The disclosure relates to a method for high-throughput, sequential measurement of live-cell parameters in isolated microchambers (e.g., “microwells”) followed by quantitative Reverse Transcription PCR, which maintains independence between results for different microchambers.
Measurement of live-cell parameters in isolated microchambers is well-established. See, e.g., Kelbauskas, et al., “Method for physiologic phenotype characterization at the single-cell level in non-interacting and interacting cells,” J. Biomed. Opt., 17, 037008 (2012). qRT-PCR [real-time RT (reverse transcription)-PCR] has become a standard for the detection and quantification of RNA targets. qRT-PCR assays utilize fluorescent reporter molecules to monitor production of amplification products during each polymerase chain reaction cycle, and combine amplification and detection steps. Fluorescence-based qRT-PCR realizes the inherent quantitative capacity of PCR-based assays. Single-cell qRT-PCR has already been described. See, e.g., International Patent Application Publication No. WO/2015/048009; Beer, et al., “On-Chip Single-Copy Real-Time Reverse-Transcription PCR in Isolated Picoliter Droplets,” Anal. Chem., 80, 1854-1858 (2008). High-throughput non-contact dispensing of small volume droplets is well established, such as shown in the Rainmaker MicroDispensing Pattern Generator by Engineering Arts. The use of one-step qRT-PCR, the use of mineral oil for minimizing evaporation in biosciences applications, and thermal cycling apparatus design for glass substrates for qRT-PCR are also well established. Harvesting of single cells from microchambers after metabolic measurement for the purpose of downstream qRT-PCR has been demonstrated. See, e.g., Zeng, et al., “Quantitative single-cell gene expression measurements of multiple genes in response to hypoxia treatment,” Anal. Bioanal. Chem., 401, 3-13 (2011). Other methods have been demonstrated for nanoliter volume, high-throughput qRT-PCR with bulk cell samples, but not for single cell samples. See, e.g., Morrison, et al., “Nanoliter high throughput quantitative PCR,” Nucleic Acids Research, Vol. 34, No. 18 (2006); Zhang, et al., “Miniaturized PCR chips for nucleic acid amplification and analysis: latest advances and future trends,” Nucleic Acids Research, Vol. 35, No. 13, 4223-4237 (2007); Dittrich, et al., “Micro Total Analysis Systems. Latest Advancements and Trends,” Anal. Chem. 78, 3887 (2006); and Lee, et al., “A Disposable Plastic-Silicon Micro PCR Chip Using Flexible Printed Circuit Board Protocols and Its Application to Genomic DNA Amplification.” IEEE Sensors J., Vol. 8, No. 5 (2008).
The art continues to seek a method for harvesting of single cells for gene expression analysis that is high-throughput, is not operator dependent, does not pose a risk of degradation of RNA during transport of the cell, and preferably uses equipment that is commercially available. Also, the speed of conventional cell harvesting processes is slow, which can lead to long dwell times that can bias qRT-PCR results. In the harvesting context, it is also difficult to verify dispensation of a single cell into lysis buffer, and performance of verification steps reduces throughput. Such matter disclosed herein addresses (e.g., eliminates or substantially resolves) some or all of the foregoing concerns.
This invention disclosure describes a method for high-throughput, sequential measurement of live-cell parameters in isolated microchambers (e.g., “microwells”, or simply “wells”) followed by one-step, quantitative Reverse Transcription PCR (qRT-PCR) which maintains independence between results for different microchambers. The method consists of live-cell microchamber measurements; removal of the microchamber lid; optional removal of a portion of microchamber fluid using evaporation, blotting, or gas flow; optional dispensation of control RNA into a subset of microchambers; microdispensation of a droplet of lysate into each microchamber; microdispensation of a droplet of RT-PCR mix into each microchamber whereby primers may be different between microchambers; microdispensation of a droplet of oil to cap each microchamber and prevent evaporation; optional application of a lid to further prevent evaporation; and incorporation of the microchamber substrate into a thermal cycling apparatus with a window, thereby enabling epifluorescence imaging. A gene or protein expression assay can be run at the single-cell level using cells that were already monitored for metabolic parameters. Correlation is possible between metabolic and gene or protein expression parameters at the single cell level and at high-throughput and relatively lower cost.
In certain aspects, the present disclosure relates to a method for analyzing cells, the method comprising: measuring one or more live-cell parameters (e.g., oxygen concentration, oxygen consumption rate, pH, glucose concentration, glucose consumption rate, adenosine triphosphate (ATP) concentration, and/or mitochondrial membrane potential (MMP)) for a plurality of cells contained in at least one liquid in a plurality of isolated microchambers of a microarray device; removing a lid bounding the plurality of isolated microchambers; microdispensing a quantity of lysate into each microchamber of the plurality of isolated microchambers; microdispensing a quantity of reverse transcription polymerase chain reaction mix into each microchamber of the plurality of isolated microchambers; microdispensing a quantity of oil into each microchamber of the plurality of isolated microchambers; and incorporating the microarray device into a thermal cycling apparatus with a window permitting epifluorescence imaging of the plurality of isolated microchambers. In certain embodiments, each microchamber of the plurality of isolated microchambers comprises a volume in a range of from about 100 picoliters (pL) to about 500 picoliters (pL). In certain embodiments, said removing of the lid bounding the plurality of isolated microchambers causes removal of a portion of the at least one liquid from the plurality of isolated microchambers. In certain embodiments, the method further comprises removing a portion of the at least one liquid from the plurality of isolated microchambers by at least one of evaporation, blotting, or application of a gas flow. In certain embodiments, the method further comprises microdispensing a quantity of control RNA into a subset of microchambers of the plurality of isolated microchambers. In certain embodiments, at least one of said microdispensing of a quantity of lysate, microdispensing of a quantity of reverse transcription polymerase chain reaction mix, or microdispensing of a quantity of oil comprises piezoelectric microdispensing. In certain embodiments, at least one of said quantity of lysate, said quantity of reverse transcription polymerase chain reaction mix, or said quantity of oil comprises a volume in a range of from about 25 pL to about 200 pL, or in a range of from about 50 pL to about 150 pL. In certain embodiments, each microchamber of the plurality of isolated microchambers contains a single cell of the plurality of cells. In certain embodiments, the measuring of one or more live-cell parameters is performed at a single-cell level. In certain embodiments, the method further comprises performing a reverse transcription polymerase chain reaction in each microchamber of the plurality of isolated microchambers. In certain embodiments, the method further comprises performing protein expression measurement at a single-cell level in each microchamber of the plurality of isolated microchambers. In certain embodiments, the method utilizes a fixture incorporating at least one piezoelectric dispensing head and incorporating an apparatus for measuring fluorescence response at a single-cell level for each microchamber of the plurality of isolated microchambers. In certain embodiments, the method utilizes a fixture incorporating the thermal cycling apparatus and an apparatus for measuring fluorescence response for each microchamber of the plurality of isolated microchambers. In certain embodiments, said one or more live-cell parameters comprises at least one of oxygen concentration, oxygen consumption rate, pH, glucose concentration, glucose consumption rate, adenosine triphosphate concentration, or mitochondrial membrane potential. In certain embodiments, said quantity of lysate and said quantity of reverse transcription polymerase chain reaction mix are combined prior to microdispensing, and are microdispensed together.
Other aspects and advantages of the disclosure will be apparent upon review of the description and drawings.
Features in the figures are not to scale unless specifically indicated to the contrary herein.
The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.
It should be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It should also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.
It should be understood that, although the terms “upper,” “lower,” “bottom,” “intermediate,” “middle,” “top,” and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed an “upper” element and, similarly, a second element could be termed an “upper” element depending on the relative orientations of these elements, without departing from the scope of the present disclosure.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including” when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having meanings that are consistent with their meanings in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Disclosed herein is a method for analyzing cells through measurement of live-cell parameters followed by measurement of gene and protein expression. An exemplary method comprises measuring one or more live-cell parameters for a plurality of cells contained in at least one liquid in a plurality of isolated microchambers of a microarray device. The method further comprises removing a lid bounding the plurality of isolated microchambers. The method further comprises microdispensing a quantity of lysate into each microchamber of the plurality of isolated microchambers. The method further comprises microdispensing a quantity of reverse transcription polymerase chain reaction mix into each microchamber of the plurality of isolated microchambers. The method further comprises microdispensing a quantity of oil into each microchamber of the plurality of isolated microchambers. The method further comprises incorporating the microarray device into a thermal cycling apparatus with a window permitting epifluorescence imaging of the plurality of isolated microchambers.
Live-cell parameters can include any number of parameters such as oxygen concentration, oxygen consumption rate, pH, glucose concentration, glucose consumption rate, ATP concentration, and mitochondrial membrane potential. The present disclosure combines measurement of one or more of these parameters with qRT-PCR at the single-cell or multiple-cell level, while maintaining one-to-one correspondence between phenotype and genotype measurements at the microchamber level.
When the live-cell measurements are made using a sensor lid that caps an array of microchambers, sensor lid disassembly will naturally remove a portion of the fluid that was originally present in the sealed microchamber. In certain embodiments, the volume of a microchamber can be 225 pL (e.g., 100 μm diameter and 32 μm deep), of which a single mammalian cell will comprise approximately 4 pL. In certain embodiments, the cell medium is removed to leave a volume of approximately 50 pL. In certain embodiments, microdispensing using conventional piezoelectric droplet dispensing technology is used to deliver chemicals to individual wells with single-well selectivity. In certain embodiments, a dispensed droplet size can be approximately 50 pL or greater. In certain embodiments, the design ratio of lysate to PCR mix is 4:6. In such an embodiment, dispensed lysate volume may be 50 pL, followed by dispensed PCR mix volume of 75 pL. This may be followed by further dispensation of a mineral oil droplet (e.g., 50 pL), which may fill a microchamber having a volume of 225 pL.
In certain embodiments, the at least one front compliant layer 31 is substantially impervious to passage of gas (e.g., air) and/or evaporation of contents of a microwell. In certain embodiments, the front compliant layer 31 is optically reflective. In certain embodiments, the front compliant layer 31 comprises a plurality of front compliant layers. In certain embodiments, the front compliant layer comprises a thickness in a range of from 0.06 μm to 100 μm.
In certain embodiments, the back compliant layer 33 comprises an adhesive (e.g., an acrylic adhesive tape or a foam adhesive tape). In certain embodiments, the back compliant layer 33 comprises foam rubber, solid rubber, or silicone rubber. In certain embodiments, a back compliant layer 33 is more compliant than the front compliant layer 31. In certain embodiments, the back compliant layer 33 comprises silicone rubber, e.g., 70 Shore A with an approximate thickness of 0.5 mm. In certain embodiments, the back compliant layer 33 may comprise acrylic Pressure-Sensitive Adhesive (PSA), 50 to 125 μm thick, such as may be embodied or included in transfer tape or double-coated tape. In certain embodiments, the back compliant layer 33 may comprise foam-based tape such as 3M 4016.
In certain embodiments, the flexural layer 32 comprises a polymeric material (e.g., polyethylene terephthalate (PET)). In certain embodiments, the flexural layer 32 comprises a thickness in a range of from 25 μm to 100 μm. In certain embodiments, the flexural layer 32 comprises a plate constant, D, in a range of from 8 kNm to 7000 kNm. In certain embodiments, the flexural layer 32 comprises a modulus of elasticity of at least 1000 MPa.
After microdispensation is complete, the microchamber 24 (e.g., as part of a microarray device) may be placed or otherwise incorporated into a thermal cycling apparatus 60 (shown in
Although
In certain embodiments, the total fluid volume dispensed in a microchambers 24 can exceed the well volume, resulting in excess fluid which, if the volume is of reasonable size, will not run away. A positive control is an RNA spike (e.g., 1 nanogram of control RNA per well in 50 pL of aqueous volume either with or without a cell) because the spike is much more concentrated than a cell. This is followed by one step qRT-PCR mix and then the oil droplet. One negative control is a no-primer control in which the primer is omitted. Another negative control could be wells with no cells.
By the nature of random seeding, some wells 24 will be empty if the seeding density is selected appropriately. Empty wells 24 are used for positive and negative controls. The exact locations of empty wells 24 can be detected prior to PCR and then used to control the droplet program, or the controls can be dispensed in a fixed manner in which case some controls would be in wells with cells and some controls would be in wells without cells. A well 24 with no cell and no primer is a well that is not used. Statistically, there will almost always be the required negative controls in each assay. In certain embodiments utilizing micro qRT-PCR, the following 4 chemicals may be dispensed: lysate; qRT-PCR mix with primers; qRT-PCR mix without primers; and oil. Piezoelectric droplet dispense can be integrated into this process by transporting the well substrate (with live cells) to a dedicated programmable droplet dispense machine (e.g., a Rainmaker MicroDispensing Pattern Generator, available from Engineering Arts, Tempe, Ariz.). Alternatively, dispensation can be accomplished by integrating standard ink-jet printer-type piezo droplet dispensing into the fixtures and equipment used to make metabolic measurements on the cells earlier in the process. (An example of such equipment is described in Kelbauskas, et al., “Method for physiologic phenotype characterization at the single-cell level in non-interacting and interacting cells.” J. of Biomed. Opt., 17, 037008 (2012)). In the latter case, the lid used for sealing the chamber is removed and replaced with the piezoelectric dispensing head (e.g., arranged for non-contact, but close proximity dispensing relative to the wells). This is convenient because the same equipment used to perform fluorescence imaging for metabolic analysis can be used for qRT-PCR measurement.
In another embodiment, the oil is dispensed by spraying rather than by piezoelectric dispensation. The accuracy of the ratio of volumes of lysate to qRT-PCR mix by piezoelectric tip dispensing can easily be calibrated by dispensing two separate controls for which output is very sensitive to ratio.
In an additional embodiment, in-cell Western Blot for protein detection is accomplished within individual wells using the same microdispensing technology. At the chip level, formaldehyde is dispensed to fix the cells in place in the microchambers followed by wash, then permeabilization of cell membranes with Triton X-100, then wash, then blocking solution. Subsequently, specific primary antibodies, and then secondary antibodies, can be microdispensed at the individual well level in a manner similar to that described above. This can be achieved using different and selectable antibodies from well to well, or using multiplexing within an individual well. This has the advantages of maintaining measurement independence between microchambers, achieving high throughput, and minimizing the volume of expensive antibodies.
Upon reading the foregoing description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.
This application claims the benefit of U.S. Provisional Patent Application No. 62/255,883 filed Nov. 16, 2015; the disclosure of which is hereby incorporated by reference herein in its entirety.
This invention was made with government support under U01 CA164250 and P50 HG002360 awarded by the National Institutes of Health. The government has certain rights in the invention.
Filing Document | Filing Date | Country | Kind |
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PCT/US2016/062208 | 11/16/2016 | WO | 00 |
Number | Date | Country | |
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62255883 | Nov 2015 | US |