Dispensing – Drop formers – With valve
Reexamination Certificate
2001-02-01
2002-07-23
Jacyna, J. Casimer (Department: 3751)
Dispensing
Drop formers
With valve
C222S001000, C222S420000
Reexamination Certificate
active
06422431
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus and process for controlling, dispensing and measuring small quantities of liquids. More specifically, the present invention senses pressure changes to ascertain and confirm the volume dispensed liquids and proper system functioning. In particular, the present invention relates to aspirating and dispensing picoliter range droplets of liquid.
BACKGROUND OF THE INVENTION
Advances in industries employing chemical and biological processes have created a need for the ability to accurately and automatically dispense small quantities of liquids containing chemically or biologically active substances for commercial or experimental use. Accuracy and precision in the amount of liquid dispensed is important both from the standpoint of causing a desired reaction and minimizing the amount of materials used.
Equipment for dispensing microvolumes of liquid have been demonstrated with technologies such as those developed for ink jet applications. However, ink jet equipment has the advantage of operating with a particular ink (or set of inks) of known and essentially fixed viscosity and other physical properties. Thus, because the properties of the ink being used are known and fixed, automatic ink jet equipment can be designed for the particular ink specified. Direct use of ink jet technology with liquids containing a particular chemical and biological substance of interest (“transfer liquid”) is more problematic. Such transfer liquids have varying viscosity and other physical properties that make accurate microvolume dispensing difficult. Automatic microvolume liquid handling systems should be capable of handling liquids of varying viscosity and other properties to accommodate the wide range of substances they must dispense. Another aspect of this problem is the need to accommodate accurately dispensing smaller and smaller amounts of transfer liquid. Especially in the utilization and test of biological materials, it is desirable to reduce the amount of transfer liquid dispensed in order to save costs or more efficiently use a small amount of material available. It is often both desirable and difficult to accurately dispense microvolumes of transfer liquid containing biological materials. Knowing the amount of transfer liquid dispensed in every ejection of transfer liquid would be advantageous to an automated system.
Another difficulty with dispensing microvolumes of transfer liquid arises due to the small orifices, e.g., 20-80 micrometers in diameter, employed to expel a transfer liquid. These small orifice sizes are susceptible to clogging. Heavy use of the nozzle promotes undesirable clogging by materials in the liquid being dispensed. Further exacerbating the clogging problem are the properties of the substances sometimes used in the transfer liquid. Clogging of transfer liquid substances at the orifice they are expelled from, or in other parts of the dispenser, can halt dispensing operations or make them far less precise. Therefore, it would be desirable to prevent or minimize clogging, be able to detect when such conditions are occurring, and to be able to automatically recover from these conditions. Failure of a microvolume dispenser to properly dispense transfer liquid can also be caused by other factors, such as air or other compressible gases being trapped in the dispensing unit. It would be desirable to detect and indicate when a microvolume dispenser is either not dispensing at all, or not dispensing the desired microvolume (“misfiring”).
Over time it may be necessary to aspirate a variety of different liquid mixtures or solutions into the microvolume dispenser in order to dispense those liquids. Because each liquid may contaminate the microvolume dispenser with regard to a later-used liquid it is desirable to thoroughly clean a microdispenser when liquids are changed. Even when liquids are not changed, cleaning is necessary to prevent buildup of materials inside the microvolume dispenser. Unfortunately, using a pump alone to flush out the microvolume dispenser is not always 100% effective. Therefore, it would be desirable to be able to easily and thoroughly clean the microvolume dispenser from time to time.
In order to achieve an automated microvolume dispensing system it would be desirable to ensure in realtime that the transfer liquid is within some given range of relevant system parameters in order to rapidly and accurately dispense transfer liquid droplets of substantially uniform size. For example, it is desirable to ensure that the transfer liquid is accurately deposited at its target surface. Because industry requires rapid dispensing of microvolume amounts of transfer liquid, it is also desirable to be able to ascertain transfer liquid volume dispensed, and to be able to detect and recover from dispensing problems in realtime.
One object of the present invention to provide a microvolume liquid handling system which is capable of accurately verifying microvolume amounts of transfer liquid dispensed by sensing a corresponding change in pressure in the microvolume liquid handling system.
A further object of the present invention to provide a microvolume liquid handling system which can accurately measure an amount of dispensed liquid regardless of transfer liquid properties, such as, viscosity.
Another object of the present invention to provide a microvolume liquid handling system which can transfer microvolume quantities of liquids containing chemically or biologically active substances.
A further object of the present invention to provide a microvolume liquid handling system that prevents or minimizes clogging.
Still another object of the present invention to provide a microvolume liquid handling system which senses pressure changes associated with clogging and misfiring to indicate such improper operation.
Yet another object of the present invention to provide a microvolume liquid handling system which can verify that the transfer liquid is maintained within a given range of negative pressure (with respect to ambient atmospheric pressure) in order to accurately dispense microvolume amounts of transfer liquid and optimize the operation of the microdispenser.
A further object of the present invention to minimize the amount of transfer liquid that needs to be aspirated into the dispenser.
A still further object of the present invention to automatically detect when the dispenser tip enters and leaves the surface of the transfer liquid and/or wash liquid.
A still further object of the present invention is to provide for a real time detection of dispensing single drops of the transfer liquid.
Other objects and advantages of the present invention will be apparent to those skilled in the art upon studying of this application.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a system of the present invention detects a pressure change resulting from ejection of a drop of a transfer liquid and generates an electrical signal indicating single drops of transfer liquid being dispersed in intervals measured by milliseconds. The dispersed drops being detected by the system can be in the range from about 5 picoliters to about 500 picoliters, preferably about 100 to about 500 picoliters. It has been discovered that by eliminating substantially all compressible fluids (gases) in the enclosed volume communicating with the ejection nozzle and containing the transfer liquid, the ejection of picoliter size drops can be detected by the present invention.
In accordance with another aspect of the present invention, it has been discovered that electrical signals indicating transient pressure changes in the transfer liquid upon dispensing of liquid drops in the range from about 5 picoliters to about 500 picoliters, preferably about 100 to about 500 picoliters can be detected even when the liquid in the enclosed volume of the dispenser is not fully enclosed, but is instead connected to a liquid reservoir. As long as substantially all compressible fluids (gases) are kept out of the dispensing conduit wh
Chibucos Nicholas S.
Meyer Wilhelm
Papen Roeland F.
Pelc Richard E.
Jacyna J. Casimer
Jenkens & Gilchrist
Packard Instrument Company Inc.
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