a liquid in a tip.

14. The method of claim 13, wherein the first light beam interacts with a material of the tip or a liquid within the tip, or both.

15. The method of any one of claims 13 to 14, wherein the analyzing comprises one or more of: determining a liquid level in the tip, determining a liquid volume in the tip, determining contact between the tip and a liquid surface, determining contact between the tip and an external container, and determining movement of the tip.

16. The method of any one of claims 13 to 14, wherein the analyzing step comprises determining a liquid level or liquid volume in the tip, and wherein the quantity is reflectance or absorbance.

17. The method according to any one of claims 13 to 14, wherein: The time-of-flight component is located within a cylinder of the liquid handling system; The liquid handling system is a handheld pipette, and The quantity measured is reflectivity.

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