Abstract:
A hand-held, single-channel dispenser/aspirator is disclosed. The present dispenser/aspirator comprises a body portion for gripping the dispenser and a head portion. In some embodiments, the head portion includes a valve, a liquid conduit and a removable liquid reservoir. The liquid conduit places the liquid reservoir and the dispensing valve in fluid communication. A gas conduit received by the body portion of the dispenser is operable to pressurize the fluid reservoir, or draw a partial vacuum therein. Controls located on the body portion operate the dispenser. The liquid reservoir is advantageously disposed near the valve, so that a relatively short length of liquid conduit is required to operatively connect the reservoir and the dispensing valve, thereby improving the accuracy of the dispensing operation.

Description:
FIELD OF THE INVENTION 
     The present invention relates to hand-held liquid dispensers. More particularly, the present invention relates to a hand-held liquid dispenser/aspirator capable of dispensing/aspirating micro-liter volumes of liquid. 
     BACKGROUND OF THE INVENTION 
     In research and development settings, there are applications that require the transfer of a micro-volume amount of a single sample of reagent. Such a reagent, for example, might be withdrawn from a reservoir and delivered to a receiver, such as a well in a multi-well microtitre plate. It is usually important to perform such a transfer without cross-contamination such as may occur, for example, if a first reagent is already present in the well before a second reagent is transferred thereto. 
     To substantially eliminate the incidence of cross-contamination, a “non-touch-off” method of fluid delivery is advantageously used. In such a method, there is no contact between a droplet being dispensed and the receiver (or fluid or other material in the receiver) until the droplet completely disengages from the tip of the dispenser. Non-touch-off transfer requires supplying kinetic energy to a droplet in an amount sufficient to overcome the surface tension of the dispensing tip and to dispense the droplet with sufficient momentum that it can be accurately and reliably directed to a desired destination. 
     Sophisticated table-top multi-channel dispensers have been developed for simultaneously dispensing micro volumes of liquid via non touch-off methods into a plurality of regularly spaced receivers. But relatively few “single channel” (e.g., one dispensing operation at a time) hand-held dispensers are available. And those that are available are relatively simple and inaccurate “syringe-” or “pipetter-” type dispensers. Such pipetter-type dispensers are typically incapable of dispensing micro volumes of fluid. 
     Thus, there remains a need for an improved hand-held single channel non-touch-off dispenser. 
     SUMMARY OF THE INVENTION 
     In accordance with some embodiments of the present invention, a hand-held, single-channel dispenser is disclosed. 
     The present dispenser comprises a body portion for gripping the dispenser and a head portion. In some embodiments, the head portion comprises a dispensing valve, a liquid conduit and a liquid reservoir. The liquid conduit places the liquid reservoir and the dispensing valve in fluid communication. A gas conduit received by the body portion of the dispenser is operable to pressure the liquid reservoir, or draw a partial vacuum therein. Controls located on the body portion operate the dispenser. 
     In accordance with the illustrated embodiments of the present invention, the liquid reservoir is advantageously disposed near the dispensing valve. As a result, a relatively short length of liquid conduit is required to operatively connect the reservoir and the dispensing valve, which improves the accuracy of the dispensing operation. 
     In some embodiments, the liquid reservoir advantageously comprises the container portion of a standard “screw-top” vial. The lid of the vial is mounted to the head portion of the dispenser. To ready the dispenser for use, the container portion is threaded into the lid. For dispensing operations, liquid is added to the container portion before it engages the lid. Alternatively, the container can be engaged to the lid empty, and, via the application of negative pressure, a liquid of choice can be aspirated into the container. Fittings are disposed through the lid so that the conduit and gas conduit can be introduced into the reservoir. 
     These and other features of the present invention are described in detail later in this Specification in the Detailed Description with reference to the attached Figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a hand-held single-channel dispenser/aspirator in accordance with an illustrated embodiment of the present invention. 
     FIG. 2 depicts a side view of the threaded top of a vial, used for engaging the reservoir to the dispenser of FIG.  1 . 
     FIG. 3 depicts several flow control features for use in conjuction with the resent invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 depicts illustrative hand-held liquid dispenser/aspirator  100  in accordance with an illustrated embodiment of the present invention. Dispenser/aspirator  100 , hereinafter referred to as simply a “dispenser,” comprises a head portion  102  detachably engaged to a body portion  104 . In the illustrated embodiment, head portion  102  is smaller than body portion  104 . 
     Head portion  102  includes dispensing valve  106  and liquid reservoir  108 . Liquid conduit  114  places reservoir  108  in fluid communication with dispensing valve  106 . As used herein, the phrase “fluid communication,” indicates that fluid (i.e., liquid and/or gas) can flow directly between two regions (i.e., the two regions that are described to be in fluid communication). It should be understood even though valve  106  is referred to as a “dispensing” valve, it is also operable to aspirate liquid. 
     In embodiments wherein the present hand-held dispenser is intended to dispense micro-liters or less of liquid, the dispensing valve (i.e., valve  106 ) will be a “micro” valve, such as is used for print heads in ink-jet printers. Such micro-valves are capable of dispensing micro-volumes of liquid in the range of about 20 nano-liters to several micro-liters. Such micro-valves are currently available, such as from The Lee Company of Essex, Conn. 
     It is advantageous for liquid reservoir  108  to be readily removable from the dispenser. Such a configuration facilitates exchanging reservoirs, as desired. In particular, after a first reservoir dispenses its charge of liquid, it may be desirable to disengage it from the dispenser and engage a second reservoir containing a different liquid thereto. One example of a configuration by which reservoir  108  can be readily removed from the dispenser is described below. 
     In the illustrated embodiment, liquid reservoir  108  is realized as an ordinary screw-top vial. Lid  110  from such a vial is attached to head portion  102  of the dispenser. In use, the container portion of the vial is threaded into lid  110 . For dispensing operations, an appropriate liquid  112  is first added to the container portion. It will be appreciated that when liquid  112  is present in the container, the dispenser should be inverted from the orientation depicted in FIG. 1 to thread the container to the lid. 
     Body portion  104  of illustrative dispenser  100  provides a means for a user to grip the dispenser for use. Power source  122 , which supplies power for actuating dispensing valve  106 , is electrically connected to dispensing valve  106  via lead  118  through button  120 . Button  120 , which is actuated by a user&#39;s finger, sends a signal to power source  122 , which responds by sending a voltage pulse of preset length that defines the opening time of dispensing valve  106 . In an aspirating mode (described below), power source  122  sends a group of pulses to dispensing valve  106  so that it remains open. 
     The present dispenser further comprises pressurization means by which reservoir  108  and liquid conduit  114  are pressurized. The present dispenser also advantageously comprises suction-flow means by which a partial vacuum is drawn through reservoir  108  and liquid conduit  114 . Such suction flow allows the “dispenser” to aspirate (suck in) liquid. An illustrative arrangement for placing reservoir  108  and liquid conduit  114  under elevated pressure, or, alternatively, under partial vacuum, is now described. 
     In the illustrated embodiment, pressurization means comprises gas conduit  116  and a pressurized gas source  124 . A first end of gas conduit  116  terminates in reservoir  108 , and a second end of gas conduit  116  is placed in fluid communication with pressurized gas source  124  through operation of a mode selector, embodied as three-way valve  128  and switch  130 . 
     When gas conduit  116  is connected to the pressurization means, reservoir  108  and liquid conduit  114  are pressurized. Such pressure imparts kinetic energy to liquid  112  when dispensing valve  106  opens, and a volume of fluid  112  is dispensed. 
     Similarly, in the illustrated embodiment, suction-flow generating means comprises gas conduit  116  and a suction flow generator  126 . The suction flow generator can be, for example, a pump, jet ejector or the like. A first end of gas conduit  116  terminates in reservoir  108 , and a second end of gas conduit  116  is placed in fluid communication with suction flow generator  126  through operation of a mode selector, embodied as a three-way valve  128  and switch  132 . 
     When gas conduit  116  is connected to suction-flow generator  126 , a suction flow (i.e., partial vacuum) is developed in reservoir  108  and liquid conduit  114 . And, when dispensing valve  106  opens, a suction flow is generated therethrough so that any liquid in contact with the valve is aspirated into reservoir  108 . 
     In the illustrated embodiment, pressurized gas source  124  and suction-flow generator  126  are figuratively depicted as being co-located in a single “box”  134 . This illustration is meant to indicate that the mode selector for selecting dispensing or aspirating operation can be accessed via a single control box. Additionally, pressure control means, such as regulator (which is simply illustrated as switch  136  for clarity of illustration) are advantageously accessed via box  134 . Also, means for controlling suction flow, such as controller  138  that is operatively connected to valve  140 , are accessed via box  134 . 
     FIG. 2 depicts an illustrative arrangement by which liquid conduit  114  and gas conduit  116  engage reservoir  108 . Stainless plate  246  overlies the lip  242  of lid  110 . Lip  242  defines opening  243 . The opening provides access for fittings  250 , such as Micro-Barb™ fittings available from Beswick Engineering of Greenland, N.H., that extend through plate  246 . Tubing, such as TYGON™ tubing available from Norton Performance Plastics, Akron, Ohio, is attached to both ends of both fittings  250 . O-ring  244  seals plate  246  to reservoir  108  preventing leakage therefrom. 
     Thus, as described above, dispensing valve  106  dispenses or aspirates an amount of liquid during its cycle. The dispensed amount, which is usually controlled to a specific volume, is primarily a function of the amount of time that dispensing valve  106  is open, and of the pressure level in liquid conduit  114  or reservoir  108 . To a lesser extent, the dispensed amount also depends on fluid properties (e.g., viscosity, etc.). 
     Various optional features for improving the accuracy the liquid dispensing operation are described below. Such features are described in further detail in applicant&#39;s co-pending U.S. patent application Ser. No. 09/395,383, entitled “Article and Method for Flow Control in Liquid Dispensing Devices,” which was filed on even date herewith and is incorporated by reference herein. 
     Dispensers that provide a constant “re-supply” of liquid to replace dispensed fluid, such as illustrative dispenser  100  depicted in FIG. 1, are susceptible to a characteristic error. The error is related to characteristics of the dispensing valve. In particular, the amount of fluid dispensed from such dispensers is proportional to the amount of time that the dispensing valve is open. The behavior of dispensing valves (e.g., valve  106 ) that are typically used in such dispensers is such that there is a rapid response to an impulse (e.g., voltage) to open, but the closure response tends to be less precise, as a function of the spring used in the valve. 
     In some embodiments of the present invention, a flow restriction, realized in the illustrative embodiment depicted in FIG. 3 as restriction orifice  352 , is disposed in liquid conduit  114 . Advantageously, the flow restriction is disposed at the input (i.e., at the interface between reservoir  108  and the liquid conduit  114 ) of liquid conduit  114 . In some embodiments, liquid conduit  114  is elastic, or has a region that is elastic, such that it functions as an accumulator or bladder. Restriction orifice  352  has an outlet orifice  354  that is smaller than opening  307  of dispensing valve  106 . As a result, liquid  112  is re-supplied to liquid conduit  114  more slowly than it is dispensed through valve  106 . Errors resulting from any delay in valve closure are therefore reduced in magnitude since the flow rate to the valve is reduced by limiting the re-supply rate. 
     It is advantageous to monitor the pressure in liquid conduit  114  as it falls and rises during respective dispensing and refilling cycles. Such pressure data can be correlated to an amount of liquid dispensed and also provide indications of operational problems (e.g., occlusions in liquid conduit  114 ). 
     As such, in some embodiments of the present invention, pressure sensing is provided. Dynamic pressure sensors are advantageously used for such pressure sensing since they are much less expensive (i.e., about an order of magnitude) than static pressure sensors and typically provide sufficient information. At least a portion of liquid conduit  114  must be elastic to use a dynamic pressure sensor. 
     Thus, in one embodiment, a dynamic pressure sensor  356  is operatively engaged to an elastic region of liquid conduit  114 . Leads  358  from sensor  356  connect to appropriate electronics (not shown) for processing sensor data and displaying and/or recording such data. In some embodiments, the present dispenser includes both a restriction orifice and dynamic pressure sensor to improve accuracy. 
     Over time, the performance characteristics of a fluid dispenser may change. For example, elastic conduit materials may lose resilience over time. Moreover, variations in fluid parameters (e.g., changes in viscosity, etc.) from use-to-use may affect the fluid dynamics within the dispenser and hence the dispensing operation itself. To the extent such a change in elasticity or fluid parameters vary from a baseline condition, an error in the amount of liquid dispensed will occur. 
     In accordance with the present teachings, in some embodiments, the present dispenser further includes resilience-adjusting means that is operable to adjust the “resilience” or “elasticity” of an elastic region of liquid conduit  114 . By appropriately adjusting the resilience-adjusting means, dispenser operation can be maintained at a baseline notwithstanding changed system conditions. Such adjustment is routinely performed via trial and error, wherein the resilience-adjusting means is changed and the dispensed volume is measured. The resilience-adjusting means is adjusted until the proper volume is dispensed. Of course, a user can adjust valve operation and/or pressure to affect changes in the dispensed volume, as well. 
     In the embodiment depicted in FIG. 3, the resilience-adjusting means comprises an enclosure  360  that defines a pressure-tight chamber  362  surrounding at least a portion of an elastic region of liquid conduit  114 , and a pressure-adjustment means. Increasing the pressure within chamber  362  effectively increases the resilience of the enclosed region of liquid conduit  114 . 
     In some embodiments, pressure-adjustment means is implemented by gas supply conduit  364  that delivers gas (e.g., nitrogen, etc.) to chamber  362 , and a pressure regulator  366 . Additionally, optional vacuum-flow conduit (not shown) for drawing a partial vacuum can be connected to chamber  362 . 
     In further embodiments, the present dispenser includes a restriction orifice, dynamic pressure sensor and resilience-adjusting means for improving dispenser accuracy. In other embodiments, the present dispenser includes various combinations of such flow-control elements. 
     It is to be understood that the above-described embodiments are merely illustrative of the invention and that many variations may be devised by those skilled in the art without departing from the scope of the invention. It is therefore intended that such variations be included within the scope of the following claims and their equivalents.