US20190262778A1 - Fabrication of Microfilters and Nanofilters and Their Applications - Google Patents
Fabrication of Microfilters and Nanofilters and Their Applications Download PDFInfo
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- US20190262778A1 US20190262778A1 US16/265,305 US201916265305A US2019262778A1 US 20190262778 A1 US20190262778 A1 US 20190262778A1 US 201916265305 A US201916265305 A US 201916265305A US 2019262778 A1 US2019262778 A1 US 2019262778A1
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Classifications
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- B01D67/0034—Organic membrane manufacture by inducing porosity into non porous precursor membranes by elimination of segments of the precursor, e.g. nucleation-track membranes, lithography or laser methods by micromachining techniques, e.g. using masking and etching steps, photolithography
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- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
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- A61M1/34—Filtering material out of the blood by passing it through a membrane, i.e. hemofiltration or diafiltration
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- B01D71/62—Polycondensates having nitrogen-containing heterocyclic rings in the main chain
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- C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
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- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
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Definitions
- the present invention relates to U.S. Provisional Patent Application Ser. No. 61/330,819, filed May 3, 2010 and U.S. Provisional Patent Application Ser. No. 61/377,797, filed Aug. 27, 2010 the entire contents of which are incorporated herein by reference.
- the invention relates to method to fabricate high-aspect-ratio precision nanopores and nanopillars in photo sensitive polymer films over large area by optical interference lithography using ultra-violet radiation. Free standing nanopores in polymer films with aspect ratio over 30 have been demonstrated in films greater than 10 micron thick. Interference lithography provides the same periodic pattern over the large area and through the entire film thickness.
- the invention relates to method to fabricate precision micropores in polymer films by ultra-violet and x-ray lithography methods that provide (1) high volume manufacturing capability and (2) low cost production for a wide variety of polymers and film thicknesses.
- the invention also describes the use of the precision microfilters for medical applications, such as capture of circulating tumor cells in peripheral blood of cancer patients and primitive fetal nucleated red blood cells in peripheral blood of pregnant women.
- Other applications include collection of stromal cells, mesenchymal cells, endothelial cells, epithelial cells, stem cells, non-hematopoietic cells, and the like from a blood sample, and tumor or pathogenic cells from urine.
- the present invention provides methods and compositions for isolating and detecting rare cells from a biological sample containing other types of cells.
- the present invention includes a procedure that uses a microfabricated filters for filtering fluid samples, from which the enriched cells can be used in downstream processes, such as identification, characterization, growth in culture, or used in other ways.
- the final enriched target cells can be subjected to a variety of analyses and manipulations, such as staining, immunofluorescence, cell counting, PCR, fluorescence in-situ hybridization (FISH), immunohistochemistry, flow cytometry, immunocytochemistry, image analysis, enzymatic assays, gene expression profiling analysis, efficacy tests of therapeutics, culturing of enriched cells, and therapeutic use of enriched rare cells.
- analyses and manipulations such as staining, immunofluorescence, cell counting, PCR, fluorescence in-situ hybridization (FISH), immunohistochemistry, flow cytometry, immunocytochemistry, image analysis, enzymatic assays, gene expression profiling analysis, efficacy tests of therapeutics, culturing of enriched cells, and therapeutic use of enriched rare cells.
- FISH fluorescence in-situ hybridization
- gene expression profiling analysis efficacy tests of therapeutics, culturing of enriched cells, and therapeutic use of enriched rare cells.
- microfabrication methods described are also applicable to fabrication of any free standing patterned polymeric films.
- the invention describes the use of microfilters, using PerMXTM 3000 series, SUEX or other similar photoresist dry film materials, to enrich circulating tumor cells from whole blood or PBMCs.
- Optical interference lithography has been successfully applied to manufacture periodic structures. Although this technique offers the advantage of submicron resolution over large sample areas and through the entire resist thickness, most papers on this subject report aspect ratios below 2, which results in thin, fragile samples requiring structural support often provided by silicon frames.
- nanopore polymer filters produced by track etch have thickness ranging from 6 to 25 microns.
- the pores are located randomly and they often overlap resulting in large holes. Often, many layers of the filters have to be used at the same time to avoid losing the analyte to be captured.
- the track etch pores are also not straight. For some applications, it is not a desirable feature.
- filters with high pore density can also be obtained by aluminum anodizing.
- the thicknesses of these filters are typically 60 ⁇ m. They have wide distribution of pore sizes and are not bio-compatible.
- Each filter is a 1 ⁇ 1 cm square with pores occupying a 6 ⁇ 6 mm area.
- the optimal pore dimension proved to be 7-8 microns in diameter.
- Within the 6 ⁇ 6 mm area 40,000 pores are evenly distributed. There was virtually no clogging. [Martin Fleisher, Circulating Tumor Cells—A New Opportunity for Therapeutic Management of Cancer Patients, Clinical Laboratory News, November 2008, Vol. 34, No. 11, 10-12].
- a parylene microfilter can be fabricated by conventional technology consisting of the following steps: (i) deposition of parylene on substrate, (ii) deposit metal that serves as a mask material for RIE, (iii) spin coat photoresist, (iv) expose photoresist through optical mask by UV lithography, (v) develop photoresist, (vi) remove metal from developed areas, (vii) perform RIE to form holes in parylene, (viii) remove photoresist, (ix) remove metal from the entire area, (x) remove parylene microfilters from substrate. The details of the process may vary.
- X-rays can be used to pattern photoresists such as PMMA and SU-8 to make microfilters in those materials attached to a substrate.
- Parylene microfilters with precise pore dimensions have been applied to isolate circulating tumor cells (CTCs) in peripheral blood.
- CTCs circulating tumor cells
- the use of parylene microfilters with 8 ⁇ m diameter pores found CTCs in 92.9% of patient samples, as compared to only 45.6% of samples using immunomagnetic beads, in a clinical trial at Memorial Sloan-Kettering, which used both devices on blood samples taken from patients with metastatic prostate cancer [Zosia Chustecka, AACR 2009: Measuring Circulating Tumor Cells Is Clinically Useful, New Technique Promises to Be Faster, http://www.medscape.com/viewarticle/701687].
- the filtration process was rapid, taking only 90 seconds to process a 7.5 ml sample of blood.
- the invention describes methods to pattern and etch predetermined pore sizes, distributions and shapes in one or more layers of polymer films simultaneously using ultra-violet (UV) lithography or x-rays lithography.
- the process can also be automated, where one or more layers of the films are supplied in rolls. For each exposure, the films advance by the appropriate amount. During the exposure, the films are held securely in place. After the exposure, the film advances and process repeats. After exposure, the exposed films are developed to form the pores.
- UV ultra-violet
- microfabrication methods described are also applicable to fabrication of any free standing patterned polymeric films.
- Exemplary embodiments of the present invention describe applications and methodologies utilizing precision microfilters. There is a wide variety of applications for microfilters including medical purposes, water filtration, beer and wine filtration, pathogen detection, etc. Exemplary polymer materials that are suitable for microfiltration are PerMXTM 3000 series, SUEX, and SU-8.
- An exemplary embodiment of this invention describes using microfilters circulating tumor cells (CTCs) from peripheral blood in cancer patients.
- CTCs circulating tumor cells
- Another exemplary embodiment of this invention describes using microfilters made from one or more of a variety of polymer materials, applied to enrich primitive fetal nucleated red blood cells in peripheral blood of pregnant women,
- stromal cells mesenchymal cells, endothelial cells, epithelial cells, stem cells, non-hematopoietic cells, etc.
- Other applications include enriching stromal cells, mesenchymal cells, endothelial cells, epithelial cells, stem cells, non-hematopoietic cells, etc., from blood samples and tumor or pathogenic cells in urine.
- the present invention provides methods and compositions for isolating and detecting rare cells from a biological sample containing other matter and other types of cells.
- the present invention includes a step that uses microfabricated filters for filtering fluid samples and the enriched cells can be used in downstream processes, such as identification, characterization, growth in culture, or used in other ways.
- the final enriched target cells can be subjected to a variety of analyses and manipulations, such as staining, immunofluorescence, cell counting, PCR, fluorescence in-situ hybridization (FISH), immunohistochemistry, flow cytometry, immunocytochemistry, image analysis, enzymatic assays, gene expression profiling analysis, efficacy tests of therapeutics, culturing of enriched cells, and therapeutic use of enriched rare cells.
- analyses and manipulations such as staining, immunofluorescence, cell counting, PCR, fluorescence in-situ hybridization (FISH), immunohistochemistry, flow cytometry, immunocytochemistry, image analysis, enzymatic assays, gene expression profiling analysis, efficacy tests of therapeutics, culturing of enriched cells, and therapeutic use of enriched rare cells.
- FISH fluorescence in-situ hybridization
- gene expression profiling analysis efficacy tests of therapeutics, culturing of enriched cells, and therapeutic use of enriched rare cells.
- Another exemplary embodiment of the present invention provides methods and devices for removing CTCs from circulation using microfilters.
- An exemplary application of this embodiment is for therapy.
- Another aspect of the invention describes methods to pattern micropores and nanopores in thick polymer films using optical interference lithography.
- FIGS. 1A, 1B, 1C, 1D, and 1E show a side view of a negative resist dry film laminated to a removable substrate.
- FIG. 1B shows a side view of an exposure by UV lithography of a negative resist dry film laminated to a removable substrate.
- FIG. 1C shows a side view of the negative resist dry film on removable substrate during post bake.
- FIG. 1D shows a side view of the negative resist film after development while still attached to the substrate.
- FIG. 1E shows a side view of the microfilters after releasing from the substrate.
- FIGS. 2A, 2B, 2C, 2D, and 2E show a side view of a negative resist dry film laminated to copper foil.
- FIG. 2B shows a side view of the exposure of a negative resist dry film by UV lithography.
- FIG. 2C shows a side view of placing the exposed negative resist film laminated to copper foil for post bake.
- FIG. 2D shows the negative resist film after development while still attached to copper.
- FIG. 2E shows negative resist microfilters after removing copper foil.
- FIGS. 3A, 3B, 3C, 3D, 3E, and 3F show a side view of a negative resist dry film laminated to KAPTON and a thin foil.
- FIG. 3B shows a side view of the exposure of a negative resist dry films by UV lithography.
- FIG. 3C shows placing the exposed negative resist films on KAPTON for post bake.
- FIG. 3D shows the negative resist films after development while still attached to KAPTON.
- FIG. 3E shows negative resist microfilters after peeling off KAPTON.
- FIG. 3F shows the finished microfilter.
- FIGS. 4A, 4B, 4C, and 4D show a side view of a positive resist dry film laminated to a removable substrate.
- FIG. 4B shows a side view of an exposure by UV lithography of a positive resist dry film laminated to a removable substrate.
- FIG. 4C shows a side view of the positive resist film after development while still attached to the substrate.
- FIG. 4D shows a side view of the microfilters after releasing from the substrate.
- FIGS. 5A and 5B show the negative resist film mounted on rolls and located beneath an exposure mask and above a support. After exposure, the film is advanced.
- FIG. 5B shows that each UV exposure will expose of the film.
- FIGS. 6A, 6B, 6C, and 6D show the top view of an array of round pores spaced equal distance from each other.
- FIG. 6B shows the top view of round pores arranged in a different array format.
- FIG. 6C shows the top view of pores with shape other than round. The pores can be arranged in groups.
- FIG. 6D shows a microfilter with more than one pore dimension.
- FIGS. 7A, 7B, 7C, and 7D show the side view of a pore where the thickness of the film is approximately the size of the pore.
- FIG. 7B shows the side view of a pore where the film thickness is larger than the pore diameter.
- FIG. 7C shows the side view of the microfilter film where the pores can have more than one dimension.
- FIG. 7D shows that the pores can have an opening on one surface that is larger than the opening on the other surface.
- FIGS. 8A, 8B, 8C, and 8D show a side view of the exposure by x-ray lithography of a stack of negative resist films.
- FIG. 8B shows the placing of the exposed negative resist films on a post bake substrate.
- FIG. 8C shows the negative resist films after development while still attached to the post bake substrate.
- FIG. 8D shows the negative resist films or microfilters after releasing from the post bake substrate.
- FIGS. 9A, 9B, 9C, and 9D show a side view of the exposure by x-ray lithography of a stack of negative resist films, each of which is laminated to a removable post bake substrate, where the substrate material is sufficiently transparent to x-rays.
- FIG. 9B shows the negative resist films on removable post bake substrate during post bake.
- FIG. 9C shows the negative resist films after development while still attached to the post bake substrate.
- FIG. 9D shows negative resist films or microfilters after release from the post bake substrate.
- FIGS. 10A and 10B show a side view of the negative resist mounted on rolls. Several rolls of film can be mounted at the same time. After exposure, the film is advanced. FIG. 10B shows that each x-ray exposure will expose all layers of the film.
- FIG. 11 shows that the films are pressed at the edges of the mask during x-ray exposure to prevent motion.
- FIGS. 12A and 12B show a side view of a stack of negative resist films laminated to a removable post bake substrate before application of electrostatic chuck to hold the negative resist films in place.
- FIG. 12B show side view of the exposure of a stack of negative resist films during x-ray exposure when the electrostatic chuck is used to hold the films in place.
- FIGS. 13A, 13B, and 13C show a side view of the exposure of a stack of positive resist films by x-ray lithography.
- FIG. 13B shows the positive resist films separated before entering development.
- FIG. 13C shows positive resist films or microfilters after development.
- FIGS. 14A and 14B show the positive resist films mounted on rolls. Several rolls of film can be mounted at the same time. After exposure, the film is advanced. FIG. 14B shows that each x-ray exposure will expose all layers of the film.
- FIG. 15 shows that the films are pressed around the border of the positive resist films during x-ray exposure to prevent motion.
- FIGS. 16A and 16B show side view of a stack of positive resist films before application of electrostatic chuck to fix the positive resist films.
- FIG. 16B show side view of exposure of a stack of positive resist films during x-ray exposure when the electrostatic chuck is used to fix the films.
- FIG. 17 shows a thin microfilter attached to a more sturdy support.
- FIGS. 18A, 18B, 18C, 18D, 18E, 18F, 18G, 18H, 18I, 18J, 18K, and 18L describe the steps to fabricate micropores using dry film in two layers.
- FIGS. 18A, 18B, 18C, 18D , and 18 E describe the steps to fabricate strips of trenches on the first layer.
- the fabrication steps for FIGS. 18A, 18B, 18C, and 18D are the same as FIGS. 2A, 2B, 2C , and 2 D.
- FIG. 18D shows the cross-sectional side view after development for the first layer from one direction
- FIG. 18E shows the cross-sectional side-view rotated by 90°.
- FIG. 18F, 18G, 18H, 18I, 18J, 18K, and 18L describe the steps to fabricate strips of trenches on the second layer.
- FIG. 18F describes lamination of a second negative resist dry film on the developed first layer of negative resist dry film.
- the fabrication steps for 18 G, 18 H, 18 I, and 18 J are the same as steps 18 B, 18 C, 18 D, and 18 E.
- FIG. 18I shows the cross-sectional side view of the two layers after development from one direction and FIG. 18J show the cross-sectional side-view rotated by 90°.
- FIG. 18K shows the cross-sectional side view of the two layers microfilter after removing substrate from one direction and FIG. 18L show the cross-sectional side-view rotated by 90°.
- FIGS. 19A, 19B, and 19C show the top view of the microfilter fabrication process.
- FIG. 19A shows the top view of the pattern of trenches in the dry film on copper after step shown in FIG. 18E .
- FIG. 19B shows the top view of trenches in the dry film on copper after step shown in FIG. 18J .
- the pattern are strips of trenches.
- the strips of trenches on one layer are perpendicular to strips of trenches on the other layer.
- the pore is at the intersection of the strips.
- FIG. 19C shows the top view of the free standing filter after removing copper substrate after step shown in FIG. 18K .
- FIGS. 20A, 20B, 20C, 20D, 20E, 20F, and 20G describe fabrication steps to fabricate micropores using dry film in three layers.
- FIG. 20A describe laminating a third negative photoresist dry film to the completed structure with already two negative photoresist dry film layers, i.e., following step FIG. 20G .
- the fabrication steps for FIGS. 20B, 20C, and 20D are the same as FIGS. 18B, 18C, and 18D .
- FIG. 20D shows the cross-sectional side view after development from one direction and FIG. 20E show the cross-sectional side-view rotated by 90°.
- FIG. 20F shows the cross-sectional side view of the final microfilter after removal of substrate from one direction and FIG. 20G show the cross-sectional side-view the rotated by 90°.
- FIG. 21 shows the top view of the microfilter after removal of copper.
- the pores on top and bottom are not aligned, but the pores are interconnected.
- FIG. 22 shows the method to expose the photoresist by interference lithography using liquid resist as a starting material.
- FIG. 23 shows the method to expose the photoresist by interference lithography using a premade dry resist film.
- FIG. 24 shows SEM of nanofilter showing the pores obtained at the front side.
- FIG. 25 is a cross-sectional SEM image of a processed resist showing pore depth to 2.7 micron.
- FIG. 26 shows pores on the back-side of the developed freestanding 9 micron SU 8 membrane (the cross section shows that the film is fully developed).
- the proposed precision microfilters can be made of variety of polymers, such as polycarbonates, polyesters, in particular polyethylene terephthalate (PET) (MylarTM), SU-8, KMPR, PerMXTM, SUEX, polymethylmethacrylate (PMMA), polymethylglutarimide (PMGI), etc.
- PET polyethylene terephthalate
- SU-8 polyethylene terephthalate
- KMPR KMPR
- PerMXTM polymethylmethacrylate
- PMGI polymethylglutarimide
- Negative resists refers to polymers that becomes polymerized when exposed to UV or x-rays
- positive resist refers to polymers in that the polymeric bonds are broken by UV or x-rays.
- negative resists are generally much more sensitive than positive resists.
- Examples of commercially available negative resists that are in liquid form are SU-8 and KMPR from MicroChem, but not limit to them.
- Commercially available negative resist dry films are PerMXTM series (DuPont), SUEX (DJ DevCorp), and others.
- PerMXTM 3000 series is manufactured in roll by DuPont.
- the commercially available thicknesses for PerMXTM are 10 ⁇ m, 14 ⁇ m, 25 ⁇ m, and 50 ⁇ m. Other thickness can also be obtained on custom order bases.
- Positive resist dry films are also commercially available, for example PMMA.
- Example 1.A Microfilter Fabrication Using Negative Resist Dry Films Laminated on Removable Substrate by UV Exposure
- the fabrication steps are:
- Example 1.B Microfilter Fabrication Using Negative Resist Dry Films Laminated on Copper Foil Substrate Using UV Exposure
- the fabrication steps are:
- Example 1.C Microfilter Fabrication Using Negative Resist Dry Films on Kapton Release Layer
- Example 1.D Microfilter Fabrication Using Liquid Negative Resist and Copper Release Layer
- the fabrication steps using copper as a release layer are:
- Coat substrate for example silicon wafer
- thin layer of copper
- Example 1.E Microfilter Fabrication Using Liquid Negative Resist and Positive Resist Release Layer
- a combination of use of negative resist and positive resist can also be used to obtain free standing microfilters.
- the steps are:
- Example 1.F Microfilter Fabrication Using Negative Resist Dry Films on Copper Release Layer on Silicon Wafer
- the fabrication steps using copper as a release layer are:
- Coat substrate for example silicon wafer
- thin layer of copper
- Laminate negative resist dry film on the positive resist c. Laminate negative resist dry film on the positive resist.
- Example 1.H Microfilter Fabrication Using Positive Resist Dry Film on the Positive Resist Release Layer
- Example 1.I Microfilter Fabrication Using Positive Resist Dry Film on Removable Substrate Such as Copper Foil
- Example 2.A Microfilter Fabrication Using a Roll of Negative Resist Dry Film
- the negative resist dry film such as PerMXTM 3000 series, is manufacture in roll form.
- the UV fabrication method described above can be used to fabricate circular uniform pores distributed as shown in FIGS. 6A, 6B or other distributions.
- the UV fabrication method can fabricate pores of different shape and grouping as shown in FIG. 6C , and other shapes.
- the UV fabrication methods can fabricate pores of different sizes as shown in FIG. 6D .
- FIGS. 7A and 7B The cross sectional view of the microfilters for various thicknesses, FIGS. 7A and 7B .
- FIG. 7C shows a cross section where the pores has different sizes 18 and 19 .
- Using negative resist it is also possible to fabricate pores that have a smaller pore opening on top 20 compared with the opening of the pore on the bottom 21 , in FIG. 7D . This can be accomplished by providing exposure dose that is higher than that is required to form uniform pore openings.
- X-ray lithography is typically performed on a beamline of a synchrotron. X-ray lithography can be used for both negative and positive resists/polymers.
- Example 3.A Using a Stack of Negative Resist Dry Films on Individual Wafers Using X-Ray Exposure
- FIG. 8 The concept of microfabricating a stack of microfilters simultaneously by x-ray lithography using negative resist is illustrated in FIG. 8 .
- the principle is very similar to that shown in FIG. 1 and described in Example 1.A. The steps of fabrication are described below.
- Example 3.B Using a Stack of Negative Resist Dry Films Laminated to a Post Bake Substrate on Individual Wafers
- FIG. 9 An alternative on the use of negative resist dry film is illustrated in FIG. 9 . This eliminates the labor required to perform step c of Example 1.B. The steps of fabrication are described below.
- Example 3.C Fabrication Microfilters in a Roll of Negative Resist Dry Film
- the negative resist dry film such as PerMXTM series
- PerMXTM series is manufactured in a roll form.
- To perform x-ray lithography of the resist in the role form as shown in FIG. 10 can simplify the fabrication. The method of implementation and steps of fabrication are described below.
- the film can be just one roll or as many rolls as appropriate for fabrication of precision pore dimensions.
- the films can be laminated with post bake substrate.
- the films can be further held fixed by additional clamp or fixture 260 around the x-ray mask, as shown in FIG. 11 .
- the stack is held secure by electrostatic force, as shown in FIG. 12 .
- Example 3.D Fabrication Microfilters in a Roll of Negative Resist Dry Film and Applying Electrostatic Chuck to Fix the Films
- FIG. 12 the concept of using electrostatic force to hold the films secure is shown, but the rollers are not shown.
- FIG. 12A the configuration of the system is shown between exposures.
- a stack of films 201 are stretched.
- the substrate structure consist of a support 292 , an insulator 267 and a conduction layer 266 .
- a clear conducting film 265 is placed on top of the film.
- Voltage 269 is set to zero and the circuit is open.
- FIG. 12B shows the configuration during exposure, where a voltage 169 is applied between the electrodes 265 and 266 . This allows the films to be tightly fixed between the electrodes to avoid motion.
- the x-ray mask is place adjacent to the electrode 265 and exposure is performed.
- Example 4.A Using a Stack of Positive Resist Sheets on Individual Wafers Using X-Ray Exposure
- FIG. 13 The concept of microfabricating a stack of microfilters simultaneously by x-ray lithography using positive resist is illustrated in FIG. 13 . The steps of fabrication are described below.
- Example 4.B Fabrication Microfilters from a Roll of Positive Resist Films
- polymers belong to the category of positive resist films. Examples are polycarbonates, polyesters such as polyethylene terephthalate (PET) (Mylar®), etc.
- PET polyethylene terephthalate
- Mylar® polyethylene terephthalate
- the film can be just one roll or as many rolls as appropriate for fabrication of precision pore dimensions.
- the films can be further held fixed by additional clamp or fixture 360 around the x-ray mask, as shown in FIG. 15 .
- the stack is held secure by electrostatic force, as shown in FIG. 16 .
- Example 4.D Fabrication Microfilters in a Roll of Positive Resist Film and Applying Electrostatic Chuck to Fix the Films
- Thin, smooth copper films are preferable as a substrate, because irregularities of the copper surface that is laminated to the negative resist dry films are transferred to the dry films after removal of copper.
- Thin copper films are preferred to minimize the amount of time required for its removal.
- Thin copper films are preferred because better contact between mask and resist film can be achieved.
- the method of fabrication to be described in this section can be performed by either UV or x-ray lithography.
- Example 5A Microfilter Fabrication Using Two Layers of Dry Films and Copper Release Layer
- FIGS. 18A-18L The fabrication steps are described in FIGS. 18A-18L . Steps shown in FIGS. 18A-18E are the same as same as steps shown in FIGS. 2A-2E . The only difference is the layout 194 of the optical mask 196 and the sample of the etched film.
- the optical mask 196 will consist of strips of metal lines 194 .
- the resultant first layer of the microfilter 125 will consists of trenches that exposes the copper substrate 180 as shown in FIG. 19A .
- Example 5B Microfilter Fabrication Using Three or More Layers of Dry Films and Copper Release Layer
- a dry film that is suitable for use for multi-layer microfilters is PerMX′. It is capable of bridging over features already formed on the surface.
- the concept using two or more layers of films to make filters can have many variations, such as
- interference lithography the image is formed by exposing resist to a standing wave formed by the interference of two coherent waves of equal amplitude.
- the optical system is well protected against vibration and air flow, and if the coherence length of a light source is long enough, we can easily generate sinusoidal intensity distribution over a large area, allowing nano-scale lines and dot arrays to be fabricated on a substrate without difficulty.
- the light was directed into a spatial filter consisting of focusing lens and a small micron sized pinhole.
- the distance between the spatial filter and the sample holder was around 1 m, and typical illumination times were 1 to 5 min.
- the area of the exposed sample is about 4 cm 2 .
- Position of the mirrors (60 ⁇ 60 ⁇ 5 mm guaranteed 120° symmetry of exposure.
- Negative-tone imaging also enhances the process latitude for patterning because the hole size can be tuned by exposure dose and various hole diameter can be obtained under the same angle of illumination.
- the typical resist thickness was ⁇ 10 ⁇ m; it is thick enough for easy handling and has relatively good mechanical stability. It is also possible to obtain a frame around nanopores for ease of use and additional mechanical stability of the fabricated membrane.
- the frame can be obtained by UV-exposure through the mask with the frame pattern.
- the invention is the sample preparation method enabling the high-aspect-ratio pore fabrication for both liquid negative photoresist, such as SU-8 and others, and negative dry films, such as PerMX, SUEX and others.
- Step d Front-side exposure of the resist through the optical mask with a frame pattern is performed using a mask aligner. This exposure is optional, and was performed for easy handling of a freestanding film.
- FIG. 24 shows SEM of nanofilter using SU-8 showing the pores from the front side.
- the front side is shown by 530 in FIG. 22 .
- FIG. 25 shows cross-sectional SEM image of a processed resist. Focused ion beam milling was used to cut the film at the 25° angle from normal. The geometry factor is 1.15; the pore depth is 2.7 ⁇ m. About half thickness of the film was developed. Freestanding film is developing from both sides, and a membrane with holes through the entire resist thickness has been obtained.
- FIG. 26 shows ores on the back-side of the developed freestanding 9 micron SU 8 membrane (the cross section shows that the film is fully developed).
- a grid support structure 129 can be implemented as shown in FIG. 17 .
- One modification is to coat the microfilters with a thin layer of parylene.
- One surface modification technique of polymer microfilters involves plasma treatment of polymers to activate the surface and graft self-assembled monolayers with a range of functionality including amine, carboxyl, hydroxyl, epoxy, aldehyde, and polyethylene glycol (PEG) groups by using silane chemistry with solution immersion or vapor deposition. For example, grafting PEG-triethoxysilane onto an oxidized polymer renders the surfaces hydrophilic in a controlled manner.
- thicker polymeric films can be used or support structure as shown in FIG. 17 .
- the support can also be provided separately by the filter holders.
- the invention also describes the uses of the precision microfilters. There are a wide variety of applications for microfilters from medical, water filtration, beer and wine filters, pathogen detection, etc.
- the present invention provides methods and compositions for isolating and detecting rare cells from a biological sample containing other types of cells.
- Fetal cells circulating in the peripheral blood of pregnant women are a potential target for noninvasive genetic analyses. They include epithelial (trophoblastic) cells, which are 14-60 ⁇ m in diameter, larger than peripheral blood leukocytes. Enrichment of circulating fetal cells followed by genetic diagnostic can be used for noninvasive prenatal diagnosis of genetic disorders using PCR analysis of a DNA target or fluorescence in situ hybridization (FISH) analysis of genes.
- FISH fluorescence in situ hybridization
- microfilters with orderly arranged pores can only be fabricated with solid parylene by RIE.
- microfilter consists of obtaining a blood sample from the patient, which can be in the range of 1-10 ml.
- the blood is flown through the microfilter.
- the microfilter can be hold in a filter holder with an inlet, an outlet, by securely holds the filter around the edges.
- This device can have built in support in the filter holder. It can have gasket above and below the filter.
- the blood is pushed through from the inlet. Most cells larger than the pore dimension are retained. Some white blood cells are deformable and can go through pores with smaller dimension than the cell size.
- the application of enriching circulating fetal cells and tumor cells are based on this principle.
- microfilter pores can be larger for cancer with large cancer cells and can be smaller for cancer with smaller cancer cells.
- Microfilters using 10-25 ⁇ m thick films can be fabricated by the method described in this invention. Thicker microfilters may provide more structural strength.
- PerMXTM 3000 series One polymer film that is well suited for microfiltration application.
- Some of the properties that make it suitable for microfiltration for diagnostic application are:
- PerMXTM 3000 series is currently used for permanent applications where it is images, cured and left on devices. It is used as an adhesive for microelectronics and packaging, bonding, bumping/pillar applications. (http://www2.dupont.com/WLP/en US/assets/downloads/pdf/PerMX3000_datasheet.pdf). According to an exemplary implementation of the present invention, PerMXTM 3000 series is utilized for microfilters as free standing film. Variations of these films can also be used without departing from the scope and spirit of exemplary embodiments of the present invention.
- the captured CTCs can be enumerated on the microfilters. They can be specifically identified by genomic DNA and fluorescently tagged antibodies for intracellular and surface markers.
- the captured CTCs can be subjected to a variety of analysis and manipulations, such as immunofluorescence, cell counting, PCR, fluorescence in-situ hybridization (FISH), immunohistochemistry, flow cytometry, immunocytochemistry, image analysis, enzymatic assays, gene expression profiling analysis, efficacy tests of therapeutics, culturing of enriched cells, and therapeutic use of enriched rare cells.
- analysis and manipulations such as immunofluorescence, cell counting, PCR, fluorescence in-situ hybridization (FISH), immunohistochemistry, flow cytometry, immunocytochemistry, image analysis, enzymatic assays, gene expression profiling analysis, efficacy tests of therapeutics, culturing of enriched cells, and therapeutic use of enriched rare cells.
- depleted plasma protein and white blood cells can be optionally recovered, and subjected to other analysis such as inflammation studies, gene expression profiling, etc.
- the microfilter can be coated with EpCAM antibody to further retain the CTCs.
- the captured CTCs can be cultured directly on the microfilters to increase the number of CTCs and to evaluate the characteristics of CTCs.
- One example of the rational for culturing the CTCs is to evaluate its expression of disease markers.
- a simple method to determine the disease marker expression is to coat the surface of channels of the microfilters with capture reagent for the disease marker and later for a fluorescent sandwich assay to specifically identify the disease marker if it is present.
- the captured CTCs can be analyzed for DNA, RNA, mRNA and microRNAs expressions for target of interest.
- the present invention provides methods and compositions for isolating and detecting rare cells from a biological sample containing other types of cells.
- the present invention includes a step that uses a microfabricated filter for filtering fluid samples and the enriched cells can be used in a downstream process such as identifies, characterizes or even grown in culture or used in other ways.
- Other applications include enriching stromal cells, mesenchymal cells, endothelial cells, epithelial cells, stem cells, non-hematopoietic cells, etc. from a blood sample and tumor cells in urine.
- the present invention provides method and microfilters to capture analytes bound to latex beads or antigen caused particle agglutination whereby the analyte/latex bead or agglutinated clusters are captured on the membrane surface.
- the present invention provides method and microfilters for erythrocyte deformability testing.
- Red blood cells are highly flexible cells that will readily change their shape to pass through pores. In some diseases, such as sickle cell anemia, diabetes, sepsis, and some cardiovascular conditions, the cells become rigid and can no longer pass through small pores. Healthy red cells are typically 7.5 ⁇ m and will easily pass through a 3 ⁇ m pore membrane, whereas a cell with one of these disease states will not.
- a 5 ⁇ m membrane is used as a screening barrier. A blood sample is applied and the membrane is placed under a constant vacuum. The filtration rate of the cells is then measured, and a decreased rate of filtration suggests decreased deformability.
- the present invention provides method and microfilters for leukocyte/Red blood cell separation.
- Blood cell populations enriched for leukocytes are often desired for use in research or therapy.
- Typical sources of leukocytes include whole peripheral blood, leukopheresis or apheresis product, or other less common sources, such as umbilical cord blood.
- the present invention provides method and microfilters for chemotaxis applications.
- Membranes are used in the study of white blood cell reactions to toxins, to determine the natural immunity in whole blood. Since immunity is transferable, this assay is used in the development of vaccines and drugs on white blood cells.
- the present invention provides method and microfilters for blood filtration/blood transfusion.
- Microfilters can be used to remove large emboli, platelet aggregates, and other debris.
- the present invention provides method and microfilters for capture of cells and the subsequent culture in the filter cartridge or backflushing.
- the arrays of precision micro-pores can be fabricated in rolls of polymer resists, it opens up applications that wafer sized microfilters are not able to satisfy. Examples are for water filtration, kidney dialysis, etc.
Abstract
Description
- This application is a continuation of U.S. patent application Ser. No. 13/345,538, filed on Jan. 6, 2012, which claims benefit under 35 U.S.C. § 119 from U.S. Provisional Application No. 61/430,818, filed on Jan. 7, 2011, the entire contents of which are incorporated herein by reference.
- The present invention relates to U.S. Provisional Patent Application Ser. No. 61/330,819, filed May 3, 2010 and U.S. Provisional Patent Application Ser. No. 61/377,797, filed Aug. 27, 2010 the entire contents of which are incorporated herein by reference.
- The invention relates to method to fabricate high-aspect-ratio precision nanopores and nanopillars in photo sensitive polymer films over large area by optical interference lithography using ultra-violet radiation. Free standing nanopores in polymer films with aspect ratio over 30 have been demonstrated in films greater than 10 micron thick. Interference lithography provides the same periodic pattern over the large area and through the entire film thickness.
- The invention relates to method to fabricate precision micropores in polymer films by ultra-violet and x-ray lithography methods that provide (1) high volume manufacturing capability and (2) low cost production for a wide variety of polymers and film thicknesses. The invention also describes the use of the precision microfilters for medical applications, such as capture of circulating tumor cells in peripheral blood of cancer patients and primitive fetal nucleated red blood cells in peripheral blood of pregnant women. Other applications include collection of stromal cells, mesenchymal cells, endothelial cells, epithelial cells, stem cells, non-hematopoietic cells, and the like from a blood sample, and tumor or pathogenic cells from urine.
- The present invention provides methods and compositions for isolating and detecting rare cells from a biological sample containing other types of cells. In particular, the present invention includes a procedure that uses a microfabricated filters for filtering fluid samples, from which the enriched cells can be used in downstream processes, such as identification, characterization, growth in culture, or used in other ways.
- The final enriched target cells can be subjected to a variety of analyses and manipulations, such as staining, immunofluorescence, cell counting, PCR, fluorescence in-situ hybridization (FISH), immunohistochemistry, flow cytometry, immunocytochemistry, image analysis, enzymatic assays, gene expression profiling analysis, efficacy tests of therapeutics, culturing of enriched cells, and therapeutic use of enriched rare cells. In addition, the depleted plasma protein and white blood cells can be optionally recovered and subjected to other analysis, such as inflammation studies, gene expression profiling, etc.
- The microfabrication methods described are also applicable to fabrication of any free standing patterned polymeric films.
- The invention describes the use of microfilters, using PerMX™ 3000 series, SUEX or other similar photoresist dry film materials, to enrich circulating tumor cells from whole blood or PBMCs.
- Optical interference lithography (IL) has been successfully applied to manufacture periodic structures. Although this technique offers the advantage of submicron resolution over large sample areas and through the entire resist thickness, most papers on this subject report aspect ratios below 2, which results in thin, fragile samples requiring structural support often provided by silicon frames.
- Commercial nanopore polymer filters produced by track etch have thickness ranging from 6 to 25 microns. The pores are located randomly and they often overlap resulting in large holes. Often, many layers of the filters have to be used at the same time to avoid losing the analyte to be captured. The track etch pores are also not straight. For some applications, it is not a desirable feature.
- Commercial filters with high pore density can also be obtained by aluminum anodizing. The thicknesses of these filters are typically 60 μm. They have wide distribution of pore sizes and are not bio-compatible.
- Use of microfilters to enrich circulating tumor cells was first published by Giovanna Vona et al. in 2000. [Giovanna Vona, Abdelmajid Sabile, Malek Louha, Veronique Sitruk, Serge Romana, Karin Schütze, Frédérique Capron, Dominique Franco, Mario Pazzagli, Michel Vekemans, Bernard Lacour, Christian Bréchot and Patrizia Paterlini-Bréchot. 2000. Isolation by Size of Epithelial Tumor Cells—A New Method for the Immunomorphological and Molecular Characterization of Circulating Tumor Cells, American Journal of Pathology. 2000; 156:57-63.] The authors used track etched filters, where the pore distribution is random and porosity is low.
- More recently, Richard Cote of the University of Miami demonstrated CTC recovery using microfilters fabricated by Yu-Chong Tai of California Institute of Technology. Tai's laboratory produced micro pores in parylene film by UV Lithography and reactive ion etching (RIE). [Siyang Zheng, Henry Lin, Jing-Quan Liu, Marija Balic, Ram Datar, Richard J. Cote, Yu-Chong Tai. 2007. Membrane microfilter device for selective capture, electrolysis and genomic analysis of human circulating tumor cells, J. Chromatography A. 1162, 154-161. Yu-Chong Tai, Siyang Zheng, Henry Lin, Ram Datar and Richard Cote, “Uses of Parylene Membrane filters, WO 2006/116327 A1, published on Nov. 2, 2006. Yu-Chong Tai, Siyang Zheng, Henry Lin, Ram Datar and Richard Cote, “Membrane Filter for Capturing Circulating Tumor Cells”, US Patent Application Publication, US 2006/0254972, Pub. Date: Nov. 16, 2006. Yu-Chong Tai, Siyang Zheng, Henry Lin, Ram Datar and Richard Cote, “Use of Parylene Membrane Filters”, US Patent Application Publication, US 2007/0025883 A1, Pub. Date: Feb. 1, 2007. Siyang Zheng, Richard Cote, Henry Lin, Bo Lu and Yu-Chong Tai, “Method and Apparatus for Microfiltration to Perform Cell Separation”, US Patent Application Publication, US 2009/0188864 A1, Pub. Date: Jul. 30, 2009.] Each filter is a 1×1 cm square with pores occupying a 6×6 mm area. The optimal pore dimension proved to be 7-8 microns in diameter. Within the 6×6 mm area, 40,000 pores are evenly distributed. There was virtually no clogging. [Martin Fleisher, Circulating Tumor Cells—A New Opportunity for Therapeutic Management of Cancer Patients, Clinical Laboratory News, November 2008, Vol. 34, No. 11, 10-12].
- The UV lithography/Reactive ion etching (RIE) fabrication process used by Tai is fairly standard, but requires many steps and manual efforts and time.
- A parylene microfilter, can be fabricated by conventional technology consisting of the following steps: (i) deposition of parylene on substrate, (ii) deposit metal that serves as a mask material for RIE, (iii) spin coat photoresist, (iv) expose photoresist through optical mask by UV lithography, (v) develop photoresist, (vi) remove metal from developed areas, (vii) perform RIE to form holes in parylene, (viii) remove photoresist, (ix) remove metal from the entire area, (x) remove parylene microfilters from substrate. The details of the process may vary.
- X-rays can be used to pattern photoresists such as PMMA and SU-8 to make microfilters in those materials attached to a substrate.
- X-rays have also been used successfully to etch mylar glued to a substrate. [Deis G A, Gavryushkina N I, Prokopenko V S, Artamonova L D, Gentcelev A N, Skrinsky A N, Sinyukov M P, Kulipanov G N, Pindyurin V P, Li C B, Mezentseva L A, Redin O A, Makarov O A, Gashtold V N (1995) Microporous membrane and method of it fabrication, Russian Federation Patent 2047334; Kulipanov G N, Makarov O A, Mezentseva L A, Mishnev S I, Naz'mov V P, Pindyurin V P, Redin O A, Skrinsky A N, Artamonova L D, Cherkov G A, Deis G A, Gashtold V N, Prokopenko V S, Chesnokov V V, Reznikova E F (1995) Fabrication and preliminary testing of regular microporous membranes manufactured by deep X-ray lithography at the VEPP-3 storage ring. Nuclear Instruments and Methods in Physics Research A 359: 404-408.]
- Parylene microfilters with precise pore dimensions have been applied to isolate circulating tumor cells (CTCs) in peripheral blood. The use of parylene microfilters with 8 μm diameter pores found CTCs in 92.9% of patient samples, as compared to only 45.6% of samples using immunomagnetic beads, in a clinical trial at Memorial Sloan-Kettering, which used both devices on blood samples taken from patients with metastatic prostate cancer [Zosia Chustecka, AACR 2009: Measuring Circulating Tumor Cells Is Clinically Useful, New Technique Promises to Be Faster, http://www.medscape.com/viewarticle/701687]. The filtration process was rapid, taking only 90 seconds to process a 7.5 ml sample of blood.
- The invention describes methods to pattern and etch predetermined pore sizes, distributions and shapes in one or more layers of polymer films simultaneously using ultra-violet (UV) lithography or x-rays lithography. The process can also be automated, where one or more layers of the films are supplied in rolls. For each exposure, the films advance by the appropriate amount. During the exposure, the films are held securely in place. After the exposure, the film advances and process repeats. After exposure, the exposed films are developed to form the pores.
- The microfabrication methods described are also applicable to fabrication of any free standing patterned polymeric films.
- Exemplary embodiments of the present invention describe applications and methodologies utilizing precision microfilters. There is a wide variety of applications for microfilters including medical purposes, water filtration, beer and wine filtration, pathogen detection, etc. Exemplary polymer materials that are suitable for microfiltration are
PerMX™ 3000 series, SUEX, and SU-8. - An exemplary embodiment of this invention describes using microfilters circulating tumor cells (CTCs) from peripheral blood in cancer patients.
- Another exemplary embodiment of this invention describes using microfilters made from one or more of a variety of polymer materials, applied to enrich primitive fetal nucleated red blood cells in peripheral blood of pregnant women,
- Other applications include enriching stromal cells, mesenchymal cells, endothelial cells, epithelial cells, stem cells, non-hematopoietic cells, etc., from blood samples and tumor or pathogenic cells in urine.
- The present invention provides methods and compositions for isolating and detecting rare cells from a biological sample containing other matter and other types of cells. In particular, the present invention includes a step that uses microfabricated filters for filtering fluid samples and the enriched cells can be used in downstream processes, such as identification, characterization, growth in culture, or used in other ways.
- The final enriched target cells can be subjected to a variety of analyses and manipulations, such as staining, immunofluorescence, cell counting, PCR, fluorescence in-situ hybridization (FISH), immunohistochemistry, flow cytometry, immunocytochemistry, image analysis, enzymatic assays, gene expression profiling analysis, efficacy tests of therapeutics, culturing of enriched cells, and therapeutic use of enriched rare cells. In addition, the depleted plasma protein and white blood cells can be optionally recovered and subjected to other analysis, such as inflammation studies, gene expression profiling, etc.
- Another exemplary embodiment of the present invention provides methods and devices for removing CTCs from circulation using microfilters. An exemplary application of this embodiment is for therapy.
- Another aspect of the invention describes methods to pattern micropores and nanopores in thick polymer films using optical interference lithography.
- A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
-
FIGS. 1A, 1B, 1C, 1D, and 1E .FIG. 1A shows a side view of a negative resist dry film laminated to a removable substrate.FIG. 1B shows a side view of an exposure by UV lithography of a negative resist dry film laminated to a removable substrate.FIG. 1C shows a side view of the negative resist dry film on removable substrate during post bake.FIG. 1D shows a side view of the negative resist film after development while still attached to the substrate.FIG. 1E shows a side view of the microfilters after releasing from the substrate. -
FIGS. 2A, 2B, 2C, 2D, and 2E .FIG. 2A shows a side view of a negative resist dry film laminated to copper foil.FIG. 2B shows a side view of the exposure of a negative resist dry film by UV lithography.FIG. 2C shows a side view of placing the exposed negative resist film laminated to copper foil for post bake.FIG. 2D shows the negative resist film after development while still attached to copper.FIG. 2E shows negative resist microfilters after removing copper foil. -
FIGS. 3A, 3B, 3C, 3D, 3E, and 3F .FIG. 3A shows a side view of a negative resist dry film laminated to KAPTON and a thin foil.FIG. 3B shows a side view of the exposure of a negative resist dry films by UV lithography.FIG. 3C shows placing the exposed negative resist films on KAPTON for post bake.FIG. 3D shows the negative resist films after development while still attached to KAPTON.FIG. 3E shows negative resist microfilters after peeling off KAPTON.FIG. 3F shows the finished microfilter. -
FIGS. 4A, 4B, 4C, and 4D .FIG. 4A shows a side view of a positive resist dry film laminated to a removable substrate.FIG. 4B shows a side view of an exposure by UV lithography of a positive resist dry film laminated to a removable substrate.FIG. 4C shows a side view of the positive resist film after development while still attached to the substrate.FIG. 4D shows a side view of the microfilters after releasing from the substrate. -
FIGS. 5A and 5B .FIG. 5A shows the negative resist film mounted on rolls and located beneath an exposure mask and above a support. After exposure, the film is advanced.FIG. 5B shows that each UV exposure will expose of the film. -
FIGS. 6A, 6B, 6C, and 6D .FIG. 6A shows the top view of an array of round pores spaced equal distance from each other.FIG. 6B shows the top view of round pores arranged in a different array format.FIG. 6C shows the top view of pores with shape other than round. The pores can be arranged in groups.FIG. 6D shows a microfilter with more than one pore dimension. -
FIGS. 7A, 7B, 7C, and 7D .FIG. 7A shows the side view of a pore where the thickness of the film is approximately the size of the pore.FIG. 7B shows the side view of a pore where the film thickness is larger than the pore diameter.FIG. 7C shows the side view of the microfilter film where the pores can have more than one dimension.FIG. 7D shows that the pores can have an opening on one surface that is larger than the opening on the other surface. -
FIGS. 8A, 8B, 8C, and 8D .FIG. 8A shows a side view of the exposure by x-ray lithography of a stack of negative resist films.FIG. 8B shows the placing of the exposed negative resist films on a post bake substrate.FIG. 8C shows the negative resist films after development while still attached to the post bake substrate.FIG. 8D shows the negative resist films or microfilters after releasing from the post bake substrate. -
FIGS. 9A, 9B, 9C, and 9D .FIG. 9A shows a side view of the exposure by x-ray lithography of a stack of negative resist films, each of which is laminated to a removable post bake substrate, where the substrate material is sufficiently transparent to x-rays.FIG. 9B shows the negative resist films on removable post bake substrate during post bake.FIG. 9C shows the negative resist films after development while still attached to the post bake substrate.FIG. 9D shows negative resist films or microfilters after release from the post bake substrate. -
FIGS. 10A and 10B .FIG. 10A shows a side view of the negative resist mounted on rolls. Several rolls of film can be mounted at the same time. After exposure, the film is advanced.FIG. 10B shows that each x-ray exposure will expose all layers of the film. -
FIG. 11 shows that the films are pressed at the edges of the mask during x-ray exposure to prevent motion. -
FIGS. 12A and 12B .FIG. 12A shows a side view of a stack of negative resist films laminated to a removable post bake substrate before application of electrostatic chuck to hold the negative resist films in place.FIG. 12B show side view of the exposure of a stack of negative resist films during x-ray exposure when the electrostatic chuck is used to hold the films in place. -
FIGS. 13A, 13B, and 13C .FIG. 13A shows a side view of the exposure of a stack of positive resist films by x-ray lithography.FIG. 13B shows the positive resist films separated before entering development.FIG. 13C shows positive resist films or microfilters after development. -
FIGS. 14A and 14B .FIG. 14A shows the positive resist films mounted on rolls. Several rolls of film can be mounted at the same time. After exposure, the film is advanced.FIG. 14B shows that each x-ray exposure will expose all layers of the film. -
FIG. 15 shows that the films are pressed around the border of the positive resist films during x-ray exposure to prevent motion. -
FIGS. 16A and 16B .FIG. 16A shows side view of a stack of positive resist films before application of electrostatic chuck to fix the positive resist films.FIG. 16B show side view of exposure of a stack of positive resist films during x-ray exposure when the electrostatic chuck is used to fix the films. -
FIG. 17 shows a thin microfilter attached to a more sturdy support. -
FIGS. 18A, 18B, 18C, 18D, 18E, 18F, 18G, 18H, 18I, 18J, 18K, and 18L describe the steps to fabricate micropores using dry film in two layers.FIGS. 18A, 18B, 18C, 18D , and 18E describe the steps to fabricate strips of trenches on the first layer. The fabrication steps forFIGS. 18A, 18B, 18C, and 18D are the same asFIGS. 2A, 2B, 2C , and 2D.FIG. 18D shows the cross-sectional side view after development for the first layer from one direction andFIG. 18E shows the cross-sectional side-view rotated by 90°.FIGS. 18F, 18G, 18H, 18I, 18J, 18K, and 18L describe the steps to fabricate strips of trenches on the second layer.FIG. 18F describes lamination of a second negative resist dry film on the developed first layer of negative resist dry film. The fabrication steps for 18G, 18H, 18I, and 18J are the same as steps 18B, 18C, 18D, and 18E.FIG. 18I shows the cross-sectional side view of the two layers after development from one direction andFIG. 18J show the cross-sectional side-view rotated by 90°.FIG. 18K shows the cross-sectional side view of the two layers microfilter after removing substrate from one direction andFIG. 18L show the cross-sectional side-view rotated by 90°. -
FIGS. 19A, 19B, and 19C show the top view of the microfilter fabrication process.FIG. 19A shows the top view of the pattern of trenches in the dry film on copper after step shown inFIG. 18E .FIG. 19B shows the top view of trenches in the dry film on copper after step shown inFIG. 18J . On each layer the pattern are strips of trenches. The strips of trenches on one layer are perpendicular to strips of trenches on the other layer. The pore is at the intersection of the strips.FIG. 19C shows the top view of the free standing filter after removing copper substrate after step shown inFIG. 18K . -
FIGS. 20A, 20B, 20C, 20D, 20E, 20F, and 20G describe fabrication steps to fabricate micropores using dry film in three layers.FIG. 20A describe laminating a third negative photoresist dry film to the completed structure with already two negative photoresist dry film layers, i.e., following stepFIG. 20G . The fabrication steps forFIGS. 20B, 20C, and 20D are the same asFIGS. 18B, 18C, and 18D .FIG. 20D shows the cross-sectional side view after development from one direction andFIG. 20E show the cross-sectional side-view rotated by 90°.FIG. 20F shows the cross-sectional side view of the final microfilter after removal of substrate from one direction andFIG. 20G show the cross-sectional side-view the rotated by 90°. -
FIG. 21 shows the top view of the microfilter after removal of copper. In this drawing the pores on top and bottom are not aligned, but the pores are interconnected. -
FIG. 22 shows the method to expose the photoresist by interference lithography using liquid resist as a starting material. -
FIG. 23 shows the method to expose the photoresist by interference lithography using a premade dry resist film. -
FIG. 24 shows SEM of nanofilter showing the pores obtained at the front side. -
FIG. 25 is a cross-sectional SEM image of a processed resist showing pore depth to 2.7 micron. -
FIG. 26 shows pores on the back-side of the developed freestanding 9 micron SU 8 membrane (the cross section shows that the film is fully developed). - Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, embodiments of the present invention are shown in schematic detail.
- The matters defined in the description such as a detailed construction and elements are nothing but the ones provided to assist in a comprehensive understanding of the invention. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, well-known functions or constructions are omitted for clarity and conciseness. Exemplary embodiments of the present invention are described below in the context of certain exemplary applications. Such exemplary implementations are not intended to limit the scope of the present invention, which is defined in the appended claims.
- We disclose methods of fabricating free standing precision micropores that is not based on track etching of polymers or use of solid parylene films.
- The proposed precision microfilters can be made of variety of polymers, such as polycarbonates, polyesters, in particular polyethylene terephthalate (PET) (Mylar™), SU-8, KMPR, PerMX™, SUEX, polymethylmethacrylate (PMMA), polymethylglutarimide (PMGI), etc.
- Many of these materials can be obtained as dry films in a variety of thickness from less than 10 μm to more than 100 μm.
- We present method of fabrication based on UV lithography and on x-ray lithography without using reactive ion etching (RIE).
- UV Lithography of Microfilters
- Negative resists refers to polymers that becomes polymerized when exposed to UV or x-rays, while positive resist refers to polymers in that the polymeric bonds are broken by UV or x-rays. For resist layers that are greater than a few microns in thickness, negative resists are generally much more sensitive than positive resists.
- Examples of commercially available negative resists that are in liquid form are SU-8 and KMPR from MicroChem, but not limit to them. Commercially available negative resist dry films are PerMX™ series (DuPont), SUEX (DJ DevCorp), and others.
PerMX™ 3000 series is manufactured in roll by DuPont. The commercially available thicknesses for PerMX™ are 10 μm, 14 μm, 25 μm, and 50 μm. Other thickness can also be obtained on custom order bases. - Positive resist dry films are also commercially available, for example PMMA.
- 1. Fabricate Microfilters from a Single Layer of Negative Resist Using UV Lithography
- There are a number of methods to fabricate microfilters using negative resists. An exemplary implementation illustrating a general concept is described first in the context of Example 1.A. Variations of the concept include, but are not limited to, other exemplary implementations which are described in the context of further Examples that follow.
- The fabrication steps are:
-
- a. Laminate negative resist
dry film 100 onremovable substrate 180, as shown inFIG. 1A . - b. Expose the negative resist
dry film 100 laminated onremovable substrate 180 to UV light though the microfilteroptical mask 199 withpattern 198 formed by thin film of chromium,FIG. 1B . - c. Post bake the exposed
dry film 110 on removable substrate,FIG. 1C . - a. Develop the exposed dry film to form microfilter 120 with
pores 10 onremovable substrate 180,FIG. 1D . The parts of the negative resists that are not exposed to the UV are dissolved by developer. - d. Hard bake developed dry film (optional).
- e. Remove substrate and to obtain
free standing microfilter 120 withpores 10,FIG. 1E .
- a. Laminate negative resist
- The fabrication steps are:
-
- f. Obtain or laminate negative resist
dry film 100 onthin copper foil 20, as shown inFIG. 2A . - g. Expose the negative resist
dry film 100 laminated oncopper foil 180 to UV though the microfilteroptical mask 199 withpattern 198 formed by thin film of chromium,FIG. 2B . - h. Post bake the exposed
dry film 110 on copper foil,FIG. 2C . - i. Develop the negative resist to form microfilter 120 with
pores 10 oncopper substrate 180,FIG. 2D . - j. Hard bake (optional).
- k. Etch away copper and to obtain
free standing microfilter 120 withpores 10,FIG. 2F .
- f. Obtain or laminate negative resist
- The fabrication steps using KAPTON as a release layer are:
-
- a. Laminate negative resist
dry film 100 onKAPTON film 181. Along the edge(s) or other pre-specified location, aseparation assistant material 182 is placed between the negative resist dry film and KAPTON as a separator, as shown inFIG. 3A . Theseparation assistant material 182 can be KAPTON, or other materials that can be laminated to the dry film and can withstand the hard bake temperature. - b. Expose the film to UV though the microfilter
optical mask 199 withpattern 198 formed by thin film of chromium,FIG. 3B . - c. Post bake the exposed
dry film 110 onKAPTON 181,FIG. 3C . - d. Develop the negative resist to form microfilter 120 with
pores 10 onKAPTON 181,FIG. 3D . - e. Hard bake (optional).
- f. Using the
edge 182 where the negative resist film is not attached to KAPTON, peel the negative resist film from KAPTON to obtain free standing microfilters,FIG. 3E - g. Remove the
separation assistant polymer 182 to obtainfree standing microfilter 120 withpores 10,FIG. 3F .
- a. Laminate negative resist
- The fabrication steps using copper as a release layer are:
- a. Coat substrate, for example silicon wafer, with thin layer of copper.
- b. Spin coat negative resist, such as SU-8 on copper, followed by pre-bake.
- c. Expose the film to UV light though the microfilter optical mask.
- d. Post bake.
- e. Develop the negative resist to form pores.
- f. Etch away copper and release the microfilters.
- A combination of use of negative resist and positive resist (PMGI, LOR from MicroChem, S1800 series photoresists from Shipley) can also be used to obtain free standing microfilters. The steps are:
-
- a. Spin coat positive resist (such as PMGI) on substrate, such as silicon wafer, and followed by prebake.
- b. Expose PMGI to UV at the appropriate dose for the coating thickness.
- c. Spin coat negative resist, such as SU-8 on the positive photoresist followed by prebake.
- d. Expose the SU-8 resist to UV though the microfilter optical mask.
- e. Post bake.
- f. Develop the negative resist to form pores.
- g. Develop PMGI to release the microfilters.
- Other positive resists can also be used as release layer.
- The fabrication steps using copper as a release layer are:
- a. Coat substrate, for example silicon wafer, with thin layer of copper.
- b. Laminate negative resist dry film on copper
- c. Expose the film to UV though the microfilter optical mask.
- d. Post bake.
- e. Develop the negative resist to form pores.
- f. Hard bake (optional).
- g. Etch away copper and release the microfilters.
- a. Spin coat positive resist (such as PMGI) on substrate, such as silicon wafer.
- b. Expose PMGI to UV at the appropriate dose for the coating thickness.
- c. Laminate negative resist dry film on the positive resist.
- d. Expose the SU-8 resist to UV though the microfilter optical mask.
- e. Post bake.
- f. Develop the negative resist to form pores.
- g. Develop the positive resist to release the microfilters.
-
-
- a. Laminate positive resist
dry film 600 onremovable substrate 180, as shown inFIG. 4A . - b. Expose the positive resist
dry film 600 laminated onremovable substrate 180 to UV light though the microfilteroptical mask 199 withpattern 190 formed by thin film of chromium,FIG. 4B . - c. Develop the exposed dry film to form microfilter 620 with
pores 10 onremovable substrate 180,FIG. 4C . The parts of the positive resists that are exposed to the UV are dissolved by developer. - d. Remove substrate and to obtain
free standing microfilter 620 withpores 10,FIG. 4D .
- a. Laminate positive resist
-
-
- a. Laminate positive resist dry film on the copper
- b. Expose the positive resist dry film to UV though the microfilter optical mask. The parts of the positive resists that are exposed to the UV can be dissolved by developer.
- b. Develop the positive resist to form pores.
- c. Wet etch copper to release the microfilters.
- 2. Fabricate Microfilters from a Roll of Negative Resists Dry Film Using UV Lithography
- The negative resist dry film, such as
PerMX™ 3000 series, is manufacture in roll form. To perform UV lithography of the resist in the role form as shown inFIG. 3 can simplify the fabrication. The method of implementation and steps of fabrication are described below. -
- a. Between each exposure, an unexposed portion of a roll of negative resist dry films is advanced as shown in
FIG. 5A . Thefilms 102 laminated onremovable substrate 182 are connected byrolls 175. They are stretched byrollers 170. The rolls advance by the distance appropriate for the optical mask and exposure system as indicated by arrow. During film advance, theoptical mask 199 andsupport 191 are moved away from the films. - b. During exposure, the stretched
film 102 is pushed into thesupport 191 to provide additional tension and stability as shown inFIG. 5B . The UV exposure is performed after theoptical mask 199 is placed on the films. - c. After the exposure, the roll of film advances through the oven for post bake.
- d. Films are developed to obtain the pores.
- e. The
substrate 182 is removed to obtain free standing microfilters with pores. Individual microfilters are diced from the roll of dry film with pores.
- a. Between each exposure, an unexposed portion of a roll of negative resist dry films is advanced as shown in
- Microfilter Variations
- Since the applications of microfilters can vary, the pattern of the pores needs to be adjusted accordingly. The UV fabrication method described above can be used to fabricate circular uniform pores distributed as shown in
FIGS. 6A, 6B or other distributions. The UV fabrication method can fabricate pores of different shape and grouping as shown inFIG. 6C , and other shapes. The UV fabrication methods can fabricate pores of different sizes as shown inFIG. 6D . - The cross sectional view of the microfilters for various thicknesses,
FIGS. 7A and 7B .FIG. 7C shows a cross section where the pores hasdifferent sizes FIG. 7D . This can be accomplished by providing exposure dose that is higher than that is required to form uniform pore openings. - These are examples and method is applicable to other geometries and applications beside microfilters.
- X-Ray Lithography of Microfilters
- The penetration of x-rays is much deeper than UV. Unlike UV, it does not diverge within the thickness of less than 1 cm even for features much smaller than one micron. X-ray lithography is typically performed on a beamline of a synchrotron. X-ray lithography can be used for both negative and positive resists/polymers.
- 3. Fabricate Microfilters from a Stack of Negative Resists Using X-Rays Lithography
- The concept of microfabricating a stack of microfilters simultaneously by x-ray lithography using negative resist is illustrated in
FIG. 8 . The principle is very similar to that shown inFIG. 1 and described in Example 1.A. The steps of fabrication are described below. -
- a. A stack of negative resist
dry films 200 are stretched and attached on asubstrate 290 along the edge, by water soluble wax, glue, electrostatic chuck, clamp, and a variety of other methods - b. Expose the stack of negative resist dry films to x-rays through an
x-ray mask 299, which is typically made ofgold 298 to block the x-rays on thin graphite sheet orsilicon wafer 297. The parts of the negative resists that are not exposed to the x-ray are dissolved by developer. - c. The individual sheets of exposed negative resists 210 are to be separated, placed on
post bake substrates 280 for post bake. During the post bake, the negative resist 210 will be attached to thepost bake substrate 280. The post bake substrates needs to be able to stand the post bake temperature and can be dissolved chemically or by water. - d. The sample is developed 220 to form the pores, but still attached to the
post bake substrate 280. - e. The post bake substrate is removed to obtain
free standing microfilter 220 withpores 20 in themicrofilter 220.
- a. A stack of negative resist
- An alternative on the use of negative resist dry film is illustrated in
FIG. 9 . This eliminates the labor required to perform step c of Example 1.B. The steps of fabrication are described below. -
- a. The negative resist
sheet 200 is laminated to apost bake substrate 180 with the properties of to be x-ray transparent, having melting point higher than post bake temperature and removable chemically. - b. A stack of negative resist sheet on
post bake substrates 201 are stretched and attached on asubstrate 290 along the edge, by water soluble wax, glue, clamp, and a variety of other methods. - c. The negative resist sheet laminated on
post bake substrates 201 are separated for post bake. - d. The negative resist dry film laminated on post bake substrates are developed to obtain pores. The developed negative resist
dry film 220 are still attached to the post bake substrates 280. - e. The post bake substrate is removed to obtain
free standing microfilter 220 withpores 20 in themicrofilter 220.
- a. The negative resist
- The negative resist dry film, such as PerMX™ series, is manufactured in a roll form. To perform x-ray lithography of the resist in the role form as shown in FIG. 10 can simplify the fabrication. The method of implementation and steps of fabrication are described below.
-
- a. Between each exposure, one or more rolls of negative resist films are shown in
FIG. 10A . Thefilms 202 are connected byrolls 275. They are stretched byrollers 270. The rolls advance by the distance appropriate for the x-ray mask and exposure system as indicated by arrow. During film advance, thex-ray mask 299,support 291,water cooling frame 292 andduct 293 are moved away from the films. - b. During exposure, the stretched
films 202 are pushed into thesupport 191 to provide additional tension and stability as shown inFIG. 10B . The x-ray exposure is performed after thex-ray mask 299 is place on the stack of stretched films. - c. After the exposure, the films are post baked on a post bake substrate
- d. Films developed.
- e. The post bake substrate is removed to obtain free standing microfilters with pores.
- a. Between each exposure, one or more rolls of negative resist films are shown in
- There are many potential variations. (i) The film can be just one roll or as many rolls as appropriate for fabrication of precision pore dimensions. (ii) The films can be laminated with post bake substrate. (iii) The films can be further held fixed by additional clamp or
fixture 260 around the x-ray mask, as shown inFIG. 11 . (iv) The stack is held secure by electrostatic force, as shown inFIG. 12 . - In
FIG. 12 , the concept of using electrostatic force to hold the films secure is shown, but the rollers are not shown. InFIG. 12A , the configuration of the system is shown between exposures. The one or more laminated negative resistfilm 200 laminated to postbake support film 280 to formfilms 201. A stack offilms 201 are stretched. The substrate structure consist of asupport 292, aninsulator 267 and aconduction layer 266. Aclear conducting film 265 is placed on top of the film.Voltage 269 is set to zero and the circuit is open. -
FIG. 12B shows the configuration during exposure, where a voltage 169 is applied between theelectrodes electrode 265 and exposure is performed. - If the films are not pre-laminated, finish fabrication following the steps c-e of Example 2.A. If the films are pre-laminated, finish fabrication following the steps c-e of Example 2.B.
- 4. Fabricate Microfilters from a Stack of Positive Resists Using X-Rays.
- The concept of microfabricating a stack of microfilters simultaneously by x-ray lithography using positive resist is illustrated in
FIG. 13 . The steps of fabrication are described below. -
- a. A stack of
polymers sheets 300 that have the properties of positive resist are stretched and attached on asubstrate 390 along the edge, by water soluble wax, glue, clamp, and a variety of other methods. - b. Expose the stack of positive resist sheets to x-rays through an
x-ray mask 399, which is typically made ofgold absorber 398 on thin graphite sheet orsilicon wafer 397. The parts of the polymer film that are exposed to the x-ray can be dissolved by developer. - c. The individual sheets of exposed positive resists 310 to be placed in the developer
- d. The finished
developed sample 320 with pores is shown inFIG. 13C
- a. A stack of
- Most polymers belong to the category of positive resist films. Examples are polycarbonates, polyesters such as polyethylene terephthalate (PET) (Mylar®), etc. To perform x-ray lithography of the resist in the role form as shown in
FIG. 14 can simplify the fabrication and allow high volume production. The method of implementation and steps of fabrication are described below. -
- a. Between each exposure, one or more rolls of positive resist films are shown in
FIG. 14A . Thefilms 300 are connected byrolls 375. They are stretched byrollers 370. The rolls advance by the distance appropriate for the x-ray mask and exposure system as indicated by arrow. During film advance, thex-ray mask 399,support 391,water cooling frame 392 andduct 393 are moved away from the films. - b. During exposure, the stretched
films 300 are pushed into thesupport 391 to provide additional tension and stability as shown inFIG. 14B . The x-ray exposure is performed after thex-ray mask 299 is place on the stack of stretched films. - c. Films are developed to obtain free standing microfilters with pores.
- a. Between each exposure, one or more rolls of positive resist films are shown in
- There are many potential variations. (i) The film can be just one roll or as many rolls as appropriate for fabrication of precision pore dimensions. (ii) The films can be further held fixed by additional clamp or
fixture 360 around the x-ray mask, as shown inFIG. 15 . (iv) The stack is held secure by electrostatic force, as shown inFIG. 16 . -
-
- a. In
FIG. 16 , the concept of using electrostatic force to hold the films secure is shown, but the rollers are not shown. InFIG. 16A , the configuration of the system is shown between exposures. The one or more laminated positive resistfilm 300 laminated to post bake support film 380 to form films 301. A stack of films 301 are stretched. The substrate structure consist of asupport 392, aninsulator 367 and aconduction layer 366. Aclear conducting film 365 is placed on top of the film.Voltage 369 is set to zero and the circuit is open. - b.
FIG. 16B shows the configuration during exposure, where avoltage 369 is applied between theelectrodes electrode 365 and exposure is performed. - c. Fabrication can be finished by developing the films.
- a. In
- The various microfabrication methods described above are also applicable to fabrication of any free standing patterned polymeric films.
- Thin, smooth copper films are preferable as a substrate, because irregularities of the copper surface that is laminated to the negative resist dry films are transferred to the dry films after removal of copper.
- Thin copper films are preferred to minimize the amount of time required for its removal.
- Thin copper films are preferred because better contact between mask and resist film can be achieved.
- 5. Fabrication of Microfilters from Two or More Layers of Filter Material
- The method of fabrication to be described in this section can be performed by either UV or x-ray lithography.
- The fabrication steps are described in
FIGS. 18A-18L . Steps shown inFIGS. 18A-18E are the same as same as steps shown inFIGS. 2A-2E . The only difference is thelayout 194 of theoptical mask 196 and the sample of the etched film. Theoptical mask 196 will consist of strips ofmetal lines 194. The resultant first layer of themicrofilter 125 will consists of trenches that exposes thecopper substrate 180 as shown inFIG. 19A . -
- a. Laminate negative resist dry film 105 on
thin copper foil 180, as shown inFIG. 18A . - b. Expose the negative resist dry film 105 laminated on
copper 180 to UV though the microfilter optical mask,FIG. 18B . - c. Post bake,
FIG. 18C . - d. Develop the negative resist to form the
trenches 11 infilm 125,FIG. 18D . - e. Hard bake (optional),
FIG. 18E .
- a. Laminate negative resist dry film 105 on
- To make the pores, a second negative resist dry film will be added and the fabrication steps are described below.
-
- f. Laminate a second negative resist
dry film 106 on developedfilm 125, as shown inFIG. 18F . - g. Expose the negative resist
dry film 106 to UV though the microfilter optical mask withmask layout 193, as shown inFIG. 18G . The mask layout consists of strips ofmetal lines 193 and theline 193 are to be orient perpendicular to the trenches infilm 125. - h. Post bake,
FIG. 18H . - i. Develop the negative resist
dry film 116 to form the trenches to obtain patterned second layer offilm 126,FIG. 18I . - j. Hard bake (optional). The side views are shown in
FIG. 18I andFIG. 18J , which is rotated by 90° fromFIG. 18I . The top view is shown inFIG. 19B . - k. Etch away copper and release the microfilters to obtain microfilter in two layers, shown in two side views,
FIGS. 18K and 18L . The top view is shown inFIG. 19C . The film on top is 126 and the film on bottom is 125. Thepores 11 are at the intersections of the trenches in 125 and 126.
- f. Laminate a second negative resist
- To make microfilters with long path between entrance and exit of the pores, additional layers of dry film can be used. An example of three layers of dry film is described here. Follow the fabrication steps of
FIGS. 18A-18J of Example 5.A to make the first two layers of thefilter -
- a. Laminate negative resist
dry film 107 on developedfilm 126, as shown inFIG. 20A . - b. Expose the negative resist
dry film 107 to UV though the microfilter optical mask withmask layout 192, as shown inFIG. 20B . The mask layout consists of strips ofmetal lines 192 and theline 192 are to be orient perpendicular to the trenches infilm 126. - c. Post bake,
FIG. 20C . - d. Develop the exposed negative resist
dry film 117 to form the trenches to obtain patterned third layer offilm 127,FIG. 20D . - e. Hard bake (optional). The side views are shown in
FIG. 20D andFIG. 20E , which is rotated by 90° fromFIG. 20D . - f. Etch away copper and release the microfilters to obtain microfilter in three layers, shown in two side views,
FIGS. 20F and 20G . The top view is shown inFIG. 21 . The film on top is 127; the film in between is 126 and the film on bottom is 125. The pores on top are at the intersections of the trenches infilms films
- a. Laminate negative resist
- A dry film that is suitable for use for multi-layer microfilters is PerMX′. It is capable of bridging over features already formed on the surface.
- The concept using two or more layers of films to make filters can have many variations, such as
-
- Thickness of films for each layer can be identical, but they do not have to be the same.
- The trenches do not have to be the same on the same layer
- The trenches do not have to be the same on different layers.
- The trenches do not have to be straight.
- The trenches on one layer can be perpendicular to the adjacent layers, but they do not have to be perpendicular.
- The pores on different layers do not have to overlap. This is the case shown in
FIG. 21 . When the pores on the top and bottom layers do not overlap. filtration path is longer. - The number of layers can be more than three.
- Nanofilter Fabrication by Optical Interference Lithography
- In interference lithography, the image is formed by exposing resist to a standing wave formed by the interference of two coherent waves of equal amplitude. In interference lithography, if the optical system is well protected against vibration and air flow, and if the coherence length of a light source is long enough, we can easily generate sinusoidal intensity distribution over a large area, allowing nano-scale lines and dot arrays to be fabricated on a substrate without difficulty.
- Three-beam Lloyd's mirror interferometer (J. de Boor, et al Optics Letters 34 (12), 1783 (2009) was used to create in a single exposure a hole pattern with hexagonal symmetry. The period of interference pattern is λ/(1.5 sin(θ)) for 3-beam (hexagonal array), where λ is the wavelength of the laser and θ is the angle between the light beam direction and the perpendicular to the substrate.
- A HeCd laser with λ=325 nm and a typical output power of 30 mW was used for illumination. The light was directed into a spatial filter consisting of focusing lens and a small micron sized pinhole. The distance between the spatial filter and the sample holder was around 1 m, and typical illumination times were 1 to 5 min. The area of the exposed sample is about 4 cm2. Position of the mirrors (60×60×5 mm guaranteed 120° symmetry of exposure.
- Both positive and negative-tone photoresist can be used, but negative photoresists are more sensitive. Negative-tone imaging also enhances the process latitude for patterning because the hole size can be tuned by exposure dose and various hole diameter can be obtained under the same angle of illumination.
- The typical resist thickness was ˜10 μm; it is thick enough for easy handling and has relatively good mechanical stability. It is also possible to obtain a frame around nanopores for ease of use and additional mechanical stability of the fabricated membrane. The frame can be obtained by UV-exposure through the mask with the frame pattern.
- The invention is the sample preparation method enabling the high-aspect-ratio pore fabrication for both liquid negative photoresist, such as SU-8 and others, and negative dry films, such as PerMX, SUEX and others.
- For interference lithography, it is important to have a very smooth surface, to have undisturbed wave front It is also important that there are no scattered or reflected light impinging on the resist. We developed a method that overcomes these problems.
- Example Using Liquid Negative Photoresist.
- The steps of fabrication are described below and shown in
FIG. 22 . -
- a. UV
transparent substrates 500 were used, and back-side exposure can be performed. Back-side exposure has an advantage of having an optically flat resist boundary. An example of UV transparent substrate is quartz. - b. A
release layer 510 is coated on the UV transparent substrate. Example of a release material is OMNICOAT (Microchem). - c.
Liquid photoresist 520, such as SU-8 5 (Microchem), is spin coated onto quartz substrate to the desired thickness and prebaked on a hot plate. - d. The angle of the UV laser light is chosen to obtain the desirable periodicity of the pores. For example, the angle of 18° obtains a pattern with a period of ˜700 nm. Interference exposure of the resist was performed from the back-side to obtain the desirable dose.
- e. Exposed sample was post-baked on the hot plate.
- f. Sample was developed in SU-8 developer.
- g. Film was released from the substrate by immersing in SU-8 developer.
- a. UV
- If a border or frame is desired, an extra step is needed after Step d. Front-side exposure of the resist through the optical mask with a frame pattern is performed using a mask aligner. This exposure is optional, and was performed for easy handling of a freestanding film.
- Example Using Premade Dry Resist Film.
- The steps of fabrication are described below and shown in
FIG. 22 . -
- a. UV
transparent substrates 600 were used, and backside exposure can be performed. Backside exposure has an advantage of having an optically flat resist boundary. An UV transparent substrate is quartz. - b. A
release layer 610 is coated on the UV transparent substrate. Example of a release material is OMNICOAT (Microchem). - c. Laminate the
dry film 620 to quartz with the other side still attached to asubstrate 630, such as Mylar, - d. The angle of the UV laser light is chosen to obtain the desirable periodicity of the pores. For example, the angle of 18° obtains a pattern with a period of ˜700 nm. Interference exposure of the resist was performed from the back-side to obtain the desirable dose.
- e. Exposed sample was post-baked on the hot plate.
- f. Sample was developed in developer.
- g. Sample is hard baked.
- h. Sample is released from quartz in developer.
- a. UV
-
FIG. 24 shows SEM of nanofilter using SU-8 showing the pores from the front side. The front side is shown by 530 inFIG. 22 . -
FIG. 25 shows cross-sectional SEM image of a processed resist. Focused ion beam milling was used to cut the film at the 25° angle from normal. The geometry factor is 1.15; the pore depth is 2.7 μm. About half thickness of the film was developed. Freestanding film is developing from both sides, and a membrane with holes through the entire resist thickness has been obtained. -
FIG. 26 shows ores on the back-side of the developed freestanding 9 micron SU 8 membrane (the cross section shows that the film is fully developed). - Microfilter Feature Options
- Microfilter Support.
- To provide some
microfilter 128 withpores 18 with structural strength, agrid support structure 129 can be implemented as shown inFIG. 17 . - Surface Functionalization of Polymeric Microfilters.
- It is important to provide the desired surface properties of polymeric microfilters, depending on the potential application.
- One modification is to coat the microfilters with a thin layer of parylene.
- One surface modification technique of polymer microfilters involves plasma treatment of polymers to activate the surface and graft self-assembled monolayers with a range of functionality including amine, carboxyl, hydroxyl, epoxy, aldehyde, and polyethylene glycol (PEG) groups by using silane chemistry with solution immersion or vapor deposition. For example, grafting PEG-triethoxysilane onto an oxidized polymer renders the surfaces hydrophilic in a controlled manner.
- Surface of the polymeric microfilters can also be functionalized with avidin, biotin, protein A, protein G, antibodies, etc.
- Microfilter Applications
- To prevent breakage of membrane during filtration, thicker polymeric films can be used or support structure as shown in
FIG. 17 . The support can also be provided separately by the filter holders. - The invention also describes the uses of the precision microfilters. There are a wide variety of applications for microfilters from medical, water filtration, beer and wine filters, pathogen detection, etc.
- The present invention provides methods and compositions for isolating and detecting rare cells from a biological sample containing other types of cells.
- One application example is for capturing circulating fetal cells in the mother's blood during 11-12 weeks of pregnancy. Fetal cells circulating in the peripheral blood of pregnant women are a potential target for noninvasive genetic analyses. They include epithelial (trophoblastic) cells, which are 14-60 μm in diameter, larger than peripheral blood leukocytes. Enrichment of circulating fetal cells followed by genetic diagnostic can be used for noninvasive prenatal diagnosis of genetic disorders using PCR analysis of a DNA target or fluorescence in situ hybridization (FISH) analysis of genes.
- A large application of precision microfilters is for detection of circulating tumor cells in blood. For this application, previous research report utilizing microfilters with orderly arranged pores can only be fabricated with solid parylene by RIE. Here, we can fabricate microfilters with precision ordered pores using a large number of available polymer materials. These materials can have a thin coating of parylene.
- The use of microfilter consists of obtaining a blood sample from the patient, which can be in the range of 1-10 ml. The blood is flown through the microfilter. The microfilter can be hold in a filter holder with an inlet, an outlet, by securely holds the filter around the edges. This device can have built in support in the filter holder. It can have gasket above and below the filter.
- The blood is pushed through from the inlet. Most cells larger than the pore dimension are retained. Some white blood cells are deformable and can go through pores with smaller dimension than the cell size. The application of enriching circulating fetal cells and tumor cells are based on this principle.
- Even though researchers only reported microfilters with pores 7-8 μm in diameter for enriching CTCs, the microfilter pores can be larger for cancer with large cancer cells and can be smaller for cancer with smaller cancer cells.
- Microfilters using 10-25 μm thick films can be fabricated by the method described in this invention. Thicker microfilters may provide more structural strength.
- One polymer film that is well suited for microfiltration application is
PerMX™ 3000 series. Some of the properties that make it suitable for microfiltration for diagnostic application are: - UV sensitive,
- Clear,
- High tensile strength, 75 Mpa.
- Can be pre-laminated to itself and to substrate and
- No auto-fluorescence in the visible wavelengths.
- Normally,
PerMX™ 3000 series is currently used for permanent applications where it is images, cured and left on devices. It is used as an adhesive for microelectronics and packaging, bonding, bumping/pillar applications. (http://www2.dupont.com/WLP/en US/assets/downloads/pdf/PerMX3000_datasheet.pdf). According to an exemplary implementation of the present invention,PerMX™ 3000 series is utilized for microfilters as free standing film. Variations of these films can also be used without departing from the scope and spirit of exemplary embodiments of the present invention. - The captured CTCs can be enumerated on the microfilters. They can be specifically identified by genomic DNA and fluorescently tagged antibodies for intracellular and surface markers.
- The captured CTCs can be subjected to a variety of analysis and manipulations, such as immunofluorescence, cell counting, PCR, fluorescence in-situ hybridization (FISH), immunohistochemistry, flow cytometry, immunocytochemistry, image analysis, enzymatic assays, gene expression profiling analysis, efficacy tests of therapeutics, culturing of enriched cells, and therapeutic use of enriched rare cells. In addition, depleted plasma protein and white blood cells can be optionally recovered, and subjected to other analysis such as inflammation studies, gene expression profiling, etc.
- The microfilter can be coated with EpCAM antibody to further retain the CTCs.
- The captured CTCs can be cultured directly on the microfilters to increase the number of CTCs and to evaluate the characteristics of CTCs. One example of the rational for culturing the CTCs is to evaluate its expression of disease markers. A simple method to determine the disease marker expression is to coat the surface of channels of the microfilters with capture reagent for the disease marker and later for a fluorescent sandwich assay to specifically identify the disease marker if it is present.
- The captured CTCs can be analyzed for DNA, RNA, mRNA and microRNAs expressions for target of interest.
- The present invention provides methods and compositions for isolating and detecting rare cells from a biological sample containing other types of cells. In particular, the present invention includes a step that uses a microfabricated filter for filtering fluid samples and the enriched cells can be used in a downstream process such as identifies, characterizes or even grown in culture or used in other ways.
- Other applications include enriching stromal cells, mesenchymal cells, endothelial cells, epithelial cells, stem cells, non-hematopoietic cells, etc. from a blood sample and tumor cells in urine.
- The present invention provides method and microfilters to capture analytes bound to latex beads or antigen caused particle agglutination whereby the analyte/latex bead or agglutinated clusters are captured on the membrane surface.
- The present invention provides method and microfilters for erythrocyte deformability testing. Red blood cells are highly flexible cells that will readily change their shape to pass through pores. In some diseases, such as sickle cell anemia, diabetes, sepsis, and some cardiovascular conditions, the cells become rigid and can no longer pass through small pores. Healthy red cells are typically 7.5 μm and will easily pass through a 3 μm pore membrane, whereas a cell with one of these disease states will not. In the deformability test, a 5 μm membrane is used as a screening barrier. A blood sample is applied and the membrane is placed under a constant vacuum. The filtration rate of the cells is then measured, and a decreased rate of filtration suggests decreased deformability.
- The present invention provides method and microfilters for leukocyte/Red blood cell separation. Blood cell populations enriched for leukocytes (white blood cells) are often desired for use in research or therapy. Typical sources of leukocytes include whole peripheral blood, leukopheresis or apheresis product, or other less common sources, such as umbilical cord blood. Microfilters with
- The present invention provides method and microfilters for chemotaxis applications. Membranes are used in the study of white blood cell reactions to toxins, to determine the natural immunity in whole blood. Since immunity is transferable, this assay is used in the development of vaccines and drugs on white blood cells.
- The present invention provides method and microfilters for blood filtration/blood transfusion. Microfilters can be used to remove large emboli, platelet aggregates, and other debris.
- The present invention provides method and microfilters for capture of cells and the subsequent culture in the filter cartridge or backflushing.
- Because the arrays of precision micro-pores can be fabricated in rolls of polymer resists, it opens up applications that wafer sized microfilters are not able to satisfy. Examples are for water filtration, kidney dialysis, etc.
- While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention, as defined by the appended claims and equivalent thereof.
Claims (21)
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