Methods and Apparatus for Coated Flowcells

Abstract

Microfluidic devises and process for making the devices include coating a substrate with an active oxygen layer and covalently bonding a polymeric microfluidic pattern to the substrate and devices made by the process.

Claims

1. A method of coating a microfluidics substrate comprising the steps of: providing a substrate having a first side and a second side wherein the substrate comprises a metal or a polymer; coating at least the first or second side of the substrate by subjecting at least one of the first or second side of the substrate to physical vapor deposition of SiO.sub.2 to produce an SiO.sub.2 coated substrate; providing a first layer of material comprising polydimethylsiloxane; and bonding an SiO.sub.2 coated side of the substrate to the polydimethylsiloxane layer with plasma bonding.

2. The method of claim 1, wherein the substrate comprises aluminum, titanium, a cyclic olefin copolymer, acrylic, or polyethylene terephthalate.

3. The method of claim 1, further comprising the step of subjecting the at least one side of the substrate to an ion beam concurrent with the physical vapor deposition step.

4. The method of claim 3, wherein the ion beam provides oxygen or argon ions to the substrate.

5. The method of claim 3, wherein the ion beam is applied to the substrate at a reduced pressure and increased temperature relative to ambient.

6. The method of claim 5, wherein the ion beam is applied within a pressure range of 1×10.sup.−6 Torr to 1×10.sup.−5 Torr, and within a temperature range of 20° C. to 125° C.

7. The method of claim 1, further comprising attaching a second layer comprising glass or a polymer to the at least one side of the substrate that is bonded with a polydimethylsiloxane layer.

8. The method according to claim 1 further comprising the step of providing one or more of microchannels, ports, reservoirs, sensors, osmotic pumps, mixers, splitters, micro-electronic mechanical systems, or combinations thereof located at least partially in the substrate.

9. The method of claim 1 wherein the first layer and the substrate comprise a flow cell.

10. The method of claim 1, wherein the substrate is coated with a layer of SiO.sub.2 to a thickness of about 1.6 nm to about 550 nm.

11. The method of claim 1, wherein bonding said SiO.sub.2 coated substrate with said polydimethylsiloxane layer comprises contacting the SiO.sub.2 coated substrate with said polydimethylsiloxane layer, and applying pressure and heat to achieve bonding.

12. The method of claim 11 wherein the substrate and polydimethylsiloxane layer are subjected to a temperature of about 20° C. to about 125° C. and pressure for about 5 to about 10 minutes.

13. The method of claim 7 wherein bonding the cap to the polydimethylsiloxane layer comprises contacting the cap with the polydimethylsiloxane layer and applying pressure and heat to achieve bonding.

14. The method of claim 42, wherein the cap and PDMS layer are subjected to a temperature of 20° C. to about 72° C. and pressure for from about 5 to about 10 minutes.

15. A process of manufacturing a microfluidic flow cell comprising: providing a substrate; applying a coating comprising SiO.sub.2 while concurrently applying an electron beam to the substrate effective to produce a substrate with a chemically active surface comprising ionic oxygen or argon; providing a layer comprising polydimethylsiloxane comprising a first surface and a second surface said layer comprising one or more fluid flow channels; and covalently bonding said chemically active surface to a first surface of said layer comprising polydimethylsiloxane.

16. The process of claim 15, further comprising bonding a cap layer comprising glass to said second surface of said layer of polydimethylsiloxane.

17. The process of claim 16 wherein said one or more fluid flow channels are formed in said layer of polydimethylsiloxane prior to covalently bonding said chemically active surface to said layer of polydimethylsiloxane.

18. The process of claim 16 wherein said one or more fluid flow channels are formed in said layer of polydimethylsiloxane after covalently bonding said chemically active surface to said layer of polydimethylsiloxane.

19. A flow cell comprising: a substrate comprising aluminum, titanium, a cyclic olefin copolymer, acrylic, or polyethylene terephthalate, and having a first surface having thereon a coating comprising SiO.sub.2, wherein the SiO.sub.2 coating is bonded to a polydimethylsiloxane layer.

20. The flow cell according to claim 19 wherein said flow cell comprises one or more biocompatible materials.

21. The flow cell according to claim 19 wherein at least one surface of said substrate is hydrophilic.

22. The flow cell according to claim 19 further comprising a layer comprising glass or a polymer, wherein said layer comprises a polydimethylsiloxane coating and is attached to said substrate.

23. A flow cell comprising: a substrate having a surface, said substrate comprising aluminum, titanium, a cyclic olefin copolymer, acrylic, or polyethylene terephthalate, a SiO.sub.2 coating covalently bonded to said surface, and a layer of polydimethylsiloxane comprising a first surface covalently bonded to said SiO.sub.2 coating.

24. The flow cell of claim 23 wherein said layer of polydimethylsiloxane comprises a second surface opposite said first surface wherein said second surface is covalently bonded to a cap.

25. The flow cell of claim 23, wherein said cap comprises an optically transparent material.

26. The flow cell of claim 23, wherein said cap comprises glass.

27. The flow cell according to claim 23 wherein layer of polydimethylsiloxane comprises one or more fluid flow channels.

28. The flow cell of claim 23, wherein said substrate comprises one or more of a microchannel, a port, a reservoir, a sensor, an osmotic pump, a mixer, a splitter, or a micro-electronic mechanical system.

29. The flow cell of 23, wherein said fluid flow channels are designed for use in an immunoassay, genetic sequencing, single nucleotide polymorphism (SNP) detection, polymerase chain reaction (PCR), genetic diagnostics, micropneumatic systems, enzymatic analysis, clinical pathology, clinical diagnostics, immunology, cancer detection, companion diagnostics, biochemical toxin detection, pathogen detection, cell separation, cell sorting, cell counting, cell manipulation, droplet manipulation, digital microfluidics, optofluidics, drug screening, drug delivery, neural cell study, axotomy, axon cutting, soma/axon separation, or integrated lateral flow.

30. The flow cell of claim 23, wherein said fluid flow channels are designed for use in an inkjet printhead, a DNA chip, a lab-on-a-chip, micro-propulsion, or a micro-thermal technology.

31. The flow cell of claim 23, wherein the substrate remains bonded to the polydimethylsiloxane layer when subjected to a fluid pressure of 135 psi.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an implementation of apparatus consistent with the present disclosure and, together with the detailed description, serve to explain advantages and principles consistent with the disclosure.

[0028] FIG. 1 is an example of a microfluidic device including a glass cap (top panel) for imaging or detection, a PDMS layer (middle panel) forming fluidic channels and an acrylic machine substrate (bottom panel) with any of fluidic channels, ports, reservoirs, sensors, osmotic pumps, mixers, splitters, or micro-electronic mechanical systems located at least partially in the substrate.

[0029] FIG. 2 is an example of processes of coating SiO.sub.2 onto a substrate surface.

[0030] FIG. 3 is an example of a glass half-cell with bonded PDMS layer.

[0031] FIG. 4 is an example of a silicon coated titanium substrate.

[0032] FIG. 5 is an example of an assembled microfluidic device with transparent cap and fluid in the channels.

[0033] FIGS. 6, 7 and 8 are diagrams of a two channel microfluidic device, a single channel microfluidic device and a Y-mixer microfluidic device, respectively.

[0034] FIG. 9 is a schematic of a substrate with attached platinum electrodes disposed in a channel formed by a PDMS layer as prepared for SiO.sub.2 coating.

DESCRIPTION OF EMBODIMENTS

[0035] The above general description and the following detailed description are merely illustrative of the generic apparatus and method, and additional modes, advantages, and particulars will be readily suggested to those skilled in the art without departing from the spirit and scope of the disclosure.

[0036] An example of a flow cell assembly 1 as shown in FIG. 1 can include a glass cap 2 for imaging or detection, a PDMS layer 3 forming fluidic channels and an acrylic machined substrate 4 with any of fluidic channels, ports, reservoirs, sensors, osmotic pumps, mixers, splitters, or micro-electronic mechanical systems formed and located at least partially in the substrate. An example of a process for making the assembly 1 is described below.

[0037] A schematic of an ion deposition and ebeam radiation chamber is shown in FIG. 2. As shown in the figure, the process is carried out in a vacuum chamber 20 that includes a port 22 connected to one or more vacuum pumps. The substrate 24 is placed on a rotor 27 providing complex planetary rotation as indicated by the circling arrows. As shown in FIG. 2, two substrates 24 may undergo the same process simultaneously. It will be appreciated that more than two substrates may undergo the process simultaneously. Power supplies 26 are connected to an ion source 28 within the chamber. A hot filament 21 provides a 270 degree path for the physical vapor deposition of SiO2 23.

[0038] An example of a glass half-cell 30 with bonded PDMS layer 32 is shown in FIG. 3. As seen in the figure, the PDMS layer 32 provides microchannels 34 for a fluid flow device.

[0039] FIG. 4 is an example of a silicon coated titanium substrate 40. The substrate includes a flat surface 42 and openings 44 in the substrate for fluid flow.

[0040] FIG. 5 is an example of an assembled microfluidic device 50 with a substrate 40 as shown in FIG. 4, and with a transparent cap 52 and fluid in the channels 34 as shown in FIG. 3.

[0041] FIGS. 6, 7 and 8 are diagrams of a two channel microfluidic device, a single channel microfluidic device and a Y-mixer microfluidic device, respectively.

[0042] FIG. 9 is a schematic of a flow cell device 90 including substrate 91 with attached platinum electrodes 92 disposed in a channel 94 formed by a PDMS layer 96 as prepared for SiO.sub.2 coating. As shown in FIG. 9, the flow cell assembly 90 may include electrodes 92 electrically connected to a power source, not shown in the FIG. 9. In the assembly shown in FIG. 9, the electrodes are platinum (although it will be appreciated that other conductive materials may be used). The platinum electrodes may be provided by depositing platinum on the surface of the substrate in a particular pattern or by etching the desired pattern after platinum has been deposited on the surface of the substrate. As shown in FIG. 9, the electrodes extend over and across the channel of the flow cell. In one particular embodiment, the electrodes can be used to determine an electrical characteristic of the fluid or material located in the channel, such as resistance, voltage or capacitance, for example, which may be helpful to determine the relative health or status of biological materials in the channel. In other applications, electrodes or other electrical devices (such as micro-electrical-mechanical systems, or MEMs) may be added to the substrate before coating the surface with the SiO.sub.2 layer. For example, the electrodes may be included, but may be used to measure or determine things other than electrical resistance, such as electrochemical reactions as may be useful for glucose measurement or oxygen content measurement and the like. In addition, such electrodes or MEMs devices may include heating elements to provide thermocycling of some or selected portions of the flow cell assembly (e.g., certain portions of the channel, certain portions of the substrate, or the like). Such MEMs devices may also include devices for pumping a fluid or for color detection, or for other purposes. In the specific example shown in FIG. 9, the substrate comprises PET, but those skilled in the art will appreciate from the discussion in this disclosure that other materials may be used.

Examples of substrates and coating parameters is shown below in Table 1.

TABLE-US-00001 TABLE 1 Chamber Base Coating Start-End Pressure Effective Substrate Process Temp. (° C. 0 (Torr) thickness(nm) Bond? Hydrophilic? Acrylic IAD with O.sub.2 20-71 1.00 × 10.sup.−5 500 Yes Yes Ion Pre- cleaning Acrylic Conventional 20-35 1.00 × 10.sup.−5 500 yes Yes e-beam Acrylic Conv. E- 30-46 1.00 × 10.sup.−5 500 No, No beam with None O.sub.2 ion pre- cleaning COC IAD with O.sub.2 20-71 1.00 × 10.sup.−5 500 yes Yes Ion Pre- cleaning COC Conv. E- 34-46 1.00 × 10.sup.−5 500 yes Yes beam with O.sub.2 ion pre- cleaning COC Conventional 20-35 1.00 × 10.sup.−5 500 yes Yes e-beam PET Conventional 20-21 1.00 × 10.sup.−5 8.5 Yes Yes e-beam PET Conventional 20-23 1.00 × 10.sup.−5 17 Yes Yes e-beam PET Conventional 20-27 1.00 × 10.sup.−5 42 Yes Yes e-beam PET Conventional 20-23 1.00 × 10.sup.−5 4.5 Yes Yes e-beam PET Conventional 20-20 1.00 × 10.sup.−5 1.5 Yes Yes e-beam Polystyrene IAD with O.sub.2 20-72 9.00 × 10.sup.−6 500 Yes Yes Ion Pre- cleaning Polystyrene Conventional 20-35 1.00 × 10.sup.−5 500 Yes Yes e-beam Polystyrene Conv. E- 20-43  9.5 × 10.sup.−6 500 Yes Yes beam with O.sub.2 ion pre- cleaning Polycarbonate Conventional 20-35 1.00 × 10.sup.−5 500 Yes Yes e-beam Polycarbonate Conv. E- 34-46 1.00 × 10.sup.−5 500 Yes Yes beam with O.sub.2 ion pre- cleaning Polycarbonate IAD with O.sub.2 20-72 1.00 × 10.sup.−5 500 Yes Yes Ion Pre- cleaning Anodized Al IAD. Sub 125-125  6.5 × 10.sup.−6 500 Yes, Yes M1 & SiO2 Best Anodized Al IAD SiO2 125-125 9.00 × 10.sup.−6 500 Yes Yes Only Coating Thickness Results Thickness Bond Material (nm) (Plasma) Comments PET Platinum 42 Yes Bond as strong as glass PET Platinum 17 Yes Bond as strong as glass PET Platinum 8.5 Yes Bond as strong as glass PET Platinum 4.5 Yes Bond as strong as glass PET Platinum 1.6 Yes Bond as strong as glass PET Platinum 505 Yes Bond as strong as glass *Ion Assisted Deposition

[0043] An ion assisted physical vapor deposition process can be utilized to deposit the SiO.sub.2 layer on the parts to be treated in a high vacuum coating chamber. The sequence of steps is as follows:

[0044] Parts are inspected, cleaned, placed in a custom coating fixture and loaded into a high vacuum coating chamber. The parts may be placed on surfaces which spin around a center axis and also which rotate around a central axis, similar to the Earth's rotation around its axis while rotating around the sun.

[0045] The vacuum chamber is pumped down to a base pressure of about 8×10.sup.−6 Torr, for titanium for example, or other vacuum strength based on the particular substrate.

[0046] During the pumpdown period, parts are heated to the appropriate temperature, such as about 125° C. for metal substrates, using substrate quartz lamp heaters.

[0047] After achieving the desired base pressure and temperature, parts are ion pre-cleaned for 3 minutes.

[0048] The SiO.sub.2 layer is deposited with electron beam physical vapor deposition with O.sub.2 plasma assist.

[0049] A quartz crystal monitor can be used to control coating deposition rate and thickness

[0050] After processing, coated substrates can be evaluated for effectiveness of bonding of the coating by an abrasion test. Hydrophilicity is evaluated with a water beading test.

[0051] Bonding strength of the SiO.sub.2 to the substrates generally was observed to be as follows: Al/Titanium<acrylic/PET/COC/polystyrene/polycarbonate.

[0052] It was observed that the plastic polymers exhibit the best results all of which performed better than anodized aluminum or titanium. It is understood, however, that all tested materials are coated with sufficient efficiency for their intended use.

[0053] A test of bonding strength of a coated machined acrylic substrate tested in single channel layer with a glass cap demonstrated no failure of the microchannel when subjected to fluid flow at a pressure of at least 135 psi.

[0054] All SiO.sub.2 coatings were approximately 1.6 nm to about 550 nm thick. In this example, the primary difference in treatment of the substrates was sample preparation (ion pre-cleaning, direct e-beam coating, or ion assisted deposition).

[0055] Due to low energy state (˜0.1 ev) the results from a typical conventional electron beam evaporation process often suffer from poor adhesion. Any particulate contamination on the substrates before deposition weakens the coating bonds, and can lead to flaking. An ion beam source as shown in FIG. 2 is used to direct high-energy oxygen ions at the substrate during the SiO.sub.2 layer deposition. These incoming ions have far greater energy than the typical electron beam evaporate (on the order of 10-100 eV), and upon striking the substrate deposit this energy into the existing layers of the coating. Importantly, the energy is high enough to embed the oxygen ions down several nanometers into the coating, providing a dose of reactive gas to regions which may not have been fully oxidized before being covered by evaporate. Further, when the energy of the incoming ions is deposited into the coating, surface atoms from the coating are liberated to move and shift along the surface. This helps create an amorphous, non-crystalline solid, removing the columnar structure that promoted water absorption and creating a denser and more durable thin layer of SiO.sub.2.

[0056] Uncoated substrates showed little to no bonding with PDMS.

[0057] In cases of glass substrates, films that are deposited at lower substrate temperature can then be baked or annealed at much higher temperature to achieve the desired optical and mechanical properties. Generally substrates made from plastics cannot be heated over 120° C. and generally should be kept below 80° C.-90° C. during the layer deposition. Therefore unlike glass substrates, plastic substrates must be coated at much lower temperature and can't be annealed after coating. However to achieve desired coating properties sometimes this limitation for the plastic substrates can be moderated by using an energetic coating process like Ion Assisted Deposition (IAD) during the layer deposition. A Mark II ion source with Oxygen plasma (O.sub.2 ions) was used in IAD coated samples and ion pre-cleanings.

TABLE-US-00002 Variation of the IAD Parameters: O2 Flow rate (SCCM**) Anode Voltage (V) Anode Current (A) 15-36 70-180 1-4 SiO.sub.2 deposition rates: 1.5 A°/Sec-5° A/Sec for both conventional & IAD depositions. **Standard Cubic Centimeters per Minute

[0058] Those skilled in the art will understand that the methods and apparatus described in the foregoing disclosure can be modified or varied without departing from the scope of the disclosure, and that the methods and apparatus described will have uses, advantages and applications beyond the specific examples provided above. For example, it will be appreciated that the methods and apparatus described can be used to manufacture complex flow cells at least in part because of the ability to combine machined plastic or polymeric parts with microchannels and glass tops (such as for imaging purposes), which can be especially useful in applications for hematology and urology. In addition, the apparatus of the present disclosure may have some or all surfaces that are hydrophilic or amenable to surface immobilization. Moreover, the ability to use materials with relatively high thermoconductivity (such as aluminum, titanium, and other metals) allows the creation of flow cells and other apparatus which allow for relatively high heat transfer properties, yet still have relatively lower manufacturing costs and are generally easier to make (such as by machining, stamping, and the like). It will also be appreciated that the methods and apparatus of the present disclosure should allow for applications with blocking with respect to air permeability or solvents, such as using PDMS to impede air permeability in microvalves. The apparatus of the present disclosure can have a wide range of useful applications, including applications involving water cooling (such as a heat exchanger), PCR, patterned and/or functionalized surfaces with self-assembled monolayers, proteins, antibodies, aptamers, oligonucleotides, extracellular matrix components for cell DNA or RNA capture or detection, ELISA assays, organ on a chip or cell culture on a chip applications (which typically will involve tightly engineered microenvironments), electrophoresis, microreactors, and solvent or air permeability barriers.

[0059] All of the devices, apparatuses and methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the devices and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the devices and/or methods and in the steps or in the sequence of steps of the methods described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.