Thermal cycling method and system

Abstract

The present disclosure relates to methods, devices and systems for thermal cycling of microfluidic cartridges comprising a permeable heat sink and / or a flexible heat spreader for sealing one or more channels on the microfluidic cartridge.

Description

[Technical Field]

[0001] Priority and Incorporation by Reference

[0002]

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 106,254, filed October 27, 2020, the disclosure of which is incorporated herein by reference in its entirety.

[0003] FIELD OF THE DISCLOSURE

[0004]

[0004] The present disclosure relates to rapid thermal cycling, such as may be provided in applications involving the amplification of genetic material. The present disclosure further relates to microfluidic chips for use in rapid thermal cycling systems. [Background technology]

[0005]

[0005] Background

[0006]

[0006] In PCR and other reactions, the thermal gradient across the target region is a critical physical characteristic for device function. Ideally, the overall heating gradient should be within a very small range so that the entire solution is heated uniformly and PCR or other reactions occur simultaneously everywhere within the reaction chamber. A consistent temperature is even more important for digital reactions such as dPCR, where uneven heating can affect performance or limit PCR reactions to occur in different regions of the cartridge, but is less of an issue for other reactions such as qPCR. Optical methods for heating microfluidic devices can achieve very fast heating, but require a transparent optical path from the light source to the cartridge, limiting the applicability of conventional cooling methods, such as applying aluminum heat sinks.

[0007]

[0007] The present application seeks to provide an alternative means for providing constant and uniform heating and cooling.

[0008]

[0008] Furthermore, when performing PCR and other reactions requiring thermal cycling in microfluidic devices, including digital PCR, sealing or closing the channels is usually a requirement. Proper closure of the microchannels is essential for achieving good thermal cycling performance. To achieve this, the fabrication process, particularly for joining cartridge pieces, is key. One example of such a joining process is the bonding of the channel substrate and the sealing substrate, as shown in Figure 1. Typically, methods such as thermal bonding, solvent bonding, adhesive bonding, and laser welding are used. However, each method has its advantages and disadvantages, and the difficulty of the bonding process largely depends on the materials used. Some materials, such as PMMA, are easier to bond than others, such as cyclic olefin polymer (COP). If the microfluidic channel is not sealed properly, delamination or the generation of air bubbles can occur (Figure 1), which can adversely affect the reaction taking place in the channel.

[0009]

[0009] Therefore, the present disclosure also seeks to provide alternative means that allow for improved sealing of microfluidic channels. Summary of the Invention

[0010]

[0010] This disclosure relates to methods and systems for thermal cycling, including for use in reactions such as PCR. To achieve rapid PCR / thermal cycling, a combination of features is provided, including an optical method in which a high-power LED illuminates a light-absorbing material, converting light to heat and enabling rapid heating. Rapid cooling may also be achieved using air cooling.

[0011]

[0011] These and other embodiments, objects, features, and advantages of the present disclosure will become apparent from the following detailed description of exemplary embodiments of the present disclosure, taken in conjunction with the accompanying drawings and the appended claims. [Brief explanation of the drawings]

[0012]

[0012] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate various embodiments, objects, features, and advantages of the present disclosure.

[0013] [Figure 1] FIG. 1 shows an air bubble trapped in a microfluidic cartridge during manufacturing.

[0014] [Figure 2] FIG. 2 illustrates one embodiment of sealing a microfluidic channel using a heat spreader.

[0015] [Figure 3] FIG. 3 is a conceptual diagram of the arrangement of components in one embodiment.

[0016] [Figure 4] FIG. 4 is a schematic diagram of the arrangement of components in one embodiment illustrating functionality during heating and cooling.

[0017] [Figure 5AB] 5A-5B are diagrams illustrating alternative component arrangements.

[0018] [Figure 6AB] , [Figure 6CD] 6A-6D show alternative component arrangements.

[0019] [Figure 7AB] , [Figure 7CD] 7A to 7D are diagrams showing alternative light source configurations.

[0020] [Figure 8] FIG. 8 illustrates an exemplary thermal cycler in one embodiment.

[0021] [Figure 9]FIG. 9 is a diagram of a thermal cycler in one embodiment.

[0022] [Figure 10] FIG. 10 is an exploded view of a thermal cycler in one embodiment.

[0023] [Figure 11] FIG. 11 is an exploded view of a thermal cycler in one embodiment.

[0024] [Figure 12] FIG. 12 illustrates a multi-LED with infrared temperature sensing configuration according to one embodiment.

[0025] [Figure 13] FIG. 13 shows ray tracing within a sapphire cube and light guide for two exemplary configurations.

[0026] [Figure 14] FIG. 14 illustrates the configuration of the gasket and vacuum sealing system of the cartridge in one embodiment.

[0027] [Figure 15] FIG. 15 is a graph showing the results of a simulation of a two-stage PCR thermal profile.

[0028] [Figure 16] FIG. 16 is a table showing the results of the simulation (high flux) and experimental (low flux) conditions.

[0029] [Figure 17] FIG. 17 is a graph showing experimental results of the heating rate and temperature of the lower thermocouple over time.

[0030] [Figure 18]FIG. 18 is a graph showing the heating rate and temperature over time at the ends and center of a microfluidic cartridge in conjunction with a diagram of a thermal cycler in one embodiment.

[0031] [Figure 19] FIG. 19 is a graph showing light guide exit surface irradiance for a diffusive surface with a specular coating on the transition region.

[0032] [Figure 20] FIG. 20 is a graph illustrating optical uniformity characteristics of a thermal cycling system in one embodiment.

[0033] [Figure 21] 21A-21B are graphs comparing the optical uniformity of hollow light pipes with a thermal cycling system in one embodiment.

[0034] [Figure 22] FIG. 22 is a graph illustrating the relationship between irradiance, input current, and distance for a thermal cycling system in one embodiment.

[0035] [Figure 23] FIG. 23 is a block diagram of a thermal model for slow heating with fast cooling and fast heating with slow cooling.

[0036] [Figure 24] FIG. 24 shows a practical implementation of the thermal cycle system used in the one-dimensional simulation.

[0037] [Figure 25] FIG. 25 is a graph illustrating thermal simulation results for various configurations of the thermal cycling system.

[0038] [Figure 26]FIG. 26 is a graph illustrating simulation results of maximum cartridge temperature for various configurations of the thermal cycling system.

[0039] [Figure 27] FIG. 27 shows two graphs illustrating the heating profile of a thermal cycling configuration in one embodiment using a 25 μm thick adhesive.

[0040] [Figure 28] FIG. 28 is a graph showing the heating and cooling curves obtained by simulation superimposed on the experimental results.

[0041] [Figure 29] FIG. 29 is a graph illustrating temperature versus time for various heating and cooling rates.

[0042] [Figure 30] FIG. 30 is an infrared thermal image plot of a cartridge in a thermal cycling system, specific points in the thermal cycle, in one embodiment.

[0043] [Figure 31] FIG. 31 is a graph summarizing the heating and cooling rates and steady-state temperature uniformity of a thermal cycling system in one embodiment.

[0044] [Figure 32]

[0044] Figure 32 is a graph illustrating the temperature versus time relationship for a complete PCR thermal cycling run using a thermal cycling system in one embodiment.

[0045] [Figure 33] FIG. 33 is a simulation result of an infrared image plot of one embodiment with a perfect mirror transition.

[0046] [Figure 34]FIG. 34 is a simulated infrared image plot of one embodiment with a 3M mirror film.

[0047] [Figure 35] FIG. 35 is a simulated infrared image plot of one embodiment having machined bare aluminum.

[0048] [Figure 36] FIG. 36 is a simulated graph showing average fluid temperature versus time and maximum cartridge temperature versus time for a thermal cycler with a heat spreader / light absorber attached to a microfluidic chip, according to one embodiment.

[0049]

[0049] Throughout the drawings, unless otherwise stated, the same reference numerals and characters are used to denote like features, elements, components, or portions of the illustrated embodiments. Moreover, while the present disclosure will now be described in detail with reference to the drawings, it is done so in connection with the exemplary embodiments for purposes of illustration. It is intended that changes and modifications can be made to the exemplary embodiments described without departing from the true scope and spirit of the present disclosure, as defined by the appended claims. DETAILED DESCRIPTION OF THE INVENTION

[0050]

[0050] This disclosure describes several embodiments and relies on patents, patent applications, and other references for details known to those skilled in the art. Accordingly, when patents, patent applications, or other references are cited or repeated in this specification, they should be understood to be incorporated herein by reference in their entirety for all purposes, not just as provided herein.

[0051] Efficient thermal cycling of microfluidic chips requires a configuration that allows both optimal heating and cooling, as well as adequate observation of the microfluidic chip. To maintain a transparent optical path and provide an efficient cooling method, the present disclosure provides the use of a heat sink that is transparent in the infrared (IR) to near-ultraviolet (UV) wavelength range. Such a heat sink also has sufficient thermal conductivity and heat capacity to operate efficiently in removing heat from the microfluidic device. This device, coupled with a radiant heating system, provides an efficient and simplified method for both heating and passively cooling the microfluidic device. In this device, the transparent heat sink forms a transparent optical path for light from a radiant heat source to be directed toward the cartridge. The transparent heat sink has a thermal diffusivity similar to that of ceramic or aluminum, making it an efficient heat sink.

[0052]

[0052] Thus, the present disclosure provides methods and systems for passively cooling optically heated cartridges, allowing for simpler and more compact designs of such devices. Such designs also provide efficient cooling, improving thermal cycling rates without significantly impacting heating rates. The present disclosure also allows for the combination of multiple light sources, such as LEDs (including arrays of LEDs), lasers, lamps, and the like, to increase the usable heating area or light intensity. Additionally, it provides an efficient means of measuring the heating area temperature via an infrared thermometer. Furthermore, the devices and systems disclosed herein minimize cooling gradients across the microfluidic chip.

[0053] In one embodiment, a device for thermal cycling a microfluidic cartridge is provided, comprising: a microfluidic cartridge contacted by a light-absorbing material; a first heat sink in contact with the microfluidic cartridge; a second heat sink proximate to the first heat sink; one or more light sources proximate to the first heat sink; and a temperature sensor for detecting temperature changes in the microfluidic cartridge, wherein the device alternately heats and cools the microfluidic cartridge. In one embodiment, the one or more light sources provide light in the infrared to UV wavelength range. In some embodiments, the first heat sink is transparent. In another embodiment, the first heat sink is transparent to light in the infrared to UV wavelength range. In other embodiments, the first heat sink comprises a thermally conductive material. The first heat sink can optionally include sapphire.

[0054] In another embodiment, the light absorbing material converts light to heat. The light absorbing material may be on or within the microfluidic cartridge or in thermal communication with the microfluidic cartridge. The light absorbing material may be included on or within a portion of the device other than the microfluidic cartridge, and this material is in thermal communication with the microfluidic cartridge when the cartridge is placed within the device. The light absorbing material may be attached to the microfluidic cartridge or other structures within the device using an adhesive. In some embodiments, the light absorbing material may be attached to a transparent heat sink.

[0055] In yet another embodiment, the first transmissive heat sink allows for the transmission of light through the heat sink to the microfluidic cartridge during heating. The first transmissive heat sink can function as a passive heat sink to cool the microfluidic cartridge during cooling. In another embodiment, the second heat sink comprises a thermally conductive material and may optionally be made of aluminum.

[0056] The one or more light sources may be one or more LEDs. In some embodiments, the light from the one or more light sources is captured and transmitted to the microfluidic cartridge by a first transparent heat sink.

[0057] In another embodiment, the device further comprises a feedback and control unit in communication with the temperature sensor to provide heating and cooling start, stop, and temperature control. Additionally, the device may further comprise one or more infrared sensors proximate the device so that the one or more sensors can observe the microfluidic cartridge. Additionally or alternatively, at least one resistive temperature sensing element may be provided in contact with a surface of the first heat sink in contact with the microfluidic cartridge. The resistive temperature detector may be configured and used in the manner described in U.S. Published Patent Application No. 20120052560, the disclosure of which is incorporated herein by reference in its entirety.

[0058] In another embodiment, the microfluidic cartridge can include an open microfluidic channel, and a flexible heat spreader can be disposed between the open microfluidic channel and a first heat sink. In another embodiment, the first heat sink can be pressurized to contact and deform the flexible heat spreader, such that the flexible heat spreader contacts the microfluidic cartridge and fluidly seals the microfluidic channel.

[0059]

[0059] In another embodiment, a method for thermal cycling a microfluidic cartridge is provided, the method comprising: (i) providing a device comprising a microfluidic cartridge having a heat absorbing material in contact therewith, a first heat sink in contact with the microfluidic cartridge, a second heat sink in proximity to the first heat sink, one or more light sources in proximity to the first heat sink, and a temperature sensor for detecting temperature changes in the microfluidic cartridge; (ii) activating the one or more light sources to heat the microfluidic cartridge; (iii) activating the one or more light sources to cool the microfluidic cartridge; and (iv) continuously repeating steps (ii) and (iii) throughout the thermal cycle.

[0060]

[0060] Figure 3 shows a model of such a system or device in one embodiment. A light-absorbing layer 312, having high light absorption in the wavelength range of radiant heat light, is placed in direct contact with a fluid reservoir 301, which may be a microfluidic cartridge or a microfluidic cartridge assembly in which multiple components are combined to form and / or hold in place a microfluidic cartridge. For example, a microfluidic cartridge can be formed using a single layer 302 with open wells or channels 303 that are closed by applying pressure to the absorbent layer 312, a gasket, or the like. For example, Figure 2 shows a microfluidic cartridge 201 with wells or channels 203 that are initially open to the environment. After applying a fluid sample to the wells or channels 203, a heat spreader 207 can be attached to the cartridge 201 using a suitable adhesive 208 (e.g., liquid adhesive, epoxy, double-sided tape, or the like). When a transparent heat sink 210, such as a sapphire block, is applied to the gasket 207, the gasket deforms to contact the top surface of the cartridge 201, effectively sealing the well or channel 203. This places the transparent heat sink 210 in thermal communication with the heat spreader 207 and the cartridge 201, so that when the radiant heat source 209 is turned on, light can pass through the transparent heat sink 210 to efficiently and uniformly heat the cartridge 201. Such an embodiment directly addresses the problems found in the art and described herein (FIG. 1) of the cartridge 101, which includes a bottom lid 102 and a top lid 104 joined at a mating surface 106 and having a well or channel 103 therebetween. Improper sealing of the well or channel 103 can cause delamination or the formation of air bubbles 105, thereby adversely affecting the reaction in the channel.

[0061] Referring again to FIG. 3 , in another embodiment, the cartridge body can be formed of upper and lower layers that, when attached to one another, enclose the well or channel 303. The absorbing layer 312 can be part of the cartridge 301, such that typical concerns about thermal contact resistance become negligible, allowing for efficient heating with lower power requirements. Alternatively, the absorbing layer 312 can be disposed on or in thermal communication with the transparent heat sink 310 described herein. The absorbing layer 312 can be a black or dark substrate or a heat spreader. In some embodiments, the absorbing layer 312 can also function as a gasket. The radiant heat source 309 is located distal to the cartridge 301, with the transparent heat sink 310 between the radiant heat source 309 and the cartridge 301. To heat, the radiant heat source 309 is turned on. To cool, the radiant heat source 309 can be turned off, allowing the (first) transmissive heat sink 310 to become substantially isothermal, thereby passively cooling the system (including the microfluidic cartridge assembly 301). Figure 3 also outlines the various temperature points and thermal contact resistances of the materials between the transmissive heat sink 310 and the fluid sample in the cartridge 301.

[0062] FIG. 4 illustrates the functionality of a transmissive heat sink 410 during the heating (left) and cooling (right) stages of a thermal cycle in another embodiment. A radiant heat source 409 is positioned so that light from the source 409 passes through a light guide with a reflective film or polished surface 414 before entering the optically transmissive heat sink 410. The transmissive heat sink 410 is positioned within a second heat sink 415. The opposite end of the heat sink 410 is in thermal communication with a sample 416, which may be contained in a microfluidic cartridge or the like. During heating, the radiant heat source 409 is turned on, and light (solid arrows) passes through the light guide and the transmissive heat sink 410 before reaching and heating the sample 416. During cooling, the radiant heat source 409 is turned off, and heat (wavy arrows) dissipates from the sample 416 through the transmissive heat sink 410 and the second heat sink 415, thereby reducing the temperature of the sample 416.

[0063] In some embodiments, the transmissive heat sink can be formed using sapphire (Al2O3) or other transmissive materials. Using a transmissive material with a refractive index close to or higher than that of glass (sapphire has a high refractive index of 1.73) as a heat sink offers the advantage of being used as a light pipe or light guide for the incident radiant heat source. This allows for an even distribution of the light profile through internal refraction, improving heating uniformity over the target area, in some implementations involving total internal refraction. FIG. 13 shows the results of a ray tracing simulation in which light originates within a second heat sink 1315, which has an inner surface with a reflective or polished surface 1314 acting as a light guide. The light then enters the transmissive heat sink 1310 at its input surface 1318, passes through the transmissive heat sink, and exits at its output surface 1319. The only difference between the left and right simulations is the view through the transmissive heat sink 1310—the left is a front view, and the right is a diagonal view—and both illustrate the even distribution of the light profile through internal refraction. This allows for the use of multiple LEDs, concentrating the total radiant flux in a single plane. This also allows for heating a larger cartridge area while maintaining a similar heat flux range and increasing the electrical flux density. Figure 12 shows a configuration using multiple LEDs with a transparent heat sink. In some embodiments, the transparent material (such as sapphire) has a high thermal diffusivity compared to other optical materials, allowing for efficient cooling of the system. Other relevant properties of the transparent material used for the first heat sink include good strength, high surface hardness, and thermal stability, as well as good optical transparency in the visible to near-infrared light spectrum.

[0064] 5A-5B illustrate another embodiment, providing an alternative configuration for the light absorbing layer 512. In FIG. 5A, a transmissive heat sink 510 is disposed within a second heat sink 515. The light absorbing layer 512 is attached to the cartridge 501 such that the light absorbing layer 512 is disposed between the cartridge 501 and the transmissive heat sink 510. In some embodiments, physical contact can be made between the light absorbing layer 512 and the transmissive heat sink 510. In other embodiments, there is no physical contact between the light absorbing layer 512 and the transmissive heat sink 510, but in all configurations, the transmissive heat sink 510 is in thermal communication with the light absorbing layer 512, and the light absorbing layer 512 is in thermal communication with the cartridge 501. In FIG. 5B, the light absorbing layer 512 is instead attached to the transmissive heat sink 510. The light absorbing layer 512 can be in physical contact with the cartridge 501, or in other embodiments, there is no physical contact between the light absorbing layer 512 and the cartridge 501. In either configuration, the transparent heat sink 510 is in thermal communication with the light absorbing layer 512, which is in thermal communication with the cartridge 501.

[0065] 6A-6D illustrate further embodiments having alternative configurations. In FIG. 6A, a transmissive heat sink 610 is disposed within or between a second heat sink 615. As illustrated in FIG. 6A, a single light absorbing layer 612 can be attached or bonded directly to the transmissive heat sink 610, disposing the single light absorbing layer 612 between the transmissive heat sink 610 and the cartridge 601. Alternatively, as shown in FIG. 6B, multiple light absorbing layers 612, 617 can be attached or bonded directly to the transmissive heat sink 610, disposing the multiple light absorbing layers 612, 617 between the transmissive heat sink 610 and the cartridge 601. In either of the configurations shown in Figures 6A-6B, when cartridge 601 is inserted into an instrument or device comprising transparent heat sink 610, second heat sink 615, and single or multiple light absorbing layers 612, 617, cartridge 601 can be positioned such that cartridge 601 is in direct contact with or in thermal communication with single or multiple light absorbing layers 612, 617, such that heating and cooling can be achieved to cartridge 601 using the processes described herein.

[0066] 6C, the transmissive heat sink 610 is disposed within or between the second heat sink 615. A single light absorbing layer 612 can be disposed between the transmissive heat sink 610 and the cartridge 601, and the single light absorbing layer 612 can be attached or bonded to the transmissive heat sink 610 via an adhesive 608 to place the adhesive between the transmissive heat sink 610 and the single light absorbing layer 612. Alternatively, as shown in FIG. 6D, multiple light absorbing layers 612, 617 can be disposed between the transmissive heat sink 610 and the cartridge 601, and the multiple light absorbing layers 612, 617 can be attached or bonded to the transmissive heat sink 610 via an adhesive 608 to place the adhesive between the transmissive heat sink 610 and at least one of the multiple light absorbing layers 612, 617. Adhesives used in the practice of the present disclosure include liquid adhesives, epoxy resins, double-sided adhesive tapes, or the like.

[0067]

[0067] In each of the configurations shown in Figures 6A-6B, when cartridge 601 is inserted into an instrument or device comprising a transparent heat sink 610, a second heat sink 615, and one or more light absorbing layers 612, 617 (with or without adhesive 608), cartridge 601 can be positioned so that cartridge 601 is in direct contact with and / or in thermal communication with one or more light absorbing layers 612, 617, such that heating and cooling can be achieved in cartridge 601 using the processes described herein. Similarly, when adhesive 608 is used between the transparent heat sink 610 and the single light absorbing layer 612 or one or more multi-layer light absorbing layers 612, 617, the transparent heat sink 610 is in thermal communication with the single light absorbing layer 612 and / or the multi-layer light absorbing layers 612, 617, which are in direct contact and / or thermal communication with the cartridge 601, such that heating and cooling can be provided to the cartridge 601 using the processes described herein.

[0068] 7A-7D illustrate different configurations of one or more radiant heat light sources 709. In each of FIGS. 7A-7D, a transmissive heat sink 710 is provided having at least one first surface disposed at one end and a second surface disposed at a distal end, the at least one first surface being one or more entrance surfaces 718, and the second surface being an exit surface 719. At least one, or alternatively each, of the at least one entrance surface 718 has at least one radiant heat light source 709 directed toward the entrance surface 718 such that light can enter the transmissive heat sink 710 from the entrance surface 718 and pass through the transmissive heat sink 710 to the exit surface 719. Light exiting the exit surface 719 then heats at least one light-absorbing layer in thermal communication with the transmissive heat sink 710 and the cartridge.

[0069] In one embodiment, the entrance surface 718 and the exit surface 719 of the transmissive heat sink 710 (which functions as a light guide) can each be any two-dimensional shape, such as circular to circular, circular to square, square to circular, or blended into another two-dimensional shape. The cross-sectional areas of the entrance surface 718 and the exit surface 719 can be the same or different. The radiant heat light source 709 can include a single light source or a set of multiple light sources, and such a single light source or a set of multiple light sources can be used with one or more entrance surfaces 718. In another embodiment, the entrance surface 718 and the exit surface 719 can optionally be smoothly polished or have a textured, diffusing surface. The entrance surface 718 and the exit surface 719 can optionally be anti-reflective coated.

[0070] 7A shows a transmissive heat sink 710 having two separate entrance surfaces 718 and a single exit surface 719. The entrance surfaces 718 and the exit surface 719 are arranged in an inverted "Y" shape, with the angle between the two entrance surfaces 718 being less than 180°. Each of the two entrance surfaces 718 has a radiant heat source 709 directed toward it, which may be a single light source or a set of multiple light sources. In FIG. 7B, the transmissive heat sink 710 has two separate entrance surfaces 718 and a single exit surface 719. The entrance surfaces 718 and the exit surface 719 are arranged in an inverted "T" shape, with the angle between the two entrance surfaces 718 being approximately 180°. In such a configuration, the transparent heat sink 710 can have structures configured to allow incident light to be reflected toward the exit surface 719, such as notches forming angled surfaces on the opposite side of each entrance surface 718. Each of the two entrance surfaces 718 has a radiant heat source 709 directed toward it, which may be a single light source or a set of multiple light sources. Both Figures 7C and 7D illustrate configurations in which at least one entrance surface 718 has a different size and / or shape than the exit surface 719. In Figure 7C, the entrance surface 718 is illustrated as having a wider shape or larger cross-sectional opening than the exit surface 719. In Figure 7D, the opposite configuration is illustrated, where the entrance surface 718 is illustrated as having a smaller shape or larger cross-sectional opening than the exit surface 719.

[0071] One embodiment of a device 832 of the present disclosure is shown in Figure 8. A radiant heat source 809 is located on a light source heat sink 827. Above the radiant heat source 809 is a second heat sink 815 having an internal (i.e., central) opening within which is disposed a transparent heat sink 810. The transparent heat sink 810 can be the same length as the second heat sink 815, or it can be longer or shorter than the second heat sink 815, and can be positioned so that the transparent heat sink 810 is coplanar or extends beyond the end of the second heat sink 815 distal from the radiant heat source 809. A polymer mounting plate 820 is attached and / or positioned on top of the device above the permeable heat sink 810, and the microfluidic cartridge 801 is positioned on the polymer mounting plate 820 and secured to the mounting plate 821 with shoulder screws and springs 822 to compress the mounting plate 821 and maintain thermal communication and / or direct contact of the microfluidic cartridge 801 with the permeable heat sink 810.

[0072] FIG. 9 illustrates another embodiment of a device 932 of the present disclosure having two second heat sinks 915 that can be positioned opposite each other to enclose a transparent heat sink (shown in FIG. 10). A radiant heat source 909 is positioned on a light source heat sink 927. Two second heat sinks 915 are positioned above the radiant heat source 909 and can be mated to form an internal opening or space for the transparent heat sink. A fan 926 can be positioned on one or both of the second heat sinks 915 to aid in rapid cooling of the device. A cartridge 910 is positioned above the transparent heat sink and second heat sink 915 by a cartridge contact plate 925, which can optionally include a polymer mounting plate and a fixation plate or be otherwise configured to firmly maintain direct contact or thermal communication of the cartridge 910 with the transparent heat sink. The vacuum connection port 923 allows for the application of a vacuum to the cartridge contact plate 925 and is useful for providing uniform contact between the cartridge 910 and other components required for thermal communication, which may include a transparent heat sink, an adhesive, one or more light absorbing layers, a gasket, etc.

[0073] 10 shows an exploded view of FIG. 9 with one of the secondary heat sinks 1015 removed from the device 1032, revealing the transparent heat sink 1010. The transparent heat sink 1010 fits into an interior opening or space created when the secondary heat sinks 1015 are joined together using fasteners 1028. The radiant heat source 1009 is located on a light source heat sink 1027, which is located below the two secondary heat sinks 1015. A fan 1026 can be placed on one or both of the secondary heat sinks 1015 to aid in rapid cooling of the device. The second heat sink 1015, located between the radiant heat source 1009 and the transmissive heat sink 1010, has a reflective or polished inner surface 1014. As a result, when the second heat sinks 1015 are joined together, the reflective or polished inner surface 1014 functions as a light guide, directing light from the radiant heat source 1009 to the incident surface of the transmissive heat sink 1010. The cartridge 1001 is positioned above the transmissive heat sink 1010 and the second heat sink 1015 by a cartridge contact plate 1025. A gasket 1024 is positioned below the cartridge 1001, and a vacuum can be applied to the gasket 1024 via a vacuum port 1023. The vacuum is useful for providing uniform contact between the gasket 1024, the cartridge 1001, and any other components required for thermal communication with the transmissive heat sink 1010, such as an adhesive, one or more light-absorbing layers, etc. In some embodiments, the gasket 1024 can function as a light absorbing layer and / or a heat spreader.

[0074] 14 shows an exemplary configuration of a gasket and vacuum sealing system for a cartridge 1401. A cartridge contact plate 1425 receives the cartridge 1401, and a gasket 1424 is positioned below the cartridge 1401 within the cartridge contact plate 1425. The gasket 1424 can be attached to the cartridge contact plate 1425 using adhesive 1408. A light absorbing layer and / or heat spreader 1412 can be attached to either the underside of the gasket opposite the microfluidic cartridge or to the permeable heat sink 1410. A vacuum can be applied to vacuum ports 1423 to hold the permeable heat sink 1410, the light absorbing layer and / or heat spreader 1412, the gasket 1424, and the cartridge 1401 in direct contact and / or to enhance thermal communication. In alternative embodiments, the light absorbing layer and / or heat spreader 1412 may be optional, for example, in situations where the gasket 1024 can function as a light absorbing layer or heat spreader, or may be located in another location such that the light absorbing layer and / or heat spreader 1412 is in direct contact with the cartridge 1401. While persistent direct contact between the components of FIG. 14 may be desirable to enhance thermal communication from the transmissive heat sink 1410 to the cartridge 1401, such direct contact is not required once thermal communication is achieved.

[0075] FIG. 11 is another exploded view of FIG. 10 , illustrating a portion of device 1132. One of the second heat sinks 1115 is positioned above the radiant heat source 1109 and the light source heat sink 1127. The inner surface of the second heat sink 1115, located between the radiant heat source 1109 and the lower surface (incident surface) of the transparent heat sink 1110, is provided with a reflective or polished surface 1114. As a result, when the second heat sinks 1115 are joined together, the inner surface with the reflective or polished surface 1114 functions as a light guide, directing light from the radiant heat source 1109 to the incident surface of the transparent heat sink 1110. The second heat sinks 1128 can be fastened together using fasteners 1128. A vacuum connection port 1123 is located on the cartridge contact plate 1125, allowing direct contact or thermal communication with the gasket and / or the cartridge's transmissive heat sink 1110.

[0076] Additionally, a key aspect of this system is the temperature measurement method and corresponding feedback control loop resulting from the rapid heating and cooling cycles. An efficient means of measuring and controlling the cartridge temperature in a manner that minimizes heat intrusion is important. For example, a large thermocouple can prevent effective thermal contact between the cartridge and the transparent heat sink. Non-contact methods of temperature sensing are preferred. However, most polymers are opaque to the range of a typical infrared thermometer, and the temperature at the top of the microfluidic cartridge can be significantly different from the heated zone below. In the proposed system shown in Figure 12, this issue is overcome by careful design of the transparent heat sink 1210. When using one or more radiant heat sources 1209 (e.g., LEDs), a cavity can be provided at the bottom of the heat sink for placement of an infrared thermometer (IR sensor) 1229. The one or more radiant heat sources 1209, the transparent heat sink 1210, and the IR sensor 1229 are enclosed within a second heat sink 1215. The IR sensor 1229 acts as a thermometer and can be viewed through the transparent heat sink 1210 (because it is transparent in the IR range) to image the heated areas of the cartridge 1201 that are most critical to performance. The IR sensor 1229 is equipped with a filter that passes only the IR range of light, so that it is not affected by the heating light provided in the visible to UV range. Multiple IR sensors 1229 can be used to monitor key areas in a similar manner. Adding LEDs 1209 increases the total power, which in turn increases the heated area. The configuration can be expanded to use any number of LEDs 1209, with the shape and configuration of the transparent heat sink 1210 being modified accordingly. Control systems that may be useful in this disclosure for providing temperature measurement and feedback include, for example, those described in U.S. Published Patent Application No. 20120052560, the disclosure of which is incorporated herein by reference in its entirety.

[0077]

[0077] The present disclosure further provides a system and method for thermal cycling a microfluidic cartridge in which a flexible heat spreader is used to seal the channels of the microfluidic cartridge. As shown in Figure 2, the flexible material is placed over the open channels of the microfluidic device and, upon contact with a heat sink or other solid heating or cooling source that pressurizes the flexible material, bends and presses against the open channels, thereby sealing the channels as long as the pressure source remains in place. Thus, the resulting thermal cycling device or system does not require a bonding process between the cartridge and the sealing substrate.

[0078] Flexible heat spreaders as provided herein can be used with any contact-based thermal cycling method, such as those described herein or known to those skilled in the art. Therefore, the use of flexible heat spreaders does not require the bonding of covers or seals on microfluidic cartridges, naturally avoiding common bonding-related issues such as delamination and bubble formation. Furthermore, the present disclosure provides simplified processes for both thermal cycling and cartridge fabrication. Cartridge construction can be simplified based on the elimination of the need for a top seal, resulting in time and cost savings. Suitable materials for use as flexible heat spreaders in the present disclosure include graphene and thin-film plastics, although those skilled in the art will recognize additional materials that may be suitable alternatives. The use of a heat sink, such as a sapphire block described herein, to provide pressure to deform the flexible heat spreader and seal the channels also offers the added benefit of providing thermal uniformity across the heat spreader, thereby allowing the use of materials not normally considered heat spreaders. Additionally, the flexible heat spreader can be used to seal channels on a microfluidic cartridge used in any thermal cycling system, providing a means to maintain pressure on the flexible heat spreader towards the microfluidic cartridge.

[0079] Example

[0080] Example 1: Feasibility Experiment

[0081] Experiments were conducted to prove the feasibility of this concept. Figure 8 shows the experimental setup. A sapphire cube was obtained and finely polished on one side to create a diffuse surface, allowing it to function as a light cube. The outside of the cube was coated with a reflective film to promote further internal reflection of the light. The cube was then covered with thermal adhesive and then mounted on an aluminum heat sink. The purpose of the aluminum heat sink was to act as a guide to direct the light from the LED (circular) into the cube (rectangular). The heat sink also served to thermally stabilize the temperature of the sapphire cube, maintaining it in an isothermal state during heating and cooling. The final setup is illustrated in Figures 9-11.

[0082] A 1 mm thick microfluidic cartridge was fabricated with a 50 μm black aluminum lid that served as a light-absorbing surface. A small thermocouple was placed at the interface between the cartridge and a sapphire cube. A thermal cycle was then performed by activating an LED and heating the cartridge; when the LED was turned off, the cartridge was passively cooled via the sapphire heat sink. The LED was not operating at 9.38 W / cm², but outputting a much lower heat flux in the range of 2–4 W / cm². Heating / cooling rate and uniformity results are shown in Figures 17 and 18, respectively. The maximum heating and cooling rates were approximately 100°C per second (°C / s). The average heating and cooling rates between 60 and 80°C were 50°C / s and 35°C / s, respectively. Uniformity was seen around ±12°C at the denaturation temperature of 95°C, but ±0.1°C to 2.5°C at the more critical annealing temperature of 55°C, which is closer to the preferred target range of ±1°C.

[0083]

[0083] Figure 16 summarizes the above experimental results compared to simulated values ​​(simulation results for a two-stage PCR thermal profile are illustrated in Figure 15). Even at low heat fluxes, the heating rate is still significantly faster than most methods, and the simulated conditions indicate that optimization can lead to faster heating rates. Furthermore, the use of thermocouples was not ideal because their physical placement affects the thermal contact resistance between the cube and the microfluidic cartridge. As explained in the previous section, non-contact temperature measurement is preferable and can improve heating and cooling rates and uniformity.

[0084] Example 2: Optical simulation and measurements

[0085] Modeling was used to predict the thermal and optical behavior of the proposed thermal cycling system in two distinct phases: one focused on optimizing optical performance and throughput, and the other focused on determining optimal thermal performance.

[0086] To determine the optical effectiveness, we used Light Tools Illumination (Synopsys, Inc.) to model the ray tracing behavior of several proposed configurations, and the results are summarized in Table 1. The total power (W) delivered by the LED at a given current was keyed in. The outputs used for evaluation were the incident power (W) at the light guide exit, the efficiency (incident power / input power), and the uniformity factor normalized to the maximum irradiance. Total internal reflection (TIR) ​​was achieved using this system, and based on several simulated reflectivity values, it was determined that a more reflective finish on the entrance's circular-to-square transition region improved overall efficiency by approximately 5%. A diffuse exit finish was approximated by defining the exit of the light guide cube as a Lambertian scattering surface, and a uniformity improvement of approximately 2.5% was observed. However, the results were closer to the simulation error or noise level of approximately 3%, suggesting that actual results may have been better than those shown, although the inherent uncertainty prevented this from being determined. FIG. 19 and FIG. 13 show exemplary results of the output irradiance plot and ray path, respectively, for a specular film on the transition region (R=0.98) plus a diffuse surface condition (R=0.2, T=0.8).

[0087] Table 1: Summary of simulations using Light Tools [Table 1]

[0088] After optical simulations revealed that the sapphire version had the highest efficiency and lowest uniformity when normalized to maximum irradiance, a 30x30x100 mm sapphire cube was fabricated with a 300-grit polished diffuse exit surface. The cube was fabricated to match the configuration from the simulation that showed the highest uniformity and mounted within an aluminum heat sink in a thermal cycling system. Optical uniformity was measured using a CCD beam profiler (Ophir Optics) and the data was evaluated using a beam gauge (Ophir Optics). The results are shown in Figure 20, and the experimental results correlated well with the simulation results. The sapphire cube data was then compared to the optical uniformity obtained using a hollow light pipe, as shown in Figure 21 (A: hollow light pipe; B: sapphire cube). The uniformity achieved with the sapphire cube was significantly improved compared to the hollow light pipe.

[0089] The output irradiance of the thermal cycling system using the sapphire cube was also measured using a photodiode power meter (Newport 2936-R, manufactured by Newport). The measurement results are shown in Figure 22. Both the output irradiance and uniformity were found to agree with the simulated values ​​within about 5%.

[0090] Example 3: Thermodynamic Simulation

[0091] Simulations were performed focusing on the thermal evaluation of the system. This was done by modeling and simulating the transient conjugate heat transfer behavior in SolidWorks Flow Simulation (Dassault Systèmes). The thermodynamic material properties used are listed in Table 2.

[0092]

[0092] Table 2: Thermodynamic material properties [Table 2]

[0093] Modeling focused on extreme cases in the system, such as when the heat spreader or light absorbing layer 2307 is in direct contact with the sapphire 2310 and when there is a large, transparent insulating layer 2331 between the heat spreader or light absorbing layer 2307 and the sapphire 2310. A diagram of these conditions is shown in Figure 23. Under conditions that include an insulating layer, heating was expected to be very fast but cooling was expected to be slow due to the added thermal insulation. Under conditions that include direct contact between the heat spreader or light absorbing layer and the sapphire, cooling was expected to be very fast because heat is more easily transferred to the sapphire, but heating was expected to be very slow for the same amount of incident power. Therefore, conditions must be optimized to determine the optimal thermal circuit for a given input irradiance.

[0094] The working model used for the one-dimensional simulations is shown in Figure 24. The input variables were the contact resistance between the cartridge (consisting of the top cover 2404 and bottom cover 2402) (to determine the effect of vacuum retention), the thickness of the heat spreader / light absorbing layer 2407, and the thickness of the adhesive / insulating layer 2408. Figure 25 summarizes the simulation results. Lower contact resistance or higher vacuum retention was observed to improve both heating and cooling due to better thermal contact. The thinner heat spreader 2507 and lower thermal mass provided very little speed advantage relative to other factors. The thickness of the insulating layer / adhesive 2508 had the greatest impact on performance. Figure 26 shows the maximum cartridge temperature results for the same series of simulations. The presence of the heat spreader / light absorbing layer 2607 on the fixture resulted in a stable maximum cartridge temperature during heating, never exceeding 100°C.

[0095] Example 4: Thermodynamic testing

[0096] After determining the optimal resistor circuit structure through thermodynamic simulations, several configurations were fabricated to confirm the results. Figures 9-11 illustrate the prototype design used for further testing. Figure 14 shows the design of the vacuum retention system. A soft 30-40A durometer silicone gasket 1424 was found to work best with a compression set of approximately 25-30%.

[0097]

[0097] A heat spreader thickness of 25 μm was selected, and prototype tests were conducted using several adhesive thicknesses to confirm the simulation predictions. As shown in Figure 27, the heating profile for the case using a thinner (25 μm) acrylic adhesive layer and a 25 μm thick pyrolytic graphite heat spreader (manufactured by Samsung) resulted in excessively long heating times, even when tested with higher LED drive currents. These results were consistent with the simulation results, indicating that a thin insulating layer was insufficient. Figures 33-36 show additional simulation results. Figure 33 shows the light irradiance simulation results for a perfect mirror transition R = 1, Figure 34 shows the light irradiance simulation results for a 3M mirror film on a transition R = 0.98, and Figure 35 shows the light irradiance simulation results for bare aluminum (machined) R = 0.90. Figure 36 shows the simulation results of a heat spreader / light absorber attached to a microfluidic chip for various light exposures, including (A) average fluid temperature vs. time and (B) maximum cartridge temperature vs. time.

[0098] Figure 28 shows the heating profile results for an experiment using a thermal cycler with a 188 μm-thick acrylic adhesive and a 25 μm-thick heat spreader (Samsung). A 12 psi vacuum was applied via a custom-made cartridge contact plate to hold the thin polycarbonate microfluidic cartridge against the sapphire. The cartridge was filled with 20 μL of deionized water. A high-speed infrared thermopile sensor (Omega #OS-PC16-2M-1V, Omega Engineering) was used to monitor the cartridge temperature, along with a custom-made software interface. An infrared camera (FLIR A8580 MWIR, Teledyne FLIR) and its associated software (Research IR, Teledyne FLIR) were used to monitor the temperature distribution on the cartridge surface. Figure 28 plots the experimental and simulation results (bold lines), demonstrating close agreement between the simulation and experimental values. Furthermore, the heating and cooling times were fast as expected, indicating good system performance.

[0099] A microfluidic cartridge as described above was mounted on a prototype thermal cycler and subjected to standard PCR thermal cycling. Figures 29 and 30 show results obtained from the thermal imaging system, allowing for objective comparison of the thermal uniformity of the cartridges at various states of thermal cycling. The letter identifiers in Figures 29 and 30 link the thermal image plot in Figure 30 to the time point during thermal cycling at which the image was obtained (Figure 29). At no time was the uniformity observed to increase by more than 1.4°C (standard deviation) over a 25x25mm area of ​​interest on the cartridge. This result was maintained even at higher denaturation temperatures, demonstrating good thermal control and stability. Furthermore, at lower annealing temperatures, where thermal control is most critical, a uniformity of 0.4°C was observed to be possible. These results were repeated for five cartridges with similar structures.

[0100] [000100] Figure 31 shows a graphical summary of the results for all cartridges tested (n=5). Results were averaged over three cycles and then averaged again across the five cartridges tested. Figure 32 shows an illustrative example of one of these cartridges tested, where a sample was subjected to a full PCR run of 40 cycles. The full PCR run involved 40 cycles of 95°C (denaturation, no hold) and 55°C (annealing, no hold) using a 20 μL sample. The total run time, including preheat cycles, was 4.6 minutes. Figure 32 demonstrates the rapid and uniform transitions between temperatures throughout the cycle achieved with this thermal cycling prototype.

[0101] [Definition] [000101] In the description, specific details are set forth to provide a thorough understanding of the disclosed embodiments. In other instances, well-known methods, procedures, components, and circuits have not been described in detail to avoid unnecessarily lengthening the present disclosure.

[0102] [000102] As used herein, "genetic material" refers to any nucleic acid, including DNA and RNA. Thus, genetic material can include a gene, a portion of a gene, a group of genes, fragments of multiple genes, a DNA or RNA molecule, multiple molecules of DNA or RNA, a fragment of a DNA or RNA molecule, or fragments of multiple DNA or RNA molecules. Genetic material can refer to anything from a small fragment of DNA or RNA to the entire genome of an organism.

[0103] [000103] As used herein, when an element or portion is referred to as being "on," "on," "connected to," or "coupled to" another element or portion, it is understood that it may be directly "on," "on," "connected to," or "coupled to" that other element or portion, or there may be intervening elements or portions. In contrast, when an element is referred to as being "directly on," "directly connected to," or "directly coupled to" another element or portion, there are no intervening elements or portions. When the term "and / or" is used, it includes any and all combinations of one or more of the associated listed items, if any.

[0104] [000104] Spatially relative terms such as "under," "beneath," "below," "lower," "above," "upper," "proximal," and "distal" may be used herein for ease of description when describing the relationship of an element or feature shown in the various figures to another element or feature(s). However, it should be understood that these spatially relative terms are intended to encompass various orientations of the device in use or operation in addition to the orientation shown in the figures. For example, if the device in the figures were inverted, elements described as "below" or "beneath" other elements or features would then be oriented "above" those other elements or features. Thus, relative spatial terms such as "below" can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or to other orientations) and the spatially relative descriptors used herein shall be interpreted accordingly. Similarly, the relative spatial terms "proximal" and "distal" may be interchangeable where applicable.

[0105] [000105] As used herein, the term "about" means, for example, within 10%, within 5%, or less. In some embodiments, the term "about" can also mean within the error of measurement.

[0106] [000106] Terms such as first, second, third, etc. may be used herein to describe various elements, components, regions, portions, and / or sections. It should be understood that these elements, components, regions, portions, and / or sections are not limited by these terms. These terms are used merely to distinguish one element, component, region, portion, or section from another region, portion, or section. Thus, a first element, component, region, portion, or section discussed below could also be referred to as a second element, component, region, portion, or section without departing from the teachings herein.

[0107] [000107] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. In the context of describing the present disclosure (e.g., in the context of the appended claims), use of the terms "a," "an," "the," and similar referents shall be construed to include both the singular and the plural unless otherwise indicated herein or unless otherwise clear from the context. The terms "comprising," "having," "includes," "including," and "containing" shall be construed as open-ended terms (i.e., meaning "including, but not limited to") unless otherwise stated. Specifically, when used herein, these terms specify the presence of a stated feature, integer, step, operation, element, and / or component, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof not expressly stated. The recitation of ranges of values ​​herein, unless otherwise indicated herein, is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, and each separate value is incorporated herein as if it were individually set forth herein. For example, if a range of 10 to 15 is disclosed, then 11, 12, 13, and 14 are also disclosed. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clear from the context. The use of any examples or exemplary language (e.g., "such as") provided herein is intended merely to clarify the disclosure and does not limit the scope of the disclosure unless otherwise recited in the claims. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the disclosure.

[0108] [000108] It should be understood that the methods and compositions of the present disclosure can be incorporated in the form of a variety of embodiments, only a few of which are disclosed herein. Variations of those embodiments will be apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors anticipate that those of ordinary skill in the art will adopt such variations as appropriate, and intend that the present disclosure may be practiced otherwise than as specifically described herein. Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the present disclosure unless otherwise indicated herein or otherwise apparent from context.

Claims

1. 1. A device for thermal cycling a microfluidic cartridge, comprising: a microfluidic cartridge contacted with a light absorbing material; a first heat sink in contact with the microfluidic cartridge; a second heat sink adjacent to the first heat sink; one or more light sources proximate the first heat sink; a temperature sensor for detecting a change in temperature of the microfluidic cartridge; the microfluidic cartridge comprises an open microfluidic channel, and a flexible heat spreader is disposed between the open microfluidic channel and the first heat sink; A device for alternately heating and cooling said microfluidic cartridge.

2. The device described in claim 1, wherein the light absorbing material converts light into heat.

3. The device of claim 1 , wherein the light absorbing material is on or within the microfluidic cartridge.

4. 10. The device of claim 1, wherein the light absorbing material is contained on or within a portion of the device other than the microfluidic cartridge, and wherein the light absorbing material is in thermal communication with the microfluidic cartridge when the cartridge is placed within the device.

5. The device of claim 1 , wherein the first heat sink is transparent.

6. The device of claim 5 , wherein the first heat sink comprises a thermally conductive material.

7. The device of claim 5 , wherein the first heat sink is transparent to light in the infrared to UV wavelength range.

8. The device of claim 5 , wherein the first transparent heat sink allows transmission of light through the heat sink to the microfluidic cartridge during heating.

9. The device of claim 5 , wherein the first permeable heat sink functions as a passive heat sink to cool the microfluidic cartridge during cooling.

10. The device of claim 1 , wherein the second heat sink comprises a thermally conductive material.

11. The device of claim 1 , wherein the one or more light sources are one or more LEDs.

12. The device of claim 1 , wherein the first heat sink captures and transmits the light from the one or more light sources to the microfluidic cartridge.

13. The device of claim 1 further comprising a feedback and control unit in communication with the temperature sensor and providing temperature control of the heating and cooling.

14. The device of claim 1 , further comprising one or more infrared sensors proximate to the device, the one or more sensors capable of observing the microfluidic cartridge.

15. The device of claim 1 , further comprising at least one resistive temperature sensing element in contact with a surface of the first heat sink in contact with the microfluidic cartridge.

16. 10. The device of claim 1, wherein the first heat sink contacts and applies pressure to the flexible heat spreader to deform it, such that the flexible heat spreader contacts a microfluidic cartridge and fluidly seals the microfluidic channel.

17. The device of claim 5 , wherein the light absorbing material is on the transparent heat sink.

18. 1. A method of thermal cycling a microfluidic cartridge, comprising: (i) a microfluidic cartridge contacted with a heat absorbing material; a first heat sink in contact with the microfluidic cartridge; a second heat sink adjacent to the first heat sink; one or more light sources proximate the first heat sink; a temperature sensor for detecting a change in temperature of the microfluidic cartridge, the microfluidic cartridge comprising an open microfluidic channel, and a flexible heat spreader disposed between the open microfluidic channel and the first heat sink; (ii) activating the one or more light sources to heat the microfluidic cartridge; (iii) turning off the one or more light sources to cool the microfluidic cartridge; and (iv) continuously repeating steps (ii) and (iii) throughout said thermal cycling.

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