WO2017019221A1

WO2017019221A1 - Reconfigurable microfluidic systems: homogeneous assays

Info

Publication number: WO2017019221A1
Application number: PCT/US2016/039619
Authority: WO
Inventors: Hong Jiao; Erik C. Jensen; Homayun Mehrabani; Liran Yosef Haller
Original assignee: Hj Science & Technology Inc
Current assignee: Hj Science & Technology Inc
Priority date: 2015-07-24
Filing date: 2016-06-27
Publication date: 2017-02-02
Anticipated expiration: 2018-01-24
Also published as: EP3325158A1; EP3325157A4; CA2992447C; CN108290154B; CA2992434A1; CA2992447A1; CN108290153A; CN108290154A; EP3325158A4; CA2992434C; WO2017019241A1; EP3325157A1

Abstract

Reconfigurable microfluidic systems are based on networks of microfluidic cavities connected by hydrophobic microfluidic channels. Each cavity is classified as either a reservoir or a node, and includes a pressure port via which gas pressure may be applied. Sequences of gas pressures, applied to reservoirs and nodes according to a fluid transfer rule, enable fluid to be moved from any reservoir to any other reservoir in a system. Such systems are suitable for automated, multi-input, multi-output homogeneous assays.

Description

Reconfigurable Microfluidic Systems: Homogeneous assays

Related Applications

0001 This appl ication is related to "Reconfigurable m icrofluidic systems: Microwell plate interface", US 14/808,933, fi led on 07/24/201 5 and "Reconfigurable microfluidic systems: Scalable, multiplexed immunoassays", US 14/808,939, filed on 07/24/2015.

0002 This application claims priority to and claims the benefit of U.S. Application Serial No. 14/808,929 filed 07/24/201 5, which is hereby incorporated by reference in its entirety.

Technical Field

0003 The disclosure is general ly related to m icrofluidic systems. Background

0004 Microfluidic systems manipulate m icroliter and smaller scale volumes of fluids. Ink-jet printing and biochemical assays are two prominent applications of microfluidics among many others. The ability to move, control and mix tiny quantities of liquids is valuable in biochemistry since it perm its more experiments to be done with a given amount of starting material. The increased surface-to-volume ratio associated with microfluidic channels as compared to traditional microwel l plates also speeds up surface reactions upon which some kinds of assays are based.

0005 Despite the profound advances in microfluidics achieved over the last 30 years, there is room for improvement. It is stil l a challenge, for example to make microfluidic valves that open and shut as reliably as conventional size valves. New approaches to interfaces between m icrofluidic devices and m icrowel l plates are needed. Final ly, microfluidic assays need to be made scalable so that hundreds or thousands of assays can be performed in paral lel on one ch ip.

Brief Description of the Drawings

0006 Fig. 1 is diagram of a reconfigurable microfluidic device, seen in cross section.

0007 Fig. 2 illustrates loading the device of Fig. 1 from an external fluid source. 0008 Fig. 3 il lustrates unloading the device of Fig. 1 to an external fluid store.

0009 Figs. 4A, 4B and 4C are diagrams illustrating operation of the device of Fig. 1 , seen in plan view.

0010 Fig. 5 is a graph of fluid volume transferred between a reservoir and a node of a device similar that of Fig. 1 .

0011 Fig. 6 in steps 0 through 6, is a diagram illustrating operation of a reconfigurable m icrofluidic device, seen in plan view.

0012 Fig. 7 is a diagram of a reconfigurable m icrofluidic device, seen in cross section, including ports for clearing microfluidic channels.

0013 Fig. 8 is a graph of absorbance representing results of an automated dilution experiment.

0014 Fig. 9 is a diagram of a reconfigurable microfluidic system, including a pressure sequencer.

0015 Figs. 10A (cross sectional view) and 1 0B (plan view) are diagrams illustrating a gas flow manifold in a reconfigurable microfluidic device.

0016 Fig. 1 1 is a plan view diagram of a reconfigurable microfluidic device for homogenous assays.

0017 Fig. 12 il lustrates steps 0 through 2 in a single-reagent-input, multiple-output operation of the device of Fig. 1 1 .

0018 Fig. 13 illustrates steps 3 through 5 in a single-reagent-input, multiple-output operation of the device of Fig. 1 1 .

0019 Fig. 14 i llustrates steps 0 through 2 in a multiple-sample-input, multiple- output operation of the device of Fig. 1 1 .

0020 Fig. 1 5 illustrates steps 3 and 4 in a multiple-sample-input, multiple-output operation of the device of Fig. 1 1 .

Detailed Description

0021 Reconfigurable m icrofluidic systems are based on networks of microfluidic cavities connected by hydrophobic microfluidic channels. Each cavity is classified as either a reservoir or a node, and includes a pressure port via wh ich gas pressure may be applied. Sequences of gas pressures, applied to reservoirs and nodes according to a fluid transfer rule, enable fluid to be moved from any reservoir to any other reservoir in a system. Such systems are suitable for automated, multi-input, multi-output homogenous assays. 0022 Reconfigurable microfluidic systems may be designed from these basic components - reservoirs, nodes and channels - to perform many different microfluidic tasks including homogenous and inhomogeneous assays and microwell plate interfacing. The systems are scalable to any number of fluid inputs and outputs, and they can manipulate very small fluid volumes necessary for multiplexing samples with analytes to perform multiple simultaneous assays.

0023 A microfluidic cavity is an internal vol ume for accumulating fluid in a microfluidic device. A reservoir is a microfluidic cavity that is connected to only one microfluidic channel. A node is a m icrofluidic cavity that is connected to more than one microfluidic channel. Finally, a channel is a microfluidic passageway between nodes or reservoirs. Each channel in a reconfigurable m icrofluidic system connects at most two cavities. Said another way, there are no channel intersections.

0024 Nodes are designed to present lower resistance to fluid flow than are channels. The fluid flow resistance of a cavity or channel is inversely proportional to the square of its cross sectional area. Therefore the difference in flow resistance between a channel and a reservoir, or between a channel and a node, may be engineered via different cross sectional areas.

0025 Reservoirs store fluids; e.g. samples or reagents. Nodes, on the other hand, do not store fluid, except temporarily during a sequence of fluid transfer steps. Provisions for automated loading fluid into, or unloading fluid from, a reservoir may be provided, with a small plastic tube extending from a reservoir to a glass bottle being a simple example.

0026 Reconfigurable m icrofluidic systems may be implemented in a variety of ways as long as: reservoirs, nodes, channels and pressure ports are provided; resistance to fluid flow is greater in the channels than in the nodes; and the channels are hydrophobic to prevent fluid flow when pressures at the two ends of a channel are equal or nearly so. A typical implementation includes a substrate layer, a hydrophobic fluid layer, and a pneumatic layer.

0027 Fig. 1 is diagram of a reconfigurable microfluidic device, seen in cross section. In Fig. 1 , microfluidic device 105 includes a substrate layer 1 10, a hydrophobic fluidic layer 1 15, and a pneumatic layer 120. Cavities in the hydrophobic fluidic layer are labeled 'Α', 'B' and 'C . Cavities A and B are connected by channel 125 while cavities B and C are connected by channel 130. Cavities A and C are classified as reservoirs because they are connected to only one channel each. Cavity B is classified as a node because it is connected to more than one channel : B is connected to both channel 125 and channel 130. 0028 Pressure sources 135, 140 and 145 are connected to reservoir A, node B and reservoir C, respectively, via gas tubes 150, 1 55 and 160 respectively. Each of the three pressure sources is capable of providing at least two different pressures: a high pressure and a low pressure. Labels Ί and 'L' in the figure refer to the capability of a pressure source to provide a high or low pressure. Pressure source 135 is also capable of providing a pressure that is less than atmospheric pressure; i.e. a partial vacuum . Label 'V in the figure refers to this capability. As an example, high pressure may be about 2 kPa, low pressure may be about 0 kPa, and partial vacuum pressure may be about -6 kPa, where all pressures are gauge pressures.

0029 Several d ifferent ways of making a structure like microfluidic device 105 are possible. As a first example, substrate 1 10 may be made of glass, polydimethylsi loxane (PDMS), polyethylene terephthalate (PET), or plastic. Hydrophobic fluidic layer 1 1 5 may be made from PDMS. A mold for casting PDMS to define hydrophobic microfluidic channels may be produced with a programmable cutter for vinyl decals or defined photol ithographica! ly in an epoxy-based negative photoresist such as SU-8. After patterned PDMS is cured and removed from a mold, it may be bonded to a flat substrate. Pneumatic layer 120 may also be made from PDMS. Gas tubes may be made from polyetheretherketone (PEEK) tubing which forms convenient seals when inserted in appropriately sized holes in PDMS. Hydrophobic materials that are suitable alternatives to PDMS include fluorinated ethylene propylene (FEP) and polytetrafluoroethylene (PTFE).

0030 In example devices, the cross-sectional dimensions of channels 125 and 130 were about 1 00 μηι by about 300 μηι. The sizes of reservoirs A and C, and of node B were between about 2 mm and about 4 mm in diameter. The distance between reservoir A and node B was between about 5 mm and about 10 mm; the distance between node B and reservoir C was about the same. The cross-sectional areas of the cavities in typical devices are approximately 1 00 to 400 times greater than the cross-sectional areas of the channels. Therefore the flow resistance of the channels is about 10,000 to 160,000 times greater than the flow resistance of the cavities. Alternative designs for channels and cavities lead to the flow resistance of channels being about 100 times greater or about 1 ,000 times greater than the flow resistance of cavities.

0031 A second way to make a structure like microfluidic device 1 05 is hot embossing a hydrophobic thermoplastic polymer such as cyclic olefin copolymer (COC) followed by solvent-assisted lamination to form enclosed, hydrophobic channels. A third way to make a structure l ike m icrofluidic device 105 is injection molding a hydrophobic polymer such as COC. Finally, hydrophilic microfluidic channels, formed in polycarbonate for example, may be made hydrophobic via chemical surface treatment. There are, no doubt, other ways to make a structure containing cavities connected by hydrophobic microfluidic channels.

0032 Fig. 2 illustrates loading the device of Fig. 1 from an external fluid source. In Fig. 2, reference numbers 105 - 160 refer to the same items as in Fig. 1 . In Fig. 2, however, pressure sources 135, 140 and 145 supply partial vacuum, low pressure and low pressure, respectively. Supply tube 165 connects reservoir A to an external fluid source 1 70 that is at atmospheric pressure. When a partial vacuum is applied to reservoir A by pressure source 135 via gas tube 150, fluid is withdrawn from fluid source 1 70 and accumulated in reservoir A. Fluid does not flow from reservoir A to node B in this situation because the gas pressure applied to node B is higher than the gas pressure applied to reservoir A .

0033 Fig. 3 i llustrates unloading the device of Fig. 1 to an external fluid store. In Fig. 3, reference numbers 105 - 160 refer to the same items as in Fig. 1 . In Fig. 3, however, pressure sources 135, 140 and 145 supply low pressure, high pressure and high pressure, respectively. Drain tube 175 connects reservoir C to an external fluid store 1 80. The fluid store is at atmospheric pressure. When high pressure is applied to reservoir C by pressure source 145 via gas tube 160, fluid is expelled from reservoir C and accumulated in fluid store 180. Fluid does not flow from reservoir C to node B in th is situation because the gas pressure applied to node B is the same as the gas pressure applied to reservoir C.

0034 In reconfigurable microfluidic systems, flu id flow through microfluidic channels is controlled by gas pressure differences appl ied to reservoirs and nodes. Fluid flow through a hydrophobic channel exhibits a pronounced threshold effect. At first, no fluid flows as the pressure difference from one end of the channel to the other is increased. However, once a threshold pressure difference is reached, fluid flow rate through the channel increases in proportion to applied pressure difference. The hydrophobicity of channels sets the threshold pressure difference, and the difference between "h igh" and "low" pressures used in a system is designed to be greater than the hydrophobic threshold pressure. Thus, when the pressure is "high" at one end of a channel and "low" at the other end, fluid flows rapidly in the channel.

0035 The hydrophobic threshold pressure of hydrophobic channels keeps fluid in nodes and reservoirs from leaking into the channels when no pressure differences are appl ied. The threshold pressure is designed to be great enough to prevent fluid flow that might be driven by the hydrodynamic pressure caused by the weight of fluid in a reservoir or node, or by residual pressure differences that might exist when applied pressures are switched between "high" and "low". Thus a "hydrophobic channel" is defined as one that exhibits a pressure threshold that prevents fluid from leaking into the channel when the pressure difference between the two ends of the channel is less than a design pressure. In an example reconfigurable microfluidic system, channels were designed to have about 1 kPa hydrophobic threshold pressure.

0036 Fluid transfer between reservoirs and nodes is accomplished by switching pressures applied to each reservoir and node in a system according to a specific pattern. The following terminology aids discussion of a fluid transfer rule for reconfigurable microfluidic systems. The origin is a reservoir or node from which fluid is to be transferred. The destination is the reservoir or node to which fluid is to be transferred. Two gas pressures are needed: high pressure and low pressure.

0037 A fluid transfer rule for reconfigurable microfluidic systems may be summarized in the following steps:

0038 Step 0: Apply low pressure to all cavities.

0039 Step 1 : Apply h igh pressure to the origin and any cavity connected to the origin by a channel, other than the destination. Apply low pressure to the destination and any cavity connected to the destination, other than the origin.

0040 Step 2 (optional): Switch origin back to low pressure. The purpose of this optional step is to ensure an air gap (i.e. section without fluid) exists in all channels after Step 1 . This optional step is useful when transferring less than all of the fluid that is in the origin cavity at Step 0.

0041 Step 3 : Return to Step 0 to prepare for the next fluid transfer operation.

0042 As explained below, the fluid transfer rule may be executed by a pressure sequencer that provides the necessary sequence of pressures to accomplish any desired fluid transfer operation. Two examples show how the fluid transfer rule is used to perform common fluid transfer experiments. The first example demonstrates flow rate control when fluid is transferred from one cavity to another; the second example demonstrates automated dilution of a fluid sample.

0043 Example 1 : Flow rate control .

0044 Figs. 4A, 4B and 4C are diagrams i llustrating operation of the device of Fig. 1 , seen in plan view. In particular, Fig. 4A shows a plan view of reservoir A, node B and reservoir C, connected by channels 125 and 1 30. In Figs. 4B and 4C, labels Ά', 'B' and 'C are replaced by 'L', 'L' and ' L' (Fig. 4B) and Ή', 'L' and ' L' (Fig. 4C). Fig. 4A serves as a key for Figs. 4B and 4C. Ή' and 'L' in Figs. 4B and 4C show which cavities have high and low pressure applied to them. Shading in Figs. 4B and 4C, and the arrow in Fig. 4C, shows that fluid moves from reservoir A to node B.

0045 The fluid transfer rule explains how the fluid transfer depicted in Figs. 4B and 4C is accomplished. Step 0 of the rule specifies that low pressure is applied to all cavities. Fig. 4B shows low pressure, 'L', applied to reservoir A, node B and reservoir C. Shading of reservoir A in Fig. 4B means that the reservoir has fluid in it, while node B and reservoir C are empty. Reservoir A is the origin.

0046 Step 1 of the fluid transfer rule specifies that high pressure is applied to the origin and any cavity connected to the origin by a channel, other than the destination. Further, low pressure is appl ied to the destination and any cavity connected to the destination, other than the origin. Th is is the situation depicted in Fig. 4C. The result is fluid transfer from the origin to the destination.

0047 All other conditions being equal, the volume of fluid transferred from the origin to the destination depends on the amount of time that pressure is applied during Step 1 of the fluid transfer rule. An experiment was conducted to demonstrate flow rate control in an apparatus sim ilar to that shown in Figs. 1 - 4.

0048 Fig. 5 is a graph of fluid volume transferred between a reservoir and a node of a device similar that of Fig. 1 . The graph shows volume of fluid transferred in m icroliters (μί,) versus time (in seconds) that pressure was applied during Step 1 of the fluid transfer rule. The six black dots on the graph represent experimental data whi le the dashed line is a linear fit to the data. The observed flow rate is approximately 10 [iL per second.

0049 During the experiment, there was no leakage of fluid to reservoir C, even though node B and reservoir C were held at the same low pressure compared to reservoir A. Leakage to reservoir C was prevented by the high flow resistance of channel 130 compared to that of node B.

0050 Example 2: Automated dilution.

0051 Fig. 6 is a diagram illustrating operation of a reconfigurable microfluidic device, seen in plan view. In Fig. 6, the same device 605 is shown seven times under headings ' STEP 0', 'STEP Γ, . . . , 'STEP 6' . Device 605 is sim ilar in construction to the device of Figs. 1 - 4, however device 605 has four reservoirs (610, 61 5, 620, 625) and one node (630). To improve visual clarity, reference numerals are not repeated for the device when it is shown under headings 'STEP 1 ' through 'STEP 6' . Each reservoir is connected to node 630 via its own channel. For example, channel 635 connects reservoir 61 0 to node 630. The other channels do not have reference numerals. The reservoirs, the channels and the node are drawn in black, gray or white during various steps. Black and gray represent two different fluids, while white represents an absence of fluid.

0052 As discussed above, the fluid transfer rule in its basic form alternates between two states. The first state is an initial, rest condition where all cavities are at low pressure. In the second state, fluid is transferred from an origin to a destination. These two states are referred to as 'Step 0' and 'Step 1 ' above.

0053 Fig. 6 uses "step" terminology. However, 'STEP 0' through ' STEP 6' in Fig. 6 are not intended to match the steps of the fluid transfer rule. Instead 'STEP 0' through 'STEP 6' are steps in an overall program during which the steps of the fluid transfer rule are appl ied repeatedly.

0054 The overall result of the program shown in Fig. 6 is that some fluid from reservoir 610 is moved to reservoir 620 and some flu id from reservoir 61 5 is also moved to reservoir 620. Thus, at the end of the program, in 'STEP 6', reservoir 620 contains a mixture of fluids from reservoirs 610 and 61 5. Equivalently, reservoir 620 contains a dilution of fluid from reservoir 610 by fluid from reservoir 61 5.

0055 A sequence of pressures is applied to the reservoirs and node of device 605. Pressures are indicated by labels 'H' for high pressure and 'L' for low pressure in Fig. 6. STEP 0 shows the reservoirs and node all at low pressure. Reservoirs 620 and 625, and node 630 do not contain fluid. Reservoirs 61 0 and 615 contain different fluids indicated by black and gray shading.

0056 In STEP 1 , high pressure is applied to origin reservoir 61 0 and low pressure is appl ied to destination node 630 and to al l cavities connected to the destination, other than the origin. Fluid flows from the origin to the destination. Although not il lustrated, after STEP 1 , system pressures are returned briefly to the initial condition, all cavities at low pressure as in STEP 0. A reset to all cavities at low pressure occurs before and after each il lustrated STEP.

0057 In STEP 2, node 630 is the origin and reservoir 620 is the destination. Therefore high pressure is applied to the origin and all cavities connected to it, other than the destination. Low pressure is appl ied to the destination. Fluid flows from the origin to the destination.

0058 STEP 3 is an example of optional Step 2 of the fluid transfer rule. The purpose of this step is to clear the channels between node 630 and reservoirs 61 0 and 620. An air gap must exist in a channel in order for the channel to present a hydrophobic barrier to fluid flow. Without the operation shown in STEP 3, channel 635, and the channel connecting node 630 to reservoir 620, could be left with fluid in them that would defeat their hydrophobic barriers.

0059 In STEP 3, reservoir 610 is switched briefly back to low pressure while all other pressures remain as in STEP 2. This causes any fluid left in channel 635 to be sent back to reservoir 610. There are alternative ways to accomplish this "channel clearing" function as discussed below. Channel clearing may be needed in cases where less than all of the fluid at the origin is moved to the destination in one cycle of the fluid transfer rule.

0060 STEP 4, STEP 5 and STEP 6 are analogous to STEP 1 , STEP 2 and STEP 3 except that fluid is moved from reservoir 61 5 to reservoir 620 instead of from reservoir 610 to 620. Since the amount of fluid moved from one cavity to another can be controlled by the time that pressures are applied, as demonstrated in Example 1 , the ratio of fluid moved to reservoir 620 from reservoir 610 to fluid moved to reservoir 620 from reservoir 61 5 can be adjusted at the discretion of the experimenter. Thus automated dilution may be performed by selecting an appropriate sequence of pressures to be applied to the cavities of device 605.

0061 An alternate means for clearing out channels when only some of the fluid in an origin cavity is transferred away involves ded icated gas tubes connected to the channels. Fig. 7 is a diagram of a reconfigurable microfluidic device, seen in cross section, including ports for clearing microfluidic channels. The device of Fig. 7 is nearly the same as that of Fig. 1 , except that gas tubes, pressure ports and gas pressure sources are provided to enable creation of air gaps in channels.

0062 In Fig. 7, microfluidic device 705 includes a substrate layer 710, a hydrophobic fluidic layer 715, and a pneumatic layer 720. Cavities in the hydrophobic fluidic layer are labeled Ά', 'B ' and 'C . Reservoir A and node B are connected by channel 725 while ndde B and reservoir C are connected by channel 730.

0063 Pressure sources 735, 740 and 745 are connected to reservoir A, node B and reservoir C, respectively, via gas tubes 750, 755 and 760 respectively. Each of the three pressure sources is capable of providing at least two different pressures: a high pressure and a low pressure.

0064 Pressure sources 775 and 780 are connected to channels 725 and 730 respectively, via gas tubes 785 and 790 respectively. The gas tubes present a higher barrier to fluid flow than the channels. In normal operation of device 705 only gas, never fluid, flows in the gas tubes.

0065 It is apparent that if device 605 of Fig. 6 were equipped with channel clearing gas tubes like gas tubes 785 and 790 of Fig. 7, then STEP 3 (optional Step 2 of the fluid transfer rule) could be replaced by a clearing STEP in which pressure is applied to channel clearing gas tubes while low pressure would be applied to all the cavities in the system.

0066 An experiment was conducted to demonstrate automated dilution in an apparatus similar to that shown in Fig. 6. Fig. 8 is a graph of absorbance representing results of an automated dilution experiment. In the automated dilution experiment, concentration of an aqueous solution was inferred from optical absorbance measurements where higher absorbance corresponded to higher concentration of solute. (Optical absorbance varies linearly with concentration according to Beer's Law.) The graph in Fig. 8 therefore plots absorbance, representing measured concentration, versus target, or expected, concentration. Target concentration is an expected result if the amounts of fluid transferred into the destination reservoir from the origin solute and solvent reservoirs are as expected.

0067 When no dilution is performed ("Zero dilution steps", "+" data point marker), absorbance 2.00 (in arbitrary units) corresponds to target concentration 1 .00 (in arbitrary units). Target concentrations of 0.50 and 0.25 may be obtained in one di lution step; i.e. one time through STEPS 0 through 6 of Fig. 6. Data obtained in this way is labeled "One dilution step" and shown with "o" data point markers on the graph.

0068 Finally data obtained after two dilution steps ("Two dilution steps (serial di lution)", "x" data point markers) is shown for target concentrations of 0.25 and 0.0625. In this case the procedure of Fig. 6 was repeated twice. Target concentration 0.25 was obtained in two ways: using one dilution step or two dilution steps. The actual concentration, as represented by absorbance data, was nearly identical in the two cases.

0069 Examples 1 and 2 discussed above demonstrate that sequences of gas pressures, applied to reservoirs and nodes according to a fluid transfer rule, enable fluid to be moved from any reservoir to any other reservoir in a reconfigurable microfluidic system. Fig. 9 is a diagram of a reconfigurable microfluidic system 905, including a pressure sequencer 91 5.

0070 In Fig. 9, microfluidic device 910 includes hydrophobic reservoirs, nodes and channels. These structures are formed in microfluidic layers of the device. Each reservoir and node is connected to pressure sequencer 915 via a gas tube, such as gas tube 920. Pressure sequencer 91 5 is connected to pressure sources 925 and 930. Pressure sequencer 91 5 includes a set of programmable gas valves.

0071 The sequencer receives pressure sequence data 940. This data includes step by step instructions specifying what pressure is to be applied to each reservoir and node in device 91 0 in order to carry out a specific fluid transfer operation. As shown in Example 2, fluid can be moved from any reservoir to any other reservoir in a reconfigurable microfluidic system by repeating the steps of the fluid transfer rule.

0072 In a laboratory experiment, pressure sequencer 915 was implemented as a set of electronically controlled pneumatic valves that were programmed using LabVIEW software (National Instruments Corporation) running on a personal computer. For the experiment, pressure sequence data necessary to move fluid from one reservoir to another in a reconfigurable microfluidic device was worked out manually. However a graphical software program may be written that allows a user to select origin and destination reservoirs, with the program then generating appropriate pressure sequence data by repeated appl ication of the fluid transfer rule. In this way an intuitive system may be created that perm its users to perform arbitrary microfluidic experiments without needing to understand the fluid transfer rule or other system operation details.

0073 Reconfigurable microfluidic systems may have many reservoirs and nodes, especially those systems designed for parallel biochemical assays. One type of parallel assay involves performing many different biochemical experiments simultaneously on small volumes of fluid taken from one sample. A second type of parallel assay involves processing many different fluid samples simultaneously, in otherwise identical biochemical experiments. Both of these cases involve parallel operations in which groups of reservoirs or nodes change pressure together during the steps of a complex fluid transfer process.

0074 When a reconfigurable microfluidic device has reservoirs or nodes that are operated in a group, it is more convenient to integrate a gas flow manifold in the pneumatic layer of the device than to dedicate a separate gas tube to each reservoir or node. Figs. 10A (cross sectional view) and 10B (plan view) are diagrams i llustrating a gas flow manifold in a reconfigurable microfluidic device 1005.

0075 In Fig. 10A, the block arrow labeled 'B ' indicates the perspective from which Fig. l OB is drawn. Device 1005 includes a substrate layer 101 0, a hydrophobic microfluidic layer 101 5, and a pneumatic layer 1020. Dashed l ines, e.g. 1 030, designate channels to microfluidic cavities that are not shown in Fig. 1 0A because they are not in the plane of the page. Gas tube 1 025 is connected via gas flow manifold 1 035 to cavity 1040 and cavity 1045. Any gas pressure supplied by the gas tube pressurizes both cavities at once. The layout of the gas flow manifold is shown in plan view in Fig. 10B. The gas flow manifold acts as a pressure port for groups of cavities that are operated in parallel. 0076 One application for reconfigurable microfluidic devices such as those described above is homogeneous assays. A homogeneous assay is one that involves mix and read procedures, but does not require processing samples via separation or washing steps.

0077 Fig. 1 1 is a plan view diagram of a reconfigurable microfluidic device for homogenous assays. The device of Fig. 1 1 is similar to that of Figs. 1 - 4; however, it has more reservoirs, nodes and channels. The device may be constructed in layers exactly as described above; it is only the layout of reservoirs, nodes and channels that is different. The plan view shown in Fig. 1 1 is analogous to that of Fig. 4. A corresponding cross-sectional view of the device of Fig. 1 1 is not provided, but would essentially be a more complicated version of Fig. 1 .

0078 In Fig. 1 1 , cavities are labeled Ά', 'Β ', 'C\ Ό', Έ', 'F', 'G', 'J', ' ',^' 'Μ', 'Ν ', 'Ρ', 'R', ' S \ 'T' and 'LP. (' Η ' and ^* L' are not used as cavity labels to avoid confusion with their use to ind icate gas pressures in Figs. 1 2 - 1 5.) Cavities 'Α', 'Β', 'C, Ό', 'J', 'Κ', 'Ρν', 'S', 'T' and ' LP are classified as reservoirs because each of them is connected to only one channel. Cavities 'Ε', 'F', 'G \ 'Μ', 'N' and 'P^* are classified as nodes because each of them is connected to more than one channel .

0079 In an example homogenous assay, reservoirs Ά', 'B ' and 'C are used as sources of reagents; hence the label 'REAGENTS' in the figure. Reservoirs 'D' and ' ' are used as sources of 'SAMPLES' ; reservoirs 'J ' and 'K' accumulate fluidic OUTPUT'; i.e. mixtures of samples and reagents.

0080 The device of Fig. 1 1 performs assays by first transferring a small amount of reagents Ά', 'B ' and 'C to reservoirs 'J ' and ' K' . ("Reagent 'Α'" is a shorthand for "reagent stored in reservoir 'A'".) Next, sample 'D' is transferred to reservoir 'J' and sample 'K' is transferred to reservoir 'R' . After these operations are complete reservoir 'J' contains a mixture of sample 'D' and reagents Ά', 'B' and 'C, while reservoir 'R' contains a mixture of sample 'K' and reagents 'Α', 'B ' and 'C.

0081 The reagent transfer steps just mentioned may be referred to as "single- reagent- input, mu ltiple-output" for one reagent is distributed among two outputs. Similarly, the sample transfer steps may be referred to as "multiple-sample-input, multiple-output" for two samples are transferred to two outputs in parallel.

0082 Figs. 12 and 1 3 illustrate steps in single-reagent-input, multiple-output operation of the device of Fig. 1 1 . ' STEP 0' through ' STEP 6' of Figs. 12 and 13 show the device of Fig. 1 1 ; however, cavity labels 'Α', ' Β ', 'C, etc. have been replaced by pressure labels Ή ' and 'L' ind icating high or low appl ied gas pressure, respectively. Shading in Fig. 12 of the reagent reservoir labeled 'A' in Fig. 1 1 , indicates the presence of fluid in the reservoir. In the fol lowing discussion, Fig. 1 1 is used as a key to identify various reservoirs and nodes.

0083 STEP 0 represents the initial condition. Reagent is stored in reservoir A and all cavities are at low pressure. STEP 1 shows the pressure pattern needed to transfer fluid from reservoir A to node E. STEP 2 shows the pressure pattern needed to transfer fluid from node E to node M. STEPS 3, 4 and 5 show pressure patterns needed to transfer fluid from nodes E and M, across the device in parallel, to reservoirs J and R respectively. The pressure patterns at each step follow the fluid transfer rule explained above. A similar pattern of steps may be used to transfer reagent from reservoir B to reservoirs J and R.

0084 Figs. 14 and 15 illustrate steps in multiple-sample-input, multiple-output operation of the device of Fig. 1 1 . Shading in Fig. 14 of sample reservoirs D and indicates the presence of fluid in the reservoirs and that a different fluid may be in each reservoir. STEP 0 represents the initial condition. Samples are stored in reservoirs D and and all cavities are at low pressure. STEP 1 shows the pressure pattern needed to transfer fluid in paral lel from reservoirs D and K to nodes E and M, respectively. STEPS 2, 3 and 4 show pressure patterns needed to transfer fluid from nodes E and M, across the device in parallel, to reservoirs J and R respectively. The pressure patterns shown for STEPS 2, 3 and 4 of Figs. 14 and 1 5 are the same as the pressure patterns show for STEPS 3, 4 and 5, respectively of Fig. 13 since the desired fluid movement pattern is the same in the two cases.

0085 The device of Figs. 1 1 - 1 5 is designed to perform simultaneous experiments on two samples, each experiment using three reagents. The device therefore is designed with two "rows" and three "columns" of nodes connected in series. Similar devices may be designed to process different numbers of samples and/or reagents. For example, experiments with j samples and k reagents may be performed in parallel with a device having j rows and k columns. Here, "rows" and "columns" indicate the topology of a device such as that shown in Fig. 1 1 . Operation of the device is not affected if the rows or columns are not straight, for example.

0086 As demonstrated by the examples described above, a reconfigurable microfluidic system is capable of moving fluid from any reservoir to any other reservoir in the system. This capabi lity is useful for a variety of microfluidic applications including homogeneous assays with an arbitrary number of samples and reagents.

0087 The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the principles defined herein may be applied to other embodiments without departing from the scope of the disclosure. Thus, the disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

0088 All elements, parts and steps described herein are preferably included. It is to be understood that any of these elements, parts and steps may be replaced by other elements, parts and steps or deleted altogether as will be obvious to those skilled in the art.

0089 Broadly, this writing discloses at least the following. Reconfigurable microfluidic systems are based on networks of microfluidic cavities connected by hydrophobic microfluidic channels. Each cavity is classified as either a reservoir or a node, and includes a pressure port via which gas pressure may be applied. Sequences of gas pressures, applied to reservoirs and nodes according to a flu id transfer rule, enable fluid to be moved from any reservoir to any other reservoir in a system. Such systems are suitable for automated, multi-input, multi-output homogeneous assays.

Concepts

This writing also presents at least the following Concepts.

1 . A reconfigurable microfluidic system comprising: a network of microfluidic cavities connected by hydrophobic microfluidic channels, wherein: reservoirs are cavities that are connected to only one channel each, and nodes are cavities that are connected to two or more channels each;

a plurality of the channels connect on ly two cavities each;

a plurality of the channels have a greater resistance to fluid flow than that of the nodes; and

a plurality of the cavities include a gas pressure port.

2. The reconfigurable microfluidic system of Concept 1 , a plural ity of the channels having a resistance to fluid flow at least 100 times greater than that of the nodes.

3. The reconfigurable microfluidic system of Concept 1 , a plurality of the channels having a resistance to fluid flow at least 1 ,000 times greater than that of the nodes.

4. The reconfigurable microfluidic system of Concept 1 , a plurality of the channels having a resistance to fluid flow at least 10,000 times greater than that of the nodes.

5. The reconfigurable microfluidic system of Concept 1 , the cavities being formed in a hydrophobic microfluidic layer that is bonded to a substrate layer, and the cavities being sealed by a pneumatic layer that is bonded to the microfluidic layer.

6. The reconfigurable microfluidic system of Concept 5, the m icrofluidic layer being made from polydimethylsiloxane.

7. The reconfigurable microfluidic system of Concept 5, the m icrofluidic layer being made from fluorinated ethylene propylene. The reconfigurable microfluidic system of Concept 5, the m icrofluidic layer being made from polytetrafluoroethylene. The reconfigurable microfluidic system of Concept 5, the pneumatic layer including a gas manifold that acts as a pressure port for two or more cavities. The reconfigurable microfluidic system of Concept 1 further comprising fluid tubing connecting a cavity to an external fluid store maintained at atmospheric pressure. The reconfigurable microfluidic system of Concept 1 further comprising gas tubing connecting one or more cavities to gas pressure sources via the cavities' gas pressure ports. The reconfigurable microfluidic system of Concept 1 , at least one m icrofluidic channel having a gas pressure port. The reconfigurable microfluidic system of Concept 1 further comprising a pressure sequencer including a set of gas valves, the pressure sequencer connected by gas tubing to: a high pressure gas source, a low pressure gas source, and at least one cavity. The reconfigurable microfluidic system of Concept 13, the pressure sequencer applying high gas pressure and low gas pressure to the at least one cavity according to pressure sequence data. The reconfigurable microfluidic system of Concept 14, a plurality of the hydrophobic m icrofluidic channels having a hydrophobic pressure barrier to fluid flow that is less than the pressure difference between the high gas pressure and the low gas pressure. The reconfigurable microfluidic system of Concept 14, the pressure sequence data following a fluid transfer rule in which high gas pressure is appl ied to an origin cavity from which a fluid is transferred and low gas pressure is applied to a destination cavity to which the fluid is transferred, and high gas pressure is applied to any cavity (other than the destination cavity) connected to the origin cavity by a channel and low gas pressure is appl ied to any cavity (other than the origin cavity) connected to the destination cavity by a channel, and where high gas pressure is a pressure greater than low gas pressure. The reconfigurable microfluidic system of Concept 1 6 where the network includes j rows and k columns of cavities, j and k being positive integers, cavities in each row or column being connected in series. The reconfigurable microfluidic system of Concept 1 where the network includes j rows and k columns of cavities, j and k being positive integers, cavities in each row or column being connected in series. A method for performing a homogeneous assay with j samples and k reagents, the method comprising operating the reconfigurable microfluidic system of Concept 1 7 with pressure sequence data that causes each of the j samples to be mixed with the k reagents thereby producing j output solutions.

Claims

What is claimed is:

1 . A reconfigiirable microfiuidic system comprising:

a network of m icrofiuidic cavities connected by hydrophobic microfiuidic channels, wherein:

reservoirs are cavities that are connected to only one channel each, and nodes are cavities that are connected to two or more channels each; a plurality of the channels connect only two cavities each;

a plurality of the cavities include a gas pressure port.

2. The reconfigiirable microfiuidic system of C laim 1 , a plurality of the channels having a resistance to fluid flow at least 100 times greater than that of the nodes.

3. The reconfigiirable m icrofiuidic system of Claim 1 , a plurality of the channels having a resistance to fluid flow at least 1 ,000 times greater than that of the nodes.

4. The reconfigiirable m icrofiuidic system of Claim 1 , a plurality of the channels having a resistance to fluid flow at least 1 0,000 times greater than that of the nodes.

5. The reconfigiirable microfiuidic system of C laim 1 , the cavities being formed in a

hydrophobic microfiuidic layer that is bonded to a substrate layer, and the cavities being sealed by a pneumatic layer that is bonded to the microfiuidic layer.

6. The reconfigiirable microfiuidic system of Claim 5, the microfiuidic layer being made from polydimethylsiloxane.

7. The reconfigiirable m icrofiuidic system of Claim 5, the microfiuidic layer being made from fluorinated ethylene propylene.

8. The reconfigiirable microfiuidic system of Claim 5, the microfiuidic layer being made from polytetrafluoroethylene.

9. The reconfigurable microfluidic system of Claim 5, the pneumatic layer including a gas manifold that acts as a pressure port for two or more cavities.

10. The reconfigurable microfluidic system of Claim 1 further comprising fluid tubing

connecting a cavity to an external fluid store maintained at atmospheric pressure.

1 1 . The reconfigurable microfluidic system of Claim 1 further comprising gas tubing

connecting one or more cavities to gas pressure sources via the cavities' gas pressure ports.

12. The reconfigurable microfluidic system of Claim 1 , at least one microfluidic channel having a gas pressure port.

13. The reconfigurable microfluidic system of Claim 1 further comprising a pressure

sequencer including a set of gas valves, the pressure sequencer connected by gas tubing to: a high pressure gas source, a low pressure gas source, and at least one cavity.

14. The reconfigurable microfluidic system of Claim 13, the pressure sequencer applying high gas pressure and low gas pressure to the at least one cavity according to pressure sequence data.

15. The reconfigurable microfluidic system of Claim 14, a plurality of the hydrophobic microfluidic channels having a hydrophobic pressure barrier to fluid flow that is less than the pressure difference between the high gas pressure and the low gas pressure.

16. The reconfigurable microfluidic system of Claim 14, the pressure sequence data

following a fluid transfer rule in which high gas pressure is appl ied to an origin cavity from which a fluid is transferred and low gas pressure is applied to a destination cavity to which the fluid is transferred, and high gas pressure is applied to any cavity (other than the destination cavity) connected to the origin cavity by a channel and low gas pressure is appl ied to any cavity (other than the origin cavity) connected to the destination cavity by a channel, and where high gas pressure is a pressure greater than low gas pressure.

17. The reconfigurable microfluidic system of Claim 16 where the network includes j rows and k columns of cavities, j and k being positive integers, cavities in each row or column being connected in series.

18. The reconfigurable microfluidic system of Claim 1 where the network includes j rows and k columns of cavities, j and k being positive integers, cavities in each row or column being connected in series.

19. A method for performing a homogeneous assay with j samples and k reagents, the method comprising operating the reconfigurable microfluidic system of Claim 1 7 with pressure sequence data that causes each of the j samples to be m ixed with the k reagents thereby producing j output solutions.