Ultra high throughput bioassay screening system

In a preferred embodiment, a method of performing biological assays, including: providing a longitudinally extending carrier tape having thermally formed therein a plurality of reagent receiving wells; adding a reagent to each of said reagent receiving wells; permitting each of said reagent receiving wells to incubate at a predetermined temperature for a predetermined time; and performing a biological analysis on each of said reagent receiving wells.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to bioassay screening generally and, more particularly, but not by way of limitation, to a novel system for ultra high throughput bioassay screening.

2. Background Art

High Throughput Screening (HTS) has been in use for at least the past ten years to screen large numbers of potential chemical compounds that may have pharmaceutical efficacy or which may be precursors to pharmaceuticals. A given investigation may involve the screening of on the order of about 10,000 compounds per day. There are three basic areas of HTS: (1) handling the compound library, (2) lead discovery, and (3) lead optimization. Handling the compound library is an essential element of the other two. Lead discovery and lead optimization tend to overlap. The objective of lead discovery is to develop “hits” or what appear to be active compounds in specific areas. Lead optimization is a refinement of these “hits” so as to pass on qualified leads to medicinal chemistry for further development. Without this refinement, medicinal chemistry is swamped and the discovery of more “hits” is negated. The success of HTS has fostered the next step—a tenfold increase in throughput or Ultra High Throughput Screening (UHTS).

The primary objective of UHTS is to achieve more qualified lead compounds. In general terms, UHTS has been described as the ability to screen, in a given investigation, a library of 500,000 compounds against 50 therapeutic targets per year. This equates to 100,000 compounds screened per day. The economics of this number dictates some form of miniaturization to conserve the precious reagents consumed.

Since compound handling is the front end of both lead discovery and optimization, it must be considered first. The long term library storage is necessarily in solid or semi-solid form, for stability reasons. However, for use in screening, the library must be converted to a liquid phase. The most commonly accepted method of such conversion is to weigh out a small aliquot of a compound and solvate it with dimethyl sulfoxide (DMSO). Speed and convenience dictate weighing out typically 10 milligram quantities as the minimum amount. These are then brought into solution form, at, say, 10 millimolar concentration, yielding 5 to 10 ml of solution. This is then subdivided into smaller aliquots of 0.5 ml and stored frozen in sets of 96 deepwell tubes at −20 or −80 degrees Centigrade as an archive library.

Several areas of concern arise in going from the archive library to the usable form for the assay. First is the concentration—many assays are tested at 10−5or 10−6concentrations. The majority of assays cannot tolerate much more than 1% DMSO. Thus, a dilution from the archive library is required. However, some compounds, while soluble in 100% DMSO, are not soluble in lesser percentages. It is desirable to make the compound dilution in the final assay volume and not in a previous dilution step. Another concern is protecting the stability or validity of the archive compound. Freezing it lengthens its shelf life. But to access the compound, it must be thawed to remove an aliquot. Each time a freeze-thaw cycle occurs, there is the potential for moisture to degrade the compound. Thus, it is desirable to minimize these cycles. The real problem is how to transfer 100,000 discreet samples per. day from the archive library to the assay, keeping the above constraints in mind.

Since the libraries may contain upwards of 500,000 discreet compounds, a means is required to both aspirate multiple samples from the compound source and dispense multiple aliquots of nanoliter quantities into the assay destination. Since in the majority of biological assays, a concentration of more than 1% DMSO is toxic to the assay results and if an assay is to run at a 5 microliter volume, only 50 nanoliters of DMSO is allowed. The molarity of the compound solution in DMSO is adjusted so that 50 nanoliters of the compound solution also provides the desired concentration of compound to the assay.

Small individual piezo electric pumps have been utilized for the purpose of aspirating and dispensing these small quantities of liquids. The common method is for the piezo to squeeze an individual glass capillary to create a pressure wave to dispense liquid from within the capillary. Reversing the action will cause the capillary to aspirate liquid. The individual piezo pumps are costly to manufacturer, as are the electronics to drive them. In the pharmaceutical application, described above, it is necessary to rinse the flow passage with a suitable solvent, normally DMSO, to prevent sample-to-sample carry over. Due to the small displacement volume of the piezo pump device a considerable number of cycles or shots is required to pass a suitable quantity of wash fluid. The wash fluid must then be cleared from the pump so as not to dilute the next sample.

In such pharmaceutical research, due to the high numbers to be processed, the samples to be aspirated and dispensed are on very close centers, typically 4.5 mm, or 2.25 mm, or smaller. This places a severe limit on the size of the dispensing device. Due to the small quantities involved, more efficient liquid movement is obtained if the device causing fluid motion is close to the outlet orifice. Otherwise, the energy of the shockwave causing displacement is absorbed by the liquid in the pathway. This results in less velocity at the orifice. If the stream does not have sufficient velocity and kinetic energy at the orifice, it does not overcome the surface tension there and the form of delivery is as liquid drops; however, an ejected stream is desired especially when dispensing. This permits non-contact dispensing. The dispensing tip is not contaminated with other fluids—only the fluid being dispensed.

Accordingly, it is a principal object of the present invention to provide method and means for ultra high throughput screening.

It is a further object of the invention to provide such method and means that are economically implemented.

It is an additional object of the invention to provide such method and means that permit the economical simultaneous aspirating and dispenses of a large number of very small volumes of liquid.

It is another object of the invention to provide such method and means that provide for the compact storage of large numbers of chemical compounds.

It is yet a further object of the invention to provide liquid transfer method and means that employs a single piezoelectric crystal to simultaneously effect the aspiration or dispensing of a large number of liquid samples.

Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.

SUMMARY OF THE INVENTION

The present invention achieves the above objects, among others, by providing, in a preferred embodiment, a method of performing biological assays, comprising: providing a longitudinally extending carrier tape having thermally formed therein a plurality of reagent receiving wells; adding a reagent to each of said reagent receiving wells; permitting each of said reagent receiving wells to incubate at a predetermined temperature for a predetermined time; and performing a biological analysis on each of said reagent receiving wells.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference should now be made to the drawing figures on which similar or identical elements are given consistent identifying numerals throughout the various figures thereof, and on which parenthetical references to figure numbers direct the reader to the view(s) on which the element(s) being described is (are) best seen, although the element(s) may be seen on other figures also.

In one aspect of the invention, there is adapted a sprocket driven carrier tape, as a processing vehicle for biological assays. A similar type of tape is known in the electronics industry for transporting electrical components, such as is described in Electronic Industries Association documents EIA/IS_704and others.

FIG. 1illustrates a carrier tape, constructed according to the present invention, and generally indicated by the reference numeral20. Carrier tape20is made from a heavy film, 15 to 20 mils thick, of a thermoformable resin. The type of resin used depends on the application. Polypropylene is a suitable candidate for those applications requiring chemical resistance. Polycarbonate film is a candidate for those applications involving growth, or supporting growth, of tissue culture and it may be supplied clear for colorimetric type assays. Polycarbonate or other materials may be supplied opaque, white, or black for fluorometric or luminescent assays.

Carrier tape20includes a substrate28which is processed to emboss therein a plurality of wells, as at30, in specific patterns to hold liquid. A plurality of sprocket drive holes, as at32, is provided along each edge. Sprocket drive holes32are precision punched to maintain a uniform spacing. This permits tractor driving carrier tape20for transport. Sprocket drive holes32also create a positional relationship to define any location on carrier tape20to provide recall to any selected well on the carrier tape.

The shape of wells30is a function of the application for carrier tape20. For chemical compound storage, the walls of the wells may have a Vee shape with a rounded bottom, as shown on FIG.2. For assays requiring an optical readout, the well may have a clear flat bottom. The required well shape is derived from the embossing tool.

The pattern of wells30is also a function of the application of carrier tape20. The defacto standard for biological assays is the 96-well microplate (see Society for Biomolecular Screening 96-well plate standard). This is an 8×12 matrix of wells or receptacles on 9-mm center spacing. The need for higher numbers of assays and their miniaturization is fostering higher density formats. To be compatible with existing instrumentation and chemical libraries, these new formats are multiples of the 96-well format. The 384-well format is a 16×24 matrix on 4.5 mm centers. The 1536-well format is a 32×48 matrix on 2.25 mm centers. Any of these formats may be embossed in carrier tape20(FIG.1). Carrier tape20has been embossed with a group40of wells30. It will be understood that a plurality of additional such groupings will be provided axially along the length of the carrier tape.

Carrier tape20, with its sprocket or tractor drive, provides a fast efficient way of transporting the reagent receiving patterns through the processing equipment. The inline processing provides considerable throughput advantages over handling the reagent patterns in individual injection molded plates. To provide pattern identification, each pattern on a roll of carrier tape is supplied with both a man readable identification number50and a machine readable identification number, in this case, a bar code52, both printed on the bottom side of carrier tape20using ink jet or other suitable methods.

Another primary advantage of the use of carrier tape20is compact storage. One hundred thousand chemical compounds for UHTS, in 5 microliter aliquots, can be stored in a carrier tape roll 4 inches wide and 16 inches in diameter. This storage requires that the liquid contents of the wells be sealed with a leak tight seal. A further requirement, since later access to the liquid wells is required, is that the seal must be removable.

For chemical compound storage the carrier tape and seal material must be inert to both the chemical compound and the dimethyl sulfoxide (DMSO) used to solvate the compound. Polypropylene meets this requirement for the carrier tape. The seal layer may be a pressure sensitive adhesive or a heat seal. If pressure sensitive material is used it must be DMSO resistant. While the latter type of material is available, there is still the question of compatibility with the chemical compounds. For this reason a heat seal material is preferred.

FIG. 3illustrates a heat seal layer, generally indicated by the reference numeral60. Heat seal layer60is a two-part structure made by lamination or co-extrusion. A seal layer62is provided which has a low melting point, low tensile strength resin such as a modified low density polyethylene or an ethylene vinyl acetate copolymer. A top, or support, layer64is provided adjacent seal layer62and is a high temperature resin with good tensile strength properties. Polyester is commonly used. The high melting point of the polyester prevents it from sticking to the heat seal apparatus at the temperature required to bond the seal layer. The high tensile strength of the polyester supports the seal layer during seal and unseal operations. This type of bi-film is commonly used in lidding applications for the prepared food industry.

To obtain a valid leak proof heat seal requires that the carrier surface and the heat seal surface be held in intimate contact for the sealing period. The sealing period is a function of time and pressure. The carrier tape is indexed with an intermittent motion, such as that which is obtained with a walking beam drive.

As is illustrated onFIG. 4, at a sealing station, carrier tape20is held flat by means of a vacuum platen80. Sealing layer60is fed from a roll (not shown) to a position between a heated sealing head82and carrier tape20. Heated sealing head82brings sealing layer60and carrier tape20together under defined conditions of time, pressure, and temperature.

Air entrapped between the seal layer62and carrier tape20(FIG. 1) will inhibit the seal. To avoid this, carrier tape20is provided with a plurality of vent holes, as at70, spaced between wells30. This allows a plurality of passageways84formed in a vacuum platen80supporting carrier tape20to evacuate any entrapped air between the two films, effecting a leak proof seal. As shown onFIG. 4, passageways84and holes70are aligned.

Removal of seal layer60may be achieved two ways.FIG. 5illustrates an automated system in which sealed carrier tape20is passed under a heated roller90. Polyester top layer64prevents sticking to roller. Roller temperature and contact time are controlled by the machine parameters. Seal layer62is softened and the strength of polyester layer64is used to separate the seal. A take up winder (not shown) on which seal layer62is wound, provides the tensile force necessary to break the seal. Carrier tape20is held down by edge guides92that are outside of the sealed pattern.

Some biological materials may be degraded by the heat from the unsealing. To eliminate that possibility, vacuum platen80supporting carrier tape20at the unsealing station may be refrigerated.

There are two basic applications of carrier tape20—use with automated systems and use with manual systems. This is particularly true where carrier tape20is used for chemical compound storage for pharmaceutical screening. Use of carrier tape20for that concept provides an exceptional method for the central compound library to distribute aliquots of compounds to outlying investigators. Each pattern40of compounds on the carrier tape has its own identification number imprinted on it. It may be cut from the carrier tape and handled as a separate entity. This creates the need of different solutions to handle individual patterns.

As is illustrated onFIGS. 6 and 7, with manual systems, the primary usage of the present invention is the introduction of compounds into assays performed in microplates. This is accomplished with a special frame of two-part construction, the frame having an outer shell100(FIG. 6) with an internal opening which meets the external footprint of the standard for a 96-well microplate. Thus, it will fit instrumentation designed for such microplates. An inner retainer102(FIG. 7) snaps into the outer frame to support a section of carrier tape pattern104. Inner retainer102holds flat carrier tape104to facilitate aspirating liquid from the wells with a multiple tip pipettor consisting of 384 or 96 tips.

Special requirements are required to unseal the individual section of carrier tape pattern104. It is desirable to unseal the pattern104after it is retained and used in outer shell frame100. The edge of the seal on carrier tape104is clamped between outer shell frame100and inner retainer102. For manual use, the seal is die cut with a steel rule die (not shown). It is die cut within the confines of the outer frame. Thus, a user can catch an edge of and strip carrier tape section104from the well area.

Most chemical compounds are solvated in dimethyl sulfoxide (DMSO). DMSO freezes at +4° C. (+40° F.). To minimize compounds being removed with the seal, inner retainer102is chilled prior to assembly of carrier tape section104in the frame. This is sufficient to solidify the DMSO to assure that the compounds remain in the wells and are not removed with the seal.

In normal operation, rolls of carrier tape20(FIG. 1) filled with chemical compound aliquots would be stored frozen at −20° C. or even −80° C. The compact nature of this storage system allows a very large number of chemical compounds to be stored in one freezer. Once removed from the freezer, the carrier tape system has a minimum of latent heat storage, both in the tape itself and in the small volume of liquid it contains. This has the advantage of a quick defrost prior to use, whereas microplate storage systems may require the better part of a day to defrost.

The disadvantage of the quick defrost is that the time in handling the roll may exceed the defrost time. The handling of the sealed roll may cause some of the well contents to move away from the bottom of the well. This is compensated for, by spinning the roll on its unwind stand prior to use in the application. Centrifugal force will move the liquid to the well bottom. Surface tension will retain it there during the gentle handling of the unwind stand during processing.

Biological assays and protocols utilizing polymerase chain reaction (PCR) require multiple cycles of different temperatures, usually three. These protocols are currently processed in microplates, 96-well or 384-well. A microplate is placed in its own thermal cycling instrument. Because of the latent heat capacity of the microplate, the majority of processing time is due to changing the temperature of the microplate—not the reagent it contains. The carrier tape system of the present invention will greatly improve the speed of processing PCR, a vital protocol in the Human Genome Project and other genomic studies.

The small latent heat capacity of the carrier tape and its speed of precise movement open a new vista for PCR. Instead of cycling temperature about a fixed microplate, the carrier tape can be quickly transported from one temperature station to the next as illustrated onFIG. 8which shows a PCR processing line employing the present invention. A first reagent processor, generally indicated by the reference numeral120, is provided and a second reagent processor, generally indicated by the reference numeral122may also be provided. Similar additional reagent processors can be provided as needed. Suitable motive means indexes carrier tape20to the right onFIG. 8. Afirst pipettor130, which may be assumed to be a 384-well pipettor, adds a first-set of reagents to wells30(FIG. 1) on carrier tape20. Sealing film60is fed from a supply roll140to a sealing station comprising a heat seal bar142which provides closure by applying pressure and heat to seal layer60and carrier tape20and a heat seal anvil144backs up the seal bar. Heat seal anvil also applies vacuum to hold carrier tape20flat similar to vacuum platen80(FIG.4). The application of vacuum will also evacuate any entrapped air between seal layer60and the surface of carrier tape20.

Carrier tape20then indexes through a series of temperature control stations, as at150. The time at each station150is a function of the index time. In many applications, a common temperature dwell time is satisfactory. In those protocols where a common time is not acceptable, an individual temperature station would be opened at its selected time interval.

As illustrated more clearly onFIG. 9, in addition to having a heated bottom portion160, each temperature control station has a heated lid162. This provides quick uniform temperature to the contents of the wells.

Referring back toFIG. 8after passing through the required temperature cycles, seal layer60may be removed for access to the contents of the wells. As described before, a heated roll170warms the seal area. A seal winder172provides tension on the seal layer60, to remove it from carrier tape20. With the wells open, the contents may be removed or additional reagents added. In the latter case, a second pipettor180adds the second set of reagents and the entire protocol repeated on second reagent processor122.

Each temperature station150is maintained at a fixed, easily regulated temperature. As carrier tape20is indexed to each station150, the temperature of the small volume of reagents within the wells will quickly reach the equilibrium temperature of the specific station.

Due to the small volume of reagents in the wells and the high temperature of PCR (typically 90° C.), evaporation is a real concern. Another concern is contamination, well to well, due to the high amplification of PCR. The ability to seal each well with a leakproof seal, as described before, provides an ideal solution for both problems. Access to the wells is required at the end of the PCR. The ability to unseal the carrier tape automatically meets that requirement.

Many biological assays require an incubation period following the addition of reagents. The incubation period may have environmental demands (i.e., elevated temperature typically 37° C., high humidity to minimize evaporation from open wells, or a CO2environment for cell viability). This may be easily provided on a carrier tape system by cutting the carrier tape into convenient length (i.e. 4 feet long).

A system providing for incubation prior to fluorescence reading is illustrated onFIG. 10where the system is indicated generally by the reference numeral180. System180includes a first supply roll182of sealed carrier tape184, similar to carrier tape20(FIG.1), containing a large number of chemical compounds, and a second supply roll190of unsealed assay carrier tape192, also similar to carrier tape20, however, having empty wells. As compound tape184is unrolled, it passes under a heated roller196which removes sealing layer60which is wound on roller198in the manner described above with reference to FIG.8.

Tapes184and192are indexed under a compound transfer manifold210which transfers chemical compounds from the wells on compound carrier tape184to the wells on assay carrier tape192. Compound carrier tape184can then be discarded as by means of a tape cutter220and a waste container222.

After the transfer of chemical compounds by compound transfer manifold210, assay carrier tape192is indexed under a first reagent manifold230for introduction of reagents into the wells on the tape, then, if required, under a second reagent manifold232for the introduction of additional reagents, and then, if required, one or more additional reagent manifolds. Assay carrier tape192is then indexed under a standards and controls manifold234and then under a tape cutter236where the tape is cut into, for example, 4-foot lengths. The cut lengths of assay carrier tape192are then transported, using a tractor drive, into an incubator240. Incubator240can be very compact, with a unit 6 inches wide by 24 inches deep by 4 feet long accommodating 100,000 wells of the type described above with reference toFIGS. 1 and 2. After the required incubation period, each strip moves to the next processing station, in this case a fluorescence reader244which may read, for example, fluorescence intensity, fluorescence polarization, luminescence, or time resolved fluorescence. After reading, each section of tape192can then be disposed of by means of a tape cutter250and a waste container252.

FIG. 11illustrates the major components of a tractor drive for moving carrier tape20. A motor270, which may be a stepper motor, has a rotatable shaft272to which is affixed a sprocket wheel274. Sprocket wheel has a plurality of sprockets, as at276, extending outwardly from the outer periphery thereof, the sprockets engaging sprocket holes32in carrier tape20. As motor270rotates sprocket wheel274, carrier tape20is driven in one direction or the other. One or more sprocket idler wheels280are provided to support and guide carrier tape20. The extent of travel of carrier tape20may be determined by an encoder (not shown) associated with one of the rotary components of the tractor drive, by counting the number of sprocket holes32passing a given point by optical or other means, and/or by identifying indicia, such as bar code52(FIG.1), on the carrier tape.

FIG. 12illustrates a compound transfer system employing the present invention, the system being generally indicated by the reference numeral300. Here, sealed carrier tape20containing a large number of chemical compounds is unrolled from a supply roll310, sealing layer60is removed from the carrier tape by means of a heated roller312and a winder roller314, and the carrier tape is indexed under a 384-well pipettor316with a transverse moving head having384needles depending therefrom. Such a pipettor may be a Quadra384 Pipettor as furnished by Tomtec, Inc., of Hamden, Conn. Included in system300are two pairs of dual reversible stackers320which, depending on programming, supply standard 384-well microplates to an six-position X-Y shuttle330or accept the microplates from the shuttle. The open wells on carrier tape20can be accessed by pipettor316. Using “pipeline” pipetting, pipettor316aspirates the various reagents in the assay using an air gap for separating the reagents. The standards and controls are aspirated from special reservoirs (not shown) to match the user's format. The ability of pipettor316to aspirate 0.5 microliter quantities permits aspirating compounds from carrier tape20in 100% DMSO, while maintaining a 1% DMSO concentration in the 50 microliter assay volume. In addition, to speed processing, pipeline pipetting uses high volume reagents (i.e., buffer) to wash out the small volume of compound from the pipettor tips, thereby maintaining precision in the assay. After dispensing the tip volume in an assay microplate, the plate is restacked in one of stackers320, the pipettor tips are washed in an ultrasonic tip wash station (not shown), and the next microplate is infed from a stacker and the cycle is repeated.

After use, carrier tape20can be discarded or, if the chemical compounds thereon are to be saved for future use, a sealing layer60may be applied and the carrier tape wound on storage roll340.

Another aspect of the present invention is to provide means to both aspirate and dispense multiple aliquots of nanoliter quantities. The unique principle of this invention is to have one piezo crystal exert sufficient force on multiple tubes to deform them to displace the desired volume. The amount of force, and thus displacement, is controlled by the electronics driving the piezo crystal. The dispensing tubes being deformed remain within their elastic limit. When the piezo crystal retracts, the cross section of each dispensing tube returns to its original cross sectional area, thereby creating the aspirate/dispense action.

The nanoliter volumes require a very small diameter orifice. This generates the back pressure against the shockwave that creates the stream velocity through the orifice. Not only must the inside diameter be small, but also the wall thickness must be thin, requiring a small outside diameter. A heavy wall section creates additional surface area at the orifice, increasing the surface tension forces. The thin walled small orifice tube results in a fragile dispensing tube. This presents both reliability and manufacturing problems.

The present invention uses a small dispensing needle400, as illustrated on FIG.13. Typically, the inside diameter of needle400is 0.003 inch with an outside diameter of 0.012 inches. This provides a 0.0045-inch wall section. Dispensing needle400is fitted inside of a supporting needle410having an inside diameter of 0.016 inch allowing a slip fit of the outside diameter of the dispensing needle. Needles400and410are bonded at the tops thereof with a suitable material, such as UV cured epoxy or polyurethane adhesive, to form a liquid-tight seal420. Needles400and410together form a needle assembly, generally indicated by the reference numeral422.

As shown onFIG. 14, each needle assembly422is connected with a sleeve430of suitable material to a pump tube432. Pump tube432is of a suitable cross section and length for the designed delivery volume. Pump tube432is retained between a rigid back up plate, or anvil,434and a piezo crystal assembly436. The available movement of piezo crystal assembly436is also a variable in this equation. As is shown onFIG. 15, multiple pump tube432and their associated delivery needle assemblies422may be operated by one piezo crystal assembly436. Piezo crystal assembly436is contained within the same anvil assembly434such that an increase in size of the piezo crystal causes a decrease in size of pump tubes432. This provides the necessary pumping action, by displacement. Referring principally toFIG. 14, the other end of pump tube432is connected to a small fast acting solenoid valve440such as used in ink jet printing. During the dispense part of the cycle solenoid valve440is closed, blocking flow from pump tube432at that end. Only the orifice end of needle400remains open to the atmosphere.

Referring again toFIG. 15, an individual solenoid valve440is connected to each pump tube432, although only one piezo crystal assembly436may be used to squeeze multiple pump tubes. Each solenoid valve440is connected through a manifold450to a common 3-way valve452(FIG.14). Three-way valve452selectively connects all solenoid valves440to a source of air pressure460, a source of vacuum462, or a source of rinse liquid464. Rinse liquid reservoir464is a closed container that is pressurized by a regulated air pressure through a valve466.

The sequence of operation is as follows. Piezo crystal assembly436is energized to an initial holding or home position. This position compensates for any variation in the outside diameter of the multiple pump tubes432. From this home position, all pump tubes432will be compressed the same dimension. The multiple delivery needles400are then dipped into the various wells, or reservoirs470(FIG. 14) containing the liquid to be aspirated. Three-way valve452connects all solenoid valves440to vacuum source462. With the tips of delivery needles400submerged, solenoid valves440open and reclose quickly and are open long enough to allow the vacuum to aspirate liquids up through the area of piezo crystal assembly436and into pump tubes432. Solenoid valve440closes before the liquid can reach the interior components of the solenoid valve. The length of pump tube432is sized to allow for variations in flow of the different liquids. The minimum flow for each liquid flow path is that the liquid line must pass the end of the pump tubes432and not reach the inlet of solenoid valve440.

With pump tubes432filled, delivery needles400are moved to the dispense position. Piezo crystal assembly436is energized to its set value, causing a uniform and quick constriction of all pump tubes432. This constriction displaces the fluid within pump tubes432, causing delivery at the orifice of needles400.

The next position of delivery needles400depends on the system function that is desired. The remaining contents of pump tube/needle assembly432/400may be reclaimed back into the origin or they may be deposited in a waste container. This is a similar function, but with the waste disposal, it is combined with the rinse function. The reclaim function is described, as follows. Three-way valve452switches to apply air pressure to all solenoid valves440. With delivery needles400in the reclaim position, solenoid valves440open. Air pressure blows the remaining contents of the pump tube/delivery needle assembly432/400back into the origin reservoir.

Solenoid valves440close and needle assemblies are then moved to the waste/rinse position. Three-way valve452switches to the rinse liquid supply464. Solenoid valves440open, admitting wash liquid to delivery needles400, rinsing them to waste. At the completion of the wash cycles, solenoid valves440close. Three-way valve452then switches to pressure. Solenoid valves440open, blowing the remaining wash fluid contents in the system to waste. With the flow passages clear, the entire cycle repeats for the next aspirate/dispense cycle.

The amount of compression on pump tubes432is directly related to the volume dispensed from the outlet orifices of needles400. In turn, the compression imparted by the piezo crystal assembly436is a function of its electrical excitation. This relationship is used to control the volume of liquid aspirated or dispensed on each cycle.

A closed loop monitoring system may be provided by locating a fiber optic transmitting and receiving pair480/482(FIG.14), looking across each dispensing orifice of a needle400. Fiber optic pair is480/482is connected to a light emitting diode and a phototransistor (not shown). A base line of conduction in the phototransistor is obtained when there is no flow from the orifice. When there is flow from the orifice, the conduction of the phototransistor is varied during the period of flow. This signal may be amplified and used to monitor or control the excitation to piezo crystal assembly436. Only one piezo crystal assembly436is used to operate multiple orifices. Thus, the phototransistor signals would be averaged to provide feedback control to the piezo excitation. The individual orifice signals would be used to monitor flow or no flow from each orifice on each dispense cycle. If an orifice becomes clogged or otherwise ceases to function properly an error signal may be generated and corrective action can be taken. If individual piezo crystals are used on each pump tube then the photo transistor pair can have full feedback control on each delivery orifice.

In the embodiments of the present invention described above, it will be recognized that individual elements and/or features thereof are not necessarily limited to a particular embodiment but, where applicable, are interchangeable and can be used in any selected embodiment even though such may not be specifically shown.

Terms such as “upper”, “lower”, “inner”, “outer”, “inwardly”, “outwardly”, and the like, when used herein, refer to the positions of the respective elements shown on the accompanying drawing figures and the present invention is not necessarily limited to such positions.

It will thus be seen that the objects set forth above, among those elucidated in, or made apparent from, the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown on the accompanying drawing figures shall be interpreted as illustrative only and not in a limiting sense.