The present teachings relate to using one or more microfluidic channels for generating binary states. In particular, the present teachings relate to incorporating such microfluidic channels into devices that use the binary states in various applications.
Controlling the flow of fluids in microfluidic channels presents many challenges, especially when the fluids have low Reynolds numbers and the control is implemented upon continuous flowing liquids. One of the challenges lies in the difficulty of scaling down conventional flow control mechanisms such as valves, pumps, switches and mixers for use in controlling fluid flow inside microfluidic channels.
In one prior art solution, in addition to a first network of fluid-carrying channels, a separate network of channels is used to transport compressed air for use in operating valves and pumps. Understandably, such a separate network of channels not only involves additional internal structures inside a device in which the fluid-carrying channels are located, but also necessitates the use of additional structures external to the device. Such external structures may include transport structures for transporting the compressed air; interface structures for coupling the compressed air into the device; and control mechanisms for selectively modifying the air flow for activating control elements such as valves and pumps. The control mechanisms not only tend to be complex and bulky but also provide a less than desired level of accuracy in controlling fluid flow inside the fluid-carrying channels.
In an alternative approach, rather than using continuous flow techniques, a droplet-based approach is used wherein nanoliter to picoliter sized droplets of a fluid are introduced into a microfluidic channel, either individually or as a mixture along with one or more other fluids. One shortcoming associated with this alternative approach is that it is difficult to detect and control individual droplets for ensuring that a correct amount of fluid is being introduced into the microfluidic channel, even when external timers are used for controlling the introduction of the droplets into the microfluidic channel. Another shortcoming may be encountered when the droplet is in the form of a gas bubble, for example. In this case, the gas bubble may tend to disperse, escape, or dissolve, thereby rendering the delivery of the gas bubble through the microfluidic channel an uncertain and imprecise process. Additionally, a gas bubble is limited in its ability to transport usable materials, like chemicals or proteins, within a microfluidic device.
It is accordingly desirable to provide an arrangement that not only provides for precise fluid control, but also permits two fluids to be transported separately without intermixing, while accommodating flow control techniques and the generation of information in the form of digital data.
According to a first aspect of the present disclosure, a fluidic device for generating binary states is provided. The device includes a first fluidic channel; and an electrode system that is arranged to provide a voltage potential that traverses at least a portion of the first fluidic channel. The device also includes a first fluid delivery system for introducing into the at least a portion of the first fluidic channel, a first fluid at a first instant in time and a second fluid at a second instant in time, wherein the first and the second instants in time correspond to a first binary state and a second binary state characterized by a first voltage differential and a second voltage differential respectively across the at least a portion of the first fluidic channel as a result of the first and second fluids being present in the at least a portion of the first fluidic channel at the first and the second instants in time.
According to a second aspect of the present disclosure, a method of generating binary states is provided. The method includes a first step of applying a voltage potential that traverses at least a portion of a first fluidic channel; and further includes a second step of positioning one of a first fluid or a second fluid inside the at least a portion of the first fluidic channel for modifying the voltage potential on the basis of at least one of a first dielectric constant or a first conductivity associated with the first fluid and at least one of a second dielectric constant or a second conductivity associated with the second fluid.
According to a third aspect of the present disclosure, a fluidic system for generating binary states is provided. The fluidic system includes a first fluidic control channel containing a first fluid through which is transported at least a first droplet comprising a second fluid; and further includes an actuator system comprising a toggle element that is settable to one of a first physical condition or a second physical condition upon subjecting the toggle element to a corresponding one of a first voltage potential or a second voltage potential that is generated as a result of the first droplet being located at one of a first position or a second position in the first fluid.
Further aspects of the disclosure are shown in the specification, drawings and claims of the present application.
Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale. Instead, emphasis is placed upon clearly illustrating various principles. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
Throughout this description, embodiments and variations are described for the purpose of illustrating uses and implementations of the inventive concept. The illustrative description should be understood as presenting examples of the inventive concept, rather than as limiting the scope of the concept as disclosed herein. For example, it will be understood that terminology such as, for example, voltage potential, voltage drop, voltage condition, voltage differential, nodes, terminals, circuits, devices, systems, and coupling are used herein as a matter of convenience for description purposes and should not be interpreted literally in a narrowing sense. For example, a voltage potential may be alternatively referred to herein as a voltage differential, or a voltage drop. A person of ordinary skill in the art will understand that these terms may be used interchangeably and as such must be interpreted accordingly. It will be also be understood that the drawings use certain symbols and interconnections that must be interpreted broadly as can be normally understood by persons of ordinary skill in the art. As one example, of such interpretation, the fluidic channels are shown to include channel walls. However, one of ordinary skill in the art will understand that fluidic channels are often created as voids or cavities in other materials and as such do not have a wall but rather may have one or more internal surfaces formed as a result of the void or cavity. Similarly, a capacitor or a dielectric element may be an integral part of a semiconductor layer inside an integrated circuit and formed using semiconductor fabrication techniques, or could be an integrated component of the microfluidic device, for example. It will be further understood that various words herein such as the word “droplet” encompasses various volumes of liquids such as a drop, a cluster of drops, a continuous flow, or an agglomerate; the phrase “fluidic channel” encompasses various sizes, such as a nanofluidic channel, a microfluidic channel and a channel of significantly larger size; the word “NOT” may be used interchangeably with “INVERTER”; and the word “voltage” encompasses voltages of various amplitudes and polarities. Specifically, in various figures the voltage labels indicate “0” V and “V” volts. However, in various embodiments, the voltage labels may be replaced with “−V” and “+V” wherein a proper usage of an appropriate voltage differential is more effective than absolute voltage values.
Attention is now drawn to
However, it will be understood that in general, fluidic control channel 110 may be used as a stand-alone element for generating binary states that can be exploited for a variety of uses. Such embodiments may not necessarily include actuator system 105. For example, actuator system 105 may be replaced by a different element that carries out one or more of a measuring, a computing, or an analytical function.
Microfluidic control channel 110 contains a first fluid 111 and a second fluid 112, wherein the second fluid 112 is shown herein in the form of droplets 112a, 112b and 112c. The dielectric constant or conductivity associated with the first fluid 111 is typically selected to be different than the dielectric constant or conductivity associated with the second fluid 112. Also, in various applications, the second fluid 112 is selected to be immiscible with the first fluid 111 so as to reduce or eliminate problems such as those associated with dispersion, solubility, and mobility. A few non-limiting examples of first fluid 111 includes fluids such as oil and water, while second fluid 112 includes oil and air (pure water, salt water etc).
One or both of the fluids are introduced into microfluidic control channel 110 by fluid delivery system 145. Fluid delivery system 145 is merely a pictorial representation of various ways by which one or more fluids can be introduced into microfluidic control channel 110. A few non-limiting examples include a real-time delivery system that introduces droplets 112a, 112b, and 112c into microfluidic control channel 110 in a periodic sequence, an intermittent sequence, or a one-time sequence, under control of a control mechanism (not shown). The control mechanism may be a manual control operated by a human being, or may be an electronic control. In certain embodiments, once introduced into microfluidic control channel 110, one or more of droplets 112a, 112b, and 112c may be further restricted to remain within the microfluidic control channel 110 and manipulated from one position to a different position. Various flow-focusing techniques may be used to form droplets 112a, 112b, and 112c inside microfluidic control channel 110.
Also shown in
To understand this arrangement in further detail, each of control channel 110 and GER channel 105 may be visualized as two capacitors arranged such that the voltage provided by voltage source 125 is applied across the two capacitors as well as any object (separation barrier 130) that may be located between the two capacitors. Each capacitor has certain properties such as a dielectric constant or an electrical conductivity that comes into play when the binary states are generated in microfluidic control channel 110. To elaborate, the properties affect the amplitude of voltage drops across each element (Δv1 and Δv2). In the case of microfluidic control channel 110, the dielectric constant (or electrical conductivity) is a variable value that is dependent on the position of second fluid 112 vis-à-vis transverse axis 135. Specifically, when second fluid 112 is located to intersect transverse axis 135, the dielectric value of the capacitor (microfluidic control channel 110) is different from when second fluid 112 is moved away and only first fluid 111, which has a different dielectric constant, is present. The change in dielectric constant/electrical conductivity results in the two different voltage values that Δv2 can take on. These two different voltage values are interpreted as the binary states, which may be used for various binary applications.
In terms of one such binary application, attention is now drawn to a microfluidic channel 105 arranged to be substantially parallel to microfluidic control channel 110. For the sake of convenience, only a portion of microfluidic channel 105 is shown in
In the embodiment shown in
Various fluids can be transported via microfluidic channel 105 and various applications can be employed in various arrangements. These various applications include analytical applications, wherein the chemical, physical, biological and/or optical parameters of the fluid can be assessed; dispensing applications wherein a measurable quantity of a fluid can be delivered via microfluidic channel 105; and control applications, wherein the fluid contained inside microfluidic channel 105 is used for controlling various elements such as a switch or a valve, for example. Channel 105 can also be a non-fluidic switch mechanism wherein no fluids are used at all.
In this particular example embodiment, as mentioned above, the fluid contained inside microfluidic channel 105 is an electrorheological fluid. Furthermore, in one specific case, the electrorheological fluid is a Giant Electrorheological (GER) fluid. As is known, electrorheological fluids react to appropriate electrical stimuli by changing physical characteristics. In the case of GER, the fluid transforms from a liquid state to a semi-solid or solid state depending upon the amplitude of a voltage potential applied across the GER fluid.
The GER fluid, or other fluid in microfluidic channel 105, referred to hereafter as GER fluid 106, is introduced into microfluidic channel 105 using a fluid delivery system 140. Fluid delivery system 140 is merely a pictorial representation of various ways by which one or more fluids can be introduced into microfluidic channel 105. A few non-limiting examples include a real-time delivery system that introduces the fluid into microfluidic channel 105 in a periodic sequence, an intermittent sequence, or a one-time sequence. The delivery may be controlled using a manual or an automatic control mechanism (not shown). When manual, the fluid is introduced into microfluidic channel 105 by a human being, in certain cases on a one-time basis. In certain embodiments, once introduced into microfluidic channel 105, the fluid may be confined within microfluidic channel 105 in order to carry out a control action, for example. This aspect will be described below in more detail using
When the fluid inside microfluidic channel 105 is GER, the GER fluid 106 in area 107 transforms from a liquid state to a semi-solid or solid state depending upon the amplitude of the voltage potential present along transverse axis 135. As explained above, this voltage potential can be set to one of two binary states by suitably positioning second fluid 112 inside microfluidic control channel 110. Specifically, when droplet 112b is located as shown (so as to intersect transverse axis 135), the voltage differential across electrodes 115 and 120 rises above a threshold voltage potential, thereby leading to a transformation of GER fluid 106 from a liquid state to a semi-solid or solid state (depending upon the amplitude of the threshold voltage potential). The threshold voltage potential can be suitably selected based on the nature of individual applications. When area 107 is in a liquid state, GER fluid 106 is permitted to flow out of GER channel 105 as indicted by arrow 108. On the other hand, when area 107 is in a solid state, the flow of GER fluid 106 out of GER channel 105 is blocked.
The electrical aspects are described below in further detail using other figures.
Attention is now drawn to
herein C=capacitance in farads; A=area of electrode plates; ∈=permittivity/dielectric constant; and separation distance (t)=d.
Charge conservation dictates that
QC=QG
Additionally, the two constraints on the voltages are
V=VC+VG
VCCC=VGCG
Solving for VG leads to:
This equation can be further simplified by assuming that microfluidic control channel 110 and microfluidic channel 105 have similar dimensions, thereby leading to the areas and distances being identical. Under this assumption:
Finally, ∈C is itself variable depending on the presence or absence of droplet 112b affecting the voltage potential between electrodes 115 and 120. Hence, VG=VG(x) wherein x=1 when droplet 112b is present, and x=0 when droplet 112b is absent. Assuming oil is the first fluid (the carrier through which the second fluid moves), water the second fluid, and GER is used as a toggle element that is settable to one of two physical conditions, then ∈G≈60, ∈H2O≈80, and ∈OIL≈2.
When droplet 112b is not present and ∈C=∈OIL then
When droplet 112b is present and ∈C=∈H2O then
As can be understood, VG(1) and VG(0) can be suitably selected in relation to one or more threshold voltage values (potential values such that the GER solidifies) using the equations shown above for transforming GER fluid 106 from a liquid state to a solid state such that Vg(0)<Vthresh and Vg(1)>Vthresh.
The location of a droplet 506 in the first microfluidic control channel 505 (intersecting voltage potential axis 507) determines the liquid/solid state of region 511 of GER fluid 106. Similarly, a location of a droplet 516 in the second microfluidic control channel 515 (intersecting voltage potential axis 517) determines the liquid/solid state of region 512 of GER fluid 106 in GER channel 510. As can be understood, when either region 511 or region 512 turns solid, the flow 513 of GER fluid 106 out of GER channel 510 is blocked. This blockage is interpreted as an asserted OR output condition. This interpretation can be generalized to any serially linked structures such that the assertion of either inputs 505 or 515 (or both) leads to a condition where flow in a third channel is blocked, whether by the solidification of GER fluid, or by the closing of a deformable membrane into another microfluidic structure.
The location of a first droplet 606 in the first microfluidic control channel 605 (intersecting voltage potential axis 607) as well as a similar position of a second droplet 616 in the second microfluidic control channel 615 (intersecting the same voltage potential axis 607) determines the liquid/solid state of region 611 of GER fluid 106. As can be understood, when either of first droplet 606 or the second droplet 616 is not positioned in the voltage potential axis 607, region 611 of GER fluid 106 does not transition from a liquid to a solid state, thereby allowing GER fluid 106 to generate a flow 612 out of GER channel 610. In contrast, when both the first and the second droplets are positioned appropriately, region 611 of GER fluid 106 transitions from a liquid to a solid state, thereby blocking the flow 612 out of GER channel 610. This blockage is interpreted as an asserted AND output condition, and results from the electrical necessity of having voltage transmitted to 607 from the left electrode and to 608 from the right electrode before sufficient voltage potential can be established across 611.
The location of a droplet 706 in the microfluidic control channel 705 (intersecting voltage potential axis 707) changes the liquid/solid state of region 716 of GER fluid 106 in GER channel 715. As can be understood, when droplet 706 is moved away from a position that intersects the voltage potential axis 707, region 716 of GER fluid 106 transitions from a solid state to a liquid state. In one embodiment, the solid state of region 716 is set as a default state, activated for default times when droplet 706 is not present. The default state is set using a capacitor system 710, which is configured to couple a voltage potential (a default, quiescent state voltage) into separation barrier 730. In an alternate embodiment, the voltage potential may be coupled directly into GER channel 715 and/or may be coupled into separation barrier 730. Irrespective of the nature of the coupling, the voltage potential causes region 716 of GER fluid 106 to be set to a default state that is changed to an opposite state (inversion) by suitably positioning droplet 706 to either intersect or not intersect voltage potential axis 707.
Capacitor system 710 may be implemented in a variety of ways. A few non-limiting examples include a capacitor that is fabricated directly on or inside a substrate (not shown) in which GER channel 715 is located. Semiconductor techniques for capacitor fabrication may be used. In another example implementation, a discrete capacitor or a portion of a discrete capacitor (a capacitor plate, for example) is mounted on the substrate. The adjacent location may be on the same layer of the substrate on which separation barrier 730 and/or GER channel 715 are located, or may be on a different layer, for example either above or below the layer on which separation barrier 730 and/or GER channel 715 are located. In a third example, the capacitor is built between layers of substrate.
The electrical behavior of the INVERTER configuration shown in
Q1=Q2+Q3 (balance of charges inside the non-grounded portion 730)
Q1=C1v1; Q2=C2v2; and Q3=CgνG
wherein “vx” represents the voltage potential across each of microfluidic control channel 705, capacitor system 710, and GER channel 715 respectively)
V1−v1=V2+v2=V3+νG (voltage in the central region must be the same regardless of which channel is chosen as a reference)
Solving for vg (and setting the capacitance CI of capacitor system 710 such that CI=f*CG where f is any selected ratio):
In one embodiment, the capacitance value of capacitor system 710 is similar to that of GER channel 715 (f≈1). The values for vG under this condition (and using values as described above in other equations) can be determined as follows:
By suitably configuring the various voltages, like an embodiment in which voltages are chosen such that V1=−V2=V and V3=0, the values for νG (0) and νG (1) are as follows:
The amplitude of voltage V is selected such that the solidification threshold of GER fluid 106 in GER channel 715 is crossed only when droplet 706 is absent, i.e. V/10<Vthresh<V/2. Droplet 706 may be positioned to intersect voltage potential axis 707 subsequently when the INVERTER action is desired.
In an alternate interpretation of the inverter mechanism, droplet 706 is an electrically conductive fluid, but the carrier fluid (the fluid present in channel 705 that contains droplet 706) is electrically non-conductive. In this embodiment, capacitor C1 can be set to be very large, such that the voltage in 730 approaches the value set by V2 when droplet 706 is not present. When droplet 706 is present along axis 707, then electrical current can pass through droplet 706, and set the voltage of 730 to V1. Because conductive droplet 706 can physically allow charge to be added to 730, its effect will dominate the polarization effect caused by the capacitor C1. If capacitor C1 is set to be large enough, the electrical voltages in 730 will approach the result: V(730)=V2 if no droplet 706; V(730)=V1 if droplet 706.
In an embodiment utilizing GER fluid in 105, when droplet 112b is positioned in microfluidic control channel 110 as shown, area 107 in GER channel 105 transitions from a liquid state to a solid state. Upon occurrence of this solidification, additional GER fluid 106 that is forced into GER channel 105 by fluid delivery system 140 along path 909 is blocked thereby causing pressure between the Fluid Delivery System 140 and area 107 to experience a buildup of pressure. Due to the flexibility of the membranes at 906, this will cause GER fluid 106 to move radially outwards. The direction indicated by arrow 907 may be used to expand surface 906 of GER channel 105 to expand and apply pressure against element 905. This pressure is used to carry out a control operation, such as for example, a switch activation when element 905 is a switch. When element 905 is a channel carrying a fluid, the pressure may result in a constriction of a surface of the channel which can modulate the flow of fluid inside. GER fluid 106 expansion in the direction indicated by arrow 908 may be similarly used for controlling the other element 910.
Specifically, universal logic device 900 includes a GER channel 7, a first microfluidic control channel 5, a second microfluidic control channel 6, an electrode system that includes electrodes 1-4, and a pair of capacitor systems 8 and 9. Each of the capacitor systems provides an INVERTER functionality to be implemented in universal logic device 900, while the remaining elements enable universal logic device 900 to be configured for a variety of logic operations. Unlike traditional approaches wherein several NAND gates or NOR gates are combined together to implement even simple binary logic functions, the universal logic device 900 permits implementation of these same binary logic functions using a single logic gate mechanism. Like NAND and NOR logic, universal logic device 900 can also be combined together with other logic devices to enable further more complicated logic functions.
The voltages applied to the various electrodes 1-4 and the position of droplets inside microfluidic control channels 5 and 6, determine which of sixteen possible logical operations can be implemented in universal logic device 900. Of the four electrodes, two electrodes 1 and 4 (V1 and V4) (in conjunction with an electrode connection area 10 if needed) are used for configuring the two control channels, while the two other electrodes 2 and 3 (V2 and V3) are used for the capacitor system in order to implement INVERTER functionality. Capacitor systems 8 and 9 couple into separation barrier 13, suitable voltages to set the GER fluid inside GER channel 7 to a default state. GER fluid is introduced into, and exits from, GER channel 7 via ports 16 and 17. Similarly, fluid introduction and exit from microfluidic control channels 5 and 6 are carried out via ports 14/15, and 18/19 respectively. Ports may also be interpreted as continuations of the microfluidic channels into other portions of a larger device, here unspecified.
The electrical behavior of universal logic device 900 will now be described using the simplified circuit diagram
The truth table of the various combinations and corresponding voltage amplitudes is shown in
The idealized voltage potential across the activation mechanism can be determined as follows:
1) The potential difference across the activation mechanism is assumed to be the absolute value of the difference between the one active voltage in set {A} (i.e. V1, V2) and the one active voltage in set {B} (i.e. V3, V4).
2) An absolute value difference of greater than 2 is sufficient to activate the actuator mechanism or signal chosen for the particular application of the logic device
3) The active voltages are determined as follows:
4) The exception to the above rules occurs when a blank value (blank space) is involved. The blank space effectively indicates no voltage potential, and is therefore set by the nearest active value.
5) The specific values displayed in the truth table are arbitrary provided that the correct absolute value is maintained when the above rules are applied.
Spin a negative photoresist (such as SU8, for example) on to a glass substrate (step 50 in
The logic device can then be manufactured using the mold as described hereafter. The electrode material (AgPDMS, for example) is filled into the cavities of the mold (step 57). Excess AgPDMS may be removed and the surface cleaned. The assembly is then baked in an oven at approximately 60 degrees for approximately 30 minutes to cure the AgPDMS. Pour a PDMS gel into the mold and bake in the oven at approximately 60 degrees for approximately 2+ hours to cure the PDMS. Peel the PDMS together with the AgPDMS electrodes from the glass substrate (step 60). Using a half-bake method, seal the device onto a flat PDMS layer (step 61). The sealed assembly is then baked on a hotplate at approximately 150 degrees for over 2 hours to finalize the manufacturing process.
All patents and publications mentioned in the specification may be indicative of the levels of skill of those skilled in the art to which the disclosure pertains. All references cited in this disclosure are incorporated by reference to the same extent as if each reference had been incorporated by reference in its entirety individually.
It is to be understood that the disclosure is not limited to particular methods or systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. The term “plurality” includes two or more referents unless the content clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosure pertains.
The examples set forth above are provided to give those of ordinary skill in the art a complete disclosure and description of how to make and use the embodiments of the enhancement methods for sampled and multiplexed image and video data of the disclosure, and are not intended to limit the scope of what the inventors regard as their disclosure. Modifications of the above-described modes for carrying out the disclosure may be used by persons of skill in the video art, and are intended to be within the scope of the following claims.
A number of embodiments of the disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, other embodiments are within the scope of the following claims.
This application claims priority under 35 U.S.C. §119(e) from U.S. Provisional Patent Application No. 61/300,329 entitled “Universal Microfluidic Logic Gate” filed on Feb. 1, 2010, which is incorporated herein by reference in its entirety.
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20110186164 A1 | Aug 2011 | US |
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61300329 | Feb 2010 | US |