Particle detector, particle detecting apparatus and method of operating a particle detector

Abstract: A particle detector (10) is designed to detect particles such as cells and blood corpuscles and includes means (14, 16, 18, 30, 32) for passing through an orifice (12) and recovering a multilayer flow consisting of an inner layer (A) of conductive liquid specimen, a middle layer (B) of conductive first sheath liquid, and an outer layer (C) of nonconductive second sheath liquid surrounding the inner and middle layers (A, B), and a pair of electrodes (16, 30) disposed upstream and downstream of the orifice (12) and in electrical contact with the conductive liquids. A particle detecting apparatus incorporates the particle detector (10) and a detector circuit (44) connected to the pair of electrodes (16, 30) so as to detect particles in the conductive liquid specimen of the inner layer (A) by detecting changes in the electrical impedance between the electrodes. An electric current flows from one electrode (16) to the other electrode (30) through the conductive liquids of the inner layer (A) and middle layer (B). Because the outer layer (C) is nonconductive, the current does not flow through that layer. Thus, the effective diameter of the orifice (12) is substantially the diameter (b) of the middle layer (B). By varying the flow rate balance of the conductive liquids and nonconductive liquid, the diameter (b) of the middle layer (B) may be easily changed. Thus, the effective diameter (b) of the orifice (12) may be changed to optimize the detection of large or small particles in the conductive liquid specimen of the inner layer (A).

Description: The present invention relates to a particle detector for detecting particles of cells, blood corpuscles or the like by passing them through an orifice in sheath liquid. The present invention also relates to particle detecting apparatus incorporating such a detector and to a method of operating a particle detector. A known particle detecting apparatus is disclosed in US-A-3,746,977 and has a pair of electrodes disposed across an orifice (aperture) for detecting particles individually on the basis of changes of electrical impedance caused when particles pass through the orifice. Another known particle detecting apparatus is disclosed in US-A-4,790,653 and in EP-A-0,068,404 and forms a sheath flow and passes a stream of the particles through the centre of its orifice. Detection electrodes are positioned upstream and downstream of the orifice. In this case, the term "sheath flow" means a laminar flow of sheath liquid which surrounds a suspension of particles, in order to pass the particles in a line through the middle of the orifice. In such particle detecting apparatus, the inside diameter of the orifice is, as a matter of course, unchanged, and the size of measurable particles is substantially fixed at one value. For example, when measuring large particles, there arise problems of clogging or loss of linearity (linear correlation) between the size of particles and magnitude of detection signal; when measuring small particles, a sufficient S/N ratio is not obtained, and signals are concealed by noise and cannot be detected. By raising the detection current, the S/N ratio may be raised somewhat, but it may result in adverse effects on particles or lead to other problems. Incidentally, the S/N ratio is the ratio of the desired signal to the noise mixed in the signal and, the higher the S/N ratio, the easier it is to detect signals. If desired to measure without problem from small particles to large particles, it is required to vary the size of the orifice depending on the particle size. That is, in the case of large particles, it is necessary to measure with a wider orifice diameter and, in the case of small particles, a narrower orifice diameter is desired. However, since the orifice is assembled into the detector body, to vary the orifice diameter it is necessary to prepare a plurality of detectors having different orifice diameters, and to exchange the detectors depending on the particles to be measured. If the diameter of the orifice is variable, a range of particle widths may be measured. In the conventional apparatus, it was time consuming because the detectors had to be exchanged. Also, the orifice diameter could only have the preset values of the various prepared detectors. If the orifice diameter can be set to any value, it is possible to measure particles of any size under optimum conditions, which would be a great advance in particle measurement. US-A-4,352,558 discloses particle detecting apparatus which does not use electrodes to detect particles as they pass through its orifice. Instead, a laser beam passes transversely across the orifice. Two or three concentric fluid flows of substantially the same sheath liquid are used to surround a central flow of a liquid specimen which contains particles. The diameter ratio of the central flow and the adjacent concentric sheath flow may be varied by longitudinally moving one or both of the tubes which discharge those two flows. According to a first aspect of the present invention, there is provided a particle detector for passing a liquid specimen containing particles through an orifice whilst surrounded by sheath liquid, and for detecting particles individually by using the difference in electrical impedance of liquid and the particles, the detector comprising: an orifice; means for passing through the orifice and recovering a multilayer flow comprising a conductive liquid specimen containing particles and forming an inner layer, with a conductive first sheath liquid surrounding the inner layer; and a pair of electrodes, one of which is disposed in electrical contact with the conductive liquids upstream of the orifice and the other of which is disposed in electrical contact with the conductive liquids downstream of the orifice; characterized in that the means for passing through the orifice and recovering the multilayer flow is arranged to form the conductive first sheath liquid as a middle layer and is arranged to include in the multilayer flow a nonconductive second sheath liquid surrounding the inner and middle layers and forming an outer layer. By varying the flow rates of the first and second sheath liquids, it is possible to continuously vary the effective orifice diameter (as defined by the diameter of the middle layer) so as to provide optimum detection conditions for particles of different size. Also, the varying of effective orifice diameter is achieved in a simple manner that does not require pieces of the detector to be physically exchanged. Preferably, the means for passing through the orifice and recovering the multilayer flow comprises: a liquid specimen outlet pipe disposed upstream of the orifice; a first sheath liquid outlet pipe disposed concentrically around the liquid specimen outlet pipe; a first recovery pipe disposed downstream of the orifice; and a second recovery pipe disposed concentrically around the first recovery pipe. Alternatively, the means for passing through the orifice and recovering the multilayer flow comprises: a liquid specimen outlet pipe disposed upstream of the orifice; a first sheath liquid outlet pipe disposed concentrically around the liquid specimen outlet pipe; and a single recovery pipe disposed downstream of the orifice. Preferably, the pair of electrodes comprise the first sheath liquid outlet pipe and first recovery pipe, both of which are made of conductive material. Particle detecting apparatus may comprise a particle detector according to the present invention and a detector circuit connected to the pair of electrodes for detecting particles in the conductive liquid specimen of the inner layer by detecting changes in the electrical impedance between the electrodes. Preferably, the means for passing through the orifice and recovering the multilayer flow further comprises liquid specimen supply means, first sheath liquid supply means and second sheath liquid supply means respectively connected to the liquid specimen outlet pipe, the first sheath liquid outlet pipe and a second sheath liquid outlet pipe disposed around the first sheath liquid outlet pipe. According to a second aspect of the present invention, there is provided a method of operating a particle detector, comprising: providing a multilayer flow comprising a flow of conductive first sheath liquid around a flow of a conductive liquid specimen containing particles and forming an inner layer; passing the multilayer flow through an orifice; providing a first electrode in electrical contact with the flows of conductive liquid upstream of the orifice, and a second electrode in electrical contact with the flows of conductive liquid downstream of the orifice; and detecting the particles by detecting changes in the electrical impedance between the first and second electrodes; characterized in that: the flow of conductive first sheath liquid is provided as a middle layer and the multilayer flow further comprises a flow of nonconductive second sheath liquid as an outer layer; and the method further comprises adjusting the balance of the flows in order to vary the effective diameter of the orifice for the flows of conductive liquid. The conductive first sheath liquid may be physiological saline or the like and the nonconductive second sheath liquid may be purified water or ethyl alcohol. If the orifice is cylindrical, the inside diameter of the orifice may be designated d. The outside diameter of the inner layer (liquid specimen flow) in the orifice may be designated a, the outside diameter of the middle layer (conductive liquid flow) may be designated b, and the outside diameter of the outer layer (nonconductive liquid flow) may be designed c (c = d). An electric current flows from one electrode to the other electrode through the conductive liquid layers (inner layer, middle layer). The outer layer is nonconductive, and the current does not flow through this layer. Accordingly, the current flows only in the internal region with the diameter b, and the diameter of the orifice is effectively b. By varying the flow rate balance of the conductive liquid and nonconductive liquid, the diameter b of the middle layer may be continuously changed. Thus, the effective orifice diameter may be continuously varied. The invention will now be described by way of a non-limiting embodiment and modifications thereof, with reference to the accompanying drawings, in which:- Fig. 1 is a vertical sectional view showing the embodiment of the particle detector in accordance with the present invention; Fig. 2 is a magnified view of the orifice area shown in Fig. 1; Fig. 3 is a sectional view showing another example of the orifice area for a particle detector in accordance with the present invention; and Fig. 4 and Fig. 5 are sectional views showing other embodiments of the recovery pipe for a particle detector in accordance with the present invention. In Fig. 1, numeral 10 is a detector and 12 is an orifice (for example, its inside diameter is 100 µm, and length is 120 µm). At the upstream side of the orifice 12, (bottom of Fig. 1), there is a liquid specimen outlet pipe 14 for discharging a liquid specimen containing particles, and a first sheath liquid outlet pipe 16 is disposed concentrically around the liquid specimen outlet pipe 14. The liquid specimen is constantly discharged from liquid specimen supply means 20 (for example, a syringe capable of discharging the liquid at a specific flow rate from a piston) connected to a supply port 15. The front end of the first sheath liquid outlet pipe 16 is located at the downstream side (upward in Fig. 1) of the liquid from the front end of the liquid specimen outlet pipe 14, and the end of the pipe 16 is tapered. This ensures the smooth formation of laminar flow. The first sheath liquid is supplied from the first sheath liquid supply means 22 (syringe or means for pushing out liquid at specific pressure) to a supply port 26 disposed in the lower part of the first sheath liquid outlet pipe 16. The first sheath liquid flow encloses and surrounds the liquid specimen. Numeral 18 is a path for the second sheath liquid. With the invention, it is so arranged that a second sheath liquid flows outside the first sheath liquid. The second sheath is a nonconductive liquid. The nonconductive second sheath liquid is supplied into a supply port 28 disposed in the lower part of the detector 10 from second sheath liquid supply means 24 (syringe or means for pushing out liquid at specific pressure). At the downstream side of the orifice 12, a first recovery pipe 30 is provided, and a second recovery pipe 32 is disposed concentrically around the first recovery pipe 30. In this embodiment, the front end of the second recovery pipe 32 is at the downstream side from the front end of the first recovery pipe 30. Numerals 34, 36 are waste liquid tubs, and the waste liquid tubs 34, 36 are respectively connected to the outlet 37 of the first recovery pipe 30 and the outlet 38 of the second recovery pipe 32. Numeral 42 is syringe liquid supply means for providing a back sheath, and it is connected to the inlet 40 above the detector 10. As shown in Fig. 2, a three-layer flow is formed, consisting of the liquid specimen as inner layer A, first sheath liquid as middle layer B, and second sheath liquid as outer layer C. Being a laminar flow, the liquid of each layer flows without mixing with the other layers. If it was not a laminar flow, each liquid would mix with the other liquid at each boundary, and particle detection would be unstable. The liquid specimen and first sheath liquid are conductive, and the second sheath liquid is nonconductive. A pair of electrodes are disposed on either side of the orifice 12 in contact with the conductive liquid (for example, the first sheath liquid). In this embodiment, the first sheath liquid outlet pipe 16 and the first recovery pipe 30 are made of conductive material and used as electrodes. More specifically, the first sheath liquid outlet pipe 16 is made of stainless steel and functions as the negative electrode, and the first recovery pipe 30 is made of platinum and functions as the positive electrode. In the first recovery pipe 30, all of the liquid specimen and a part of the first sheath liquid are recovered and, in the second recovery pipe 32, the remainder of the first sheath liquid and all of the second sheath liquid are recovered together with syringe liquid. Numeral 44 is a detector circuit for supplying a current between the positive electrode 30 and negative electrode 16, and detecting the changes in electric impedance. Numeral 46 is an electric wire. The current flows through the conductive liquid, but does not flow through the nonconductive liquid. Accordingly, by varying the sectional area of the conductive liquid flows (inner layer A and middle layer B) in this three-layer flow, the size of the orifice may be substantially changed. To vary the sectional area of the conductive liquid flows (inner layer A and middle layer B), it is enough to change the flow rate balance of the conductive liquid and nonconductive liquid. This requires, at least, means for varying the first sheath liquid supply rate and second sheath liquid supply rate. Numeral 48 is the control means for controlling the liquid supply rate. For obtaining a better laminar flow, it is preferable that the control means 48 also controls the supply rate and discharge rate of all liquids. What has been described is one example of a detector such as flow cell of a flow cytometer or the like, but alternative constructions are possible. For example, as shown in Fig. 3, a circular orifice 12 may be formed in the center of a disc-shaped orifice plate 46 made of artificial ruby, ceramics or similar material. In the embodiment shown in Figs. 4, 5, instead of the first recovery pipe 30 and second recovery pipe 32, a recovery pipe 50 of nearly the same shape as the second recovery pipe is provided, and all of the liquid specimen of inner layer A, first sheath liquid of the middle layer B and second sheath liquid of the outer layer C is recovered in the recovery pipe 50. Inside this recovery pipe 50, a positive electrode 52 is disposed so as to contact the conductive liquid. Otherwise, the construction and operation are the same as for Figs. 1 to 3. The above described embodiments of the invention offer the following benefits. (1) A flow of a nonconductive liquid is provided as the outer layer, and current does not flow in this nonconductive layer, so that the apparent diameter of the orifice (the sectional area) may be reduced. Also, since the thickness of the nonconductive liquid layer may be freely varied as necessary, the diameter of the orifice may be substantially changed. (2) To vary the diameter of the orifice, it is enough to change the balance of the flowing liquids, and it does not require the trouble of exchanging the detector or the like. The construction is simple, too. (3) Since the diameter of the orifice may be freely changed, the range of measurable particles may be extremely wide. That is, from small particles to large ones, it is always possible to measure in optimum conditions without causing problems such as clogging, noise and lack of linearity (linear correlation).

Claims: A particle detector (10) for passing a liquid specimen containing particles through an orifice (12) whilst surrounded by sheath liquid, and for detecting particles individually by using the difference in electrical impedance of liquid and the particles, the detector (10) comprising: an orifice (12); means (14, 16, 18, 30, 32, 50) for passing through the orifice (12) and recovering a multilayer flow comprising a conductive liquid specimen containing particles and forming an inner layer (A), with a conductive first sheath liquid surrounding the inner layer (A); and a pair of electrodes (16, 30, 52), one of which is disposed in electrical contact with the conductive liquids upstream of the orifice (12) and the other of which is disposed in electrical contact with the conductive liquids downstream of the orifice (12); characterized in that the means (14, 16, 18, 30, 32, 50) for passing through the orifice (12) and recovering the multilayer flow is arranged to form the conductive first sheath liquid as a middle layer (B) and is arranged to include in the multilayer flow a nonconductive second sheath liquid surrounding the inner and middle layers (A, B) and forming an outer layer (C). A particle detector (10) according to claim 1, wherein the means (14, 16, 18, 30, 32) for passing through the orifice (12) and recovering the multilayer flow (A, B, C) comprises: a liquid specimen outlet pipe (14) disposed upstream of the orifice (12); a first sheath liquid outlet pipe (16) disposed concentrically around the liquid specimen outlet pipe (14); a first recovery pipe (30) disposed downstream of the orifice (12); and a second recovery pipe (32) disposed concentrically around the first recovery pipe (30). A particle detector (10) according to claim 1, wherein the means (14, 16, 18, 50) for passing through the orifice (12) and recovering the multilayer flow (A, B, C) comprises: a liquid specimen outlet pipe (14) disposed upstream of the orifice (12); a first sheath liquid outlet pipe (16) disposed concentrically around the liquid specimen outlet pipe (14); and a single recovery pipe (50) disposed downstream of the orifice (12). A particle detector (10) according to claim 2, wherein the pair of electrodes (16, 30) comprise the first sheath liquid outlet pipe (16) and first recovery pipe (30), both of which are made of conductive material. Particle detecting apparatus comprising a particle detector (10) according to any one of claims 1 to 4 and a detector circuit (44) connected to the pair of electrodes (16, 30, 52) for detecting particles in the conductive liquid specimen of the inner layer (A) by detecting changes in the electrical impedance between the electrodes (16, 30, 52). Particle detecting apparatus according to claim 5, wherein the particle detector (10) is in accordance with claim 2, 3 or 4 and the means (14, 16, 18, 30, 32, 50) for passing through the orifice (12) and recovering the multilayer flow (A, B, C) further comprises liquid specimen supply means (20), first sheath liquid supply means (22) and second sheath liquid supply means (24) respectively connected to the liquid specimen outlet pipe (14), the first sheath liquid outlet pipe (16) and a second sheath liquid outlet pipe (18) disposed around the first sheath liquid outlet pipe (16). A method of operating a particle detector (10), comprising: providing a multilayer flow comprising a flow (B) of conductive first sheath liquid around a flow (A) of a conductive liquid specimen containing particles and forming an inner layer; passing the multilayer flow through an orifice (12); providing a first electrode (16) in electrical contact with the flows (A, B) of conductive liquid upstream of the orifice (12), and a second electrode (30, 52) in electrical contact with the flows (A, B) of conductive liquid downstream of the orifice (12); and detecting the particles by detecting changes in the electrical impedance between the first and second electrodes (16, 30, 52); characterized in that: the flow (B) of conductive first sheath liquid is provided as a middle layer and the multilayer flow further comprises a flow (C) of nonconductive second sheath liquid as an outer layer; and the method further comprises adjusting the balance of the flows in order to vary the effective diameter (b) of the orifice for the flows (A, B) of conductive liquid. A method according to claim 7, wherein the balance of the flows (A, B, C) of conductive and nonconductive liquids is adjusted by varying the balance of the flow rates of the middle and outer layers (B, C). A method according to claim 7 or 8, wherein downstream of the orifice (12) a single recovery pipe (50) recovers all of the flows (A, B, C) of nonconductive liquid and conductive liquid, and the second electrode (52) is positioned inside the recovery pipe (50).

Inventors: KOUZUKI CHIHIRO, KOUZUKI, CHIHIRO
Applicants: TOA MEDICAL ELECTRONICS, TOA MEDICAL ELECTRONICS CO., LTD.
Application year: 1991
Main classification: G01N15
IPC codes: G01N15