Method and apparatus for sorting particles

A method and apparatus for sorting particles moving through a closed channel system of capillary size comprises a bubble valve for selectively generating a pressure pulse to separate a particle having a predetermined characteristic from a stream of particles. The particle sorting system may further include a buffer for absorbing the pressure pulse. The particle sorting system may include a plurality of closely coupled sorting modules which are combined to further increase the sorting rate. The particle sorting system may comprise a multi-stage sorting device for serially sorting streams of particles, in order to decrease the error rate.

FIELD OF THE INVENTION

The invention relates to a method and apparatus for the sorting of particles in a suspension, where the input flow path of a sorting module can be split into several output channels. More particular, the invention relates to a particle sorting system in which a plurality of sorting modules are interconnected as to yield an increased particle throughput.

BACKGROUND OF THE INVENTION

In the fields of biotechnology, and especially cytology and drug screening, there is a need for high throughput sorting of particles. Examples of particles that require sorting are various types of cells, such as blood platelets, white blood cells, tumorous cells, embryonic cells and the like. These particles are especially of interest in the field of cytology. Other particles are (macro) molecular species such as proteins, enzymes and poly-nucleotides. This family of particles is of particular interest in the field of drug screening during the development of new drugs.

Methods and apparatus for particle sorting are known, and the majority described in the prior art work in the condition where the particles are suspended in a liquid flowing through a channel network having at least a branch point downstream and are operated according to the detect-decide-deflect principle. The moving particle is first analyzed for a specific characteristic, such as optical absorption, fluorescent intensity, size etc. Depending on the outcome of this detection phase, it is decided how the particle will be handled further downstream. The outcome of the decision is then applied to deflect the direction of specific particle towards a predetermined branch of the channel network.

Of importance is the throughput of the sorting apparatus, i.e. how many particles can be sorted per unit of time. Typical sorting rates for sorters employing flows of particle suspension in closed channels are in the range from a few hundred particles per second to thousands of particles per second, for a single sorting unit.

An example of a sorting device is described in U.S. Pat. No. 4,175,662, the contents of which are herein incorporated by reference (hereinafter referred to as the '662 patent). In the '662 patent, a flow of particles, cells in this case, flows through the center of a straight channel, which branches into two perpendicular channels at a branching point downstream (T-branch). The entering particles are surrounded by a sheath of compatible liquid, keeping the particles confined to the center of the channel. In normal conditions, the flow ratio through the two branches is adjusted so that the particles automatically flow through one of the branches. In a section of the channel a characteristic of the particles is determined using a detector, which can be an optical system (detection phase). The detector generates a signal when the detector detects a particle possessing a predetermined characteristic in the decision phase. Once a particle is detected, a deflector is activated for deflecting the particle in a deflection phase. In this case, the deflector comprises an electrode pair, positioned in the branch of the channel where the particles normally flow through in the inactivated state of the deflector. By the application of current pulses, the aqueous liquid is electrolysed, yielding a gas bubble evolving between the electrode pair. As the gas bubble increases in size, the flow rate through this branch is reduced during the evolving phase. After the current pulse is applied, the bubble growth stops and the gas bubble is carried along with the flow. As a result, the flow through the specific branch is momentarily reduced and the particle of interest changes paths and flows down the other branch.

The device of the '662 patent is effective for sorting particles. However one serious drawback is that gas bubbles are created which potentially can accumulate at certain points of the fluidic network. This bubble generation can clog the flow channels, yielding erroneous sorting. Another drawback is that the generated gasses (mostly oxygen and hydrogen) and ionic species (mostly OH−and H+) influence the particles flowing through the branch with the electrode pair. In addition, cells and delicate proteins such as enzymes are very fragile and can be destroyed by the fouling constituents co-generated with the gas bubble. Another drawback is the complexity of the overall sorting apparatus. In particular, the micro electrode construction is very complex to mount and assemble in the small channels of the system. As a result, the cost of a sorting unit is relatively large.

Another example of a particle sorting system of the prior art is disclosed in U.S. Pat. No. 3,984,307, the contents of which are herein incorporated by reference (hereinafter the '307 patent). In the '307 patent, the particles are flowing, confined by a flowing sheath liquid, through the center of a channel. After passing a detector section, the channel branches into two channels forming an acute angle therebetween (e.g., Y-branch). Just before the branching point, an electrically activated transducer is located in the channel for deflecting a specific particle having an appropriate, predetermined characteristic. The transducer described is a piezo actuator or ultrasonic transducer, yielding upon electrical activation a pressure wave in the channel. The generated pressure wave momentarily disturbs the flow in one branch thus deflecting the particle of interest into the other branch.

In the device of the '307 patent, as in the previous discussed device, the deflector is incorporated within the channel system, resulting in relatively large construction costs. Another drawback of this device is the deflector principle used. The generated pressure waves are not confined to the branching point, but rather propagate upstream into the detector section, as well as down both branches. This influences the overall flow through the channel. This is particularly a drawback if sorters of this type are connected either in series or in parallel, as is typically done to construct a high throughput sorting system. Pressure waves generated in one sorter can then influence the flows and deflection of particles in neighboring sorter units.

Another sorter is described in U.S. Pat. No. 4,756,427, the contents of which are herein incorporated by reference. This sorter is analogous to the sorter in the '662 patent. In this case, however, the flow in one branch is disturbed by momentarily changing the resistance of the branch. The resistance is changed by changing the height of the branch channel by an external actuator. In the preferred embodiment, this external actuator is a piezo disc glued on top of the channel, causing it to move downwards upon activation.

Although the construction of the sorter described in the '427 patent is less complex than the previously described sorter structures, it is still problematic to couple multiple sorter modules of the described type together to increase the sorting rate. This is, as in the sorter described in the '307 patent because of the generated pressure waves causing interference with other sorter modules.

Another particle sorting device is described in U.S. Pat. No. 5,837,200, the contents of which are herein incorporated by reference. The '200 patent describes a sorting device that uses a magnetic deflection module to classify or select particles based on their magnetic properties. The '200 patent further describes processing and separating individual particle streams in parallel.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for sorting particles moving through a closed channel system of capillary size. The particle sorting system of the invention provides a sorting module that can be assembled at low cost while providing an accurate means of sorting large amounts of particles per unit of time. The particle sorting system may include a plurality of closely coupled sorting modules which are combined to further increase the sorting rate. The particle sorting system may comprise a multi-stage sorting device for serially sorting streams of particles, in order to decrease the error rate.

The particle sorting system implements an improved fluidic particle switching method and switching device according to the present invention. The particle sorting system comprises a closed channel system of capillary size for sorting particles. The channel system comprises a first supply duct for introducing a stream of particles and a second supply duct for supplying a carrier liquid. The first supply duct forms a nozzle to introduce a stream of particles into the flow of carrier liquid. The first supply duct and the second supply duct are in fluid communication with a measurement duct, which branches into a first branch and a second branch at a branch point. A measurement region is defined in the measurement duct and is associated with a detector to sense a predetermined characteristic of particles in the measurement region. Two opposed bubble valves are positioned in communication with the measurement duct and are spaced opposite each other. The bubble valves communicate with the measurement duct through a pair of opposed side passages. Liquid is allowed to partly fill these side passages to form a meniscus therein which interfaces the carrier liquid with the reservoir of the bubble valves. An external actuator is also provided for actuating one of the bubble valves. When the external actuator is activated, the pressure in the reservoir of the activated bubble valve increases, deflecting the meniscus and causing a flow disturbance in the measurement duct to deflect the flow therein.

When a sensor located in the measuring region senses a predetermined characteristic in a particle flowing through the measurement region, the sensor produces a signal in response to the sensed characteristic. The external actuator is responsive to the sensor to cause a pressure pulse in a compression chamber of a first bubble valve to deflect the particle with the predetermined characteristic, causing the selected particle to flow down the second branch duct.

In one aspect, the invention comprises a method of sorting particles including the steps of providing a measurement duct having an inlet and a branching point at which the duct separates into two branch ducts, and conducting a stream of fluid into the duct inlet with a stream of particles suspended therein, such that the particles normally flow through a first one of the branch ducts and providing upstream from the branching point two opposing side passages for momentarily deflecting the stream in the duct. A first one of the side passages is hydraulically connected to a compression chamber of a first bubble valve, which is acted upon by an external actuator for varying the pressure therein. A second of the side passages is hydraulically connected with a buffer chamber of a second bubble valve for absorbing pressure variations. The method further comprises providing a measurement station along the measurement duct upstream of the side passages for sensing a predetermined characteristic of particles in the stream and for producing a signal when the predetermined characteristic is sensed. The method further comprises the step of, in response to sensing the predetermined characteristic, activating the external actuator for creating a flow disturbance in the duct between the side passages, thereby deflecting the particle having the predetermined characteristics and causing the selected particle to flow down the second branch duct.

In further aspects of the invention, the particle sort rate is respectively increased or the type of particles sorted being increased, by respectively connecting a plurality of sorting modules in parallel or serially connecting a plurality of sorting modules in a binary tree like configuration.

According to one aspect of the invention, a particle sorting system is provided. The particles sorting system comprises a first duct for conveying a stream of suspended particles confined in a carrier liquid, comprising an inlet, a first outlet and a second outlet, a sensor for sensing a predetermined characteristic in a particle, a side channel in communication with the first duct, a sealed chamber positioned adjacent to the side channel, wherein the carrier fluid forms a meniscus in the side channel to separate the sealed chamber from the carrier fluid; and an actuator. The actuator modifies the pressure in the sealed chamber to deflect the meniscus when the sensor senses the predetermined characteristic. The deflection of the meniscus causes the particle having the predetermined characteristic to flow into the second outlet while particles that do not have the predetermined characteristic flow into the first outlet.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a particle sorting system for sorting particles suspended in a liquid. The particle sorting system provides high-throughput, low error sorting of particles based on a predetermined characteristic. The present invention will be described below relative to illustrative embodiments. Those skilled in the art will appreciate that the present invention may be implemented in a number of different applications and embodiments and is not specifically limited in its application to the particular embodiments depicted herein.

The terms “duct” “channel” and “flow channel” as used herein refers to a pathway formed in or through a medium that allows for movement of fluids, such as liquids and gases. The channel in the microfluidic system preferably have cross-sectional dimensions in the range between about 1.0 μm and about 500 μm, preferably between about 25 μm and about 250 μm and most preferably between about 50 μm and about 150 μm. One of ordinary skill in the art will be able to determine an appropriate volume and length of the flow channel. The ranges are intended to include the above-recited values as upper or lower limits. The flow channel can have any selected shape or arrangement, examples of which include a linear or non-linear configuration and a U-shaped configuration.

The term “particle” refers to a discrete unit of matter, including, but not limited to cells.

The term “sensor” as used herein refers to a device for measuring a characteristic of an object, such as a particle.

The term “bubble valve” as used herein refers to a device that generates pressure pulses to control flow through a channel.

The term “carrier fluid” as used herein refers to a sheath of compatible liquid surrounding a particle for carrying one or more particles through a duct or channel.

FIG. 1is a schematic depiction of a particle sorting system10according to the teachings of the present invention. According to one application of the present invention, the particle sorting system10comprises a closed channel system of capillary size for sorting particles. The channel system comprises a first supply duct12for introducing a stream of particles18and a second supply duct14for supplying a carrier liquid. The first supply duct12forms a nozzle12a, and a stream of particles is introduced into the flow of the carrier liquid. The first supply duct12and the second supply duct14are in fluid communication with a measurement duct16for conveying the particles suspended in the carrier liquid. The measurement duct branches into a first branch channel22aand a second branch channel22bat a branch point21. A measurement region20is defined in the measurement duct16and is associated with a detector19to sense a predetermined characteristic of the particles passing through the measurement region20. Two opposed bubble valves100aand100bare positioned relative to the measurement duct and disposed in fluid communication therewith. The valves are spaced opposite each other, although those of ordinary skill will realize that other configurations can also be used. The bubble valves100aand100bcommunicate with the measurement duct16through a pair of opposed side passages24aand24b, respectively. Liquid is allowed to partly fill these side passages24aand24bto form a meniscus25therein. The meniscus defines an interface between the carrier liquid and another fluid, such as a gas in the reservoir of the associated bubble valve100. An actuator26is also provided for actuating either bubble valve, which momentarily causes a flow disturbance in the duct to deflect the flow therein when activated by the actuator26. As illustrated, the actuator is coupled to the bubble valve100b. The second bubble valve100aserves as a buffer for absorbing the pressure pulse created by the first bubble valve100b.

The first side passage24bis hydraulically connected to a compression chamber70bin the first bubble valve100b, so that if the pressure in this chamber is increased, the flow in the measurement duct near the side passage is displaced inwards, substantially perpendicular to the normal flow in the duct. The second side passage24a, positioned opposite of the first side passage24bis hydraulically connected to a buffer chamber70ain the second bubble valve100afor absorbing pressure transients. This first side passage24bco-operates with the second side passage24ato direct the before mentioned liquid displacement caused by pressurizing the compression chamber70b, so that the displacement has a component perpendicular to the normal flow of the particles through the measurement duct.

Upon pressurizing the compression chamber70ban amount of liquid is transiently discharged from the first side passage24b. The resiliency of the second side passage24aresults upon a pressurized discharge, in a transient flow of the liquid in the duct into the second side passage24a. The co-operation of the two side passages and the fluidic structures they interconnect causes the flow through the measurement duct16to be transiently moved sideways back and forth upon pressurizing and depressurising of the compression chamber70binduced by the external actuator26in response to the signal raised by the detection means19. This transient liquid displacement, having a component perpendicular to the normal flow in the duct, can be applied in deflecting particles having predetermined characteristics to separate them from the remaining particles in the mixture.

As shown, the measurement duct16branches at the branch point21into two branches22a,22band the flow rates in these branches are adjusted so that the particles normally stream through the second of the two branches22b. The angle between the branches22a,22bis between 0 and 180 degrees, and preferably between 10 and 45 degrees. However, the angle can even be 0 degrees, which corresponds to two parallel ducts with a straight separation wall between them.

The particles to be sorted are preferably supplied to a measurement position in a central fluid current, which is surrounded by a particle free liquid sheath. The process of confining a particle stream is known, and often referred to as a ‘sheath flow’ configuration. Normally, confinement is achieved by injecting a stream of suspended particles through a narrow outlet nozzle into a particle free carrier liquid flowing in the duct16. By adjusting the ratio of flow rates of the suspension and carrier liquid, the radial confinement in the duct as well as the inter particle distance can be adjusted. A relatively large flow rate of the carrier liquid results in a more confined particle stream having a large distance between the particles.

In a suspension introduced by the first supply duct12, two types of particles can be distinguished, normal particles18aand particles of interest18b. Upon sensing the predetermined characteristic in a particle18bin the measurement region20, the detector19raises a signal. The external actuator26activates the first actuator bubble valve100b, when signaled by the detector19in response to sensing the predetermined characteristic, to create a flow disturbance in the measurement duct16between the side passages24a,24b. The flow disturbance deflects the particle18bhaving the predetermined characteristic so that it flows down the first branch duct22arather than the second branch duct22b. The detector communicates with the actuator26, so that when the detector19senses a predetermined characteristic in a particle, the actuator activates the first bubble valve100bto cause pressure variations in the reservoir70bof the first bubble valve. The activation of the first bubble valves deflects the meniscus25bin the first bubble valve100band causes a transient pressure variation in the first side passage24b. The second side passage24aand the second bubble valve100aabsorb the transient pressure variations in the measurement duct16induced via the actuator26. Basically, the reservoir70aof the second bubble valve100ais a buffer chamber having a resilient wall or containing a compressible fluid, such as a gas. The resilient properties allow the flow of liquid from the measurement duct into the second side passage24a, allowing the pressure pulse to be absorbed and preventing disturbance to the flow of the non-selected particles in the stream of particles.

At the measurement region20, individual particles are inspected, using a suitable sensor19, for a particular characteristic, such as size, form, fluorescent intensity, as welt as other characteristics obvious to one of ordinary skill. Examples of applicable sensor, known in the art, are various types of optical detection systems such as microscopes, machine vision systems and electronic means for measuring electronic properties of the particles. Particularly well known systems in the field are systems for measuring the fluorescent intensity of particles. These systems comprise a light source having a suitable wavelength for inducing fluorescence and a detection system for measuring the intensity of the induced fluorescent light. This approach is often used in combination with particles that are labelled with a fluorescent marker, i.e. an attached molecule that upon illuminating with light of a particular first wavelength produces light at another particular second wavelength (fluorescence). If this second wavelength light is detected, the characteristic is sensed and a signal is raised.

Other examples include the measurement of light scattered by particles flowing through the measurement region. Interpreting the scattering yield information on the size and form of particles, which can be adopted to raise a signal when a predetermined characteristic is detected.

The actuator26for pressurizing the compression chamber of the first bubble valve can comprise an external actuator that responds to a signal from the sensor that a particle has a selected predetermined characteristic. There are two classes of external actuators that are suitable for increasing the pressure. The first class directly provides a gas pressure to the liquid in the first side passage24b. For example, the actuator may comprise a source of pressurized gas connected with a switching valve to the liquid column in the side passage24b. Activation of the switch connects the passage to the source of pressurized gas, which deflects the meniscus in the liquid. Upon deactivation, the switch connects the passage24bback to the normal operating pressure.

Alternatively, a displacement actuator may be used in combination with a closed compression chamber having a movable wall. When the displacement actuator displaces the wall of the compression chamber inward, the pressure inside increases. If the movable wall is displaced back to the original position, the pressure is reduced back to the normal operating pressure. An example of a suitable displacement actuator is an electromagnetic actuator, which causes displacement of a plunger upon energizing a coil. Another example is the use of piezoelectric material, for example in the form of a cylinder or a stack of disks, which upon the application of a voltage produces a linear displacement. Both types of actuators engage the movable wall of the compression chamber70to cause pressure variations therein.

FIGS. 2 through 4illustrate the switching operation of switch40in the particle sorting system10ofFIG. 1. InFIG. 2, the detector19senses the predetermined characteristic in a particle and generates a signal to activate the actuator26. Upon activation of the actuator, the pressure within the reservoir70bof the first bubble valve100bis increased, deflecting the meniscus25band causing a transient discharge of liquid from the first side passage24b, as indicated by the arrow. The sudden pressure increase caused at this point in the duct causes liquid to flow into the second side passage24a, because of the resilient properties of the reservoir of the second bubble valve100a. This movement of liquid into the second side passage24ais indicated with an arrow. As a result, as can be seen in the figure, the flow through the measurement duct16is deflected, causing the selected particle of interest18blocated between the first side passage24band the second side passage24ato be shifted perpendicular to its flow direction in the normal state. The flow resistances to the measurement duct16, the first branch22aand the second branch22bis chosen so that the preferred direction of the flow to and from the first side passage24band the second side passage24ahas an appreciable component perpendicular to the normal flow through the measurement duct16. This goal can for instance be reached by the first branch22aand the second branch22bso that their resistances to flow is large in comparison with the flow resistances of the first side passage24band the second side passage24a.

FIG. 3shows the particle sorting system10during the relief of the first bubble valve reservoir when the particle of interest18bhas left the volume between the first side passage24band the second side passage24a. The actuator26is deactivated, causing the pressure inside the reservoirs70a,70bto return to the normal pressure. During this relief phase there is a negative pressure difference between the two reservoirs70a,70bof the bubble valves, causing a liquid flow through the first side passage24band the second side passage24aopposite to the liquid flow shown in the previous figure and as indicated by the arrows.

FIG. 4illustrates the particle sorting system10after completion of the switching sequence. The pressures inside the reservoirs of the bubble valves are equalized, allowing the flow through the measurement duct16to normalize. As the particle of interest18bhas been displaced radially, it will flow into the first branch22a, while the other particle continue to flow into the second branch22b, thereby separating the particles based on the predetermined characteristic.

This process of detecting and selective deflecting of particles may be repeated many times per second for sorting particles at a high rate. Adopting the fluid switching as described, switching operations may be executed up to around several thousand switching operations per second, yielding sorting rates in the order of million sorted particles per hour.

According to another embodiment of the invention, the actuator bubble valve100band the buffer bubble valve100amay be placed in different positions. For example, as shown inFIG. 5, the actuator bubble valve100band the first side passage24band/or the buffer bubble valve100aand the second side passage24amay be place upstream from the branch point21. The components may be placed in any suitable location, such that the flow resistance between the actuator chamber70band the buffer chamber70ais less than the flow resistance between any of these latter components and other pressure sources. More particularly, the actuator chamber70band the buffer chamber70amay be placed such that the flow resistance between them is less than the flow resistance between a selected particle and a subsequent particle in the stream of particles. The positioning of the components in this manner thus prevents a pressure wave generated by the above-described method of deflecting a single selected particle, from travelling upstream or downstream and affecting the flow of the remaining particles in the stream of particles. A larger difference in flow resistances results in a higher level of isolation of the fluidic switching operation with associated pressure transients from the flow characteristics in the rest of the system. Moreover, the in-situ dampening of generated pressure pulses applied for sorting allows the implementation of sorting networks comprising a plurality of switches40, each of which is hydraulically and pneumatically isolated from the others.

According to another embodiment, shown inFIG. 6, the particle sorting system of the present invention may use any suitable pressure wave generator (in place of a bubble valve) in combination one or more bubble valves serving as a buffer, such as valve100b. For example, the pressure wave generator260may comprise an actuator such as a piezoelectric column or a stepper motor, provided with a plunger that can act upon the flowing liquid, either directly or via deflection of the channel system, to selectively deflect particles when the actuator is activated by a signal. Other suitable pressure wave generators include electromagnetic actuators, thermopneumatic actuators and a heat pulse generator for generating vapor bubbles in the flowing liquid by applying heat pulses. The buffer bubble valve100bis positioned to absorb the pressure wave created by the pressure wave generator260to prevent flow disturbance in the other particles of the particle stream. The spring constant of the buffer100bmay be varied according to the particular requirements by varying the volume of the buffer chamber70b,the cross-sectional area of the side passage24band/or the stiffness or the thickness of a flexible membrane (reference72inFIG. 7) forming the buffer chamber70b.

FIG. 7illustrates an embodiment of a valve100suitable for creating a pressure pulse to separate particles of interest from other particles in a stream of particles and/or acting as a buffer for absorbing a pressure pulse according to the teachings of the present invention. As shown, the valve100is formed adjacent to a side passage24aor24bformed in a substrate which leads to the measurement duct16. The side passage24aincludes a fluid interface port17formed by an aperture in the side wall of the passage. A sealed compression chamber70is positioned adjacent to the side passage24aand communicates with the side passage through the fluid interface port. The illustrative chamber70is formed by a seal71and a flexible membrane72. The carrier fluid in the side passage24aforms a meniscus25at the interface between the side passage and the chamber. The actuator26depresses the flexible membrane to increase the pressure in the chamber, which deflects the meniscus and causes a pressure pulse in the carrier fluid.

FIG. 8shows a sorting module50having an appropriate supply duct52for providing a stream of particles to be sorted as well as a first outlet duct54and a second outlet duct56, either of which can carry the particles sorted in the sorting module50. The sorting module50comprises a detector system19for sensing particles entering the sorting module50via the supply duct52can be operationally connected to a switch40for providing the required switching capabilities to sort particles. The first branch22band the second branch22a,FIG. 1, can be disposed in fluidic connection with the outlet duct54and the second outlet duct56.

FIG. 9shows a particle sorting system500according to an alternate embodiment of the invention, comprising a plurality of sorting modules50that can be coupled together in any appropriate configuration. For example, the modules50in this embodiment are coupled in parallel. The outlet ducts54of the sorting modules50are coupled to a first combined outlet58, the second outlet ducts56are coupled to a second combined outlet60. The parallel arrangement of sorting modules yields a system of combined sorting module50having an overall sorting rate of N times the sorting rate of an individual sorting module50, where N is the number of parallel connected sorting module50.

FIG. 10shows a particle sorting system550according to another embodiment, comprising a first sorting module50ain series with a second sorting module50b. The second sorting module50bmay be equipped for sorting particles having a predetermined characteristic the same or different than the predetermined characteristic of the particles sorted by the first sorting module50a. The particle stream enters the first sorting module50athrough the supply duct52and may contain at least two types of particles. A first type of particle is sorted in the first sorting module50aand exits through the first outlet duct54a. The remaining particles exit the first sorting module50athrough second outlet duct56aand are introduced into the second sorting module50bvia the second supply duct52b. From this stream of particles, particles having the other predetermined characteristic are sorted and exit through the second outlet duct54b. Particles that posses neither of the two predetermined characteristics exit the second sorting module50bvia the second outlet duct56b. Those of ordinary skill will readily recognize that any suitable type of sorting module50can be used, and can be coupled together in a variety of ways, depending upon the desired results.

FIG. 11shows a hierarchical architecture for high throughput-low error sorting according to another embodiment of the present invention. The illustrated embodiment is a two-stage particle sorting system800for sorting a plurality of parallel particles streams in a first stage, aggregating the outputs of the first stage and then performing a secondary sorting process on the output of the first stage. An input stream of particles in suspension80from a particle input chamber88is split among N single sorting channels81a–81n, each channel being capable of sorting a selected number of particles per second. Each channel81includes a detection region84for examining the particles and identifying particles that have a predetermined characteristic, and a switching region82for separating the particles having the predetermined characteristic from the other particles in the stream, as described above. The switching region82produces two output streams of particles: a “selected” stream and a “rejected” stream in its switching region82based on the measured particle characteristics at the detection region84. The “selected” streams from each channel are aggregated in an aggregation region86into one stream to be sorted again in a secondary sorting channel810. As shown, the secondary sorting channel810repeats the sorting process of detecting and sorting based on a predetermined characteristic.

Given that each single channel sorting process produces some error (y) rate (y is a probability less than one of a particle being “selected” by mistake) of mistaken selections, the hierarchical architecture produces an lower error rate of y2for a 2-stage hierarchy as drawn or ynfor an n-stage hierarchy. For example, if the single channel error rate is 1% the 2-stage error rate is 0.01% or one part in 104.

Alternatively, the architecture could have M primary sets of N sorting channels per secondary channel. Given that the application wants to capture particles that have a presence in the input at rate z and single channel sorters have a maximum sorting rate x particles per second. The system throughput is M*N*x in particles per second. The number of particles aggregated in N channels per second is N*x*z and so N*z must be less than 1 so that all particles aggregated from N channels can be sorted by a single secondary channel. To increase throughput above N=1/z one must add parallel groups of N primary+1 secondary channels. Overall throughput then comes from M*N*x with M secondary channels.

FIG. 12show a parallel-serial particle sorting system160according to another embodiment of the invention. The parallel-serial particle sorting system160includes a first parallel sorting module161and a second parallel sorting module162. The first sorting module161is applied in multiple marked particles and particles having both markers are sorted out and conveyed through the exit channel165.

FIG. 13shows another parallel-serial particle sorting system170. The first parallel sorting module171separates particles having a first marker, collects the particles from the different channels and conveys the particles having the first marker through the first exit channel175. All other particles are then fed into a second parallel sorter172for sorting particles having a second marker. The particles having the second marker are collected and conveyed through a second exit channel176. Particles having neither the first marker nor the second marker are conveyed through a third exit channel177.

According to one embodiment of the invention, shown inFIGS. 14aand14b, the particle sorting system may include sensors for measuring velocity, location and/or size of particles. The measurement of velocity, location and/or size may be made simultaneously with classification of the particles for sorting or at a different time. In parallel channel based systems, as shown inFIG. 11, the different channels may have different flow resistances, causing the velocity of the particles or cells in each channel to be different. In systems where the detection region84is separated from the switching region82by a distance L, the velocity of the particles in the channel81must be known in order to set the switching time delay T (i.e., the time to delay switch actuation relative to the moment of detection of a target particle).

In most optical systems for detecting cells or particles, the region in which the cell creates light on the photo detector in the detection region will have a much greater size than the size of a cell diameter. Therefore, when light is detected in the detection region, the cell may be anywhere in the region, making it difficult to pinpoint the exact location of the cell. To provide more accurate detection, many pixels of an optical detector could be packed across the detection region, but this would have a large cost and require complex support electronics.

According to an illustrative embodiment of the invention, an optical mask140may be added to the detection region to provide accurate velocity detection by depositing a “masking pattern” directly on the sorting chip. The masking patterns can be deposited so that an edge in the masking pattern is precisely located (to<1 μm precision with current technology) relative to the cell sorting actuator region82. A single optical detector catching light from the cell in the detection region84will see light when the cell is not masked. The duration of the light being turned off by one of the connected opaque parts “bars” of the mask of known length gives a measurement of velocity.

A mask pattern that has several bars141of size ranging from 10 um to 30 um in 1 um steps results in only bars of size larger than the cell minimizing the signal from the cell. Therefore, such a pattern can also be used to measure the size of the cell independently of its signal. Such a “gradient mask” also produces a pattern in the optical detector that can be analyzed to measure velocity several times for reducing the variance in the velocity estimate. The pattern in the light induced by the mask140also allows the detector to identify each edge in the mask140. If the bars141were all the same, the light signal for each bar would be the same, and one could only tell them apart by sequence. Therefore, a gradient mask pattern will allow a single detector looking at a broad region (several times the size of a cell) to measure the velocity of the cell, measure the exact position inside the detection region84with about 1 um precision relative to the channel structures and the actuator location on chip and identify the size of the cell to precision given by the gradient pattern. The gradient mask140allows the detector to measure these parameters independent of the magnification of the optical system or the nature of the optical detector itself.

One skilled in the art will recognize that other devices for measuring the size, position and or velocity of a particle in the sorting system in accordance with the teachings of the invention. Suitable devices are readily available and known to those of ordinary skill in the art.

According to another embodiment, shown inFIG. 15, the particle sorting system comprises an array8000of non-identical sorting channels. The use of a parallel array comprising a series of non-identical sorter channels810a–810nis more efficient in terms of space, use of optical power and adaptation to optimal external actuators. Since the velocity of particles can be accurately sensed using a sensor as described above, the channels do not require a fixed delay between the detection of a property and actuation of a switch to deflect a particle having the detected property. Therefore, certain parameters of the channel, such as the distance L between a detector84and a switch82or the shape of the path between the detector84and the switch82can be varied.

Using a single laser for each wavelength optical illumination directed perpendicular to the chip, the laser is required to illuminate an area defined by: (number of channels)X((channel width at detection region)+(inter channel spacing C)) (SeeFIG. 15). However, the active area where light can be absorbed to create fluorescence is only the area of the channels: (number of channels)×(channel width), which leaves a fill factor of: (channel width)/(channel width+C). The fill factor is preferably close to 100% to avoid wasting available input light.

Therefore, minimizing the interchannel spacing in a parallel sorting system is important to the optical detection region and optical system efficiency. In the variable array design of the present invention, shown inFIG. 16, the spacing of the channels in the detection region84approaches the width of the channels, so that light utilization approaches about 50%. The channel spacing in the actuation region82may be larger, as shown inFIG. 16. The location of actuators26along the channel may also be varied to make a larger available radius for external driver actuators.

The variable array8000may also include meanders in selected channels for balancing flow resistances of all the channels so that given a constant pressure drop across all the channels the velocities of particles are nearly matched. These can be added either upstream or downstream of the illustrated system, i.e., on in the region between the detectors and actuators. As the lengths Li between each channel's detection region82I and its actuator26iis known from the design, the measurement of the particle velocity at the same time as the determination regarding which particles to keep provides an improved cell sorting system.

FIG. 17illustrates a particle sorting system1700according to yet another embodiment of the invention. The particle sorting system1700includes a plurality of sorting modules1701operating in parallel. The system1700includes an input region1710for introducing samples to each sorting module and a detection region1720for measuring a predetermined characteristic of particles each sorting channel1702in the detection region. The system also includes a switch region1730, including an actuator in each sorting module for separating particles having a predetermined characteristic from particles that do not have the predetermined characteristic. As shown, in the embodiment ofFIG. 17, the sorting channels1702distance between each sorting channel in the detection region1720is less than the inter-channel distance in the switch region1730. The close spacing in the detection region enables cost saving when a laser is used to detect the particles, while the more distant separation in the switch region1730accommodates various sized actuators.

The particle sorting system1700may also include a secondary sorting module1740for repeating the sorting process of detecting and sorting based on a predetermined characteristic to increase the accuracy of the sorting process. According to one embodiment, the system may include an enrichment region1750between the array of primary sorting modules1701and the secondary sorting module1740for transitioning the particles from the primary sorting process to the secondary sorting process. According to an illustrative embodiment, the enrichment region1750transitions the particles by removing excess carrier fluid from the particles before passing the particles to the secondary sorting module1740. The enrichment region1750may also include a hydration device for adding secondary sheet fluid to the particles after enrichment. The enrichment region1750may comprise a membrane inserted into outlet channel1703, an enrichment channel intersecting the outlet channel1703and a membrane separating the outlet channel from the enrichment channel. Excess carrier fluid is removed from the stream of selected particles in the outlet channel1703through the membrane and into the enrichment channel before passing the selected particles into the secondary sorting module1740.

A suitable system for forming the enrichment region is described in Attorney Docket No. TGZ-023, filed on even date herewith, the contents of which are herein incorporated by reference.

According to the illustrative embodiment, the removed carrier fluid may be recycled and fed back into the inlet of the primary channels. A recycling channel or other device may connect the enrichment region to the primary channel to allow re-use of the carrier fluid for subsequent sorting process. Alternatively, the carrier fluid may be removed from rejected particles and introduced into the primary channel inlets prior to discarding the rejected particles.

The present invention has been described relative to an illustrative embodiment. Since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.