FR2542110A1 - METHOD AND DEVICE FOR DETECTING THE CHANGE OF THE DETACHMENT POINT OF A DROPLET PRODUCTION SYSTEM - Google Patents

Abstract

THE INVENTION RELATES TO A DEVICE FOR ANALYZING AND SORTING PARTICLES IN SUSPENSION IN A LIQUID, THIS DEVICE INCLUDING A JET-FORMING MEANS FOR PRODUCING A CURRENT FROM A JET OF THE LIQUID SUSPENSION, A VIBRATORY MEANS FOR VIBRATING THE CURRENT TO PRODUCE WAVE A THE SURFACE OF THE CURRENT AND A SUBSEQUENT DISINTEGRATION OF THE CURRENT INTO DROPS TO RECOVER THEM DOWNSTREAM AND A RADIATION MEDIA TO FORCE A RADIATION BEAM TO IMPACT THE CURRENT IN A LOCATION WITH THE DROPPING POINT OF THE DROPLET. ACCORDING TO THE INVENTION, A DETECTION MEANS 44 TORQUE TO VIBRATORY MEANS 24 AND RESPONDING TO THE RADIATION DISPERSED BY CURRENT 16, PRODUCES AN OUTPUT SIGNAL WHICH IS A FUNCTION OF THE Ripple at that location. THE INVENTION IS APPLIED IN PARTICULAR TO PARTICLE ANALYZERS.

Description

The present invention relates to a device for sorting

  tiny particles in a fluid, and in particular to such a device where a current of a liquid jet containing these particles is vibrated to produce corrugations on the surface of the jet stream and a subsequent disintegration of the stream into droplets which are then sorted according to the characteristics of

particles and collected downstream.

  Devices of the above kind can be considered flow flow cytometric sorting systems and are used in the field of research and medical diagnostics for the rapid analysis of blood cells and other biological cells. cells and for sorting them are described in U.S. Patents 4,038,556; 3,963,606; 3,710,933 and 3,380,584, in SCIENCE, volume 198, pages 149-157, published October 14, 1977 and in references

which are quoted there.

  U.S. Patent No. 4,038,556 discloses a method and a device for simultaneous optical measurement of several characteristics of each particle of a group of small particles while the particles are in suspension

in a liquid.

  U.S. Patent No. 3,963,606 discloses a particle separator for separating particles in a liquid according to certain features including a device for adjusting an electrical delay to be equal to the time between the emergence of a particle from an opening

  forming a jet and its point of detachment.

  U.S. Patent No. 3,710,933 discloses a device for automatically analyzing and sorting tiny particles suspended in a liquid on the basis of

  certain preselected characteristics.

  U.S. Patent No. 3,380,584 discloses a particle separator where electrical pulses force an acoustic coupler to vibrate the fluid that contains

the particles.

  SCIENCE article, volume 198, pages 149-157 discloses a flow cytometer The fluorescence of biological cells in a fluid stream is measured at the intersection with a laser beam The droplets containing the cells of interest are sorted out of the fluid stream The above patents are incorporated

  here as a reference because they may be necessary

  to the full understanding of the techniques used

  involved and teachings of the present invention.

  A major problem in the use of cell sorter systems where a jet stream subjected to vibration is released into droplets is to determine whether a change has occurred at the point where the stream current is transformed into droplets. the detachment from the detection point changes, then the instrument ceases to be a cell sorter and becomes a sorter of water or saline with an unknown cell content. An even less desirable result is obtained. naked if unwanted particles are sorted

  when there is such a change in the point of detachment.

  Such a change is often due to changes in the mechanical coupling coefficients, such as air bubbles entering the flow chamber and partial plugs in the jet outlet port. Optical sensitivities, such as presence of unwanted light, make it impossible to use an illuminance scanning source to observe the point of detachment of the jet stream while the system takes data or sorts the cells.

  sorting a monitor is most needed.

  The object of the present invention is to detect, in a droplet generation system, a change in the amplitude of the undulations at a fixed point on the surface of a liquid suspension jet stream before the point of detachment of the droplet, and indicate

that such a change has occurred.

  Another object of the present invention is the automatic inhibition of the sorting function in a particle analyzer and sorting system when there is a significant change in the droplet detachment point. Another object of the present invention is the use of information derived from a change in the amplitude of the ripple at a fixed point on the surface of a current

  jet to restore the amplitude level of the waveform.

  lation at this fixed point, to its original state.

  Other objects will become more apparent to the

  reading of the detailed description which follows.

  The liquid jet stream containing the minute particles in suspension is driven at the rate at which it is desired to produce the droplets, normally 20 to 40 k C depending on the diameter of the jet outlet port; for example, a frequency of 32 k C for a diameter of the jet outlet orifice of 76 and a frequency of k C for a diameter of the jet outlet orifice of -60, where the jet is vibrated. introducing a small disturbance, for example by a piezoelectric driven crystal, to the outlet of the stream of the jet This disturbance has the form of a ripple or a stable wave on the surface of the jet stream and this ripple As the jet advances and forces the detachment of the droplets downstream, the amplitude of the wave or wave at any point along the stream current is a function of the distance between this point and the point of detachment of the droplet and this aspect is described

  in the report by Richard G Sweet, SEL-64-004, March 1964, -

  Stanford University Stanford University According to the invention, the amplitude of the ripple at a fixed point is monitored A change of this amplitude at this point

  fixed point indicates a change of the detachment point.

  A laser beam, used as a source of illumination in the optical cell sorting systems described in the above-mentioned US patents, is used as a concentrated source of light rays in the scheme.

4 2542110

  The laser beam impacts the jet stream at a fixed point and then the laser current disperses to produce a lobe light pattern which is in the same plane as the laser beam and which is perpendicular to the beam. As is well known, this scattered light of the laser is modulated by the surface ripples of the jet. Until now, this modulation has been considered as an undesirable phenomenon when the

  scattering of light by the cell and was generally

  The present invention detects this modulation by placing a photodiode in the plane of laser light scattering. The output of the photodiode is converted into a voltage which can

  to be used (1) to alert the operators and

  audibly that a change has occurred at the point where the jet current breaks up into

  droplets, (2) to automatically control the inten-

  the vibration applied to the jet to restore the amplitude of the undulation to the point on the jet where it is monitored S or (3) to automatically inhibit the

  deviceo All the above events or a combination

  These can be used in the implementation of

practice of the invention.

  If desired, a secondary source of concentrated light rays other than the laser beam may be used to impact or to interrogate the jet stream at a point fairly close to the point of detachment of the droplet where the ripples are larger. and therefore o the signal that is obtained is more important In this case, the photodiode will be judiciously placed to receive the light

scattered or reflected from the jet.

  A feature of the invention resides in the sort inhibition circuit which comprises a fast change detector responding to a rectified output whose DC level is proportional to the percentage of modulation of the beam of concentrated light rays (laser beam, for example) affected by ripples at the surface of the jet stream This detector controls a latching mechanism (relay attack that serves to inhibit the sorting function of the particle analyzer whenever there is a significant change in the amplitude of the ripple on the jet current This circuit is provided with an operator reset device and an alarm which, if desired, can indicate the type of change in based on the polarity of the detector's output

quick change.

  Another feature is an automatic gain control loop (AGC) system for varying the intensity of the vibrations applied by the piezoelectric crystal to the jet current, for slow changes in the amplitude of the modulation. rectified above serves as the control voltage of the AGC loop This loop system varies the current

  which is applied to attack the piezoelectric crystal.

  As a result, precise corrections, to distinguish them from coarse corrections, of amplitude on the surface of the

  current of the jet, can be obtained

  the AGC system allows the establishment of

  initial point of the detachment point of the droplet.

  The invention will be better understood, and other purposes, features, details and advantages thereof

  will become clearer during the description

  explanatory text which will follow with reference to the accompanying schematic drawings given solely by way of example illustrating an embodiment of the invention and in which: FIG. 1 gives a schemablock of the manner in which the electrical elements of the invention are coupled a particle and sorter analyzer of a known type; Figure 2 shows the electrical circuit of the quick change detector, the locking mechanism

6 2542110

  relay driver and alarm circuits of the scheme of Figure 1; FIG. 3 schematically shows the electric circuit for converting the signal obtained at the photodiode into a rectified direct current which is proportional to the modulation of the light rays by the surface ripples of the stream current; and Figures 4 to 8 illustrate in more detail

  the electric circuit of the blocks of FIG.

  In all the figures of the drawings, the same

  parts are designated by the same reference numerals.

  The block diagram of FIG. 1 is subdivided into two parts by a dashed line. The system components to the left of the dashed line are those that normally exist in an analyzer and particle sorter system of a type sometimes known. Such a known sorting system can be found in the TPS and EPICS series of instruments manufactured and sold by Coulter Electronics, Inc. at Hialeah, Florida 33010, United States of America. particle analyzer and sorter that are needed to explain

  the operation of the present invention have been illustrated.

  The system components to the right of the dotted line 10 include those parts of the present invention that have been added and coupled to the known particle analyzer and sorter to achieve the objects of the invention. Automatic gain control (AGC) and the muting characteristic comprising a relay drive latch mechanism according to the invention are inserted at two locations in the normal signal paths of the particle-like analysis and sorting systems. it

will become better apparent below.

  The known particle analysis and sorting system shown to the left of the dotted line 10 will now be briefly described. It includes a chamber

  12 in which a saline solution (normal

  0.896 bar) is introduced under pressure and exits through a small orifice 14 (diameter between 50> to and -), depending on the application of the system) to form a stream of a liquid jet 16 The sample (a suspension of tiny particles such as blood cells or biological cells) is introduced into the flow chamber 12 through a tube 18 Below the outlet 14 and above and before the point of detachment, the jet stream 16 is interrogated by a light source and a radiation medium (normally a laser beam) and the response of the tiny particle in the sample to illumination (normally light scatter and fluorescence) is detected by the sensor system 22 also in one point before and above the

point of detachment.

  The flow chamber 12 is mounted on a piezoelectric crystal assembly 24 and is supported therein, which causes the chamber 12 to vibrate at a high frequency. The exact frequency at which the chamber 12 vibrates depends on the chosen diameter of the outlet orifice 14. , which

  Frequency is normally 20-40k Co These vibrations.

  impart small disturbances, normally ripples, to the surface of the jet 16, which grow due to well-known surface tension effects, and possibly pinch the jet at a point of detachment 26 into well-defined droplets 28 The exact distance of the tubing containing the orifice 14 at the point of detachment 26 is inversely proportional to the amplitude of the initial disturbance or waviness The dimension of the perturbation is proportional to the magnitude of the signal voltage applied to the crystal 24 j if the coefficients '

  The mechanical coupling factors of the system are constant.

  Unfortunately, there are several factors that can cause changes in the mechanical coupling coefficients and these factors are difficult to eliminate. It is the air bubbles that enter the flow chamber 12 with the sample or with the saline solution. Part-plugs of the outlet orifice 14 due to debris, such as broken cells or grease. The piezoelectric crystal is driven by a power amplifier 30 which normally derives its signal from a frequency generator 32 by a potentiometer. variable 34 that is used to vary the amplitude of the signal applied to the crystal 24 and thereby vary the nominal point of detachment 26 The potentiometer 34 serves

  coarse correction source to attack the amplifier

  The indicator 30 which drives the crystal 240 The line 36 designates the normal path from the potentiometer 34 to the amplifier

  in the absence of the components of the present invention.

  In the system according to the invention is incorporated a switch 59 which is not present in the systems

  according to the prior art for a purpose - which will be described hereinafter.

  At the sensor 22 is connected the sorting decision logic circuit 38 o the signals obtained from the detectors (not shown but forming part of the sensor system 22) are applied to a group of criteria to decide whether it is desirable or not to capture the particle At the origin of these signals O If the capture is desired, this decision must be delayed, for example by the sorting delay 40 while the particle is moving from the detection point to the point of detachment. A sorting pulse is then formed by the jitter pulse forming circuit 41 and is amplified and applied by the amplifier

  43 to the stream as a tension just at.

  When the droplets containing the desired particle separate from the jet Because of this printed voltage, the droplets separate with a net charge. The jet of droplets passes through a constant intense electric field which accelerates the droplets.

  loaded-in a horizontal Ian while they go down.

  Thus, the charged droplets move along a different path of the uncharged droplet path and fall into different capture vessels,

  to thereby perform a physical sorting of the particles.

  A typical sorting rate for this process is 4,000 particles per second. US Pat. No. 3,380,584 discloses a way of printing a voltage on a portion of the downstream jet stream containing particles to be charged for subsequent recovery and to an article by Hulett, Bonner, Sweet and Hertzenberg, CLINICAL CHEMISTRY, Volume 19, No. 8, 1973, where the impression of a tension on a part of the

jet-upstream, for the same purpose.

  The above system is known and no claim is made here concerning this method according to the prior art of analysis and sorting of tiny particles. Such a device is disclosed in US Pat.

  mentioned above and the references cited therein.

  In the present invention, the relationship between the amplitude of the ripple at the surface of the jet stream at any fixed point and the position of the point of detachment of the droplet is used to determine if there is a change in the point of contact. detachment of the droplet As previously indicated, the amplitude of the ripples increases while the point of detachment

  An increase in the amplitude of the corrugation

  at any given point along the jet is an indication that the detachment point is closer while a decrease in amplitude is an indication that the detachment point is further away. The device according to the invention monitors the position of the detachment. detachment point to obtain one of the following three results: (1) to give an indication, either visually, for example by means of a measuring device, or audibly, by means of an alarm, a change of the detachment point, (2) to inhibit the triage process and sound an alarm if there is a quick change

  from the point of detachment, or (3) to restore automatic-

  the point of detachment, for example by means of an automatic gain

  slow and slow changes in the detachment point.

  The system components to the right of the dotted line 10 in the block diagram of FIG. 1 form portions of the present invention which are connected to the known particle analyzer and sorter appearing to the left of line 10 in FIG. dotted, and comprise a photodiode or detection means 44 which detects the light scattered by the jet stream 16 as a result of the impact by the concentrated beam of intense light 20 This scattered light has two components: a dc component which is proportional to the size of the current of the jet 16 at the detection point 21, the point on the current 16 o the light beam is impacting, and the power of the intense light beam 20 (the laser) The diode 44 operates in current mode, that is, it is terminated at low impedance, thus producing a linear relationship of optical power to current and reducing the effects of capacitance

  of the diode for a maximum electronic bandwidth.

  The photodiode 44 is coupled to an operational amplifier

  46 which functions as a trans-

  impedance Amplifier 46 converts the current of diode 44 linearly to a voltage. The output of amplifier 46 is divided into an ac path including the AC amplifier.

  48 and a DC path including amplification

dc generator 50.

  The AC path contains the basic information to be used in the practice of the invention, i.e. the amplitude of the ripples on the jet current As the amplitude of the ripple signals produced in the photodiode detector 44 is

  low, the signal receives a considerable gain through the ampli-

  In order to improve the ratio of the signal to the noise in this AC path, the bandwidth of the alternating current amplifiers is limited to the range of oscillation frequencies applied to the AC signal amplifier. Since the size of the jet 16 is kept constant during a test of the particles of the sample and seldom changes, the DC component is proportional to the size of the jet 16 and the power of the laser 20, so a change in the DC level in the path containing the DC amplifier 50 can be considered as a change in the power of the laser.

  the DC path controls the gain of an amplifier

  A voltage-adjusted gain indicator 52 at the output of the AC path, thereby allowing the signal in the AC path to be normalized with respect to laser power, whereby recalibration of the device is eliminated. Whenever the power of the laser changes, in other words, the DC path suppresses the effect of a change in the power of the laser on the measurement of the distance from the detection point 21 to the point of detachment.

  The AC signal of the amplification

  The voltage regulator 52 is rectified by the rectifier 54 (preferably a full-wave rectifier to provide a smoother DC signal at its output) to produce a DC signal to the driver 56 which is proportional to the amplitude. current ripples 16 and proportional to the distance between the detection point 21 and the detachment point 26 The details of a suitable full-wave rectifier that can be used are shown in FIG. The easiest way is to drive a percentage modulation meter 56 which gives a visual indication of the position of the detachment point 26 of the droplet on the jet stream 16 Well calibrated, a Such measuring apparatus 58 may be used to establish the detachment point 26 by manually adjusting the potentiometer 34 and using it. the normal path 36 in the analyzer and sorter device known to bypass

  the automatic gain control system described here.

  The measuring apparatus 58 is connected so as to be able to

operate at any time.

  The rectified voltage at the lead 56 (the output of the rectifier 54) can also be set as a set voltage in an automatic gain control loop (AGC) which will produce accurate corrections for

  distinguish them from gross corrections, amplification

  power supply or voltage driver 30 supplying the piezoelectric crystal transducer 24 through the path 60, and therefore accurate corrections of the sliding point of detachment 26 assuming of course that the control of the normal path 36 is transferred by any switching means 59 when the automatic gain adjustment feature of the invention is used. This automatic gain control loop comprises an AGC amplifier system 64 which is powered by the voltage on the conductor 56 by means of the lead 66, and whose design is similar to that of the gain-set gain amplifier circuit-52 which can be seen in Figure 7 o A bipolar switch

  59 is connected between the conductors 36 and 37.

  The switch 59 serves to effectively disable the automatic gain control loop of the system when it is desired to initially prepare the analyzer and sorter for a specific delay of the droplets. When the appropriate delay has been established, the automatic gain control system 64 is armed or activated to maintain the desired point of detachment. Before activation of the automatic gain adjustment system, the voltage output terminal Vo (conductor 37) is adjusted to the same amplitude as that on the normal path 36 by means of the potentiometer 67 as indicated by the zero detection apparatus 68, then the switch 59 can be toggled to transfer the control of the amplifier

  30 power to the automatic gain adjustment system.

  Another way of monitoring the detachment point 26 on the jet 16 is to use a system comprising a quick change detector 70

  to which the rectified voltage to the conductor 56 is applied.

  The output 80 of the fast change detector 70 is zero if a DC signal is applied (which is the case when the detachment point 26 is constant) and changes to zero if a "fast" change of the droplet detachment point The polarity of the change at the output 80 of the fast change detector 70 indicates whether the level of the rectified signal at the output of the rectifier 54 has increased or decreased. The output of the detector 70 can drive an alarm circuit 72 to alert the operator of a change in the detachment point This same output can also attack a relay system composed of a locking mechanism

  Attack 76 which, in turn, serves to automatically inhibit

  The resetting system 74 by the conductors 78 in the particle analyzer and sorter is reset by the operator to manually reset the drive lock mechanism 76. Alarm 72 may be given to indicate the type of change of the detachment point based on the polarity of the output

of the detector 70.

  FIG. 2 schematically illustrates a form that the electrical circuit of the quick change detector can take, including the drive mechanism

  relay and reset by the operator and the alarm.

  Figure 2 shows both the audible alarm 72 and a visual alarm 71 The signal change to the driver

  56 is coupled to the amplifier 70 by the capacitor Ci.

  This AC signal is amplified and applied to the conductor 80. If the signal to the conductor 56 is a constant, direct current, the conductor 80 is near zero potential. The conductor 80 is connected to two comparators 77 and 79 which are configured to sense the variations of the signal to the conductor 80 of each polarity deviating from a zero potential A slight guard band is used to allow an offset of the amplifier When the signal to the conductor 80 changes, the appropriate comparator detects the change and switches The switching is detected and locked by the latch 81 The output U of the latch 81 switches, inhibiting MON AND gate 78, thereby interrupting the sorting signals. The switching of the latch also activates both a visual alarm 71 and an audible alarm. The values of capacitor Ci and resistor R 1 are chosen for the speed of change while R 1 and R 2 are chosen for r sensitivity

to change.

  Figure 4 illustrates the circuit of the pre-

  Transimpedance amplifier 46 of Figures 2 and 3.

  FIG. 5 illustrates the circuit of the AC amplifier 48 of FIGS. 2 and 3 FIG. 6 illustrates the circuit of the DC amplifier of FIGS. 2 and 3 FIG. 7 illustrates the circuit of the gain amplifier set in FIG. voltage 52 of FIGS. 2 and 3 FIG. 8 illustrates the rectifier circuit

  double alternation 58 of Figures 2 and 3.

  The values of the components as well as the parts of the components illustrated in FIGS. 2 to 8 are merely given by way of example and may be replaced by equivalent parts and circuits for

  achieve the desired results.

  Modifications may be made to the system according to the invention without departing from its scope and spirit. For example, as the AC path 48 contains the basic information constituting the amplitude of the ripples on the jet current. the DC path 50 should not be used in

  a simplified form of an embodiment of the invention.

Claims (17)

R E V E N D I C A T IO N S   A method for use in a droplet generation system where a stream of a liquid jet is produced and vibrations are applied to it to produce   ripples on the surface of said current and a disintegration   subsequent flow of said stream into droplets at a detachment point which are collected downstream, and   detects the amplitude of the undulation on the surface of a   uninterrupted flow of said jet stream at a point on said stream prior to the detachment point, characterized by the step of controlling the position of the detachment point as a function of or proportionally to the amplitude of the ripple at said detection point; 2 o Process according to claim 1 characterized in that the aforementioned detection is carried out before the region or the point of detachmento   Process according to one of Claims 1 to 2,   characterized in that the aforementioned detection is sensitive   radiation dispersed by the aforementioned current.   Process according to any one of the claims   1 to 3, characterized in that the aforementioned vibrations are controlled as a function of, or proportionally to,   the amplitude of the corrugations at this point.   Process according to any one of the claims   1 to 4, characterized in that said point is fixed.   Process according to any one of the claims   1 to 5, characterized in that the aforementioned detection is   performed during a method of analysis and / or sorting.   Process according to any one of the claims   4 to 6, characterized in that the aforesaid vibration control step includes automatically controlling the intensity of the vibrations applied to said current in response to a change in the amplitude of the ripple at the aforementioned point in a direction such that this restores the amplitude of the ripple at said point to its original state, thereby emitting a slip of the detachment point beforehand 8 Device for analyzing and sorting particles suspended in a liquid, said device comprising a first means (12, 14) for producing a jet stream (16) from said suspension liquid, vibratory means (24) for vibrating said stream (16) to produce undulations at the surface of said stream and subsequent disintegration said droplet stream (28) at a detachment point (26) to collect downstream, a second means (24) for controlling the position of the detachment point -26), a radiating means (20) for forcing a radiation beam (20) at a location (21) of said stream (16), a radiation sensitive or radiation responsive detection means (44) (20) of the radiation means (20) the current (16), characterized in that it comprises means for controlling the detachment point (46, 48, 50, 52, 54, 56, 64) to maintain the position of the point of detachment (26) constant O said detachment point control means having an input (66) and an output (67), said input (66) being coupled to the detecting means (44), said output (34) being coupled to said second means (24), said detachment point control means further providing an output to said second means which is   function of, or proportional to, the amplitude of the waveform   placing the current (16) in jet at said location (21).   9 Device according to claim 8, characterized in that the radiation (20) impacts the current (16) at a location (21) of the jet stream before the region or point of detachment Device according to claim 8 or 9, characterized in that the detachment point control means (46, 48; 50, 52, 54, 56, -64) includes a control terminal, said apparatus further includes reference means (32) for providing a signal reference having an amplitude which is a function of, or proportional to, the nominal position (26) of the detachment point current (16).   11 Device according to any one of the claims   8 to 10, characterized in that the detecting means (44) is sensitive to the radiation (20) dispersed by the current (16).   Apparatus according to any of the claims   8-11, characterized in that the second means (24) includes vibratory means (24).   Apparatus according to any of the claims   8 to 12, characterized in that the suspension of aforementioned liquid is non-opaque.   Apparatus according to any of the claims   8 to 13, characterized in that the radiation (20) impacts the above-mentioned current (16) at a location (21) fixed on said current.   Apparatus according to any one of the claims   8 to 14, characterized in that said detachment control means includes an automatic gain control or adjustment circuit (64) having an input coupled to the output of the detecting means (44) and having an output coupled to the means vibratory device (24) for modifying the intensity of the vibrations applied to said current (16) in response to a change in the level of the amplitude of the ripple at the location (21) of said current in such a direction   that it restores the amplitude of the ripple at said location   said current (21) to its original state to thereby correct a change in the detachment point (26) of said current.