WO2023003547A1

WO2023003547A1 - Fluidic devices with multiple interface properties

Info

Publication number: WO2023003547A1
Application number: PCT/US2021/042495
Authority: WO
Inventors: Fausto D'APUZZO; Viktor Shkolnikov
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2021-07-21
Filing date: 2021-07-21
Publication date: 2023-01-26

Abstract

An example microfluidic device includes an optically transparent first layer having an index of refraction. The microfluidic device also includes an optically scattering second layer spaced from the optically transparent first layer to receive a first fluid and a second fluid between the optically transparent first layer and the optically scattering second layer. The index of refraction is selected to cause total internal reflection where the first layer interfaces with the first fluid and to cause refraction where the first layer interfaces with the second fluid.

Description

FLUIDIC DEVICES WITH MULTIPLE INTERFACE PROPERTIES

BACKGROUND

[0001] Fluidic devices may manipulate or analyze fluidic reagents. For example, a digital microfluidic (DMF) device may be used for sample preparation. The DMF device can move, mix, react, divide, store, etc. small volumes of reagents. A digital droplet polymerase chain reaction (PCR) device may produce a quantitative indication of whether or how much of a target nucleic acid strand is present. The digital droplet PCR device may do so by analyzing numerous small volumes of fluid.

BRIEF DESCRIPTION OF THE DRAWINGS [0002] Figures 1 a and 1 b are cross-section views of example microfluidic devices to illuminate a fluid in each device.

[0003] Figure 2 is a cross-section view of another example microfluidic device to illuminate a fluid in the device.

[0004] Figure 3 is a cross-section view of still another example microfluidic device to illuminate a fluid in the device.

[0005] Figure 4a is a block diagram representing a side view of an example system to illuminate a fluid in a microfluidic device.

[0006] Figure 4b is a block diagram representing a side view of another example system to illuminate a fluid in a microfluidic device.

[0007] Figure 5a is a block diagram representing a top or bottom view of an example system to illuminate a fluid in a microfluidic device.

[0008] Figure 5b is a block diagram representing a top or bottom view of another example system to illuminate a fluid in a microfluidic device.

[0009] Figure 6 is a block diagram representing a side view of still another example system to illuminate a fluid in a microfluidic device.

[0010] Figure 7 is a block diagram representing a side view of still another example system to illuminate a fluid in a microfluidic device.

[0011] Figure 8 is a block diagram representing a side view of still another example system to illuminate a fluid in a microfluidic device. [0012] Figure 9 is a flow diagram of an example method to illuminate a fluid in a microfluidic device.

[0013] Figure 10 is a flow diagram of another example method to illuminate a fluid in a microfluidic device.

[0014] Figure 11 is a flow diagram of still another example method to illuminate a fluid in a microfluidic device.

[0015] Figure 12 is a flow diagram of still another example method to illuminate a fluid in a microfluidic device.

DETAILED DESCRIPTION

[0016] Fluidic devices that operate on small volumes of fluid may include optical systems to analyze the fluids. For example, digital microfluidic (DMF) devices may perform a long, complex series of operations. One failure in the series of operations (e.g., a droplet failing to move when instructed) may result in droplets crashing into one another, which may collapse the long series of operations. The failure may increase costs due to wasted reagents and additional operator time to restart the process. An optical system may be used to detect failures and cease operations before droplets crash into one another, for example, by detecting droplet locations. In a digital droplet polymerase chain reaction (PCR) device, a fluorescent signal may be produced by droplets that include the target nucleic acid. The digital droplet PCR device may include an optical system to detect the fluorescent signal.

[0017] The droplets in the DMF droplets may be transparent and have very low contrast relative to other locations in the DMF device without droplets. In addition, the DMF device may move the droplets at high speed. The digital droplet PCR device may illuminate a large number of droplets with light and distinguish which droplets fluoresce in response to the illumination and which do not. For an optical system to accurately distinguish droplets in a DMF device (e.g., under high speed conditions) or distinguish fluorescing and non-fluorescing droplets in a digital droplet PCR device, the optical system may need to achieve a high signal-to-noise ratio (SNR). In some examples, the optical system may include expensive components to achieve a high SNR (e.g., high-quality lenses, filters, etc.). The optical system may also, or instead, include high intensity illumination to improve the SNR, but the high intensity illumination can degrade molecules in the droplets and affect the operations being performed (e.g., reduce test sensitivity). Alternatively, or in addition, a processing system coupled to the optical system may use computationally expensive analysis techniques to make up for the lack of SNR. However, such techniques may need large amounts of computational resources, which increases cost, and/or such techniques may not be implementable in real time. For example, the processing system may not be able to detect that a failed operation occurred in a DMF device operating at high speed until after the droplets have crashed and the sequence of operations has collapsed. Accordingly, microfluidic devices, such as DMF devices and digital droplet PCR devices could be improved by increasing SNR without expensive components or processing techniques and without using damaging levels of illumination.

[0018] Figure 1a is a cross-section view of an example microfluidic device 100a to illuminate a fluid in the device 100a. The illustrated device 100a includes an optically transparent first layer 110a having an index of refraction. In some examples, the first layer 110a may include an optically transparent polymer, glass, or the like. The device 100a also includes an optically scattering second layer 120a spaced from the optically transparent first layer. The second layer 120a may cause diffuse scattering of incident light, may reflect light, or the like. The second layer 120a may include metal, glass, polymer (e.g., a metal, glass, or polymer with a roughened surface), or the like. The first and second layers 110a, 120a may be planar. The term “optically” refers to a property that is true for a portion of the optical spectrum. For example, the device 100a may be designed for a particular wavelength or range of wavelengths. It may have the specified property at that wavelength or range of wavelengths while not having the specified property at another optical wavelength. As used herein, the term “optical spectrum” refers to electromagnetic radiation wavelengths between 10 nanometers (nm) and 1 millimeter (mm) in vacuum. The term “light” refers to electromagnetic radiation in the optical spectrum. Unless otherwise specified, the term “wavelength” in relation to electromagnetic radiation refers to the wavelength in vacuum.

[0019] The first and second layers 110a, 120a are spaced to receive a first fluid 151a and a second fluid 152a between the first layer 110a and the second layer 120a. The layer thicknesses and spacing size are not shown to scale. The first or second fluid 151a, 152a may include air, an inert gas, water, oil, or the like. The first or second fluid 151a, 152a may include various other substances dissolved or suspended in it. For example, the first or second fluid may include a biological compound. In examples, the second fluid may include an aqueous analyte in a first fluid selected from air, inert gas, or oil, or the first fluid may include an aqueous analyte in a second fluid selected from air, inert gas, or oil. In some examples, the microfluidic device is a DMF device ora cartridge fora DMF device (e.g., a cartridge that attaches to electrodes or ion emitters that manipulate droplet in the cartridge). In some examples, the microfluidic device is a PCR device, such as a digital droplet PCR device, a cartridge for a PCR device (e.g., digital droplet PCR device), or the like.

[0020] In the illustrated example, the index of refraction of the first layer 110a is selected to cause total internal reflection where the first layer 110a interfaces with the first fluid 151 a and to cause refraction where the first layer 110a interfaces with the second fluid 152a. Whether light is reflected or refracted at the interface of two materials depends on the ratio of the indices of refraction for the materials and the angle of incidence as reflected in Snell’s law. The indices of refraction depend on the wavelength of the light. The angle of incidence is the angle between a vector normal to a point on the interface and a vector corresponding to the direction of travel of a light ray as it reaches the point on the interface. The critical angle for two materials is the angle of incidence above which light will be reflected rather than refracted.

[0021] In some examples, the microfluidic device 100a may receive light at a predetermined angle, and the angle of incidence may correspond to the predetermined angle (e.g., may equal the predetermined angle). In such examples, the index of refraction of the first layer 110a may be selected to cause total internal reflection where the first layer 110a interfaces with the first fluid 151a for light at the predetermined angle (but not necessarily for other angles). Similarly, the index of refraction of the first layer 110a may be selected to cause refraction where the first layer 110a interfaces with the second fluid 152a for light at the predetermined angle (but not necessarily for other angles). In some examples, the first layer 110a may include a coating that causes refraction at the interface with the second fluid and total internal reflection at the with the first fluid. For example, the coating may be an antireflective coating. The coating may create a preferential interface with the second fluid (e.g., an interface that increases refraction into the second fluid).

[0022] In some examples, the microfluidic device 100a may receive light at a predetermined wavelength or a predetermined range of wavelengths (e.g., a narrow band of wavelengths). In such examples, the index of refraction of the first layer 110a may be selected to cause total internal reflection where the first layer 110a interfaces with the first fluid 151 a for light at the predetermined wavelength(s) (but not necessarily for other wavelength(s)). Similarly, the index of refraction of the first layer 110a may be selected to cause refraction where the first layer 110a interfaces with the second fluid 152a for light at the predetermined wavelength(s) (but not necessarily for other wavelength(s)). The microfluidic device 100a may be coupleable to a system that delivers light at the predetermined angle or the predetermined wavelength or range of wavelengths. The index of refraction may be selected to be compatible with a system that delivers light at a particular angle or a particular wavelength or range of wavelengths.

[0023] In some examples, the light may arrive at a range or plurality of angles or may arrive at a large range of wavelengths. For example, the light may be diffuse light or white light. In such examples, the index of refraction of the first layer 110a may be selected so that significantly more light is refracted at the interface with the second fluid 152a than is refracted at the interface with the first fluid 151 a or so that significantly more light is reflected at the interface with the first fluid 151a than is reflected at the interface with the second fluid 152a. As used herein, the term “significantly more” refers a value that is at least a non-unitary, positive integer multiple larger. For example, significantly more may be at least 2x, 3x, 5x, 10x, or 100x larger or the like. The amount of light refracted or reflected may be the radiance or luminance of the light refracted or reflected for a particular solid angle and a particular area. Despite arriving at many angles or wavelengths, the light may be delivered according to a predetermined set of conditions. For example, uncollimated light may be delivered to an edge of the first layer 110a. The index of refraction or the predetermined set of conditions may be selected to ensure that significantly more light arrives between the critical angles of the two types of interfaces (i.e., the first layer 110a-first fluid 151a interface and the first layer 110b- second fluid 152a interface) than arrives below both critical angles for the wavelengths of the light. The first layer material, coating, first fluid, second fluid, wavelength, or delivery angle may be selected or tuned to have indices of refraction that cause reflection at the interface between the first layer and the first fluid and cause refraction at the interface between the first layer and the second fluid.

[0024] Light is more likely to arrive below both critical angles near where the light is delivered to the device 100a. Accordingly, bleeding into the first fluid 151a near where the light is delivered may be mitigated. For example, an outer surface (e.g., a top surface) of the first layer 110a or of the second layer 120a may be made opaque or light absorbing near where the light is delivered, or opaque or light absorbing layers may be included on the first layer 110a or the second layer 120 near where the light is delivered. As used herein, the term “top” is relative to the figure in question and is not meant to imply the gravity vector points in any particular direction. The device 100a may be oriented in any direction relative to gravity. To mitigate bleeding, an active area of the device 100a in which the second fluid 152a is manipulated or analyzed may be a predetermined distance from where the light is delivered. The portion of the device 100a near where the light is delivered may be outside the field of view of a light sensor when the device 100a is coupled to a light sensor.

[0025] Light refracted at the interface between the first layer 110a and the second fluid 152a travels through the second fluid 152a to the second layer 120a. The light is scattered by the second layer 120a, and at least some of the light returns back through the second fluid 152a to the first layer 110a and escapes from an outer surface of the first layer 110a. A minimal amount of light reflected by the first fluid 151a escapes from the outer surface of the first layer 110a. A light sensor (not shown) may be positioned to receive the light escaping from the outer surface of the first layer 110a. Because more light escapes at locations of the second fluid 152a compared to locations of the first fluid 151a, the light sensor will achieve a high SNR. [0026] Figure 1b is a cross-section view of an example microfluidic device 100b to illuminate a fluid in the device 100b. The illustrated device 100b includes an optically transparent first layer 110b and an optically scattering second layer 120b that are spaced apart to receive a first fluid 151b and a second fluid 152b. The discussion of Figure 1 a also applies to Figure 1 b. Figure 1 b is included to disabuse the reader of the notion that the second fluid 152b needs to be an analyte or be of a smaller volume than the first fluid 151 b. All of the examples herein, including the examples of Figures 1a, 2, and 3, are meant to apply regardless of whether the first fluid or the second fluid is an analyte or has a smaller volume unless otherwise indicated.

[0027] Figure 2 is a cross-section view of another example microfluidic device 200 to illuminate a fluid in the device 200. The illustrated device 200 includes an optically transparent first layer 110 and a reflective second layer 220 that are spaced apart to receive a first fluid 151 and a second fluid 152. The discussion of Figures 1a and 1b also applies to the device 200 except the optically scattering second layer 220 is more specifically reflective. For example, the second layer 220 may be metallic, a mirror, or the like. In an example, the second layer 220 may be an electrode (e.g., a gold or gold-plated electrode) for a DMF device. In an example, the second layer 220 may be a metal that conducts heat from a heater (e.g., a thermal cycler) to the first or second fluid. The reflective second layer 220 may return more light to and through the first layer relative to a non-reflective scattering surface, which will improve the SNR experienced by a light sensor (not shown) aimed to receive light escaping through the first layer.

[0028] Figure 3 is a cross-section view of still another example microfluidic device 300 to illuminate a fluid in the device 300. The illustrated device 300 includes an optically transparent first layer 110 and a reflective second layer 120 that are spaced apart to receive a first fluid 151 and a second fluid 152. The discussion of Figures 1a, 1b, and 2 also applies to the device 300. The device 300 also includes a prism 330 to transfer light to the first layer at an angle between a critical angle of the first layer 110-first fluid 151 interface and a critical angle of the first layer 100- second fluid 152 interface. The prism 330 may be used to tune the angle of received light and may be easier to tune than tuning an angle or location of a light source (not shown). The prism 330 may have a flat interface that allows light to be efficiently transmitted into the device. The angle of the prism may be adjusted to control which wavelengths illuminate the second fluid. For example, a broadband light source may be used without a filter, and the angle of the prism can be controlled to select which wavelengths illuminate the second fluid. The device 300 may include a prism for each light source of a system to illuminate the device 300 (see, e.g., the light sources discussed in Figures 5a and 5b below) or a single, extended prism that couples light from multiple sources. For example, the prism(s) may extend into the page for Figure 3. The prism 330 may be molded, for example, as part of the molding process to create the first layer. The prism 330 may be affixed to the first layer.

[0029] Because the prism delivers the light at a particular angle or narrow range of angles, the light is more likely to be at an angle between the critical angles of the two types of interfaces. As a result, less light leaks into the first fluid 151 , and the SNR is improved. In some examples, the critical angles may be near each other. Considering an example in which the first layer 110 has index of refraction of 1.52, the first fluid has an index of refraction of 1.29, and the second fluid has an index of refraction of 1.33, the critical angles are 58.1° at the interface with the first fluid 151 and 61.0° at the interface with the second fluid 152. The prism allows light to be delivered at an angle between 58.1 ° and 61.0° so that a large contrast and SNR are achieved despite the similar indices of refraction for the two fluids.

[0030] Figure 4a is a block diagram representing a side view of an example system 400a to illuminate a fluid in a microfluidic device 450a. The illustrated system 400a includes an interface 410a to mechanically couple the microfluidic device 450a to the system 400a. For example, the interface 410a may include a latch (e.g., a rotating latch, a laterally sliding latch, etc.), a rail, a bolt, a screw, a hook, an adhesive, Velcro, or the like to mechanically couple the microfluidic device 450a to the system 400a. The interface 410a may hold the microfluidic device 450a in stable location so that movement is minimized relative to the system 400a. In some examples, the microfluidic device 450a is the microfluidic device 100a, the microfluidic device 100b, the microfluidic device 200, the microfluidic device 300, or the like. [0031] The system 400a includes a plurality of light sources 420a. Each light source is aligned in a first dimension (not shown) with a row of cells of the microfluidic device and angled in a second dimension to create total internal reflection within a layer of the microfluidic device where the layer interfaces with a first fluid and to create refraction where the layer interfaces with a second fluid. In the illustrated example, the plurality of light sources 400a are angled to be aligned with an edge of the microfluidic device 450a. The plurality of light sources 420a may be positioned adjacent to the edge of the layer and emit light onto the edge of the layer, or the light source may be attached to the edge of the layer. The system 400a may include an optical fiber or light pipe to couple the light into the layer. The edge may include a coating, such as an anti-reflective coating. In some examples, the angle in the second dimension may be an angle 15°, 30°, 45°, 60°, 75°, 90°, etc. with respect to a normal vector for an outer surface of the layer of the microfluidic device 450a. The angle in the second dimension may be between the critical angles for the layer-first fluid interface and the layer-second fluid interface. [0032] The plurality of light sources 420a may include an uncollimated light source, such as a light emitting diode (LED), an incandescent light, a fluorescent light, or the like. The plurality of light sources 420a may include a collimated light source, such as a laser (e.g., a vertical cavity surface emitting laser (VCSEL)), an uncollimated light source with a collimating lens, or the like. The plurality of light sources 420a may be wideband or narrowband. As used herein, the term “narrowband” refers to a bandwidth (e.g., a power spectral density bandwidth at half maximum) below a predetermined threshold. The predetermined threshold may be 0.5 nm, 1 nm, 2, nm, 3 nm, 5 nm, 10 nm, 20 nm, etc. As used herein, the term “wideband” refers to a bandwidth larger than a narrowband bandwidth. In some examples, the plurality of light sources 420a may include light sources that emit light at wavelengths different from each other. The critical angle varies based on wavelength, so each light source of the plurality of light sources 420a may be angled in the second dimension based on the critical angles for the wavelength(s) emitted by that light source. In some examples, a fluorescent reporter included in the first or second fluid may be selected based on a desired wavelength, and the desired wavelength may be chosen to cause total internal reflection at the layer- first fluid interface and refraction at the layer-second fluid interface.

[0033] In some examples, the light sources 420a may include light sources for detection of locations of the first or second fluid (e.g., droplets of the first or second fluid) and light sources to cause fluorescence in the detected droplets. The detection light sources may emit light at different wavelengths from the fluorescence light sources. Using different wavelengths produces less noise when measuring the fluorescence signal. The detection light sources may be used to deliver light to most or all of the microfluidic device 450a. The fluorescence light sources may deliver light to targeted locations on the microfluidic device 450a, such as locations where droplets are detected, or to most or all of the microfluidic device 450a.

[0034] The system 400a includes a light sensor 430a to detect light from the second fluid. In some examples, the light sensor 430a may detect light from the plurality of light sources 420a that has passed through the microfluidic device 450a and escaped from it. In some examples, the microfluidic device 450a may include molecules that fluoresce in response to the light from the plurality of light sources 420a, and the light sensor 430a may detect fluorescence that results from the light delivered by the plurality of light sources 420a. For example, the first or second fluid may include a biological compound that includes a reporter added to it, which reporter fluoresces under particular conditions (e.g., when a target molecule is present). The light sensor 430a may receive light escaping from the layer of the microfluidic device 450a. For example, light refracted at the interface with the second fluid may be reflected or scattered back to the layer (e.g., by another reflective or scattering layer) and may travel through the layer to escape from the microfluidic device 450a. In some examples, an optical axis of the light sensor 430a may be approximately aligned with a normal vector of the layer. As used herein, the term “approximately aligned” means an angle between the optical axis and normal vector of no more than a predetermined value. The predetermined value may be 1 °, 2°, 5°, 10°, or the like. In other examples, the optical axis may be at angle to the normal vector. [0035] The light sensor 430a may include an image sensor (e.g., an array of light sensors). In some examples, the light sensor 430a may include a point detector (e.g., a photomultiplier tube, an avalanche photodiode, or the like) or a plurality of point detectors. There may be a point light sensor 430a for each row of cells or each cell in the microfluidic device 450a. The light sensor 430a may measure the intensity of the detected light or generate signal proportional to the intensity of the detected light. In some examples, the system 400a may include an enclosure to reduce the amount of light or prevent light external to the system 400a from reaching the light sensor 430a.

[0036] Figure 4b is a block diagram representing a side view of another example system 400b to illuminate a fluid in a microfluidic device 450b. The illustrated system 400b includes an interface 410b, a plurality of light sources 420b, and a light sensor 430b. The discussion of Figure 4a also applies to Figure 4b. In Figure 4b, the plurality of light sources 420b deliver light to a first layer of the microfluidic device 450b, and the light sensor 430b receives light passing through and escaping from a second layer of the microfluidic device 450b. For example, the second layer may be transparent so that light refracted at the interface with the second fluid passes through the second layer to the light sensor 430b.

[0037] Figure 5a is a block diagram representing a top or bottom view of an example system 500a to illuminate a fluid in a microfluidic device 550a. The illustrated system 500a includes an interface 510a and a plurality of light sources 521a, 522a, 523a, 524a. The discussion of Figures 4a and 4B also applies to Figure 5a. In the illustrated example, the microfluidic device 550a is a DMF device that includes rows of cells. A square with four rows is illustrated, but there may be tens, hundreds, or thousands of rows in other examples. The shape can be rectangular or have varying numbers of cells per row in examples. The microfluidic device 550a or the system 500a may include electrodes or ion emitters to move droplets among the cells. Each cell may be a location to which the electrodes or ion emitters can move fluids. The microfluidic device 550a may include markings indicating the location of each cell. Each light source 521a, 522a, 523a, 524a is aligned with one row of cells in a first dimension. [0038] Figure 5b is a block diagram representing a top or bottom view of another example system 500b to illuminate a fluid in a microfluidic device 550b. The illustrated system 500b includes an interface 510b and a plurality of light sources 521b, 522b, 523b, 524b, 525b. The discussion of Figures 4a and 4B also applies to Figure 5b. In the illustrated example, the microfluidic device 550b is a digital droplet PCR cartridge that includes rows of cells. Five rows are illustrated, but there may be tens, hundreds, or thousands of rows in other examples. Each cell may be a droplet that contains reporters that fluoresce in the presence of a target molecule (e.g., a target nucleic acid). Each light source 521b, 522b, 523b, 524b, 525b is aligned with one row of cells in a first dimension. The plurality of light sources 521b, 522b, 523b, 524b, 525b delivers light at a wavelength that causes fluorescence in the reporter when the target molecule is present.

[0039] Figure 6 is a block diagram representing a side view of still another example system 600 to illuminate a fluid in a microfluidic device 650. The illustrated system 600 includes an interface 610, a plurality of light sources 620, an image sensor 630, and a processor 640. The discussion of Figures 4a, 4b, 5a, and 5b also applies to Figure 6. In the illustrated examples, the image sensor 630 captures an image of a second fluid. The image sensor 630 may capture the image by detecting light that escapes the microfluidic device 650 at locations corresponding to the second fluid. The second fluid may receive light that refracts from a layer of the microfluidic device 650, and that light may escape from the microfluid device 650 or may cause fluorescence that produces light that escapes the microfluidic device 650.

[0040] In the illustrated example, the processor 640 analyzes the image to determine a location of the first fluid or the second fluid, or the processor 640 analyzes the image to determine an intensity at a location of the first fluid or the second fluid. For example, the first fluid or second fluid may be an analyte, and the processor 640 may determine the location of the analyte. Because light escapes at locations of the second fluid and little or no light escapes at locations of the first fluid, there is a high SNR (e.g., a high contrast). Locations of the second fluid will be bright and locations of the first fluid will be relatively darker than locations of the second fluid. Signal processing techniques may be used to segment the image into locations of the first fluid and the second fluid based on the difference in brightness (e.g., using a simple brightness threshold or more sophisticated machine learning techniques). The processor 640 may use the determined locations to evaluate whether the microfluidic device 650 (e.g., a DMF device) is functioning properly. The processor 640 may determine the intensity at the location of the first fluid or the second fluid based on the gray value of a pixel or the gray values of a group of pixels at a location corresponding to the location of the first fluid or the second fluid. Based on the intensity, the processor 640 may determine whether a target molecule is present (e.g., whether fluorescence indicates the presence of a target nucleic acid).

[0041] Figure 7 is a block diagram representing a side view of still another example system 700 to illuminate a fluid in a microfluidic device 750. The illustrated system 700 includes an interface 710, a plurality of light sources 720, and a light sensor 730. The discussion of Figures 4a, 4b, 5a, 5b, and 6 also applies to Figure 7. In the illustrated example, the microfluidic device 750 includes a prism. The plurality of light sources 720 may be angled to be aligned with the prism. For example, the plurality of light sources 720 may emit light in a direction parallel to a normal vector of a face of the prism. The angle of the plurality of light sources 720, the angle of the prism, or the angle of the microfluidic device 750 may be adjustable to ensure that light from the light sources 720 arrives at the proper angle (e.g., an angle between the critical angles for the layer-first fluid interface and the layer- second fluid interface).

[0042] Figure 8 is a block diagram representing a side view of still another example system 800 to illuminate a fluid in a microfluidic device 850. The illustrated system 800 includes an interface 810, a plurality of light sources 820, a light sensor 830, and a scintillator 835. The discussion of Figures 4a, 4b, 5a, 5b, 6, and 7 also applies to Figure 8. In the illustrated example, the scintillator 835 converts light from a first wavelength not detectable by the light sensor 830 to a second wavelength detectable by the light sensor 830. For example, the light sources 820 may emit light at a wavelength not detectable by the light sensor 830, or the second fluid may fluoresce light at a wavelength not detectable by the light sensor. The scintillator 835 may convert ultraviolet light not detectable by the light sensor 830 to visible light that is detectable.

[0043] Figure 9 is a flow diagram of an example method 900 to illuminate a fluid in a microfluidic device. The method 900 may be performed with any of the microfluidic devices 100a, 100b, 200, 300 or any of the systems 400a, 400b, 500a, 500b, 600, 700, 800 previously described. For illustrative purposes, the method 900 is described in relation to the microfluidic device 100a and the system 400a. At block 902, the method 900 includes delivering a first fluid or a second fluid to a microfluidic device 100a. The microfluidic device 100a includes a first layer 110a and a second layer 120a. The first fluid or second fluid is delivered to a location between the first layer 110a and the second layer 120a. Delivering the fluid may include pumping the fluid, using the capillary forces, applying an electrowetting force to the fluid (e.g., using electrodes or ion emitters), or the like to deliver the fluid between the first layer 110a and the second layer 120a. In some examples, the fluid may be pipetted or dispensed into a well and transported from the well to the location between the first layer 110a and the second layer 120a. In some examples, both the first and second fluid may be delivered, or one of the first and second fluid may be an ambient fluid that does not need to be delivered.

[0044] Block 904 includes delivering light to the first layer 110a at an angle that causes total internal reflection where the first layer 110a interfaces with the first fluid located between the first layer 110a and the second layer 120a and causes refraction where the first layer 110a interfaces with the second fluid. As previously discussed, a light source (e.g., light sources 420a) may deliver the light to an edge of the first layer 110a or may deliver the light at an angle selected based on critical angles of the first layer-first fluid interface and the first-layer-second fluid interface. The critical angles may depend on the indices of refraction of the first layer, the first fluid, and the second fluid.

[0045] At block 906, the method 900 includes detecting the light or a fluorescent emission caused by the light from the second fluid. Light refracted into the second fluid may escape from the first layer 110a or the second layer 120a or may generate fluorescent emissions that escape from the first layer 110a or the second layer 120a. The light sensor 430a may detect the light by receiving light escaping from the first layer 110a or the second layer 120a of the microfluidic device 100a and generating a signal based on the received light. Detecting the light or fluorescent emission may include aligning an optical axis of the light sensor 430a with a normal vector of the first layer or the second layer or angling an optical axis of the light sensor 430a relative to a normal vector of the first layer or the second layer prior to receiving the escaping light.

[0046] Figure 10 is a flow diagram of another example method 1000 to illuminate a fluid in a microfluidic device 100a. The method 1000 may be performed with any of the microfluidic devices 100a, 100b, 200 previously described that can receive light at a layer edge or any of the systems 400a, 400b, 500a, 500b, 600, 800 previously described that can deliver light to a layer edge. For illustrative purposes, the method 1000 is described in relation to the microfluidic device 100a and the system 400a. At block 1002, the method 1000 includes delivering a first fluid or a second fluid to a microfluidic device 100a including a first layer 110a and a second layer 120a. For example, the fluid may be delivered in the manner previously discussed for the method 900.

[0047] Block 1004 includes delivering uncollimated light to an edge of the first layer 110a to cause total internal reflection where the first layer interfaces with the first fluid located between the first layer and the second layer and cause refraction where the first layer interfaces with the second fluid. For example, a light source (e.g., light sources 420a) may be adjacent to or attached to the edge of the layer and may deliver the light by emitting the light towards the edge. At block 1006, the method 1000 includes detecting the light or a fluorescent emission caused by the light from the second fluid. For example, the light may be detected in the manner previously discussed for the method 900.

[0048] Figure 11 is a flow diagram of still another example method 1100 to illuminate a fluid in a microfluidic device 300. The method 1100 may be performed with any of the microfluidic devices 100a, 100b, 200, 300 previously described when equipped with a prism or any of the systems 400a, 400b, 500a, 500b, 600, 700, 800 previously described when adjusted or modified to deliver light to a prism. For illustrative purposes, the method 1100 is described in relation to the microfluidic device 300 and the system 700. At block 1102, the method 1100 includes delivering a first fluid or a second fluid to a microfluidic device 300 including a first layer 110 and a second layer 120. For example, the fluid may be delivered as in any previously discussed method 900, 1000.

[0049] Block 1104 includes delivering collimated, narrowband light to a prism 330 coupled to the first layer 110 to cause total internal reflection where the first layer interfaces with the first fluid located between the first layer and the second layer and cause refraction where the first layer interfaces with the second fluid. For example, a light source (e.g., light sources 720) may be angled to be aligned with a normal vector of the prism 330. The light source 720 and prism 330 may be oriented to deliver the light at a predetermined angle (e.g., an angle between the critical angles of the first layer-first fluid interface and the first layer-second fluid interface). In some examples, the light source 720 may be selected to deliver narrowband light that includes a wavelength at which the first fluid absorbs light. For example, the light source 720 may deliver the light at the wavelength at which the first fluid absorbs light without delivering light at other wavelengths (e.g., a laser may deliver 970 nm light to water that absorbs light at 970 nm). Accordingly, if light does escape from the first layer into the first fluid, the first fluid will absorb at least some of that light, which will further improve the SNR. In some examples, the wavelength of the narrowband light may be selected to be a wavelength that cause a molecule (e.g., a reporter molecule) in the second fluid to fluoresce. At block 1106, the method 1100 includes detecting the light or a fluorescent emission caused by the light from the second fluid. For example, the light may be detected as in any previously discussed method 900, 1000.

[0050] Figure 12 is a flow diagram of still another example method 1200 to illuminate a fluid in a microfluidic device 100a. The method 1100 may be performed with any of the microfluidic devices 100a, 100b, 200, 300 previously described or any of the systems 400a, 400b, 500a, 500b, 600, 700, 800 previously described. For illustrative purposes, the method 1200 is described in relation to the microfluidic device 100a and the system 600. At block 1202, the method 1200 includes delivering a first fluid or a second fluid to a microfluidic device 100a including a first layer 110a and a second layer 120a. For example, the fluid may be delivered as in any previously discussed method 900, 1000, 1100. [0051] Block 1204 includes delivering light to the first layer 110a at an angle that causes total internal reflection where the first layer 110a interfaces with the first fluid located between the first layer 110a and the second layer 120a and causes refraction where the first layer 110a interfaces with the second fluid. For example, the light sources 620 may deliver light as in any previously discussed method 900, 1000, 1100.

[0052] At block 1206, the method 1200 includes capturing an image of fluorescence emitted from the second fluid in response to the light. For example, the second fluid may be distributed at a plurality of locations between the first layer 110a and the second layer 120a. There may be a plurality of cells, and some or all of them may include the second fluid. The second fluid at each cell may include a reporter that fluoresces in response to the delivered light (e.g., when a target molecule is present). The image sensor 630 may capture an image of the plurality of cells including fluorescence emitted from the second fluid at each cell. Based on the captured image, the processor 640 may determine which or how many of the cells are emitting fluorescence to determine whether or how much of a target molecule is present.

[0053] The above description is illustrative of various principles and implementations of the present disclosure. Numerous variations and modifications to the examples described herein are envisioned. Accordingly, the scope of the present application should be determined only by the following claims.

Claims

CLAIMS What is claimed is:

1. A microfluidic device comprising: an optically transparent first layer having an index of refraction; and an optically scattering second layer spaced from the optically transparent first layer to receive a first fluid and a second fluid between the optically transparent first layer and the optically scattering second layer, wherein the index of refraction is selected to cause total internal reflection where the first layer interfaces with the first fluid and to cause refraction where the first layer interfaces with the second fluid.

2. The microfluidic device of claim 1 , wherein the first fluid includes oil, wherein the second fluid includes water, and wherein the index of refraction is selected to cause total internal reflection where the first layer interfaces with the first fluid for a selected wavelength of light and to cause refraction where the first layer interfaces with the second fluid for the selected wavelength of light.

3. The microfluidic device of claim 1, wherein the second fluid includes oil, wherein the first fluid includes water, and wherein the second layer includes a reflective surface.

4. The microfluidic device of claim 1 , further comprising a prism to transfer light to the first layer at an angle between a critical angle of the first fluid and a critical angle of the second fluid.

5. The microfluidic device of claim 1 , wherein the first layer includes a polymer or glass.

6. A method, comprising: delivering a first fluid or a second fluid to a microfluidic device, the microfluidic device including a first layer and a second layer, wherein the first or second fluid is delivered to a location between the first layer and the second layer; delivering light to the first layer at an angle that causes total internal reflection where the first layer interfaces with the first fluid located between the first layer and the second layer and causes refraction where the first layer interfaces with the second fluid; and detecting the light or a fluorescent emission caused by the light from the second fluid.

7. The method of claim 6, wherein delivering light comprises delivering uncollimated light to an edge of the first layer.

8. The method of claim 6, wherein delivering light comprises delivering collimated, narrowband light to a prism coupled to the first layer.

9. The method of claim 8, wherein the narrowband light includes a wavelength at which the first fluid absorbs light.

10. The method of claim 6, wherein detecting the light comprising capturing an image of fluorescence emitted from the second fluid in response to the light.

11. A system comprising: an interface to mechanically couple a microfluidic device to the system; a plurality of light sources, each light source aligned in a first dimension with a row of cells of the microfluidic device and angled in a second dimension to create total internal reflection within a layer of the microfluidic device where the layer interfaces with a first fluid and to create refraction where the layer interfaces with a second fluid; and a light sensor to detect light from the second fluid.

12. The system of claim 11 , wherein the light sensor includes an image sensor to capture an image of the second fluid, and wherein the system further comprises a processor, the processor to analyze the image to determine a location of the first fluid or the second fluid or the processor to analyze the image to determine an intensity at a location of the first fluid or the second fluid.

13. The system of claim 11, wherein the plurality of light sources includes a plurality of narrowband, collimated light sources.

14. The system of claim 11, wherein each light source is angled in the second dimension at an angle between a first critical angle where the layer interfaces with the first fluid and a second critical angle where the layer interfaces with the second fluid.

15. The system of claim 11 , further comprising a scintillator to convert light from a first wavelength not detectable by the light sensor to a second wavelength detectable by the light sensor.