Patent Publication Number: US-2006002824-A1

Title: Dispensing systems, software, and related methods

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
      This application claims the benefit of U.S. Provisional Application No. 60/577,849, filed Jun. 7, 2004, the disclosure of which is incorporated by reference in its entirety for all purposes. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates generally to material dispensing. In addition to dispensing systems, related software and methods for efficiently and accurately dispensing selected quantities of materials are provided.  
     BACKGROUND OF THE INVENTION  
      High-throughput screening devices and systems are important analytical tools in the process of discovering and developing new drugs. Drug discovery procedures typically involve synthesis and screening of candidate drug compounds against selected targets. Candidate drug compounds are molecules with the potential to modulate diseases by affecting given targets. Targets are typically biological molecules, including proteins such as enzymes and receptors, or nucleic acids, which are thought to play roles in the onset or progression of particular diseases. A target is typically identified based on its anticipated role in the progression or prevention of a disease. Recent developments in molecular biology and genomics have led to a dramatic increase in the number of targets available for drug discovery research.  
      Once a target is identified, a library of compounds is typically selected to screen against the target. Enormous compound libraries have been compiled from natural sources and via various synthetic routes, including multi-step solution- or solid-phase combinatorial synthesis schemes. In fact, many pharmaceutical companies and other institutions have access to libraries that include hundreds of thousands of compounds. Following the selection of a target and compound library, the compounds are screened to determine if they have any affect on the target. Compounds that affect the target are denominated as hits. A basic premise for screening larger numbers of compounds against a particular target is the increased statistical probability of identifying a hit.  
      Before screening compounds against a target, the assay is developed. The assay development process includes selecting and optimizing an assay that will measure the performance of a compound against the selected target. Assays are generally classified as either biochemical or cellular. Biochemical assays are typically performed with purified molecular targets, whereas cellular assays are performed with living cells. While cellular assays often provide more biologically relevant information than biochemical assays, they are typically more complex and time-consuming to perform than biochemical counterparts.  
      In performing biochemical and cellular assays, samples are routinely characterized by examining properties, such as fluorescence, luminescence, and absorption. In a fluorescence study, for example, selected tissues, specific binding partners, chromosomes, or other structures are treated with a fluorescent probe or dye. The sample is then irradiated with light of a wavelength that causes the fluorescent material to emit light at a longer wavelength, thus allowing the treated structures to be identified and to at least some extent quantified. In a luminescence analysis, the sample is not irradiated in order to initiate light emission by the material. Instead, one or more reagents are typically added to the sample in order to initiate the luminescence phenomena. In an absorption analysis, a dye-containing sample is typically irradiated by an electromagnetic radiation source of a selected wavelength. The amount of light transmitted through the sample is generally measured relative to the amount of light transmitted through a reference sample without dye. Analytical devices and systems utilized to determine the fluorescence of a sample typically include at least one electromagnetic radiation source capable of emitting radiation at one or more excitation wavelengths and a detector for monitoring the fluorescence emissions. In many cases, these devices and systems can also be adapted for use in both luminescence and absorption analyses.  
      To produce or accommodate the large number of compounds and targets, multiple synthesis reactions or screens are often performed in parallel in the wells of standard multi-well containers (e.g., microtiter plates, reaction blocks, etc.) of selected well-densities and even on the surfaces of various supports, such as membranes or treated glass. Parallel syntheses or screens typically include dispensing multiple reaction components (e.g., beads or other solid supports, reactants, buffers, etc.) or samples into the wells of multi-well containers or onto the surfaces of supports. Many conventional systems include pipetting devices in which fluids are aspirated from sources through, e.g., pipette tips using syringe pumps before being dispensed from the same pipette tips. While suitable for some applications, the cost of replacing pipette tips adds to the overall cost of performing compound synthesis or screening. The cost of replacing these consumables can be substantial, given the large numbers of synthesis reactions or screens that are typically performed to ultimately identify hits. In addition, pipette tip openings can become obstructed by beads, cells, or precipitate or other debris, which typically necessitates halting the synthesis or screen in order to clear the obstruction or to replace the tip. Moreover, certain dispensing systems include valves that contact dispensed fluid, such as suspensions of beads for combinatorial synthesis protocols. The valves used in these configurations often also readily clog and beads can destroy their sealing ability. Another exemplary shortcoming of many of these dispensing systems is that they commonly dispense volumes that lack uniform densities. The limited robustness of these pre-existing dispensing systems can severely limit the throughput of synthesis or screening procedures, which have become increasingly automated.  
     SUMMARY OF THE INVENTION  
      The present invention relates to rapid and reliable material dispensing. In some embodiments, for example, dispensing systems that include peristaltic pumps and other pressure sources are provided for the efficient delivery of accurate volumes of fluidic materials, such as bead suspensions or other fluids into the wells of multi-well plates and reaction blocks or into other types of fluid containers or onto substrate surfaces. Typically, the systems described herein are configured to dispense volumes of fluid having substantially uniform densities. Density variations among volumes of dispensed fluids can lead to biased assay results and to inconsistent synthetic yields, among many other possible detrimental effects depending upon the particular dispensing application. In certain embodiments, the dispensing systems described herein include fluid junction blocks for introducing gases into system conduits, e.g., to purge fluids from the conduits, to create gaps between system and source fluids disposed in the conduits, or the like. To illustrate, gaseous gaps (e.g., air gaps, etc.) can be used to separate system and source fluids from one another to prevent system fluids from diluting the source fluids. In addition to system software, methods of dispensing fluidic materials are also provided.  
      In one aspect, the invention provides a dispensing system that includes at least one peristaltic pump configured to convey at least a first fluidic material into or through at least a portion of at least one conduit when the conduit is operably connected to the peristaltic pump and is in fluid communication with at least a first fluidic material source. In some embodiments, the peristaltic pump comprises a multi-channel peristaltic pump. The dispensing system also includes at least one pressure source other than the peristaltic pump. The pressure source is configured to apply pressure in the conduit when the pressure source is operably connected to the conduit such that selected aliquots of the first fluidic material are dispensed from at least one opening in the conduit when the first fluidic material is present in the conduit. In some embodiments, the pressure source includes one or more pumps.  
      In addition, the dispensing system also includes at least one controller operably connected to the pressure source. The controller is configured to control operation of the pressure source to effect dispensing of the first fluidic material from the opening in the conduit when the conduit is in fluid communication with the first fluidic material source. In some embodiments, the controller is also operably connected to the peristaltic pump. In these embodiments, the controller is optionally configured to effect rotation of a roller support of the peristaltic pump in at least one rotational increment that substantially corresponds to an integral multiple of an angular distance disposed between adjacent rollers supported by the roller support such that quantities of the first fluidic material that correspond to the rotational increment are conveyed into or through the conduit when the conduit is operably connected to the peristaltic pump and is in fluid communication with the first fluidic material source. The phrase “integral multiple of an angular distance disposed between adjacent rollers” refers to the product of the angular distance disposed between adjacent rollers supported by a roller support of a peristaltic pump by an integer, that is, any of the natural numbers, the negatives of these numbers, or zero. Typically, the dispensing system includes a mounting component to which the peristaltic pump, the pressure source, the controller, and/or another system component is attached.  
      In some embodiments, the dispensing system includes at least one pinch valve configured to regulate conveyance of fluidic materials through the conduit when the conduit is operably connected to the pinch valve. Typically, at least one air table is operably connected to the pinch valve. The air table is configured to effect operation of the pinch valve. In these embodiments, the controller is optionally also operably connected to the air table. The controller is configured to control operation of the air table to effect regulation of fluidic material conveyance through the conduit when the conduit is operably connected to the pinch valve.  
      The dispensing system generally includes the conduit. Typically, at least one dispensing tip or nozzle fluidly communicates with the conduit and comprises an opening to the conduit. In some embodiments, for example, at least one waste collection component is configured to selectively communicate with the opening in the conduit such that waste fluids can be dispensed into the waste collection component for disposal. To further illustrate, a fluid reservoir is optionally in fluid communication with the conduit.  
      In certain embodiments, a substantial portion of the conduit is disposed other than parallel to a Z-axis of the dispensing system. To illustrate, at least a segment of the conduit disposed between the opening and the peristaltic pump comprises a conduit coil in some of these embodiments. Generally, at least one coil in the conduit coil is disposed other than parallel to a Z-axis of the dispensing system in these embodiments. This conduit orientation prevents beads or other materials in fluids from settling toward an opening in the conduit such that volumes having uniform densities are dispensed from the conduit. Optionally, at least a segment of the conduit that comprises the opening is disposed at an angle of between about 0° and about 90° relative to a Z-axis of the dispensing system. For example, fluids dispensed into the wells of multi-well containers from conduits having this configuration contact the sides of the wells before other parts of the wells. This minimizes the disruption of other materials disposed in the wells during fluid dispensing. In addition, this configuration also minimizes the foaming of reagents or media (e.g., Bright-Glo™ reagent, fetal bovine sera (FBS) media, etc.) in the wells during dispensing by dissipating the kinetic energy of the fluid on the walls of the wells. Foam is typically undesirable, because it can interfere with optical plate readers or the like.  
      To further illustrate, the dispensing system comprises multiple conduits in certain embodiments. In some of these embodiments, openings in at least two of the conduits are spaced at a distance from one another to simultaneously fluidly communicate with different wells disposed in at least one multi-well container. Optionally, the opening in the conduit comprises at least one manifold that is configured to fluidly communicate with multiple fluidic material sites, e.g., multiple wells disposed in a multi-well plate, a reaction block, etc.  
      In some embodiments, the peristaltic pump is operably connected to at least a first conduit and the pressure source is operably connected to at least a second conduit, which first and second conduits fluidly communicate with one another. In these embodiments, at least one three-way valve is optionally operably connected to the first conduit, which three-way valve is structured to selectively vent the first conduit.  
      In certain embodiments, the pressure source is in fluid communication with the conduit. To illustrate, the pressure source optionally comprises a pressurized gas source and/or a pressurized second fluidic material source. Optionally, at least one filter (e.g., 0.45 μm or less) is operably connected to the conduit. In some embodiments, the second fluidic material source comprises at least one buffer, e.g., used as a system fluid. The pressure source is typically operably connected to the conduit via at least one solenoid or other type of valve that regulates pressure applied by the pressure source. The controller is optionally operably connected to the valve. In these embodiments, the controller is generally configured to control operation of the valve to effect regulation of the applied pressure.  
      A port is disposed through at least one wall of the conduit and communicates with at least one cavity disposed through the conduit in certain embodiments. For example, the port is typically disposed between the peristaltic pump and the pressure source in the conduit. The port typically comprises a length of about 5 mm or less. Moreover, a region of the conduit that comprises the port comprises a fluid junction block in some of these embodiments. To illustrate, at least one gas valve is optionally operably connected to the port. The gas valve regulates gas flow into the conduit through the port when the gas valve is operably connected to at least one pressurized gas source. In some embodiments, for example, the gas valve includes a plunger comprising a compliant seal material that forms a face seal with the port when the plunger pushes the compliant seal material into contact with the port. Typically, the gas valve is operably connected to the pressurized gas source that flows gas (e.g., air, nitrogen, helium, argon, etc.) to the gas valve at a pressure of between about zero pounds per square inch and about 10 pounds per square inch. In certain embodiments, at least one air table is operably connected to the gas valve. The air table is configured to effect operation of the gas valve. In some of these embodiments, the controller is operably connected to the air table and is configured to control operation of the air table to effect regulation of gas flow into the conduit through the port when the gas valve is operably connected to the pressurized gas source.  
      In some embodiments, the dispensing system includes the first fluidic material source. To illustrate, the first fluidic source optionally comprises one or more of, e.g., beads, cells, enzymes, reagents, or the like. In certain of these embodiments, at least one fluid agitation mechanism is operably connected to the first fluidic material source.  
      The dispensing system optionally includes at least one positioning component operably connected to the controller. The positioning component is configured to moveably position one or more conduits and/or one or more fluidic material sites relative to one another. To illustrate, the positioning component optionally comprises at least one X/Y-axis linear motion component operably connected to at least one control drive that controls movement of the X/Y-axis linear motion component along an X-axis and a Y-axis of the dispensing system. In these embodiments, the controller is typically operably connected to the pressure source and is configured to simultaneously effect application of pressure in the conduits from the pressure source and moveably position the conduits and/or the fluidic material sites relative to one another such that volumes of fluid are conveyed from the conduits synchronous with the relative movement of the conduits and/or the fluidic material sites. In certain embodiments, the positioning component comprises at least one Z-axis linear motion component comprising at least one conduit support head that is configured to support at least segments of the conduits and that moves along a Z-axis of the dispensing system. The positioning component optionally comprises at least one object holder that is structured to support at least one fluidic material site. In some embodiments, at least one cleaning component is operably connected to the controller. The cleaning component is configured to clean at least segments of the conduits when the conduits are operably connected to the positioning component and the positioning component moves the conduit segments at least proximal to the cleaning component. For example, the cleaning component optionally comprises at least one vacuum chamber comprising at least one orifice into or proximal to which the positioning component moves the conduit segments such that an applied vacuum removes adherent material from at least external surfaces of the conduit segments.  
      In some embodiments, the dispensing system includes at least one detector configured to detect detectable signals produced in fluidic materials. Typically, the controller is operably connected to the detector and is configured to control the detector to effect detection of the detectable signals.  
      In another aspect, the invention provides a computer program product comprising a computer readable medium having one or more logic instructions for: operating at least one peristaltic pump to effect conveyance of at least a first fluidic material into at least one conduit through at least a first opening of the conduit, and operating at least one pressure source other than the peristaltic pump to effect application of pressure on the first fluidic material in the conduit such that at least one aliquot of the first fluidic material is dispensed from at least a second opening of the conduit. In certain embodiments, the computer program product includes at least one logic instruction for receiving one or more input parameters selected from the group consisting of: (i) a quantity of the first fluidic material to be conveyed to a fluidic material site; (ii) an initial density of the first fluidic material; (iii) a quantity of a second fluidic material to be added to the first fluidic material to modify a density of the first fluidic material; (iv) a quantity of gas to convey into the conduit to separate the first fluidic material from a second fluidic material; and (v) a fluidic material site format. In some embodiments, the computer program product includes at least one logic instruction for: operating at least one valve operably connected to the conduit to effect regulation of material conveyance into and/or out of the conduit. In certain embodiments, the computer program product includes at least one logic instruction for: operating at least one X/Y-axis linear motion component and/or at least one Z-axis motion component to effect movement of one or more other components attached to or positioned on the X/Y-axis linear motion component or the Z-axis motion component.  
      In another aspect, the invention relates to a method of dispensing a fluidic material. The method includes (a) conveying at least a first fluidic material (e.g., beads, cells, enzymes, reagents, and/or the like) into at least one conduit through at least a first opening of the conduit using at least one peristaltic pump. Typically, at least a segment of the conduit comprises a non-vertical flow path to prevent one or more components of the first fluidic material from settling proximal to the second opening. The method also includes (b) applying pressure on the first fluidic material in the conduit using at least one pressure source other than the peristaltic pump such that at least one aliquot of the first fluidic material is dispensed from at least a second opening of the conduit. In certain embodiments, the method includes dispensing the aliquot of the first fluidic material unto a wall of a container (e.g., a well of a multi-well container, etc.), e.g., to minimize the disruption of materials disposed on the bottom of the container, to prevent reagents or media from foaming, etc. Optionally, the method includes conveying a gas into the conduit to purge fluidic materials from at least one segment of the conduit prior to (a). In some embodiments, the method includes dispensing multiple aliquots of the first fluidic material during (b). Optionally, the method includes performing at least one synthesis reaction or assay using one or more components in the aliquot of the first fluidic material after (b). In certain embodiments, the method includes restricting fluidic material conveyance in the conduit directed towards the peristaltic pump during (b). In some embodiments, the method includes performing (a) and (b) substantially simultaneously with one another. Optionally, the method includes repeating (a) and (b). In some embodiments, the method includes moveably positioning at least one fluidic material site relative to the second opening. In certain embodiments, the method includes detecting one or more detectable signals produced in the conduit and/or in the aliquot of the first fluidic material.  
      In some embodiments, the method includes conveying at least a second fluidic material (e.g., a buffer, etc.) through one or more segments of the conduit using the pressure source such that the second fluidic material expels the aliquot of the first fluidic material from the second opening of the conduit during (b). In certain of these embodiments, the method includes diluting the first fluidic material with the second fluidic material prior to or substantially simultaneously with (b). In some of these embodiments, the method includes conveying a gas into the conduit through a port to form a gap between the first and second fluidic materials to prevent the first and second fluidic materials from mixing with one another.  
      In another aspect, the invention provides a method of dispensing aliquots of fluidic materials having substantially uniform densities. The method includes conveying selected aliquots of at least one fluidic material from at least one dispensing tip that fluidly communicates with at least one conduit through which the fluidic material is conveyed. The conduit comprises a non-vertical flow path such that components in the fluidic material are prevented from settling proximal to the dispensing tip prior to being dispensed, thereby dispensing the aliquots of fluidic materials having substantially uniform densities.  
      In another aspect, the invention provides a method of dispensing a fluidic material. The method includes (a) providing a dispensing system having a fluid junction block comprising: (i) at least a portion of a first conduit that fluidly communicates with a first fluidic material source; (ii) at least a portion of a second conduit having: (I) at least first and second openings, and (II) at least one port disposed through a wall of the second conduit. The port communicates with a cavity disposed through the second conduit. Further, the first conduit intersects and fluidly communicates with the second conduit between the port and the second opening of the second conduit. The method also includes (b) conveying a volume of a second fluidic material through the first opening of the second conduit proximal to the port, (c) restricting fluidic material conveyance through the first opening of the second conduit and through the first conduit, and (d) conveying at least one gas into the second conduit through the port to purge fluidic materials from the second conduit downstream from the port through the second opening of the second conduit. In addition, the method also includes (e) restricting fluidic material conveyance through the first opening of the second conduit and gas conveyance through the port, (f) conveying a volume of a first fluidic material from the first fluidic material source through the first conduit and into the second conduit proximal to and downstream from the intersection of the first and second conduits such that a volume of the gas is disposed between the first and second fluidic materials in the second conduit, (g) restricting fluidic material conveyance through the first conduit and gas conveyance through the port, and (h) applying pressure to the second fluidic material in the second conduit such that at least one selected aliquot of the first fluidic material is dispensed from the second opening of the second conduit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1A  schematically shows a dispensing system that includes a conduit coil according to one embodiment of the invention.  
       FIG. 1B  schematically depicts a reservoir that is optionally substituted in the dispensing system of  FIG. 1A .  
       FIG. 2  schematically depicts a dispensing system according to one embodiment of the invention.  
       FIG. 3  schematically shows a dispensing system according to one embodiment of the invention.  
       FIG. 4  schematically illustrates a dispensing system according to one embodiment of the invention.  
       FIG. 5A  schematically shows a cross-sectional view through a dispensing system according to one embodiment of the invention.  
       FIG. 5B  schematically depicts a detailed cross-sectional view of a fluid junction block from the dispensing system of  FIG. 5A .  
       FIG. 6  schematically illustrates a dispense head that includes a fluid manifold according to one embodiment of the invention.  
       FIG. 7A  schematically shows a dispensing system from a perspective view according to one embodiment of the invention.  
       FIG. 7B  schematically illustrates a detailed bottom perspective view of a dispensing component from the dispensing system of  FIG. 7A .  
       FIG. 7C  schematically depicts a detailed top perspective view of a dispensing component from the dispensing system of  FIG. 7A .  
       FIG. 8  schematically shows a multi-channel peristaltic pump from a top perspective view.  
       FIG. 9  schematically depicts an object holder from a top perspective view.  
       FIG. 10A  schematically shows a top view of a microtiter plate.  
       FIG. 10B  schematically illustrates a bottom view of the microtiter plate shown in  FIG. 10A .  
       FIG. 10C  schematically depicts a cross-sectional view of the microtiter plate shown in  FIG. 10A .  
       FIG. 11A  schematically shows a partially transparent perspective view of a vacuum chamber of a cleaning component according to one embodiment of the invention.  
       FIG. 11B  schematically illustrates a detailed cross-sectional view of a dispensing tip disposed proximal to an orifice of a portion of the vacuum chamber of  FIG. 11A .  
       FIG. 12  schematically shows a representative example logic device in which various aspects of the present invention may be embodied. 
    
    
     DETAILED DESCRIPTION  
      I. Introduction  
      While the present invention will be described with reference to a few specific embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Various modifications can be made to the embodiments of the invention described herein by those skilled in the art without departing from the true scope of the invention as defined by the appended claims. It is also noted here that for a better understanding, certain like components are designated by like reference letters and/or numerals throughout the various figures. Further, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Certain terms defined herein, and grammatical variants thereof, are more fully defined by reference to the specification in its entirety.  
      The present invention relates to accurate and efficient fluidic material dispensing. The term “fluidic material” refers to matter in the form of gases, liquids, semi-liquids, pastes, and combinations of these physical states. Exemplary fluidic materials include reagents for performing a given assay or synthesis reaction, suspensions of cells, beads, or other particles, and/or the like. The invention provides dispensing systems that include peristaltic pumps in addition to other pressure sources for delivering selected volumes of fluidic materials into various types of containers, onto substrate surfaces, and to other fluidic material sites. In some embodiments, these systems are further configured to dispense volumes of fluid that have substantially uniform densities. The term “substantially uniform densities” refers to densities that are approximately equal to one another. In some embodiments, for example, the densities of fluidic materials (e.g., solutions with particle suspensions, etc.) with substantially uniform densities vary by about 20% or less from one another. To illustrate, dissolved solutions are generally uniformly dense at equilibrium, whereas the density of solutions with particle suspensions may vary due, e.g., to improper mixing or settling. Density variations among volumes of dispensed fluids can, for example, generate biased assay results, cause synthetic protocols to produce inconsistent yields, or otherwise negatively impact the reproducibility of a particular application. In addition, the dispensing systems described herein typically include fluid junction blocks for introducing gases into system conduits, e.g., to purge fluids from the conduits, to create gaps between system and source fluids disposed in the conduits, or the like.  
      In addition to the dispensing systems described herein, system software for controlling the operation of these systems and related methods of dispensing fluidic materials are also provided.  
      II. Dispensing Systems  
      Referring initially to  FIGS. 1-7 , which schematically illustrate some embodiments of the dispensing systems of the invention. For example,  FIG. 1A  schematically shows dispensing system  100 . As shown, dispensing system  100  includes fluidic material source  102  in fluid communication with peristaltic pump  104 . As used herein, the term “fluid communication” or “fluidly communicate” in the context of dispensing system components refers to the ability of fluidic materials (e.g., liquids, gases, etc.) to be conveyed between those components. In some embodiments, system components fluidly communicate with one another via tubing or other conduits, whereas in other embodiments, at least some system components are directly connected with one another and fluidly communicate with one another in the absence of, e.g., tubing. As shown in  FIG. 1A , components of dispensing system  100  fluidly communicate with one another via conduits.  
      During operation, peristaltic pump  104  flows fluidic material (e.g., bead suspensions, cell suspensions, etc.) from fluidic material source  102  into reservoir  106  via “T” junction  108 . In some embodiments, the fluidic material flowed from fluidic material source  102  displaces existing buffer or other fluids disposed in reservoir  106 , which fluids are directed to, e.g., a waste collection component (e.g., a waste tray, etc.) (not shown) of dispensing system  100 . Once a selected volume of the fluidic material is flowed into reservoir  106 , pinch valve  114  is typically engaged to restrict flow between peristaltic pump  104  and “T” junction  108 . As shown, reservoir  106  also fluidly communicates with dispensing tip  110 . As also shown, reservoir  106  includes a conduit coil in which the coils are disposed other than parallel with the Z-axis of dispensing system  100  so that fluidic materials flowed through reservoir  106  follow a non-vertical flow path. The term “non-vertical flow path” refers to a flow path that is not directly or entirely vertical (e.g., entirely parallel with a Z-axis). Non-vertical flow paths prevent beads, cells, or other particles in the fluidic materials from settling towards the bottom of reservoir  106 . This provides a substantially uniform density to the fluidic material disposed in reservoir  106 . Coiled reservoir design will vary depending on, e.g., the density of fluidic materials to be dispensed from dispensing tip  110 . As used herein, the term “top” refers to the highest point, level, surface, or part of a device or system, or device or system component, when oriented for typical designed or intended operational use, such as dispensing fluidic materials. In contrast, the term “bottom,” as used herein, refers to the lowest point, level, surface, or part of a device or system, or device or system component, when oriented for typical designed or intended operational use.  
      In some embodiments, reservoirs having substantially vertical flow paths are utilized, e.g., for dispensing applications in which the uniformity of fluid density is typically not a concern, such as dissolved solution dispensing. An example of such a reservoir is schematically shown in, e.g.,  FIG. 1B . As shown, reservoir  112 , which is shown as a tube lacking coils, can be substituted for reservoir  106  in dispensing system  100 . Reservoir  112  typically includes a sufficient volume capacity to handle a series of dispenses from dispensing tip  110 . In certain embodiments, reservoirs are designed to minimize mixing between source and system fluids. In other embodiments, source and system fluids are intentionally mixed to produce fluidic materials of selected concentrations for dispensing. Each of these embodiments is described further herein.  
      As additionally shown in  FIG. 1A , dispensing system  100  also includes valve  116  (e.g., a solenoid valve, a syringe valve, etc.) in fluid communication with “T” junction  108  and pressurized fluidic material source  118 , which typically contains a system fluid (e.g., a buffer or the like). Pressurized fluidic material source  118  also fluidly communicates with gas source  120 , which applies pressure on fluidic materials disposed in pressurized fluidic material source  118 . In some embodiments, reservoir  106  is primed with fluid from pressurized fluidic material source  118  prior to dispensing fluid from dispensing system  100 . In certain embodiments, after fluidic material is flowed from fluidic material source  102  into reservoir  106 , valve  116  is typically opened such that a calculated volume of fluid from pressurized fluidic material source  118  is added behind the fluidic material disposed in reservoir  106 , e.g., to ensure that any waste fluids are eliminated from dispensing tip  110  (e.g., directed to a waste collection component) and that the fluidic material from fluidic material source  102  is disposed in, and ready to be dispensed from, dispensing tip  110 . Dispensing tip  110  is then typically moved by a positioning component (not shown) of dispensing tip  110  over a fluidic material site (e.g., a well of a multi-well container, a surface of a substrate, etc.) at which a selected volume of the fluidic material is to be dispensed. Optionally, materials sites are moved relative to dispensing tips in the systems described herein. Once so positioned, valve  116  is typically opened for an amount of time that is sufficient to dispense the selected volume of the fluidic material. This process is generally repeated until all selected volumes have been dispensed or until additional fluidic material from fluidic material source  102  needs to be added to reservoir  106 . In this process, fluid from pressurized fluidic material source  118  displaces the fluidic material from in reservoir  106  to effect dispensing from dispensing tip  110 .  
      To further illustrate other embodiments,  FIG. 2  schematically depicts dispensing system  200 , which includes fluidic material source  202  in fluid communication with peristaltic pump  204 . In addition, dispensing system  200  includes dispensing tip  206  in fluid communication with peristaltic pump  204 . Dispensing tip  206  also fluidly communicates with valve  208  and pressurized gas source  210 . During operation, peristaltic pump  204  typically conveys fluidic material from fluidic material source  202  to dispensing tip  206 . The volume of fluidic material conveyed to dispensing tip  206  is generally equal to the volume a user selects to be dispensed from dispensing system  200 . When valve  208  is opened, the pressure applied by pressurized gas source  210  forces the selected volume of fluidic material from dispensing system  200  into well  212  of multi-well container  214 . In automated formats, this process is typically repeated, e.g., until all selected wells of multi-well container  214  are dispensed into.  
       FIG. 3  schematically illustrates a variant of dispensing system  200 , described above. In the embodiment shown, valve  208  is in fluid communication with pressurized fluidic material source  310 , which fluidly communicates with pressurized gas source  312  of dispensing system  300 . In some embodiments, a solvent disposed in pressurized fluidic material source  310  is the same solvent included in fluidic material source  202 . As used herein, the term “solvent” refers to a liquid substance capable of dissolving or dispersing one or more other substances or something that provides a solution. In these embodiments, the solution contained in fluidic material source  202  is typically concentrated (e.g., a concentrated bead solution, etc.). During operation, peristaltic pump  204  conveys the concentrated solution to dispensing tip  206 . When valve  208  is opened, solvent flows from pressurized fluidic material source  310  to dilute the volume of concentrated solution disposed in dispensing tip  206  to a selected level. In addition, the solvent flow from pressurized fluidic material source  310  also causes the diluted solution to be dispensed from dispensing tip  206  into well  212  of multi-well container  214 . As above, this process can be repeated until volumes of solution have been dispensed into all selected wells of multi-well container  214 .  
       FIG. 4  schematically illustrates another exemplary embodiment of a dispensing system. As shown, dispensing system  400  includes fluidic material source  402  in fluid communication with peristaltic pump  404 . In addition, dispensing system  400  includes dispensing tip  406  in fluid communication with peristaltic pump  404  via mixing chamber  408 . Dispensing tip  406  also fluidly communicates with valve  410  via mixing chamber  408 . Valve  410  also fluidly communicates with pressurized fluidic material source  412 , which fluidly communicates with pressurized gas source  414  of dispensing system  400 . In certain applications, dispensing system  400  is used to continuously dispense fluidic material into wells of multi-well containers or at other fluidic material sites. In these embodiments, peristaltic pump  404  and valve  410  are generally run simultaneously with one another. To illustrate, peristaltic pump  404  typically continuously delivers a concentrated fluidic material or solution from fluidic material source  402  into mixing chamber  408 . Solvent contained in pressurized fluidic material source  412  is typically the same as that used in the concentrated solution contained in fluidic material source  402 . Control software typically controls the opening and closing of valve  410  so that the diluting solvent enters mixing chamber  408  from pressurized fluidic material source  412  to dilute the concentrated solution conveyed from fluidic material source  402  by a selected amount. As fluids are conveyed into mixing chamber  408 , selected volumes of diluted solution are also dispensed from dispensing tip  406  into selected wells  416  of multi-well container  418 .  
      As also shown in  FIG. 4 , dispensing system  400  also includes three-way valve  420  disposed between and in fluid communication with peristaltic pump  404  and mixing chamber  408 . When three-way valve  420  is actuated, the line to peristaltic pump  404  is vented to atmosphere. Further, peristaltic pump  404  is optionally run in reverse such that concentrated solution in the line is returned to fluidic material source  402 . This can be important, for example, when expensive materials are being dispensed from fluidic material source  402  and waste is to be minimized. Three-way valves are also optionally included in other embodiments of these dispensing systems.  
      To further illustrate,  FIG. 5A  schematically shows a cross-sectional view of dispensing system  500 . As shown, dispensing system  500  includes peristaltic pump  502  operably connected to first conduit  504 , which fluidly communicates with first fluidic material source  506 . Peristaltic pump  502  is configured to reversibly convey a first fluidic material (e.g., a bead suspension, a cell suspension, reagents, etc.) into or through at least a portion of first conduit  504 . As used herein, the term “reversibly convey” refers to a process of conveying material in which the material or portions thereof are capable of being, e.g., removed from a fluidic material site after being dispensed at the site, dispensed at one fluidic material site after being removed from another fluidic material site, and/or the like. In certain embodiments, for example, fluidic materials are aspirated from fluidic material sites (e.g., wells of a micro-well plate or other fluidic material source) and dispensed at other sites (e.g., wells of a micro-well plate, surfaces of substrates, fluidic material waste containers, etc.). Reversible material conveyance is typically effected by rotating the peristaltic pump roller support in a direction that is opposite from the direction the roller support is rotated to convey the material to the particular fluidic material site from which the material is removed. As also shown, fluid agitation mechanism  508  is operably connected to first fluidic material source  506  to prevent components (e.g., beads, cells, etc.) of the first fluidic material from settling toward the bottom of first fluidic material source  506  and to otherwise mix the components of the first fluidic material. Mixing of components in first fluidic material source  506  can be achieved during operation of dispensing system  500  using various approaches including, e.g., aspiration and dispensing, impeller movement, ultrasonics, physical shaking, and the like. Suitable fluid agitation mechanisms, such as impellers are readily available from many different commercial suppliers including, e.g., Bellco Glass, Inc. (Vineland, N.J., USA), Philadelphia Mixing Solutions (Palmyra, Pa., USA), and the like.  
      As further shown in  FIG. 5A , dispensing system  500  also includes pinch valve  510 , which is configured to regulate conveyance of fluidic materials through first conduit  504 . Air table  512  is operably connected to the pinch valve  510  and effects operation of pinch valve  510 .  
      Dispensing system  500  also includes second conduit  514 , which fluidly communicates with first conduit  504  via fluid junction block  516 . Second conduit  514  also fluidly communicates with pressure source  518  (e.g., a pressurized gas source, a pressurized second fluidic material source, a pump, etc.) via valve  520  (e.g., a microsolenoid valve, etc.). Pressure source  518  is configured to apply pressure in second conduit  514  such that selected aliquots of the first fluidic material are dispensed from opening  522  in third conduit  524 . To illustrate, pressure sources optionally comprise pressurized fluidic material sources that include buffers or other fluids used as system fluids. Valve  520  regulates pressure applied by pressure source  518 .  
      As shown, dispensing tip or nozzle  526  is disposed in dispense head  527  and fluidly communicates with third conduit  524  and includes opening  522  in third conduit  524 . In some embodiments, the segment of, e.g., third conduit  524  that includes opening  522  is disposed at an angle of between about 0° and about 90° relative to the Z-axis of dispensing system  500 , more typically disposed at an angle of between about 15° and about 75° relative to the Z-axis, and still more typically disposed at an angle of between about 35° and about 55° (e.g., about 40°, about 41°, about 42°, about 43°, about 44°, about 45°, about 46°, about 47°, about 48°, about 49°, etc.) relative to the Z-axis. As also shown in  FIG. 5A , the segment of third conduit  524  that includes opening  522  is disposed at an about a 45° angle relative to the Z-axis of dispensing system  500 . For example, fluids dispensed into the wells of multi-well containers from conduits having this configuration typically contact the sides of the wells before other parts of the wells. This minimizes the disruption of other materials, such as beads, cells, etc. disposed in the wells during fluid dispensing. These conduit and tip configurations also assist in maintaining the uniform densities of dispensed solutions by providing non-vertical flow paths in these regions. In certain embodiments, dispensing tips are disposed substantially parallel to the Z-axis. Dispensing tips  716  of dispensing system  700  (see, e.g.,  FIG. 7A ) schematically illustrate one embodiment of this configuration, which can help to prevent droplets of solution from forming on the tips. Dispensing system  700  is described further below.  
      As referred to above, a substantial portion of a conduit is disposed other than parallel to a Z-axis in certain embodiments of the dispensing systems described herein. To illustrate, third conduit  524 , which forms a fluid reservoir in dispensing system  500 , includes conduit coil  528 . As shown, conduit coil  528  includes multiple coils that are disposed around vertically mounted posts  529  other than parallel to the Z-axis of dispensing system  500 . As also shown, other segments of third conduit  524  are also disposed other than parallel to the Z-axis of dispensing system  500 . This conduit orientation prevents beads, cells, or other materials in fluids to be dispensed from settling toward opening  522  in third conduit  524  such that volumes having uniform densities are dispensed from third conduit  524 .  
      Now referring additionally to  FIG. 5B , which schematically depicts a detailed cross-sectional view of fluid junction block  516  of dispensing system  500 . As shown, port  530  is disposed through a wall of fluid junction block conduit  532  and communicates with the cavity disposed through fluid junction block conduit  532 . Gas valve  534  is operably connected to port  530 . Gas valve  534  is also operably connected to a pressurized gas source  536  and regulates gas flow into fluid junction block conduit  532  through port  530 . Gas valve  534  is generally used to introduce gaseous gaps between fluids disposed in fluid junction block conduit  532  to prevent those fluids from mixing with one another in fluid junction block conduit  532 . In some embodiments, for example, such gaps fill the portion of fluid junction block conduit  532  corresponding to distance V shown in  FIG. 5B . Although other distances can be utilized, distance V is typically between about 5 mm and about 50 mm, and more typically between about 10 mm and 25 mm. Typically, pressurized gas source  536  flows gas (e.g., air, nitrogen, helium, argon, etc.) to gas valve  534  at a pressure of between about zero pounds per square inch and about 10 pounds per square inch. In embodiments where the openings to dispensing tips are large enough to permit fluids to be pulled from the tips under the force of gravity when gas valves are open, an applied pressure is optionally not utilized to push the fluids from these tips. Methods of introducing gas into fluid junction block conduits to create these gaseous gaps are described further below.  
      Gas valve  534  is designed so that a minimal dead volume of gas is introduced into a fluid stream in fluid junction block conduit  532  during a dispense cycle. This low dead volume of gas is achieved by minimizing the distance or length W. More specifically, port  530  typically includes a length W of about 5 mm or less, more typically a length W of about 2.5 mm or less, and still more typically a length W of about 1 mm or less (e.g., about 0.9 mm, about 0.7 mm, about 0.5 mm, about 0.3 mm, about 0.1 mm, etc.).  
      As also shown, gas valve  534  includes plunger  538 , which includes compliant seal material  540  that forms a face seal with port  530  when plunger  538  pushes compliant seal material  540  into contact with port  530 . Essentially any chemically resistant rubber or elastomeric material, many of which are well known in the art, is optionally adapted for use as a compliant seal material. For example, suitable compliant seal materials are optionally selected from, e.g., KALREZ®, VITON®, SANTOPRENE®, TEFLON®, CELERUS™, or the like. Many of these materials are readily available from various commercial suppliers, such as W.L. Gore &amp; Associates (Newark, Del.). In addition, gas valve  534  also includes linear seal  541  disposed around plunger  538 . Linear seal  541  prevents gas from escaping from gas valve  534  around plunger  538 .  
      Dispensing system  500  also includes air table  542  operably connected to gas valve  534 . Air table  542  is configured to move plunger  538  to effect operation of gas valve  534 .  
      To further illustrate, the dispensing systems described herein include multiple conduits (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or more conduits) in certain embodiments. In some of these embodiments, for example, the openings in at least two of the conduits are spaced at a distance from one another to simultaneously fluidly communicate with different wells disposed in a multi-well container (e.g., multi-well containers having 2, 4, 6, 12, 24, 48, 96, 384, 1536, or more wells). Dispensing system  700  (described further below), for example, includes eight conduits, which are spaced at distances from one another to simultaneously dispense fluidic materials into standard 384-well plates having 16×24 arrays of wells. In some embodiments, dispensing systems include manifolds that fluidly communicate with single conduits. These manifolds are also typically configured to fluidly communicate with multiple fluidic material sites, e.g., multiple wells disposed in a multi-well plate, a reaction block, etc. For example, manifolds include dispensing tips that are spaced at distances from one another to simultaneously dispense fluidic materials into different wells disposed in a multi-well container, onto substrate surfaces, or the like. To further illustrate,  FIG. 6  schematically illustrates dispense head  600  that includes manifold  602 , which is shown as a chamber that fluidly communicates with dispensing tips  604  and a conduit. In certain embodiments, for example, dispense head  600  replaces dispense head  527  in dispensing system  500  such that third conduit  524  fluidly communicates with manifold  602 . During operation, fluidic materials are conveyed from third conduit  524  into manifold  602  and dispensed from dispensing tips  604 .  
      To further illustrate aspects of the invention, FIGS.  7  A-C schematically depict dispensing system  700  according to one embodiment of the invention. As shown, dispensing system  700  includes peristaltic pump  702  (e.g., a multi-channel low volume peristaltic pump) mounted on mounting component  704  (shown as a rigid frame). Dispensing system  700  also includes a feedback component that comprises drive motor  706 , which typically includes a position encoder and gear reduction, and which is operably connected to peristaltic pump  702  to effect precisely controlled rotation of the rotatable roller support of peristaltic pump  702 . The feedback component also includes a control system for drive motor  706  (not shown in  FIG. 7 ) that is capable of position feedback control.  
      During operation, conduits (not shown in  FIG. 7 ) are generally disposed between the compression surfaces and rollers of peristaltic pump  702 . In addition, one set of termini of the conduits fluidly communicate with the same or different material sources (not shown in  FIG. 7 ), while the other set of termini are operably connected to and fluidly communicate with fluid junction block  708  of dispensing component  710 . An exemplary fluid junction block is also described above. As also shown, dispensing system  700  includes tube stretchers  703 , which are designed to give the user fine adjustment over the flow rate of each peristaltic channel. More specifically, tube stretchers  703  mechanically increase the length of associated peristaltic tubing or conduits. As the length of a given tube is increased, the inner diameter of that tube decreases and the volume conveyed per pulse or rotational increment is also decreased. This gives the user a fine adjustment to the flow rate for each peristaltic channel. In some embodiments, further adjustments can be made by varying the spacing between peristaltic pump cartridges and rollers.  
       FIGS. 7 B  and C schematically illustrate detailed bottom and top perspective views, respectively, of dispensing component  710  from dispensing system  700 . Solenoid valves  712  fluidly communicate with the same or different pressure sources (not within view) (e.g., a pressurized gas source, a pressurized second fluidic material source, a pump, etc.) and with fluid junction block  708  via conduits (not shown in  FIG. 7 ). Outlets  714  of fluid junction block  708  fluidly communicate with dispensing tips  716  disposed in dispense head  718  via conduits (not shown in  FIG. 7 ), which conduits form conduit coils disposed around vertically mounted posts. Exemplary conduit coils are also described above. As also shown, dispensing component  710  also includes air tables  722  and  724 . Air table  722  effects operation of pinch valve  726 , whereas  724  is operably connected to a gas valve (not within view) of fluid junction block  708  to regulate the flow of gas into fluid junction block  708  to introduce gaseous gaps to prevent fluid mixing as described above.  
      In addition, dispensing component  710  of dispensing system  700  also includes Z-axis linear motion component  728  (e.g., a compact, high speed, short travel Z-axis motion component or system), which is a positioning component that effects Z-axis translation of dispensing tips  716  relative to fluidic material sites (e.g., multi-well plates, membranes, etc.) disposed on object holder  730 . Object holder  730  is operably connected to X/Y-axis linear motion components  732  (shown as tables), which move object holder  730  relative to dispensing tips  716  along the X- and Y-axes. X/Y-axis linear motion components  732  are also mounted on support element  734 , which forms part of mounting component  704 . One or more motors (e.g., solenoid motors, etc.) are generally operably connected to the dispensing systems of the invention to effect motion of object holders on X/Y-axis linear motion tables. For example, solenoid motor  736  effects motion of object holder  730  in dispensing system  700 . Although not within view in FIGS.  7  A-C, dispensing system  700  also generally includes control drives, e.g., for X/Y-axis linear motion components  732  and position feedback for drive motor  706 . As also shown, cleaning component  738 , which is used to clean dispensing tips  716  is also included. In particular, cleaning component  738  includes vacuum chamber  740  having orifices  742  that correspond to dispensing tips  716  such that when dispensing tips  716  are disposed proximal to orifices  742  under a vacuum applied by vacuum chamber  740 , adherent material is removed at least from external surfaces of dispensing tips  716 . Cleaning component  738  also includes fluid container  744  disposed next to vacuum chamber  740 . In certain embodiments, fluid container  744  contains a cleaning solvent into which dispensing tips  716  can be lowered by Z-axis linear motion component  728 , e.g., prior to applying a vacuum to dispensing tips  716  at vacuum chamber  740 . Optionally, fluid container  744  is used as a waste collection component.  
      The dispensing systems of the invention also typically include controllers (also not shown in  FIGS. 1-7 ) that are configured to effect rotation of peristaltic pump roller supports in selected rotational increments, to effect application of pressure from pressure sources, to effect motion of linear motion components, and/or the like. These and other aspects of the invention are described in greater detail below.  
      A. Peristaltic Pumps  
      The dispensing systems described herein generally include rotating peristaltic pumps with precisely regulated accelerations, velocities, and decelerations to effect accurate angular displacements. In certain embodiments, for example, these systems account for periodic variations produced, e.g., by roller disengagement events such that accurate and repeatable conveyance of fluidic material is achieved using rotary peristaltic pumps. The term “periodic variation” refers to a recurrent change in output or other characteristic of a given device or system. To illustrate, there is typically a periodic variation in the quantity of material conveyed by a rotary peristaltic pump, e.g., when a roller disengages from a material conduit during a displacement cycle. More specifically, there is generally a substantially linear relationship between angular displacement and the quantity of material conveyed during a displacement cycle when the lead roller (i.e., the roller whose contact with a material conduit is furthest advanced in a particular displacement cycle) applies constant pressure on the material conduit. However, this relationship tends to become non-linear as the lead roller undergoes a disengagement event during which the pressure applied by the lead roller on the material conduit decreases to zero. This produces a repeatable aberration or periodic variation in the function relating displaced quantity of material with angular displacement of the pump.  
      Essentially any rotary peristaltic pump can be used in the systems described herein. Peristaltic pumps typically use a turning mechanism to move fluids or other materials through a tube or other conduit that is compressed at a number of points in contact with, e.g., rollers, shoes, etc. of the pump such that the fluid is moved through the tube with each rotating motion. Peristaltic pumps generally include rotatable roller carriers or supports that support at least two rollers. In some embodiments, the controllers used in these systems are configured to rotate roller supports in rotational increments that substantially correspond to integral multiples of angular distances disposed between adjacent rollers supported on the roller supports such that quantities of fluidic materials that correspond to these rotational increments are conveyed into or through system conduits. In these embodiments, substantially identical roller disengagement events generally occur for each conveyed volume of fluid, thereby minimizing roller disengagement as a source of variation among conveyed fluid volumes. Peristaltic pumps and related methods of pump control are also described in, e.g., U.S. Provisional Patent Application No. 60/527,125, entitled “MATERIAL CONVEYING SYSTEMS AND METHODS,” filed Dec. 4, 2003 by Mainquist et al., which is incorporated by reference.  
      In some embodiments, for example, the peristaltic pump comprises a multi-channel peristaltic pump such that multiple quantities of material can be conveyed simultaneously. To illustrate,  FIG. 8  schematically shows multi-channel peristaltic pump  800  from a top perspective view. In the embodiment shown, multi-channel peristaltic pump  800  comprises five channels  802 . Optionally, additional channels  802  are added to multi-channel peristaltic pump  800 , or one or more of channels  802  are removed from multi-channel peristaltic pump  800 . Typically, the number of channels is selected to correspond to the number of dispensing tips to be utilized in a dispensing system for a particular dispensing application. Rollers  804  of the roller support of multi-channel peristaltic pump  800  and conduits  806  are also schematically shown in  FIG. 8 .  
      Although rotatable rollers (e.g., passively or actively rotatable) that rotate relative to roller supports are typically utilized in the systems of the invention, non-rotatable functionally equivalent components, such as fixed rollers or shoes are also optionally used. However, rotatable rollers generally produce less wear on material conduits (e.g., flexible tubing or the like) than non-rotatable equivalents for comparable amounts of usage.  
      Peristaltic pumps that can be adapted for use in the systems of the invention are available from a wide variety of commercial suppliers including, e.g., ABO Industries Inc. (San Diego, Calif., USA), Analox Instruments Ltd. (London, UK), ASF Thomas Industries GmbH (Puchheim, Germany), Barnant Co. (Barrington, Ill., USA), Cole-Parmer Instrument Company (Vernon Hills, Ill., USA), Fluid Metering Inc. (Syosset, N.Y., USA), Gorman-Rupp Industries (Bellville, Ohio, USA), I &amp; J Fisnar Inc. (Fair Lawn, N.J., USA), Möller Feinmechanik GmbH &amp; Co. (Fulda, Germany), PerkinElmer Instruments (Shelton, Conn., USA), Terra Universal Inc. (Anaheim, Calif., USA), and the like. Additional details relating to rotary pumps are described in, e.g., Karassik et al. (Eds.),  Pump Handbook , The McGraw-Hill Companies (2000) and Nelik,  Centrifugal and Rotary Pumps: Fundamentals with Applications , CRC Press (1999), which are both incorporated by reference.  
      B. Motion Control  
      The motion control systems used in the dispensing systems of the invention typically include matched components such as controllers, motor drives, motors, encoders and resolvers, user interfaces and software. Controllers, user interfaces, and software are described in greater detail below. Peristaltic pump drive motors generally include at least one position encoder and at least one gear reduction component. Exemplary motors utilized in the systems of the invention typically include, e.g., servo motors, stepper motors, or the like. In some embodiments, feedback components of the systems of the invention include at least one drive mechanism that is operably connected to the motor. The drive mechanism typically includes at least one control component that effects position feedback control of the motor.  
      As referred to above, the movement of peristaltic pump roller supports is typically effected by a motor operably connected to the pump. Exemplary motors that are optionally utilized in the systems of the invention include, e.g., DC servomotors (e.g., brushless or gear motor types), AC servomotors (e.g., induction or gearmotor types), stepper motors, linear motors, or the like. Servomotors typically have an output shaft that can be positioned by sending a coded signal to the motor. As the input to the motor changes, the angular position of the output shaft changes as well. Stepper motors generally use a magnetic field to move a rotor. Stepping can typically be performed in full step, half step, or other fractional step increments. Voltage is applied to poles around the rotor. The voltage changes the polarity of each pole, and the resulting magnetic interaction between the poles and the rotor causes the rotor to move.  
      The systems of the invention also generally include motor drives (e.g., AC motor drives, DC motor drives, servo drives, stepper drives, etc.), which act as interfaces between controllers and motors. In certain embodiments, motor drives include integrated motion control features. For example, servo drives typically provide electrical drive output to servo motors in closed-loop motion control systems, where position feedback and corrective signals optimize position and speed accuracy. Servo drives with integrated motion control circuitry and/or software that accept feedback, provide compensation and corrective signals, and optimizes position, velocity, and acceleration.  
      Suitable motors and motor drives are generally available from many different commercial suppliers including, e.g., Yaskawa Electric America, Inc. (Waukegan, Ill., USA), AMK Drives &amp; Controls, Inc. (Richmond, Va., USA), Enprotech Automation Services (Ann Arbor, Mich., USA), Aerotech, Inc. (Pittsburgh, Pa., USA), Quicksilver Controls, Inc. (Covina, Calif., USA), NC Servo Technology Corp. (Westland, Mich., USA), HD Systems Inc. (Hauppauge, N.Y., USA), ISL Products International, Ltd. (Syosset, N.Y., USA), and the like. Additional detail relating to motors and motor drives are described in, e.g., Polka,  Motors and Drives , ISA (2002) and Hendershot et al.,  Design of Brushless Permanent - Magnet Motors , Magna Physics Publishing (1994), which are both incorporated by reference.  
      C. Pressure Sources  
      The dispensing systems of the invention include pressure sources in addition to the peristaltic pumps that convey fluidic materials into the systems in preparation for dispensing. As described herein, these additional pressure sources are configured to apply pressure in system conduits such that selected aliquots of the fluidic materials that have been conveyed into the systems by the peristaltic pumps are forced or otherwise dispensed from the conduits. Essentially any pressure source can be adapted to effect fluidic material dispensing in this manner. To illustrate, pressure sources comprise pressurized gas sources that fluidly communicate with conduits from which fluidic materials are dispensed are used in certain embodiments. As schematically shown in  FIG. 2 , pressure source  210  is an example of this type of system configuration. A wide variety of pressurized gas can be utilized. In some embodiments, for example, air compressors are used to provide air pressure to force the selected aliquots from system conduits. Other gases, such as nitrogen, helium, argon, or the like are also optionally used to effect fluidic material conveyance. In certain embodiments, gas from pressurized gas sources is filtered (e.g., using 22 μm filters, etc.) to prevent contamination of the dispensing fluid by, e.g., bacteria, yeast, or the like. In some embodiments, these pressurized gas sources fluidly communicate with conduits from which fluidic materials are dispensed via one or more fluidic material sources, such as a system fluid source (e.g., a buffer or other solvent). In these embodiments, the pressurized gas typically forces fluidic material from these pressurized fluidic material sources into these conduits to effect the dispensing of selected fluidic material aliquots from the conduits. An example of this system configuration is schematically depicted in  FIG. 1A , which is described further above. Various pumps, such as syringe pumps, other peristaltic pumps, etc. can also be configured to function as these pressure sources in the dispensing systems described herein.  
      The pressure applied by these pressure sources to effect dispensing of selected fluidic material aliquots can be regulated using a wide variety of techniques. In certain embodiments, for example, valves are positioned between pressure sources and the openings of conduits from which fluidic materials are dispensed. In some of these embodiments, solenoid valves, such as microsolenoid valves are utilized. Suitable valves are commercially available from various suppliers including, e.g., The Lee Company USA (Westbrook, Conn., USA). In these embodiments, valves are typically operably connected to controllers, which effect operation of the valves. Controllers are described in greater detail below.  
      D. Positioning and Mounting Components  
      In some embodiments, the dispensing systems of the invention include positioning components. Positioning components are generally structured to moveably position conduits and/or fluidic material sites relative to one another. Positioning components typically include at least one object holder that is structured to support the fluidic material site (e.g., a multi-well plate, a substrate, etc.). Typically, positioning components are operably connected to system controllers, which are configured to simultaneously effect fluidic material dispensing from conduits and moveably position the conduits and/or fluidic material sites relative to one another such that fluidic material volumes are conveyed to the fluidic material sites synchronous with the relative movement of the conduits and/or the fluidic material sites, e.g., to effect high throughput “on-the-fly” fluidic material dispensing.  
      For positioning along two different axes, the object holders of the dispensing systems of the invention generally have one or more alignment members positioned to receive, e.g., each of the two axes of a multi-well container. For example,  FIG. 9  shows a top perspective view of object holder  900  that can be used in the dispensing systems described herein. Another embodiment of an object holder (i.e., object holder  730 ) is schematically depicted in  FIG. 7A , which is described further above. As shown in  FIG. 9 , container station  901  is disposed on support structure  902  of object holder  900 . Support structure  902  supports vacuum plate  904 . Protrusions  906  and  908  function as alignment members. The illustrated embodiment of the container station  901  has two x-axis protrusions  908  and one y-axis protrusion  906  extending from support structure  902 . Accordingly, x-axis protrusions  908  and y-axis protrusion  906  are fixedly positioned relative to the vacuum plate  904 , which, in this embodiment, acts to hold a multi-well container in position once it has been positioned. X-axis locating protrusions  908  are constructed to cooperate with an x-axis surface of a multi-well container (e.g., a y-axis wall of a microtiter plate), while y-axis protrusion  906  is constructed to cooperate with an y-axis surface of the container (e.g., a y-axis wall of a microtiter plate).  
      The alignment members can be, for example, locating pins, tabs, ridges, recesses, or a wall surface, and the like. In some embodiments, an alignment member includes a curved surface that contacts a properly positioned multi-well container. The use of a curved surface minimizes the effect of, for example, roughness of the container surface that contacts the alignment member. The use of two alignment members along one axis and one alignment member along the second axis, as shown in  FIG. 9 , is another approach to minimize the effect of surface irregularities on the proper positioning of the container. The multi-well container contacts three points along the surface of the container, so proper alignment is not dependent upon the entire container surface being regular.  
      Certain embodiments of the invention apply specifically to the positioning of microtiter plates when used as the fluidic material sites. To illustrate, microtiter plate  1000  is shown in FIGS.  10 A-C. As shown, microtiter plate  1000  comprises well area  1002 , which has many individual sample wells for holding samples and reagents. Microtiter plates are available in a wide variety of sample well configurations, including commonly available plates with 6, 12, 24, 48, 96, 192, 384, 768, 1536, or more wells. It will be appreciated that microtiter plates are available from a various manufacturers including, e.g., Greiner America Corp. (Lake Mary, Fla., USA), Nalge Nunc International (Rochester, N.Y., USA), and the like. Microtiter plate  1000  has outer wall  1004  having registration edge  1006  at its bottom. In addition, microtiter plate  1000  includes bottom surface  1008  below the well area on the plate&#39;s bottom side. Bottom surface  1008  is separated from outer wall  1004  by alignment member receiving area  1010 . Alignment member receiving area  1010  is bounded by a surface of outer wall  1004  and by inner wall  1012  at the edge of bottom surface  1008 . Although there may be some lateral supports  1014  in alignment member receiving area  1010 , these areas are generally open between inner wall  1012  and an inner surface of the outer wall  1004 .  
      According to the invention, to position a microtiter plate the alignment members of the container station are optionally arranged to cooperate with inner wall  1012  of the microtiter plate. Inner wall  1012  is advantageously used, as inner wall  1012  is typically more accurately formed and is more closely associated with the perimeter of the sample well area, as compared to an outer wall of plate  1000 , such as wall  1004 . Accordingly, aligning an inner wall (e.g., inner wall  1012 ) of a microtiter plate relative to alignment members is generally preferred to aligning with an outer wall, such as wall  1004 . The increased positioning precision that is obtained by using an inner wall as the alignment surface makes possible the use of high-density microtiter plates, such as 1536-well plates. Further, by having the alignment members (e.g., alignment protrusions  906  and  908 ) cooperate with an inner wall  1012  of plate  1000 , minimal structures are needed adjacent the outside of the plate. In such a manner, a robotic arm or other transport device is able to readily access plate  1000 . Having the protrusions positioned adjacent inner wall  1012  thereby facilitates translocating plate  1000 . However, it will be appreciated that the alignment members or protrusions can be placed in alternative positions and still facilitate the precise positioning of the plate.  
      Object holders generally include one or more movable members. The movable members function to move a container against one or more alignment members. For example, once a multi-well container is placed in the general location of the alignment members, the movable members (termed “pushers” herein) move the container so that an alignment surface of the container is in contact with one or more of the alignment members of the positioning device. The positioning device can have pushers for positioning of the container along one or more axes. For example, a positioning device will often have one or more pushers that position a container along an x-axis, and one or more additional pushers that position the container along a y-axis. The pushers can be moved by means known to those of skill in the art. For example, air cylinders, springs, pistons, elastic members, electromagnets or other magnets, gear drives, and the like, or combinations thereof, are suitable for moving the pushers so as to move containers into a desired position.  
      One embodiment of a container station of an object holder having pushers for positioning a microtiter plate along both the x-axis and the y-axis is shown in  FIG. 9 . When the microtiter plate is generally positioned adjacent the x- and y-axis protrusions, the bottom surface of the microtiter plate is directly above top surface  910  of vacuum plate  904 . Y-axis pusher  912 , which extends through slot  914  in support structure  902 , is used to apply pressure to a y-axis side wall of the microtiter plate. Sufficient force is applied to the plate to push the microtiter plate against y-axis protrusion  906 . When the microtiter plate is pushed against y-axis protrusion  906 , x-axis pusher  918 , which extends through slot  920  of support structure  902 , is used to push an x-axis wall of the microtiter plate towards x-axis protrusions  908 . In this manner, the microtiter plate is accurately and precisely positioned relative both the x-axis and y-axis protrusions. It is sometimes advantageous, although not necessary, to have one or more of the pushers contact an inner wall of a microtiter plate rather than an outer wall. With this arrangement, the alignment members and pushers are underneath the microtiter plate. This leaves the area surrounding the exterior of the plate free of protrusions that could otherwise interfere with other devices that, for example, place the microtiter plate on the support.  
      As referred to above, the object holder embodiment shown in  FIG. 9  includes vacuum plate  904  that functions as a retaining device to hold a properly positioned container in a desired position. With both y-axis pusher  912  and x-axis pusher  918  applying sufficient force to precisely place the microtiter plate, a vacuum source (not shown) applies a vacuum through vacuum line  922  into vacuum openings or holes  924 . Air source (not shown) applies air pressure through an air line (not shown) to effect movement of the pushers.  
      In certain embodiments, positioning components also include X/Y-axis linear motion tables operably connected to position feedback control drives that control movement of the X/Y-axis linear motion tables along X- and Y-axes. In certain embodiments, linear motion tables are configured to move only along a single axis, such as an X-axis or a Y-axis. Typically, object holders are mounted on, e.g., X/Y-axis linear motion tables. As an example,  FIG. 7A  schematically shows object holder  730  mounted on X/Y-axis linear motion table  732 . Positioning components also generally include Z-axis linear motion components that include dispense heads (see, e.g., dispense head  718  schematically shown in  FIG. 7A ) that supports portions of conduits and that move along the Z-axis. The Z-axis linear motion components generally include a solenoid motor or the like to effect movement of the dispense heads along the z-axis. In certain embodiments, Z-axis linear motion components also include material removal heads, e.g., mounted proximal to dispense heads. For example, certain material removal heads are configured to noninvasively remove materials from the wells of multi-well plates, e.g., to effect plate washing during certain applications. Material removal heads are typically structured to prevent cross-contamination among wells of multi-well plates as materials are removed from the plates. Additional details relating to material removal heads, systems and related methods, that are optionally adapted for use with the systems of the present invention are provided in, e.g., Provisional U.S. Pat. Appl. No. 60/461,638, entitled “MATERIAL REMOVAL DEVICES, SYSTEMS, AND METHODS,” filed Apr. 8, 2003 by Micklash II et al., which is incorporated by reference.  
      Various other positioning components or portions thereof can be utilized in the systems of the invention. In certain embodiments, for example, detectable signals produced at fluidic material sites (e.g., multi-well plates, substrate surfaces, etc.) disposed on the object holders of the systems described herein are detected. In some of these embodiments, orifices are disposed through object holders to facilitate such detection. To further illustrate, object holders optionally comprise nests in which multi-well plates or other fluidic material sites can be positioned in some embodiments of the invention. These or other types of object holders that can be utilized in the systems of the present invention are described in, e.g., International Publication No. WO 01/96880, entitled “AUTOMATED PRECISION OBJECT HOLDER,” filed Jun. 15, 2001 by Mainquist et al., U.S. Provisional Pat. Appl. No. 60/492,586, entitled “MULTI-WELL CONTAINER POSITIONING DEVICES AND RELATED SYSTEMS AND METHODS,” filed Aug. 4, 2003 by Evans, and U.S. Provisional Pat. Appl. No. 60/492,629, entitled “NON-PRESSURE BASED FLUID TRANSFER IN ASSAY DETECTION SYSTEMS AND RELATED METHODS,” filed Aug. 4, 2003 by Evans et al., which are each incorporated by reference.  
      In some embodiments, dispensing systems include mounting components that mount peristaltic pumps, pressure sources, controllers, positioning component, and/or other system components relative to one another. Mounting component are typically substantially rigid, e.g., fabricated from steel or other materials that can adequately support the other system components during operation of the system. An exemplary mounting component (i.e., mounting component  704 ) is schematically depicted in  FIG. 7A , which is described further above.  
      E. Cleaning Components  
      The dispensing systems of the invention optionally also include cleaning components that are structured to clean conduits (e.g., dispensing tips thereof), e.g., when positioning components move the conduits at least proximal to the cleaning components. As fluidic materials are dispensed, some fluid can wick up or otherwise adhere to the outer surface of dispensing tips. This generally leads to additional wicking if the adherent fluid is not removed from the tips, because as the surface finish of a tip becomes coated with fluid it tends to attracts more fluid, e.g., during subsequent dispensing steps. Moreover, this also typically leads to inaccurate quantities of material being dispensed, since wicked materials are not dispensed at the selected fluidic material sites and/or are dispensed at non-selected sites. This inaccuracy may be compounded when multiple quantities of material are simultaneously dispensed from multiple material conduits, because fluidic material wicking tends to occur at different rates at the material conduit tips. Accordingly, wicked fluidic material is generally cleaned from material conduit tips, e.g., between dispensing steps using a cleaning component in certain embodiments of the invention.  
      In some embodiments, for example, cleaning components include vacuum chambers that comprise at least one orifice into or proximal to which the positioning component moves the conduits such that an applied vacuum removes wicked or otherwise adherent material from external surfaces of the conduits or dispensing tips. Typically, outer cross-sectional dimensions of the conduits are smaller than cross-sectional dimensions of the orifices. To illustrate,  FIG. 11A  schematically shows a partially transparent perspective view of vacuum chamber  1102  of cleaning component  1100  according to one embodiment of the invention. As shown, multiple orifices  1104  are disposed in cleaning component  1100  and communicate with outlet  1106 , which is typically operably connected to a vacuum source (not shown). Also shown is dispense head  1108  is disposed over cleaning component  1100 . Orifices  1104  are structured to correspond to conduit tips  1110  of dispense head  1108  such that conduit tips  1110  can be lowered at least partially into orifices  1104  to effect removal of adherent materials from conduit tips  1110  under an applied vacuum.  FIG. 11B  schematically illustrates a detailed cross-sectional view of conduit tip  1110  disposed proximal to orifice  1104 . Arrows  1112  represent the velocity of the air, V A , flowing through orifice  1104 . As conduit tip  1110  is lowered into orifice  1104 , the area of orifice  1104  is decreased such that V A  increases in the gap that remains between vacuum chamber  1102  and conduit tip  1110  and pulls or otherwise removes adherent material from the outer surfaces of conduit tip  1110 . Vacuum chambers are optionally disposed, e.g., on surfaces of object holders of the positioning components of the systems of the invention. In embodiments where dispensing tips are angled (see, e.g., dispensing tip  526 , which is described further above), vacuum chamber orifices are typically modified to accommodate these tips. In some of these embodiments, for example, these orifices are fabricated as grooved openings.  
      F. Conduits  
      The conduits used in the systems of the invention include various embodiments. In some embodiments, for example, a terminus of a conduit includes a dispensing tip (e.g., a tapered tip, such as a nozzle or the like) that is fabricated integral with the conduit or is connected to the conduit, e.g., directly or via an insert. The size (e.g., internal cross-sectional dimension) of the conduit (e.g., pump tubing, etc.) and/or tip utilized is typically dependent, at least in part, on, e.g., the desired dispense volume, the viscosity of the fluidic material being conveyed, and the like. Although larger sizes are optionally utilized, cavities disposed through conduits and/or tips typically include, e.g., cross-sectional dimensions of between about 100 μm and about 100 mm, more typically between about 500 μm and about 50 mm, and still more typically between about 1 mm and about 10 mm. Optionally, cavities disposed through conduits or tips include at least two different cross-sectional dimensions.  
      Conduits, tips, and inserts are optionally fabricated from a wide variety of materials. Exemplary materials used to fabricated conduits, dispensing tips, and/or inserts include polypropylene, polystyrene, polysulfone, polyethylene, polymethylpentene, polydimethylsiloxane (PDMS), polycarbonate, polyvinylchloride (PVC), polymethylmethacrylate (PMMA), fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE) (TEFLON™), perfluoroalkoxy (PFA), autoprene, C-FLEX® (a styrene-ethylene-butylene (SEBS) modified block copolymer with silicone oil), NORPRENE® (a polypropylene-based material), PHARMED® (a polypropylene-based material), silicon, TYGON®, VITON® (includes a range of fluoropolymer elastomers), and the like. Dispensing tips and inserts are also optionally fabricated from other materials including glass and various metals (e.g., stainless steel, etc.). Materials for fabricating conduits, tips, and inserts are typically readily available from many different commercial suppliers including, e.g., Saint-Gobain Performance Plastics (Garden Grove, Calif., USA), DuPont Dow Elastomers L.L.C. (Wilmington, Del., USA), and the like.  
      G. Fluidic Material Sites  
      The systems and methods of the present invention can be adapted for use with essentially any type of fluidic material site. Typical fluidic material sites used in the systems of the invention include containers, substrate surfaces, and the like. Exemplary containers include multi-well containers, such as micro-well plates, reaction blocks, and other containers used, e.g., to perform multiple assays, synthesis reactions, or other processes in parallel. Multi-well containers such as these typically include, e.g., 6, 12, 24, 48, 96, 192, 384, 768, 1536, or more wells, and are generally available from various commercial suppliers including, e.g., Greiner America Corp. (Lake Mary, Fla., USA), Nalge Nunc International (Rochester, N.Y., USA), H+ P Labortechnik AG (Oberschleiβheim, Germany), and the like. Additional details relating to reaction blocks that are suitable for use in the systems of the invention are provided in, e.g., International Publication No. WO 03/020426, entitled “PARALLEL REACTION DEVICES,” filed Sep. 5, 2002 by Micklash II, et al., which is incorporated by reference.  
      To further illustrate, the systems of the invention are also optionally configured to dispense fluidic materials on substrate surfaces. For example, the systems described herein can be utilized to produce dot arrays or the like on substrate surfaces at various different densities. Arrayed materials are commonly used in, e.g., clinical testing (e.g., blood cholesterol tests, blood glucose tests, pregnancy tests, ovulation tests, etc.) in addition to many other applications known in the art. Essentially any substrate material is optionally adapted for use with the systems of the invention. In certain embodiments, for example, substrates are fabricated from silicon, glass, or polymeric materials (e.g., glass or polymeric microscope slides, silicon wafers, etc.). Suitable glass or polymeric substrates, including microscope slides, are available from various commercial suppliers, such as Fisher Scientific (Pittsburgh, Pa., USA) or the like. Optionally, substrates utilized in the systems of the invention are membranes. Suitable membrane materials are optionally selected from, e.g. polyaramide membranes, polycarbonate membranes, porous plastic matrix membranes (e.g., POREX® Porous Plastic, etc.), porous metal matrix membranes, polyethylene membranes, poly(vinylidene difluoride) membranes, polyamide membranes, nylon membranes, ceramic membranes, polyester membranes, polytetrafluoroethylene (TEFLON™) membranes, woven mesh membranes, microfiltration membranes, nanofiltration membranes, ultrafiltration membranes, dialysis membranes, composite membranes, hydrophilic membranes, hydrophobic membranes, polymer-based membranes, a non-polymer-based membranes, powdered activated carbon membranes, polypropylene membranes, glass fiber membranes, glass membranes, nitrocellulose membranes, cellulose membranes, cellulose nitrate membranes, cellulose acetate membranes, polysulfone membranes, polyethersulfone membranes, polyolefin membranes, or the like. Many of these membranous materials are widely available from various commercial suppliers, such as, P.J. Cobert Associates, Inc. (St. Louis, Mo., USA), Millipore Corporation (Bedford, Mass., USA), or the like.  
      H. Controllers, Computer Program Products, and Additional System Components  
      The controllers of the automated systems of the present invention are generally operably connected to and configured to control operation of pressure sources to effect dispensing of fluidic materials from the openings in conduits. In some embodiments, controllers are also operably connected to peristaltic pumps (e.g., via motor drives). Controllers are also typically operably connected to other system components, such as motors (e.g., via motor drives), positioning components (e.g., X/Y-axis linear motion tables, Z-axis motion components, etc.), cleaning components, detectors, fluid sensors, robotic translocation devices, or the like, to control operation of these components. More specifically, controllers are generally included either as separate or integral system components that are utilized, e.g., to effect fluidic material dispensing, the movement of positioning components, the detection and/or analysis of detectable signals received from sample containers by detectors, etc. Controllers and/or other system components is/are optionally coupled to an appropriately programmed processor, computer, digital device, or other logic device or information appliance (e.g., including an analog to digital or digital to analog converter as needed), which functions to instruct the operation of these instruments in accordance with preprogrammed or user input instructions (e.g., conduit cross-sectional dimensions, rotational increments, volumes to be conveyed, etc.), receive data and information from these instruments, and interpret, manipulate and report this information to the user.  
      A controller or computer optionally includes a monitor which is often a cathode ray tube (“CRT”) display, a flat panel display (e.g., active matrix liquid crystal display, liquid crystal display, etc.), or others. Computer circuitry is often placed in a box, which includes numerous integrated circuit chips, such as a microprocessor, memory, interface circuits, and others. The box also optionally includes a hard disk drive, a floppy disk drive, a high capacity removable drive such as a writeable CD-ROM, and other common peripheral elements. Inputting devices such as a keyboard or mouse optionally provide for input from a user. An exemplary system comprising a computer is schematically illustrated in  FIG. 12 .  
      The computer typically includes appropriate software for receiving user instructions, either in the form of user input into a set of parameter fields, e.g., in a GUI, or in the form of preprogrammed instructions, e.g., preprogrammed for a variety of different specific operations. The software then converts these instructions to appropriate language for instructing the operation of one or more controllers to carry out the desired operation, e.g., varying or selecting the rate or mode of movement of positioning components, conveying fluidic materials through conduits with peristaltic pumps, opening valves to permit applied pressure from pressure sources to effect fluidic material dispensing, or the like. The computer then receives the data from, e.g., sensors/detectors included within the system, and interprets the data, either provides it in a user understood format, or uses that data to initiate further controller instructions, in accordance with the programming, e.g., such as in monitoring detectable signal intensity, multi-well container positioning, or the like.  
      More specifically, the software utilized to control the operation of the systems of the invention typically includes logic instructions that direct, e.g., the system to convey fluidic material to fluidic material sites, the pushers of an object holder of a positioning component to push containers into contact with alignment members when the containers are positioned on the object holder, a robotic handling device to translocate containers, and/or the like. To further illustrate, the invention provides control software, or computer program products that include computer readable media, having one or more logic instructions for operating at least one peristaltic pump to effect conveyance of at least a first fluidic material into at least one conduit through at least a first opening of the conduit, and operating at least one pressure source other than the peristaltic pump to effect application of pressure on the first fluidic material in the conduit such that at least one aliquot of the first fluidic material is dispensed from at least a second opening of the conduit. In certain embodiments, the computer program product includes at least one logic instruction for receiving one or more input parameters selected from the group consisting of: (i) a quantity of the first fluidic material to be conveyed to a fluidic material site; (ii) an initial density of the first fluidic material; (iii) a quantity of a second fluidic material to be added to the first fluidic material to modify a density of the first fluidic material; (iv) a quantity of gas to convey into the conduit to separate the first fluidic material from a second fluidic material; and (v) a fluidic material site format. In some embodiments, the computer program product includes at least one logic instruction for: operating at least one valve operably connected to the conduit to effect regulation of material conveyance into and/or out of the conduit. In certain embodiments, the computer program product includes at least one logic instruction for: operating at least one X/Y-axis linear motion component and/or at least one Z-axis motion component to effect movement of one or more other components attached to or positioned on the X/Y-axis linear motion component or the Z-axis motion component. The computer readable medium of, e.g., the computer program product optionally includes one or more of: a CD-ROM, a floppy disk, a tape, a flash memory device or component, a system memory device or component, a hard drive, a data signal embodied in a carrier wave, or the like.  
      The computer can be, e.g., a PC (Intel x86 or Pentium chip-compatible DOS™, OS2™, WINDOWS™, WINDOWS NT™, WINDOWS95™, WINDOWS98™, WINDOWS2000™, WINDOWS XP™, LINUX-based machine, a MACINTOSH™, Power PC, or a UNIX-based (e.g., SUN™ work station) machine) or other common commercially available computer which is known to one of skill. Standard desktop applications such as word processing software (e.g., Microsoft Word™ or Corel WordPerfect™) and database software (e.g., spreadsheet software such as Microsoft Excel™, Corel Quattro Pro™, or database programs such as Microsoft Access™ or Paradox™) can be adapted to the present invention. Software for performing, e.g., fluidic material dispensing into selected wells of a multi-well plate, assay detection, and data deconvolution is optionally constructed by one of skill using a standard programming language such as AppleScript, Visual basic, C, C++, Perl, Python, Fortran, Basic, Java, or the like.  
      The automated systems of the invention are optionally further configured to detect and quantify absorbance, transmission, and/or emission (e.g., luminescence, fluorescence, etc.) of light, and/or changes in those properties in samples that are arrayed in the wells of a multi-well container, on a substrate surface, or at other fluidic material sites. Alternatively, or simultaneously, detectors can quantify any of a variety of other signals from multi-well containers or other fluidic material sites including chemical signals (e.g., pH, ionic conditions, or the like), heat (e.g., for monitoring endothermic or exothermic reactions, e.g., using thermal sensors) or any other suitable physical phenomenon. In addition to other system components described herein, the material conveying systems of the invention optionally also include illumination or electromagnetic radiation sources, optical systems, and detectors. Because the systems and methods of the invention are flexible and allow essentially any chemistry to be assayed, they can be used for all phases of assay development, including prototyping and mass screening.  
      In some embodiments, the systems of the invention are configured for area imaging, but can also be configured for other formats including as a scanning imager or as a nonimaging counting system. An area imaging system typically places an entire multi-well container or other specimen onto the detector plane at one time. Accordingly, there is typically no need to move photomultiplier tubes (PMTs), to scan a laser, or the like, because the detector images the entire container onto many small detector elements (e.g., charge-coupled devices (CCDs), etc.) in parallel. This parallel acquisition phase is typically followed by a serial process of reading out the entire image from the detector. Scanning imagers typically pass a laser or other light beam over the specimen, to excite fluorescence, reflectance, or the like in a point-by-point or line-by-line fashion. In certain cases, confocal-optics are used to minimize out of focus fluorescence. The image is constructed over time by accumulating the points or lines in series. Nonimaging counting systems typically use PMTs or light sensing diodes to detect alterations in the transmission or emission of light, e.g., within wells of a multi-well container. These systems then typically integrate the light output from each well into a single data point.  
      A wide variety of illumination or electromagnetic sources and optical systems can be adapted for use in the systems of the present invention. Accordingly, no attempt is made herein to describe all of the possible variations that can be utilized in the systems of the invention and which will be apparent to one skilled in the art. Exemplary electromagnetic radiation sources that are optionally utilized in the systems of the invention include, e.g., lasers, laser diodes, electroluminescence devices, light-emitting diodes, incandescent lamps, arc lamps, flash lamps, fluorescent lamps, and the like. One preferred type of laser used in the assaying systems of the invention are argon-ion lasers. Exemplary optical systems that conduct electromagnetic radiation from electromagnetic radiation sources to sample containers and/or from multi-well containers to detectors typically include one or more lenses and/or mirrors to focus and/or direct the electromagnetic radiation as desired. Many optical systems also include fiber optic bundles, optical couplers, filters (e.g., filter wheels, etc.), and the like.  
      Suitable signal detectors that are optionally utilized in these systems detect, e.g., emission, luminescence, transmission, fluorescence, phosphorescence, absorbance, or the like. In some embodiments, the detector monitors a plurality of optical signals, which correspond in position to “real time” results. Example detectors or sensors include PMTs, CCDs, intensified CCDs, photodiodes, avalanche photodiodes, optical sensors, scanning detectors, or the like. Each of these as well as other types of sensors is optionally readily incorporated into the systems described herein. The detector optionally moves relative to fluidic material sites, such as multi-well plates or other assay components, or alternatively, multi-well plates or other assay components move relative to the detector. In certain embodiments, for example, detection components are coupled to translation components that move the detection components relative to fluidic material sites positioned on container positioning devices of the systems described herein. Optionally, the systems of the present invention include multiple detectors. In these systems, such detectors are typically placed either in or adjacent to, e.g., a multi-well plate or other vessel, such that the detector is in sensory communication with the multi-well plate or other vessel (i.e., the detector is capable of detecting the property of the plate or vessel or portion thereof, the contents of a portion of the plate or vessel, or the like, for which that detector is intended). In certain embodiments, detectors are configured to detect electromagnetic radiation originating in the wells of a multi-well container.  
      The detector optionally includes or is operably linked to a computer, e.g., which has system software for converting detector signal information into assay result information or the like. For example, detectors optionally exist as separate units, or are integrated with controllers into a single instrument. Integration of these functions into a single unit facilitates connection of these instruments with the computer, by permitting the use of a few or even a single communication port for transmitting information between system components. Detection components that are optionally included in the systems of the invention are described further in, e.g., Skoog et al.,  Principles of Instrumental Analysis,  5 th  Ed., Harcourt Brace College Publishers (1998) and Currell,  Analytical Instrumentation: Performance Characteristics and Quality , John Wiley &amp; Sons, Inc. (2000), which are both incorporated by reference.  
      The systems of the invention optionally also include at least one robotic translocation or gripping component that is structured to grip and translocate fluidic material sites, such as multi-well plates between components of the automated systems and/or between the systems and other locations (e.g., other work stations, etc.). In certain embodiments, for example, systems further include gripping components that move multi-well plates between positioning components, incubation or storage components, etc. A variety of available robotic elements (robotic arms, movable platforms, etc.) can be used or modified for use with these systems, which robotic elements are typically operably connected to controllers that control their movement and other functions. Exemplary robotic gripping devices that are optionally adapted for use in the systems of the invention are described further in, e.g., U.S. Pat. No. 6,592,324, entitled “GRIPPER MECHANISM,” issued Jul. 15, 2003 to Downs et al., and International Publication No. WO 02/068157, entitled “GRIPPING MECHANISMS, APPARATUS, AND METHODS,” filed Feb. 26, 2002 by Downs et al., which are both incorporated by reference.  
       FIG. 12  is a schematic showing a representative example dispensing system including an information appliance in which various aspects of the present invention may be embodied. As will be understood by practitioners in the art from the teachings provided herein, the invention is optionally implemented in hardware and software. In some embodiments, different aspects of the invention are implemented in either client-side logic or server-side logic. As will also be understood in the art, the invention or components thereof may be embodied in a media program component (e.g., a fixed media component) containing logic instructions and/or data that, when loaded into an appropriately configured computing device, cause that apparatus or system to perform according to the invention. As will additionally be understood in the art, a fixed media containing logic instructions may be delivered to a viewer on a fixed media for physically loading into a viewer&#39;s computer or a fixed media containing logic instructions may reside on a remote server that a viewer accesses through a communication medium in order to download a program component.  
       FIG. 12  shows information appliance or digital device  1200  that may be understood as a logical apparatus (e.g., a computer, etc.) that can read instructions from media  1217  and/or network port  1219 , which can optionally be connected to server  1220  having fixed media  1222 . Information appliance  1200  can thereafter use those instructions to direct server or client logic, as understood in the art, to embody aspects of the invention. One type of logical apparatus that may embody the invention is a computer system as illustrated in  1200 , containing CPU  1207 , optional input devices  1209  and  1211 , disk drives  1215  and optional monitor  1205 . Fixed media  1217 , or fixed media  1222  over port  1219 , may be used to program such a system and may represent a disk-type optical or magnetic media, magnetic tape, solid state dynamic or static memory, or the like. In specific embodiments, the aspects of the invention may be embodied in whole or in part as software recorded on this fixed media. An exemplary computer program product is described further above. Communication port  1219  may also be used to initially receive instructions that are used to program such a system and may represent any type of communication connection. Optionally, aspects of the invention are embodied in whole or in part within the circuitry of an application specific integrated circuit (ACIS) or a programmable logic device (PLD). In such a case, aspects of the invention may be embodied in a computer understandable descriptor language, which may be used to create an ASIC, or PLD.  FIG. 12  also includes dispensing system  700 , which is operably connected to information appliance  1200  via server  1220 . Optionally, dispensing system  700  is directly connected to information appliance  1200 . During operation, dispensing system  700  typically conveys fluidic materials to selected fluidic material sites on a positioning component of dispensing system  700 , e.g., as part of an assay or other process.  FIG. 12  also shows detector  1224 , which is optionally included in the systems of the invention. As shown, detector  1224  is operably connected to information appliance  1200  via server  1220 . In some embodiments, detector  1224  is directly connected to information appliance  1200 . In certain embodiments, detector  1224  is configured to detect detectable signals produced at fluidic material sites positioned on the positioning component of dispensing system  700 . In other embodiments, fluidic material sites (e.g., multi-well containers, etc.) are transferred (e.g., manually or using a robotic translocation device) to detector  1224  before and/or after fluidic materials are dispensed at the fluidic material sites on the positioning component of dispensing system  700 .  
      III. System Component Fabrication  
      System components (e.g., dispense heads, positioning components, cleaning components, etc.) are optionally formed by various fabrication techniques or combinations of such techniques including, e.g., machining, stamping, engraving, injection molding, cast molding, embossing, extrusion, etching (e.g., electrochemical etching, etc.), or other techniques. These and other suitable fabrication techniques are generally known in the art and described in, e.g., Altintas,  Manufacturing Automation: Metal Cutting Mechanics, Machine Tool Vibrations, and CNC Design , Cambridge University Press (2000), Molinari et al. (Eds.),  Metal Cutting and High Speed Machining , Kluwer Academic Publishers (2002), Stephenson et al.,  Metal Cutting Theory and Practice , Marcel Dekker (1997), Rosato,  Injection Molding Handbook,  3 rd  Ed., Kluwer Academic Publishers (2000),  Fundamentals of Injection Molding , W. J. T. Associates (2000), Whelan,  Injection Molding of Thermoplastics Materials , Vol. 2, Chapman &amp; Hall (1991), Fisher,  Extrusion of Plastics , Halsted Press (1976), and Chung,  Extrusion of Polymers: Theory and Practice , Hanser-Gardner Publications (2000), which are each incorporated by reference. In certain embodiments, following fabrication, system components are optionally further processed, e.g., by coating surfaces with a hydrophilic coating, a hydrophobic coating (e.g., a Xylan 1010DF/870 Black coating available from Whitford Corporation (West Chester, Pa.), etc.), or the like, e.g., to prevent interactions between component surfaces and reagents, samples, or the like.  
      IV. Dispensing Methods  
      In addition to the systems and computer program products described herein, the invention also relates to methods of dispensing fluidic materials. To illustrate, certain methods relate to dispensing aliquots of fluidic materials that have substantially uniform densities. As referred to herein, density variations among dispensed fluidic materials can negatively impact dispensing applications in various ways including leading to biased assay results and to inconsistent synthetic yields. To minimize these density variations, some of these methods include conveying selected aliquots of fluidic materials from dispensing tips that fluidly communicate with conduits that include non-vertical flow paths. These non-vertical flow paths prevent components (e.g., beads, cells, etc.) in the fluidic materials from settling proximal to the dispensing tips prior to being dispensed. In this manner, subsequently dispensed aliquots generally have substantially the same densities as previously dispensed aliquots for a given dispensed fluidic material.  
      In some embodiments, the dispensing methods of the invention include conveying a first fluidic material (e.g., a source fluid, such as a solution comprising beads, cells, enzymes, reagents, and/or the like) into a conduit through a first opening of the conduit using a peristaltic pump. These methods also include applying pressure on the first fluidic material in the conduit using another pressure source such that selected aliquots of the first fluidic material are dispensed from a second opening of the conduit at material sites, such as into the wells of multi-well containers, onto substrate surfaces, etc., e.g., as part of synthesis reactions, screens, assays, or the like. This process is typically repeated as desired. Peristaltic pumps and other pressure sources are described further above.  
      In addition, these dispensing methods optionally include conveying a second fluidic material (e.g., a system fluid, such as a buffer, etc.) through one or more segments of the conduit using the pressure source such that the second fluidic material expels the aliquots of the first fluidic material from the second opening of the conduit. In some of these embodiments, the methods include diluting the first fluidic material with the second fluidic material prior to or substantially simultaneously with expelling the aliquots of the first fluidic material from the second opening of the conduit. Further, the methods optionally include conveying a gas into the conduit through a port to form a gap between the first and second fluidic materials to prevent the first and second fluidic materials from mixing with one another. Moreover, the methods optionally include conveying a gas into the conduit to purge fluidic materials from at least one segment of the conduit prior to conveying the first fluidic material into the conduit.  
      In certain embodiments, fluidic material conveyance is restricted in the conduit directed towards the peristaltic pump during the application of pressure by the pressure source, e.g., to prevent fluidic materials from flowing towards the peristaltic pump and the fluidic material source. In some embodiments, these methods include moveably positioning fluidic material sites and the second opening of the conduit relative to one another, e.g., using a positioning component described herein. The moving and conveying steps are typically performed substantially simultaneous with one another, e.g., to effect “on-the-fly” fluidic material dispensing. Furthermore, the methods optionally include detecting detectable signals produced in the conduit and/or in the aliquots of the first fluidic material dispensed from the conduit.  
      To further illustrate an exemplary embodiment, some methods of dispensing fluidic materials include the use of dispensing systems having fluid junction blocks, such as those schematically shown in  FIGS. 5 A  and B, which are also described above. Fluid junction blocks are typically utilized to inject small, precise, and repeatable gaseous gaps into these systems to separate system and source fluids from one another, such that system fluids do not dilute the source fluids in these embodiments. These fluid junction blocks typically include at least a portion of a first conduit (e.g., first conduit  504 ) that fluidly communicates with a first fluidic material source (e.g., first fluidic material source  506 ). Fluid junction blocks also typically include at least a portion of a second conduit (e.g., fluid junction block conduit  532 ), which has at least first and second openings (e.g., first opening  531  and second opening  533 ) and at least one port (e.g., port  530 ) disposed through a wall of the second conduit. The port communicates with a cavity disposed through the second conduit. In addition, the first conduit generally intersects and fluidly communicates with the second conduit between the port and the second opening of the second conduit.  
      These methods of dispensing fluidic materials also include conveying a volume of a second fluidic material (e.g., a system fluid, etc.) through the first opening of the second conduit proximal to the port. During this step, the port is typically closed and a valve (e.g., valve  520 ) is generally opened long enough ensure that no air (e.g., ˜100% system fluid) is disposed between the source of the second fluidic material (e.g., pressure source  518 ) and the port. A pinch valve of the system (e.g., pinch valve  510 ) is opened or closed during this step. These methods also generally include restricting fluidic material conveyance through the first opening of the second conduit and through the first conduit. During this step, the valve (e.g., valve  520 ) is typically closed to restrict fluidic material conveyance through the first opening of the second conduit. The pinch valve can be opened or closed during this step, since the peristaltic pump acts as a valve to prevent fluidic material flow into the first fluidic material source. These methods also include conveying gas (e.g., air, nitrogen, argon, etc. at between about 5-10 psi) into the second conduit through the port to purge fluidic materials, if any, from the second conduit downstream from the port through the second opening of the second conduit.  
      In addition, these methods also include restricting fluidic material conveyance through the first opening of the second conduit (e.g., using valve  520 ) and gas conveyance through the port (e.g., using gas valve  534 ). In certain embodiments, the pinch valve is opened and the peristaltic pump is turned on in reverse so that source fluid that may be in, e.g., the first or another conduit is conveyed back into the first fluidic material source. Then, with the flow through the first opening of the second conduit and port restricted, the methods typically include conveying a volume of a first fluidic material (e.g., a source fluid, etc.) from the first fluidic material source through the first conduit and into the second conduit proximal to and downstream from the intersection of the first and second conduits such that a volume of the gas is disposed between the first and second fluidic materials in the second conduit. Furthermore, the methods also typically include restricting fluidic material conveyance through the first conduit, e.g., by closing the pinch valve and restricting gas conveyance through the port, e.g., by closing the port, and applying pressure to the second fluidic material (e.g., using pressure source  518  with valve  520  open) in the second conduit such that at least one selected aliquot of the first fluidic material is dispensed from the second opening of the second conduit or another conduit that fluidly communicates with the second conduit (e.g., third conduit  524 ). One or more of these steps is optionally repeated.  
      Although other fluidic material volumes may be conveyed using the systems and methods described herein, dispensed volumes or aliquots generally include at least about 0.1 μL of fluidic material. Microliter volumes are generally desirable, e.g., when conveying fluidic materials to and/or from high-density multi-well plates, such as 1536-well plates having total volume capacities that are typically between about 10 to about 15 μL/well, with the systems of the present invention. Larger volumes of fluidic material (e.g., milliliter volumes, liter volumes, etc.) are also optionally conveyed using the systems of the present invention.  
      Essentially any biochemical or cellular assay, or synthesis reaction, can be adapted for performance in the systems and according to the methods of the invention. To illustrate, common types of assays performed in, e.g., multi-well plates include those relating to signal transduction, cell adhesion, apoptosis, cell migration, GPCR, cell permeability, receptor/ligand binding, intracellular calcium flux, membrane potential, nucleic acid hybridization, cell growth/proliferation, among many others that are known in the art. Additional details relating to certain of these and other assays involving multi-well plates are described in, e.g., Parker et al. (2000) “Development of high throughput screening assays using fluorescence polarization: nuclear receptor-ligand binding and kinase/phosphatase assays,”  J. Biomolecular Screening  5(2):77-88, Asa (2001) “Automating cell permeability assays,”  Screening  1:36-37, Norrington (1999) “Automation of the drug discovery process,”  Innovations in Pharmaceutical Technology  1(2):34-39, Fukushima et al. (2001) “Induction of reduced endothelial permeability to horseradish peroxidase by factor(s) of human astrocytes and bladder carcinoma cells: detection in multi-well plate culture,”  Methods Cell Sci.  23(4):211-9, Neumayer (1998) “Fluorescence ELISA, a comparison between two fluorogenic and one chromogenic enzyme substrate,”  BPI  10(Nr. 5), Graeff et al. (2002) “A novel cycling assay for nicotinic acid-adenine dinucleotide phosphate with nanomolar sensitivity,”  Biochem J.  367(Pt 1):163-8, Rogers et al. (2002) “Fluorescence detection of plant extracts that affect neuronal voltage-gated Ca 2+  channels,”  Eur. J. Pharm. Sci.  15(4):321-30, and Rappaport et al. (2002) “New perfluorocarbon system for multilayer growth of anchorage-dependent mammalian cells,”  Biotechniques  32(1):142-51, which are each incorporated by reference.  
      While the foregoing invention has been described in some detail for purposes of clarity and understanding, it will be clear to one skilled in the art from a reading of this disclosure that various changes in form and detail can be made without departing from the true scope of the invention. For example, all the techniques and apparatus described above can be used in various combinations. All publications, patents, patent applications, and/or other documents cited in this application are incorporated by reference in their entirety for all purposes to the same extent as if each individual publication, patent, patent application, and/or other document were individually indicated to be incorporated by reference for all purposes.