Abstract:
Various techniques for dispensing liquids are disclosed herein. In one embodiment a dispenser retention apparatus includes a frame. The frame includes a top surface configured to retain a liquid dispensing assembly. The frame also includes a bottom surface opposite the top surface. The bottom surface includes a first channel extending from a first lateral edge of the frame to a droplet passage between the top and bottom surfaces. The first channel is configured to allow a light beam introduced to the frame at the first lateral edge to intersect a droplet in the passage.

Description:
BACKGROUND 
     Dispensing of liquids in volumes from picoliters to microliters is an essential operation in many areas of pharmaceutical and biology research, as well as in medical and veterinary diagnostics, forensics testing, and agricultural testing. Even within these fields, low-volume liquid dispensing is used for many different operations. 
     One stage of pharmaceutical research, during which low-volume liquid dispensing is important, is directed to determining the concentration of a compound needed to effectively attack or inhibit a target (e.g., a virus). Many different concentrations of the compound are created in containers, such as the wells of a microplate (also known as a “well plate”) to determine the effective concentration. Dispensing systems direct liquids into the wells. Serial dilution is applied to achieve a required concentration when the dispensing system is incapable of providing sufficiently small volumes of the compound. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of exemplary embodiments of the invention, reference will now be made to the accompanying drawings in which: 
         FIG. 1  shows a top view of a head assembly in accordance with various embodiments; 
         FIG. 2  shows a top view of a frame configured to support a head assembly in accordance with various embodiments; and 
         FIGS. 3A and 3B  show top and bottom views of a head assembly module in accordance with various embodiments; 
         FIGS. 4 and 5  show a top view of a head assembly module including a handling feature in accordance with various embodiments; 
         FIGS. 6A and 6B  show a top views of frames configured to support one and two-dimensional arrays of head assemblies in accordance with various embodiments; 
         FIG. 7  shows a top view of a head assembly module including a one-dimensional array of head assemblies in accordance with various embodiments; 
         FIG. 8  shows a top view of a frame configured for user insertion of head assemblies in a one dimensional array in accordance with various embodiments; 
         FIG. 9A  shows a top view of a fully populated frame configured for user insertion of a head assemblies in a one dimensional array in accordance with various embodiments; 
         FIG. 9B  shows a top view of a head assembly module that includes alignment/retention features in accordance with various embodiments; 
         FIG. 10  shows a top view of a partially populated frame configured for user insertion of head assemblies in a two dimensional array in accordance with various embodiments; 
         FIGS. 11-18  show a bottom view of a frame including channels for light scattering drop detection in accordance with various embodiments; 
         FIG. 19  shows a side view of a populated frame in accordance with various embodiments; 
         FIG. 20  shows a top view of a head assembly module with spring loaded pin connection in accordance with various embodiments; and 
         FIG. 21  shows a flow diagram for a method of titration in accordance with various embodiments. 
     
    
    
     NOTATION AND NOMENCLATURE 
     Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, computer companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . . ” Also, the term “couple” or “couples” is intended to mean either an indirect, direct, optical or wireless electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, through an indirect electrical connection via other devices and connections, through an optical electrical connection, or through a wireless electrical connection. 
     DETAILED DESCRIPTION 
     The following discussion is directed to various embodiments of the invention. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment. 
     One stage of pharmaceutical research is directed to determining the concentration of a compound needed to effectively attack a target (e.g., a virus). To determine an effective concentration of a compound, many different concentrations of the compound are created in trays of miniature test tubes called “well plates.” A dispensing system distributes the compound into the well. If the dispensing system is unable to dispense sufficiently small volumes of the compound, serial dilution is applied to achieve a desired concentration. 
     Disclosed herein are techniques for using a frame conveying one or more liquid dispensing assemblies (e.g., titration head assemblies (“THA”)) to dispense small volumes (e.g., pico-liters) of liquid very quickly. Such techniques provide a method to titrate solutions across many orders of magnitude of concentration without serial dilution. Those same techniques can be used to dispense low-volumes of a wide-variety of liquids containing active biological ingredients, assay components, markers, tags, or a wide variety of other fluids relevant to the fields of pharmaceutical research, bio research, forensics study, veterinary research and diagnostics, and medical diagnostics, to name a few. Embodiments of the frame may include one or two-dimensional arrays of THAs spaced in accordance with the wells of a microplate. Frame embodiments can also include multiple THA designs for dispensing a variety of fluids into many bioassay and other applications requiring similar technology. 
     Embodiments of the frame also include channels formed in the bottom surface of the frame. The channels improve the accuracy of light scattering drop detection by reducing the distance between dispenser nozzles a light beam passing below the nozzles, thereby permitting laser light to pass through and not be reflected, and enabling use of a higher numerical aperture fiber. 
     In some embodiments, THAs are rigidly attached to a frame with a solid bottom surface, and/or the frame includes features for ease and stability of stacking the frames, and/or the frame includes numbers for each THA or other human or machine readable ID marks on the frames to denote each THA or features of the frame or THAs. 
       FIG. 1  shows a top view of a THA  100  in accordance with various embodiments. The THA  100  includes a flexible substrate  102  (e.g., polyimide), electrical contact pads  104 , a liquid reservoir  112 , and a printhead  106  including an array of nozzles  108 . The THA  100  may also include an alignment mark, for example, fiducials  110  for aligning the THA on a frame. The THA also includes conductive traces between the pads  104  and the printhead  106 . 
     The printhead  106  may be based on, for example, thermal inkjet technology, or any other liquid dispensing technology capable of producing a desired droplet size. Embodiments of the printhead  106  may differ as to the number of nozzles  108 , distribution of the nozzles  108 , the type of fluid accommodated by the printhead  106  fluid chamber (e.g., aqueous, dimethyl sulfoxide, etc.), droplet volume, etc. With regard to droplet volume for example, one embodiment of the printhead  106  discharges  1 -pico-liter droplets, another embodiment discharges  10 -pico-liter droplets, and yet another embodiment discharges  100 -pico-liter droplets. Similarly, embodiments of the THA  100  may include different liquid reservoirs  112  capable of holding different volumes of liquid (e.g., a 5 micro-liter reservoirs  112 , a 50 micro-liter reservoirs receptacles  112 , etc). 
       FIG. 2  shows a top view of frame  200  configured to support a titration head assembly  100  in accordance with various embodiments. The upper surface of the frame  200  is non-conductive in some embodiments to allow the titration head assembly  100  to be bonded to the frame  200  without shorting conductors of the THA  100 . The frame  200  may be formed of a polymer material or may be metal or ceramic. A metallic frame may include a non-conductive coating in some areas to prevent the conductors of the THA  100  from shorting. An opening  202  is disposed in the frame  200  to allow droplets produced by the printhead  106  to pass through the frame  200 . The frame  200  may also include alignment features  210  that guide placement of the THA  100  on the frame  100 . The frame  200  is rigid enough to maintain its shape when electrical connections are made with the pads  104  via spring-loaded pins or another electrical connection method. 
       FIG. 3A  shows a top view of a THA module  300  in accordance with various embodiments. The THA module  300  includes a THA  100  mounted onto a frame  200 . The THA  100  may be bonded to the frame  200  by an adhesive. The THA  100  is aligned and secured to the frame  200  such that the nozzles  108  face into the opening  202  of the frame  200 . The frame  200  provides support for the electrical contact pads  104  allowing electrical connections to be made with the pads  104  via spring-loaded pins when the frame is positioned in a dispensing instrument. The bottom surface  302  of the frame  300  may extend no more than 2 millimeters (“mm”) (e.g., 0.50-2 mm in some embodiments) below the printhead  106 , in some embodiments, to provide small printhead to drop receptacle spacing. 
     The frame  200  provides a reference for positioning the THA  100  for use. For example, by positioning the frame  200  relative to a receptacle intended to receive liquid from the THA  100 , and/or a liquid delivery system configured to load the reservoir  112 , the reservoir  112 , printhead  106 , pads  104 , etc. are positioned for proper operation. By affixing the THA  100  to the rigid frame  200 , the orientation of the THA  100  (e.g., horizontality of the printhead  106  and/or reservoir  112 ) can be controlled by controlling the orientation of the frame  200 . 
       FIG. 3B  shows a bottom view of the THA module  300  in accordance with various embodiments. The THA module  300  may include alignment features  310  allowing the module  300  to be properly positioned in a dispensing instrument and/or relative to a container positioned to receive liquid from the module  300 . In some embodiments, the module  300  may be 9 mm or less in width and/or 25 mm or less in length. In some embodiments, the module  300  may be 4.5 mm or less in width. 
       FIGS. 4 and 5  show a top view of a THA module  400  in accordance with various embodiments. The module  400  includes a THA  100  affixed to a frame  402 . The frame  402  is similar to the frame  200 , and further includes a handling feature  404  (i.e., a grip area) to facilitate handling by a user. 
       FIG. 6A  shows a top view of a frame  600  configured to support a one-dimensional array of THAs  100  in accordance with various embodiments. The frame  600  is configured to support up to eight THAs  100 . Other embodiments may be configured to support more or fewer THAs  100 . For example, an embodiment of the frame may be configured to support up to 16 THAs  100 . The frame  600  includes a handling feature  404 . Some embodiments may omit the handling feature  404 . The openings  202  may be spaced to in accordance with a desired droplet receptacle spacing. For example, in some embodiments the openings  202  may be spaced by an integer multiple of 2.25 mm to align with industry standard microplate well spacing. Some embodiments of the frame  600  are dimensioned (e.g., 1″×3″) to allow manipulation by microscope slide robotics. Some embodiments of the frame  600  are dimensioned (e.g.; 3.5″×5″) to allow manipulation by microplate handling grippers and storage in microplate stacks and shelves. 
       FIG. 6B  shows a top view of a frame  602  configured to support a two-dimensional array of THAs  100  in accordance with various embodiments. The frame  602  is configured to support up to eight THAs  100 . Other embodiments may be configured to support more (e.g., 16) or fewer THAs  100 , by providing for a different number of rows and/or columns of THAs  100 . The openings  202  may be spaced to in accordance with a desired droplet receptacle spacing (e.g., microplate well spacing, D=2.25 mm, D=4.5 mm, D=9 mm, etc). The frame  602  may be dimensioned to allow manipulation by microplate handling grippers and storage in microplate stacks and shelves. 
       FIG. 7  shows a top view of a head assembly module  700  including a one-dimensional array of THAs  100  affixed to the frame  600  in accordance with various embodiments. Different liquids and/or different volumes of liquid may be loaded into different ones of the receptacles  112 , and the THAs  100  of the module  700  may be dispensed from serially or in parallel to reduce microplate processing time. Electrical connections can be made to the electrical contact pads  104  one THA  100  at a time or to many or all THAs  100  simultaneously. 
       FIG. 8  shows a top view of a carrier frame  800  configured for user insert on of head assembly modules  300  (or other one-dimensional modules, e.g., 1×2, 1×4, etc.) in a one-dimensional array in accordance with various embodiments. The carrier frame  800  allows for provision of a user selectable number of THA modules  300  to a dispensing instrument. The THAs  100  may snap into the carrier frame  800  using an alignment/retention feature  802  of the carrier frame  800  that cooperatively engages an associated feature of the module  300 . The carrier frame  800  may be configured for handling by microscope slide robotics. Some embodiments of the carrier frame  800  are dimensioned to allow manipulation by microplate handling grippers and storage in microplate stacks and shelves. Some embodiments of the carrier frame  800  space the THA modules  300  in accordance with a desired drop receptacle spacing (e.g., an industry standard spacing, such as 9 mm, 4.5 mm, or 2.25 mm, or an integer multiple thereof). 
       FIG. 9A  shows a top view of the carrier frame  800  fully populated with THA modules  300  in accordance with various embodiments.  FIG. 9B  shows a top vie of a THA module  300  that includes alignment/retention features  902 . In some embodiments, friction between the alignment/retention features  802 ,  902  retains the THA module  300  in the carrier frame  800 . In some embodiments, the carrier frame  800  extends no more than 2 millimeters below the printhead  106  to provide small printhead to drop receptacle spacing. 
       FIG. 10  shows a top view of a partially populated carrier frame  1000  configured for user insertion of THA modules  300  (or other one or two-dimensional THA modules) in a two dimensional array in accordance with various embodiments. The carrier frame  1000  is configured to support up to 16 THA modules  300 . A user may mount as many THA modules  300  as desired in the carrier frame  1000  at a time selected by the user (e.g., at time of use). Other embodiments of the carrier frame  1000  support more or fewer rows and/or columns of THA modules. The carrier frame  1000  may be configured for automated handling by microplate idling robotics. 
       FIGS. 11-15  show a bottom view of a THA module  300  including channels for light scattering drop detection (“LSDD”) in accordance with various embodiments. Light scattering drop detection uses light scattered by a droplet passing through a light beam to detect the presence of the droplet. Performance of LSDD may be compromised when a THA  100  is mounted on a frame because the frame thickness increases the distance between the light beam and the surface of the printhead  106 . To improve LSDD performance, embodiments of the frame  200 ,  400 ,  600 ,  800 ,  1000  include channels formed in the bottom side of the frame to reduce the distance between the light beam and the surface of the printhead  106 . Channels also let the light beam pass through the frame without being reflected into a light collector. The channels also enable use of a higher numerical aperture light collector which allows for detection of more scattered light. Channel depth may range, for example, from 0.1 mm to 1.9 mm for a 2 mm frame (i.e., thickness of frame material above a channel may range from about 0.1 mm to about the frame thickness less 0.1 mm). A thicker frame may have a deeper channel in order to reduce spacing between the light beam and the surface of the printhead  106 . 
       FIG. 11  shows a THA module  1100  including a frame  1102 . The frame  1102  is similar to the frame  200  and includes channels (grooves)  1104  and  1110  provided in the bottom of the frame  1102 . The channel  1104  allows light beam  1114  provided by light source  1112  to pass between the bottom surface of the frame  200  and the printhead  106 , thereby reducing the distance between the beam  1114  and the printhead  106 . As a droplet is discharged from the printhead  106  the beam  1114  intersects the droplet, and the droplet scatters the light beam  1114 . Scattered light  1108  is collected by light collector  1106  via a channel  1108  formed in the bottom of the frame  200 . In some embodiments, the light source  1112  is a laser light source (e.g., a laser diode), and the light collector  1106  is an optical fiber. The light collector  1106  provides light to a processing system that analyzes the collected light to identify droplets. Embodiments provide the channel  1110  at an angle of 15 degrees plus or minus 10 degrees from the channel  1104 . 
       FIG. 12  shows a THA module  1200  including a frame  1202 . The frame  1202  is similar to the frame  1102 , but includes a triangular channel  1210  for collection of scattered light  1108 . In some embodiments, the channel  1210  occupies an area extending from 0 degrees to 25 degrees from the channel  1104 . 
       FIG. 13  shows a THA module  1300  including a frame  1302 . The frame  1302  is similar to the frame  1102 , but includes an additional channel  1114  for passage of scattered light  1112  for collection by a second instance of the light collector  1106 . Embodiments provide the channel  1114  at an angle of 15 degrees plus or minus 10 degrees from the channel  1104 . 
       FIG. 14  shows a THA module  1400  including a frame  1402 . The frame  1402  is similar to the frame  1202 , but includes an enlarged triangular channel  1410 . The channel  1410  provides passage for reception of scattered light  1108  and  1112  by light detectors. The channel  1410  allows capture of detected light at up to approximately a 25 degree angle from the light beam  1114 . 
       FIG. 15  shows a THA module  1500  including a frame  1502 . The frame  1502  is similar to the frame  1302 , but includes additional channels  1506  and  1510  for passage of back-scattered light  1508 ,  1504  for collection by light collectors  1106 . Embodiments provide the channels  1506 ,  1510  at an angle of 15 degrees plus or minus 10 degrees from the channel  1104 . 
       FIG. 16  shows a THA module  1600  including a frame  1602 . The frame  1602  is similar to the frame  1502 , but includes enlarged triangular channels  1604 ,  1606 . 
       FIG. 17  shows a THA module  1700  including a frame  1702 . The frame  1702  is similar to the frame  1502 , but omits the channels  1110  and  1114 . Thus, the frame  1702  is configured for collection of back-scattered light  1504 ,  1508 . 
       FIG. 18  shows a THA module  1800  including a frame  1802 . The frame  1802  is similar to the frame  1702 , but includes an enlarged triangular channel  1604 . Thus, the frame  1802  is configured for collection of back-scattered light  1504 ,  1508 . 
       FIG. 19  shows a side view of a frame (e.g., frame  600  or frame  800 ) populated with THAs  100  in accordance with various embodiments. The printhead  106  is positioned in the opening  202  in the frame  600 . Liquid is provided from the reservoir  112  to the printhead  106 . The printhead  106  is activated to expel a droplet  1902  (e.g., a pico-liter droplet) that descends through the opening  202  in the frame  600  into a container  1904  located below the frame  600 . The container  1604  may be a well of a microplate. 
       FIG. 20  shows a top view of a THA module  300  with spring-loaded pin connection in accordance with various embodiments. The frame  200  provides support for the contact pads  104  allowing the spring-loaded pin  2002  to make an electrical connection with the pad  104  without deforming the flexible substrate  102  of the THA  100 . Only a single spring-loaded pin  2002  is shown for purposes of illustration. In practice however, a spring-loaded pin  2002  may be provided for as many of the pads  104  as needed to provide power and control signals to the print head  106  from the dispense controller  2004  of a dispensing instrument  2006  with which the module  300  is used. Furthermore, spring-loaded pins  2002  may be provided for as many THAs  100  as are mounted on a module  700  and/or a user configurable carrier frame  800 ,  1000 . 
       FIG. 21  shows a flow diagram for a method of titration in accordance with various embodiments. Though depicted sequentially as a matter of convenience, at least some of the actions shown can be performed in a different order and/or performed in parallel. Additionally, some embodiments may perform only some of the actions shown. At least some of the actions shown may be performed by logic of a dispensing instrument  2006 . In some embodiments, such logic may include a processor executing software instructions stored in a computer readable medium. 
     In block  2102 , a user affixes THA modules (e.g., THA module  300 ) to a carrier frame (e.g., carrier frame  800 ). The carrier frame  800  may support a one or two-dimensional array of modules. The number of THA modules  300  mounted to the carrier frame  800  is user selectable, and may be based, for example, on the number of wells to be processed, the number of different liquids to be dispensed, etc. The carrier frame  800  need not be fully populated. 
     In block  2104 , the user installs the carrier frame  800  into the dispensing instrument  2006 . The user may physically latch the carrier frame  800  into the instrument  2006  or the instrument  2006  may automatically position and latch the carrier frame  800 . 
     In block  2106 , the contact pads  104  of the modules  300  are electrically connected to the dispensing instrument  2006  via spring-loaded pins  2002 . The dispensing instrument  2006  provides power and control signals to the printhead  106  via the electrical connections. In some embodiments, only a single module  300  at a time is electrically connected to the dispensing instrument  2006 . In some embodiments, multiple modules  300  are individually/simultaneously connected to the dispensing instrument  2006 . In such embodiments, the dispense controller  2004  can cause multiple modules  300  to dispense the same or different volumes of liquid in parallel. 
     In block  2108 , the dispensing instrument  2006  electrically verifies some or all of the THAs on carrier frame  800 . Electrical verification involves ensuring that the printhead is of the correct type and that it is electrically functional. 
     In block  2110  liquid is added to the reservoir  112  of one or more THA modules  300  mounted on the frame  800 . In various embodiments, liquid may be added to the reservoir  112  before or after the carrier frame  800  is coupled to a dispensing instrument  2006 . Different liquids may be loaded into different reservoirs  112 , and different volumes of liquid may be added to different reservoirs  112 . Reservoirs may be loaded at any time before the module  300  is used, including immediately prior to use. Liquid can be added to the reservoirs  112  manually or automatically and in serial or parallel fashion. 
     In block  2112 , the dispensing instrument  2006  provides electrical signals that cause the modules  300  to discharge different numbers of droplets (e.g., pico-liter droplets) from printheads  106  of the modules  300 . The different numbers of droplets form different concentrations of the liquid in the different containers  1604  (e.g., wells of a microplate) positioned beneath the carrier frame  800 . Because some embodiments of the printhead  106  are capable of discharging a pico-liter droplet, serial dilution is not needed to provide a desired concentration of the liquid in the container  1604 . 
     In block  2114 , droplets discharged by the module  300  are detected using light scattering drop detection. A light source  1112  produces a light beam  1114  that propagates in a channel  1104  formed in the bottom surface of the module  300 . The channel  1104  allows the light beam  1114  to pass closer to the printhead  106  that would be otherwise possible. The light beam  1114  is scattered as a droplet is discharged from the printhead  106  and passes through the beam  1114 . The scattered light  1108  travels through a channel  1110  in the bottom surface of the module  300  to a light detector. The channel  1110  is provided at an angle of 5-25 degrees from the light beam  1114 . The light detector provides the scattered light  1108  to a droplet detection system. 
     In block  2116 , the dispensing instrument determines whether a desired number of droplets has been discharged. If the desired number of droplets has not been discharged, the dispensing instrument provides electrical signals that cause the modules to continue to discharge droplets. If the desired number of droplets has been discharged, the dispensing system stops droplet dispensing and performs the next operation. 
     The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.