Patent Application
20090314861
The invention relates generally to dispensing electrically conductive fluids. More particularly, the present invention relates to biological fluid droplet ejection using high voltage pulses.
A substantial need exists for accurate low cost microarrays or bioarrays for biopharmaceutical, genetic research, and emerging clinical applications, such as identifying chemicals and pathogens, screening patients for drug sensitivity, diagnosing diseases, and genetic or proteomic research. Current methods for producing microarrays can be expensive and impractical. Typically, microarray production is a slow complicated process that requires building up genes individually base by base on a slide.
Some existing techniques of printing microarrays use contact methods that require dipping pins into solution and touching the dipped pins on a substrate. In addition to being time-consuming, contact methods for microarray production are prone to contamination as the pins come in direct contact with substrates, have problems with substrate fragility, and are typically wasteful as excess biochemical material is discarded after printing.
Because of the above difficulties, particularly cost, researchers often rely on custom-made or “homebrew” techniques. However, homebrew array printers are often non-standard, unreliable, slow, and only capable of producing relatively large (about 100 μm) spots. In addition, homebrew printers typically require a dedicated operator and frequent maintenance. Furthermore, the homebrew array printers use contact methods, which have the above-mentioned disadvantages.
Existing techniques of printing microarrays oftentimes also use modified standard well plates by storing and dispensing fluids directly in the wells of the well plates. By using standard well plates, standard handling equipment need not be replaced with custom or dedicated handling equipment. However, existing techniques using standard well plates have difficulties with filling, storing, transporting, and cleaning the well plates. In addition, keeping track of which fluids are in each well and sealing the partially-used well for future use are difficult to accomplish for the modified standard well plates of existing techniques. Precise modification of the standard well plates, such as welding small nozzles onto the wells of the well plates, causes the well plates to be fragile during filling, transporting, and storage. The use of existing modified standard well plates can also be wasteful as damage to printing equipment at one well could require the replacement of the entire well plate. Furthermore, existing modified well plates are not easily reusable, since wells could run dry at different rates.
The present invention addresses at least the difficult problems of precise fluid printing and advances the art with electrically conductive fluid ejection using high voltages.
The present invention is directed to printing or ejecting a conductive fluid or powder using high voltage pulses. A nozzle, including a first conductor, is provided for transporting an electrically conductive fluid, such as a biological fluid, a DNA sample, a virus, a cell, a protein, or any mixture thereof, is provided. A second conductor, positioned below the nozzle, is also provided. A first voltage pulse is applied across the first and second conductors to form an approximately hemispherical hanging drop of the conductive fluid on the tip of the nozzle. A second voltage pulse is applied across the first and second conductors to change the approximately hemispherical hanging drop to be approximately conical. A droplet of the conductive fluid is ejected from the approximately conical hanging drop.
In a preferred embodiment, the width of the second voltage pulse ranges between about 0 ms and about 20 ms, and the rise time of the second voltage pulse ranges between about 3 μs and about 5 μs. The magnitude of the second voltage pulse can be greater than the magnitude of the first voltage pulse and the width of the first voltage pulse can be greater than the width of the second voltage pulse.
A substrate, positioned below the second conductor, is also provided for receiving the droplet. In a preferred embodiment, the second conductor includes a conducting ring. The conducting ring is positioned below and concentric about the first conductor. In this configuration, the electric fields produced by the first and second voltage pulses are approximately symmetric about a vertical axis of the nozzle. The conducting ring can also be used to measure the presence of and an approximate size of the ejected droplet. The presence and approximate size of the droplet is measured based on an induced electromagnetic signal. The electromagnetic signal is induced by the droplet passing through the center of the conducting ring. The measured approximate size of the droplet can also be used to adjust the width of the first and/or second voltage pulses.
In an embodiment of the present invention, the location of the ejected drop can also be focused by applying a focusing electric field. A conducting pin positioned below the second conductor preferably generates the focusing electric field.
The present invention is also directed to a device for ejecting an electrically conductive fluid. The device includes a well plate having a plurality of sockets, one or more well modules that can be inserted and removed from the sockets, a conducting ring corresponding to each of the sockets of the well plate, a substrate for receiving the conductive fluid, and a high voltage source for producing high voltage pulses. Each of the well modules includes a reservoir for storing the conductive fluid and a conducting nozzle for ejecting the conductive fluid. The conductive fluid can be transported from the reservoir to the nozzle. Each of the conducting rings are positioned below and aligned with the corresponding socket. The substrate is positioned below the conducting rings. The high voltage pulses are produced between the conducting nozzle of each well module inserted into a socket and the conducting ring corresponding to the same socket. The high voltage pulses cause the ejection of one or more droplets of the conductive fluid from the nozzle. The droplets fall through the center of the conducting ring corresponding to the same socket.
In an embodiment, a sensing circuit is attached to one or more of the conducting rings for sensing the presence and approximate size for one or more the droplets passing through the center of the conducting ring. The presence and approximate size of the droplets can be used to adjust properties of the applied high voltage pulses.
The conducting nozzle preferably includes a metal capillary tube that allows the conductive fluid to flow in the center of the tube. Alternatively, the conducting nozzle includes a solid cylindrical electrode that allows the conductive fluid to flow on the surface of the electrode. The well modules can also include an embedded memory chip for storing data related to the ejection of the conductive fluid. The fluid ejector device can also include a control circuit electrically connected to the conducting nozzle of one or more of the well modules. The control circuit can provide independent control of the high voltage pulses.
The present invention together with its objectives and advantages will be understood by reading the following description in conjunction with the drawings, in which:
Many applications, particularly in biopharmaceutical and genetic research, require printing conductive fluids onto a surface, such as for microarray printing. Oftentimes, these applications require precise fluid ejection to accurately place a desired amount of the fluid onto a substrate. Precision printing is a difficult task that generally requires extensive time and/or cost. The present invention is directed to ejection of electrically conductive fluid for precise droplet size and location control using multiple high voltage pulses.
In a preferred embodiment, the second conductor 120 is located between the nozzle 110 and the substrate 130. Furthermore, the second conductor 120 includes a conducting ring that is positioned below and concentric about the conductor of the nozzle 110. With such a configuration, the electric field produced by the first and second voltage pulses is approximately symmetrical about a vertical axis of the conductors. The symmetrical field directs the droplet to fall at a precise location directly below the center of the conducting ring 120.
The conducting ring 120 can be an electrically grounded copper ring or a metallic coil, preferably of a fine magnet wire. In an embodiment, the conducting ring 120 is located about 2-3 mm below the nozzle 10 and has a diameter of about 3 mm.
In addition to precise location control, the multiple voltage pulse ejection method of the present invention allows for size control of the deposited droplets. Droplet size is controlled by tuning the voltage pulse widths and magnitudes. In an embodiment, a fluid spot 190 dispensed onto the substrate 130 can have a diameter ranging from about 20 μm to about 1 mm. In an exemplary embodiment, multiple spots are deposited onto the substrate 130, each spot having a diameter of about 200 μm and a spacing of about 400 μm between spots.
In an embodiment of the present invention, the first 140 and second 160 voltages pulses are high voltage pulses, ranging from between 0 V to 5000 V, with a pulse width between about 0 s and 20 ms, and a rise time less than about 10 μs. The rise time preferably ranges between about 3 μs and about 5 μs. The optimal magnitudes and widths of the voltage pulses can depend on properties and position of the nozzle 110, position and size of the second conductor 120, position of the substrate 130, as well as properties of the conductive fluid. For example, uncontrollable spraying or spitting jets can result when very large voltages are applied. In a preferred embodiment, the magnitude of the second voltage pulse 160 is greater than or equal to the magnitude of the first voltage pulse 140. In addition, the width of the first voltage pulse 140 is preferably greater than the width of the second voltage pulse 160.
Each well module 230 includes a reservoir 240 for storing the conductive fluid and a nozzle 250 fluidically connected to the reservoir 240. The nozzle 250 is preferably a conducting nozzle and is electrically connected to the high voltage source 280. The device 200 ejects fluid by the application of multiple high voltage pulses as described above and in
It is important to note that the well module 230 of the present invention can be independently inserted and removed from the sockets 220 of the well plate 210 in contrast to existing designs where the fluid is stored directly in the wells of the well plate. Removable well modules 230 allow for independent control of the droplet ejection. In other words, any desired pattern of ejection can be accomplished simply by either inserting well modules 230 only in the desired sockets 220 or by electronically controlling the application of the voltage pulses. In addition, each of the well modules 230 can be refilled as needed due to the typically non-uniform ejection rates of each well module 230. The independent filling and refilling of the well modules 230 also decreases the possibility of contamination between fluids in the modules. Since the removable well modules 230 can be manipulated separately from the well plate 210, the cost of maintenance can be further reduced. Furthermore, the removable well modules 230 can also be easily stored separately from the rest of the device 200.
It is also important to note that the substrate 270 is positioned below the conducting rings 260. This position of the substrate 270 minimizes the effect of the substrate 270 on the electric fields formed by the voltage pulses. In other words, when the substrate 270 is placed below the conducting rings 260, material properties of the substrate 270, such as the dielectric constant, do not have a significant effect on the ejection performance of the device 200. For this reason, the substrate 270 can include a large variety of materials, including paper or metal. Due to this flexibility in substrate materials, printing in the present invention can be extended to areas, such as high precision etching of printing plates or circuit boards.
Unlike the substrate, dielectric effects from the well plate 210 can be significant to the formation of the electric fields. By extending the length of the conducting nozzle 250, the dielectric effects of the well plate 210 can be reduced. In a preferred embodiment, the conducting nozzle 250 has a length in the millimeter scale.
A cross-section of an example removable well module 300 is shown in
In certain embodiments, a nozzle structure at the tip can be used to mechanically pre-form the Taylor cone before any voltage pulse is applied. The structure can include a glass, plastic, or metal thin filament, such as a wire.
In an embodiment, the valve 350 between the reservoir 310 and the nozzle 320 can be open or closed to allow or prevent, respectively, fluid from flowing from the reservoir 310 to the nozzle 320. When closed, the valve 350 allows the nozzle 320 to be cleaned or otherwise maintained without contaminating the conductive fluid stored in the reservoir 310. In addition, the valve 350 can be closed during filling. A venting valve 340 can also be provided at the top of the well module 300. When open, the venting valve 340 allows the fluid reservoir 310 to equalize with the ambient air pressure. The valve 350 and/or the venting valve 340 can be opened automatically when the well module 300 is inserted into the well plate. Conversely, the valve 350 and/or the venting valve 340 can be closed automatically upon removable of the well module 300 from the well plate.
As shown by
The device as shown in
It is important to note that a preferred embodiment of the fluid ejector device includes a sensing circuit 530 connected to one or more of the conducting rings 410. Amplifiers and other electronic components can be included with the sensing circuit 530. The sensing circuit 530 is capable of sensing a presence of and charge on the ejected droplet. The presence and charge on the droplet is measured based on an induced electromagnetic signal, such as a electric current. The electromagnetic signal is induced by the droplet passing through the center of the conducting ring 410. The measured charge on the droplet passing through the conducting ring for a given conducting fluid can be related to the size of the droplet by calibrating the droplet charge with a recorded video image of the droplet in flight. Thus, the sensing circuit 530 is effectively capable of sensing a presence and approximate size of the ejected droplet.
The detection of the presence and size of the droplets can be merely informative for the operator of the fluid ejector device. In addition, the measured presence and approximate size of the droplet can also provide feedback to adjust properties of the voltage pulses, such as the magnitude and width of the pulses.
As one of ordinary skill in the art will appreciate, various changes, substitutions, and alterations could be made or otherwise implemented without departing from the principles of the present invention, e.g. the nozzle can include any electrically conductive material. Accordingly, the scope of the invention should be determined by the following claims and their legal equivalents.
