Integrated electrowetting nano-injector and aspirator

Abstract

A new simple transfection method using an integrated electrowetting nano-injector (INENI) with controlled dosage delivery and high transfection efficiency is disclosed. The volume of delivery can be controlled via voltage application to an inner and outer electrode integrated into a nano-pipette. With higher voltages, more liquid enters the INENI and with lower voltages liquid is expelled. This method can be used to deliver plasmid DNA directly into the nuclei of cells. The INENI requires only the use of a single probe since both electrodes are integrated into the same nano-pipette. Hence, more space is available, and ergo the INENI offers a simplistic means for direct injection of metered amounts of exogenous material into the confines of a cell cytoplasm and/or nucleus while retaining full cell viability.

Claims

1. A system configured to use an integrated electrowetting to stimulate an injection or an aspiration of a biomaterial, wherein the biomaterial is an aqueous solution comprising an organic phase and an aqueous phase, the system comprising a single probe which comprises: (a) a nano-pipette having an aperture with dimensions in the nanoscale region, wherein an organic phase is disposed in the nano-pipette; (b) an outer electrode coupled to and directly attached on an outer surface of the nano-pipette; (c) an inner electrode disposed in the organic phase within the nano-pipet, wherein a potential difference is applied between the outer electrode and the inner electrode to electrically change a wetting angle at an interface between the organic phase and the aqueous solution, said change effectively stimulating the movement of the aqueous solution, wherein when the potential difference exceeds a threshold voltage, the aqueous solution is extracted and drawn into the nano-pipette, and wherein When the potential difference is lower than the threshold voltage, the aqueous solution is injected and drawn out of the nano-pipette.

2. The system of claim 1, wherein a source meter is disposed between the inner and outer electrodes for controlling the potential difference between said electrodes.

3. The system of claim 1, wherein a volume of the aqueous solution has a range of 1 femto-liter to tens of femto-liters.

4. The system of claim 3, wherein the volume of the aqueous solution extracted or injected is dependent on a magnitude of the potential difference applied.

5. The system of claim 1, wherein the aqueous solutionis extracted from or injected into a nucleus or a cytoplasm of a living cell.

6. The system of claim 5, wherein the aqueous solution is a DNA vector extracted from or injected into the nucleus of the living cell.

7. The system of claim 6, wherein the DNA vector is extracted from or injected into a cytoplasm of the living cell.

8. The system of claim 1, wherein the inner electrode is a wire composed of silver chloride with a dimension in the order of 0.2 mm.

9. The system of claim 1, wherein the outer electrode comprises an iridium/ platinum layer for coating an outer surface of the nano-pipette.

10. The system of claim 1, wherein the potential difference is a positive bias applied from the source meter between the outer electrode and the inner electrode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features and advantages of the present invention will become apparent from a consideration of the following detailed description presented in connection with the accompanying drawings in which:

(2) FIG. 1A shows a scanning electron microscopy image of the integrated electrowetting nano-injector and aspirator (INENI) of the present invention.

(3) FIG. 1B shows a diagrammatic representation of the INENI for pick up, where voltages higher than 0.5V produce an upward movement of the aqueous solution.

(4) FIG. 1C shows a diagrammatic representation of the INENI for ejection, where voltages lower than 0.5V induce an ejection of the aqueous solution.

(5) FIG. 1D shows a diagrammatic representation of a cellular injection used in a prior art.

(6) FIG. 2A shows a diagrammatic representation of governing forces in the INENI.

(7) FIG. 2B shows an image of PBS/1,2-DCE meniscus for different applied voltages.

(8) FIG. 2C shows a comparison of theoretically predicted ejected volumes with experimental data.

(9) FIG. 3A shows the injection of tetramethylrhodamine isothiocyanate-dextran (TRITC) into the cytoplasm of a cell. The image on the left shows an optical image of the cell. The image on the right shows the fluorescent image of the cell.

(10) FIG. 3B shows the injection of TRITC into the nucleus of a cell. The image on the left shows an optical image of the cell. The image on the right shows the fluorescent image of the cell.

(11) FIG. 4 shows the injection of DNA tagged Fluorescein amidite (FAM) into two representative fat body cells.

(12) FIG. 5A shows a bright field image of a cell at a lower (10) magnification (left image) and a cell fluorescence image using a Fluorescein Isothiocyanate (FITC) filter (right image).

(13) FIG. 5B shows a bright field image, of the same cell shown in FIG. 5A, under 40 magnification (left image) and a cell fluorescence image using an FITC filter under 40 magnification (right image).

(14) FIG. 5C shows a bright field image of the cell at 10 magnification (left image), the cell using an FITC filter at 10 magnification (middle image), and the cell using an FITC filter at 40 magnification.

(15) FIG. 5D shows a bright field image of a daughter cell expressing green fluorescent protein (GFP) 48 hours after transfection (left image) and the same cell using an FITC filter (right image).

DETAILED DESCRIPTION OF THE INVENTION

(16) Referring now to FIGS. 1A-5D the present invention features a method of using electrowetting to stimulate an injection or an aspiration of a biomaterial out of or into a nano-pipette (102) having an aperture with dimensions in the nanoscale region. In some embodiments, the biomaterial is an aqueous solution (104) comprising an organic phase and an aqueous phase, where execution of said electrowetting comprises changing a wetting angle at an interface between the organic phase and the aqueous solution. In further embodiments, an outer electrode (106) is coupled to an outer surface of the nano-pipette (102), which has the aqueous solution (104) disposed therein. Further, an inner electrode (108) may be disposed in the aqueous solution (104) within the nano-pipette (102). In an embodiment, the inner electrode (108) is a wire composed of silver chloride. In another embodiment, the outer electrode (106) is an iridium platinum layer coating the outer surface of the nano-pipette (102).

(17) Consistent with previous embodiments, a potential difference applied between the outer electrode (106) and the inner electrode (108) electrically changes the wetting angle between the organic phase and the aqueous solution. In one embodiment, a source meter (110) is disposed between the inner (108) and outer (106) electrodes for controlling the potential difference between said electrodes. The potential difference is a positive bias applied from the source meter (110) between the outer electrode (106) and the inner electrode (108).

(18) The change in the wetting angle effectively stimulates the movement of the aqueous solution (104). Specifically, when the potential difference exceeds a threshold voltage the aqueous solution (104) is extracted and drawn into the nano-pipette (102), whereas when the potential difference is lower than the threshold voltage the aqueous solution (104) is injected and drawn out of the nano-pipette (102). Further, the volume of the aqueous solution (104) extracted or injected is dependent on the magnitude of the potential difference applied. In some embodiments, the volume of the aqueous solution (104) has a range of 1 femto-liter to tens of femto-liters.

(19) In exemplary embodiments, the aqueous solution (104) is a DNA vector extracted from or injected into the nucleus or cytoplasm of a living cell.

(20) Details of the Integrated Electrowetting Nano-Injector

(21) In the present invention, a new simple transfection method using an integrated electrowetting nano-injector (INENI) with controlled dosage delivery and high transfection efficiency is disclosed. INENIs were fabricated by coating a layer of iridium/platinum (Ir/Pt) on the outside of a drawn capillary and inserting a silver chloride (AgCl) electrode inside the drawn pipette containing 1,2-dichloroethane (1,2-DCE). The INENIs were calibrated for a femtoliter volume of solution with respect to applied voltages. This calibration data was compared to the proposed theory of the present invention. Following calibration, the INENIs were used to deliver femtoliter volumes of macromolecules such as plasmids inside single cells. Lastly, the transfection efficiency of plasmid injection was verified.

(22) Results

(23) The capillaries were drawn and coated with a 30 nm layer of Ir/Pt. The INENI openings were roughly 139 nm3.5 nm compared to commercial microinjection tips (0.5-5 m) (FIGS. 1A-1C). With positive bias applied on the outer Ir/Pt coating layer and a silver wire electrode inside 1,2-DCE, small volumes can be injected or picked-up from a single cell depending on the magnitude of the voltages applied. To experimentally quantify the fluid volume uptake with respect to applied potential difference, different voltages were applied and the corresponding increase in fluid height within the INENIs were measured using a known distance as a reference with ImageJ software. The radius corresponding to the height of the fluid was calculated based on the angle of the cone. The cone angle from scanning electron microscope (SEM) images was measured to be 4.3 degrees and the average radius was 70.2 nm. Higher applied voltages were related to increased fluid uptake as noted in FIGS. 2A-2C.

(24) With sufficiently high voltage, a force is generated to move the aqueous solution inside the INENI. There is a force due to surface tension acting on the organic phase, which is constant. This force is dependent on the wetting angle of the organic phase with glass, and the surface tension between the vapor/organic phase. The weight of the organic phase and the aqueous solution are the two other forces (FIG. 2A) that must be considered for the INENI force balance equation (used to balance forces acting on the liquid column inside the INENI). While the weight of organic phase is constant, the weight of aqueous solution will depend on how much liquid remains inside the INENI. Lastly, there is a force due to surface tension acting on the aqueous solution. A double layer forms between the two immiscible solutions of 1,2-DCE and electrolyte. In this study, the capacitor for the double layer was considered constant and the capacitor at the point of zero charge was used in the force balance equation.

(25) The theory (solid line in the graph in FIG. 2C) matches closely with the experimental data (square markers in FIG. 2C) where voltages exceeding 0.5 V result in increased solution uptake in the INENI and voltages less than 0.5 V result in solution being expelled from the INENI. One advantages of the INENI is the ability to accurately control the dosage delivery via applied voltages.

(26) The INENIs were used to inject 50-70 femto-liters of tetramethylrhodamine isothiocyanate-dextran into the cytoplasm as well as the nuclei of mouse NIH 3t3 cells. Dextran molecules are hydrophilic polysaccharides that are conjugated to a dye so that the dye does not escape the membrane of nucleus or cell. The INENI was inside the cell for 10 seconds during injection. After injection, cells were imaged using a fluorescence microscope with Tetramethyl Rhodamine IsoThiocyanate (TRITC) filter (FIGS. 3A-3B). The INENI was used to preferentially inject this macromolecule dye inside the nucleus or the cytoplasm. By placing the INENI on the targeted region (nucleus or cytoplasm), the technique can be used to elicit spatial localization at the point of injection. The dye solution was collected from a separate container and was injected into each cell. The large molecular weight of dextran allowed dye molecules to stay localized and not escape the cell membrane or the nuclear membrane.

(27) Cell viability experiments were not performed after injection of this dye. The injection of the dye into nucleus or cytoplasm was solely performed to prove that this technique can be used to inject and localize molecules in different compartments of a cell. It is not known whether the dextran conjugated dye at the concentration used had long term toxic effects on cells.

(28) Additionally, the technique was used to inject 10 M DNA tagged Fluorescein amidite (FAM) into several fat body cells, cell number 1 and cell number 2 are shown in FIG. 4. Since DNA is negatively charged, with no injection, DNA tagged FAM did not get into cells.

(29) FIGS. 5A-5D shows the capability of INENIs in single cell studies, an estimated 1,800 molecules of 3.5 kb plasmid were injected with an INENI inside NIH 3T3 cells and 48 hours after injection cells expressed green fluorescent protein (GFP).

(30) Published works on microinjection indicate that 1,000 molecules of injected plasmid resulted in a faint fluorescent signal, whereas 100,000 molecules resulted in bright fluorescence. Below 1,000 molecules, cells were rarely transfected using microinjection. The same INENI could be used for injection of up to six cells. To have a high throughput within the hour, collection and ejection of plasmid happened inside the chamber where cells resided. Plasmid was combined with Dulbecco's Modified Eagle Medium (DMEM) solutions inside a small polydimethylsiloxane (PDMS) chamber and INENIs were not withdrawn from the aqueous solution each time for pick up. PDMS chambers were designed to minimize the amount of plasmid needed for injection. To maintain cell viability, cells were kept outside of the incubator for no more than one hour. The transfection efficiency of the technique was evaluated to be close to 100%. In a series of two experiments, twelve cells were injected with plasmid and, after 48 hours, 13 cells were fluorescing indicating GFP expression not only in the injected cells, but also in daughter cells (FIG. 5D). Within an hour, up to 15 cells could be injected. A negative control was performed, where cells residing in the chamber were exposed for one hour to the same concentration of plasmid without any injection. No GFP expression was observed 48 hours after the experiment.

(31) Higher throughput can be achieved by automating the present system. By combining the INENI with vision system and registering the INENI and cells with respect to a reference coordinate in the image plane, the movement time of the injector from cell to cell can be reduced to one or two seconds. The transfection time from cell to cell is primarily limited by fluid ejection time (10 seconds) rather than movement of INENI from cell to cell.

(32) Methods

(33) Fabrication of INENIs.

(34) INENIs were fabricated from borosilicate glass capillaries (Sutter Instrument, Novato, Calif.) using a P-97 puller (Sutter Instrument, Novato, Calif.).

(35) INENIs were sputter coated with a 10 nm layer of iridium followed by a 20 nm layer of platinum on one side. The nano-injectors were oxygen plasma treated at a power of 100 watts for 6 minutes before the experiment. Nano-injectors were filled with a solution of 1,2-DCE containing 10 millimeters of tetrahexyl ammonium bromide. A silver wire coated with AgCl was then inserted into the barrel of the nano-injector.

(36) Injection Set Up.

(37) The injection set-up comprised X, Y, and Z translational micrometer stages for coarse movement (Newport, M-433 for Z movement and M-TSX-1D for X and Y movements) and a nanocube piezo actuator (Physik Instrument, P-280) for finer axial motions of the INENI. These stages were placed on an IX71 Olympus microscope via adaptors that were 3D printed. For current measurement and voltage application, a 2116 Keithly Sourcemeter was employed. For pulsing purposes, an Agilent function generator was used (Model number 33220A), and fluorescent image acquisition employed a SBIG camera (Model number ST-7xMEI). The system was operated using custom coded software written in Labview (National Instruments). The volume of liquid entry was measured via the height of the aqueous solution using ImageJ software and a transmission electron microscopy (TEM) reference grid.

(38) Cell Culture.

(39) NIH3T3 mouse fibroblasts were cultured with high glucose DMEM media supplemented with 10% fetal bovine serum (ThermoFisher Scientific). All cells were cultured in 5% CO.sub.2 at 37 C. and washed with 1 phosphate buffered saline (PBS). PDMS chambers were made by a 10:1 w/w base prepolymer curing agent formulation. PDMS was cut into small pieces and square holes of 1 mm by 1 mm by 1 mm were created in each PDMS chamber. PDMS chambers were cleaned with 70% ethanol, dried and placed on top of sterile petri dishes (Sigma Aldrich). A gridded petri dish (polymer coated, Ibidi, Germany) was used for tracking cells. Cells at 60-70% confluency were used in experiments.

(40) Wild type Fruit flies were purchased and were dissected to isolate fat body cells. Adipocyte tissues were attached to coverslips that were coated overnight with Poly-L-lysine (Sigma-Aldrich). Cells were used immediately after dissection.

(41) Dye Preparation.

(42) Tetramethylrhodamine isothiocyanate-dextran was acquired. The final concentration of the dye injected was 8-10 mg/m L.

(43) DNA tagged fluorescein acquired and diluted to 10 M in Schneider's drosophila medium. After the injection, DNA tagged FAM was removed and the cells were washed 3 times with PBS and were imaged with the fluorescent camera.

(44) Plasmid Preparation.

(45) PmaxGFP plasmid was acquired. The final concentration of plasmid was 0.12 g/L. The plasmid was diluted in DMEM and placed in a PDMS chamber for further experiments. After the experiment, cells were covered with 10% FBS, 90% DMEM, and 1% antibiotic-antimycotic.

(46) As used herein, the term about refers to plus or minus 10% of the referenced number.

(47) Various modifications of the invention, in addition to those described herein, will be apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims. Each reference cited in the present application is incorporated herein by reference in its entirety.

(48) Although there has been shown and described the preferred embodiment of the present invention, it will be readily apparent to those skilled in the art that modifications may be made thereto which do not exceed the scope of the appended claims. Therefore, the scope of the invention is only to be limited by the following claims. Reference numbers recited in the claims are exemplary and for ease of review by the patent office only, and are not limiting in any way. In some embodiments, the figures presented in this patent application are drawn to scale, including the angles, ratios of dimensions, etc. In some embodiments, the figures are representative only and the claims are not limited by the dimensions of the figures. In some embodiments, descriptions of the inventions described herein using the phrase comprising includes embodiments that could be described as consisting of, and as such the written description requirement for claiming one or more embodiments of the present invention using the phrase consisting of is met.

(49) The reference numbers recited in the below claims are solely for ease of examination of this patent application, and are exemplary, and are not intended in any way to limit the scope of the claims to the particular features having the corresponding reference numbers in the drawings.