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Xie H, Guo W, Jiang H, Zhang T, Zhao L, Hu J, Gao S, Song S, Xu J, Xu L, Sun X, Ding Y, Jiang L, Ding X. Photosensitive Hydrogel with Temperature-Controlled Reversible Nano-Apertures for Single-Cell Protein Analysis. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2024; 11:e2308569. [PMID: 38483955 PMCID: PMC11109651 DOI: 10.1002/advs.202308569] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2023] [Revised: 02/15/2024] [Indexed: 05/23/2024]
Abstract
Single cell western blot (scWB) is one of the most important methods for cellular heterogeneity profiling. However, current scWB based on conventional photoactive polyacrylamide hydrogel material suffers from the tradeoff between in-gel probing and separation resolution. Here, a highly sensitive temperature-controlled single-cell western blotting (tc-scWB) method is introduced, which is based on a thermo/photo-dualistic-sensitive polyacrylamide hydrogel, namely acrylic acid-functionalized graphene oxide (AFGO) assisted, N-isopropylacrylamide modified polyacrylamide (ANP) hydrogel. The ANP hydrogel is contracted at high-temperature to constrain protein band diffusion during microchip electrophoretic separation, while the gel aperture is expanded under low-temperature for better antibody penetration into the hydrogel. The tc-scWB method enables the separation and profiling of small-molecule-weight proteins with highly crosslinked gel (12% T) in SDS-PAGE. The tc-scWB is demonstrated on three metabolic and ER stress-specific proteins (CHOP, MDH2 and FH) in four pancreatic cell subtypes, revealing the expression of key enzymes in the Krebs cycle is upregulated with enhanced ER stress. It is found that ER stress can regulate crucial enzyme (MDH2 and FH) activities of metabolic cascade in cancer cells, boosting aerobic respiration to attenuate the Warburg effect and promote cell apoptosis. The tc-scWB is a general toolbox for the analysis of low-abundance small-molecular functional proteins at the single-cell level.
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Affiliation(s)
- Haiyang Xie
- Department of Anesthesiology and Surgical Intensive Care UnitXinhua HospitalSchool of Medicine and School of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200092China
- State Key Laboratory of Oncogenes and Related GenesInstitute for Personalized MedicineSchool of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200030China
| | - Wenke Guo
- Department of Anesthesiology and Surgical Intensive Care UnitXinhua HospitalSchool of Medicine and School of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200092China
- State Key Laboratory of Oncogenes and Related GenesInstitute for Personalized MedicineSchool of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200030China
| | - Hui Jiang
- Department of Anesthesiology and Surgical Intensive Care UnitXinhua HospitalSchool of Medicine and School of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200092China
- State Key Laboratory of Oncogenes and Related GenesInstitute for Personalized MedicineSchool of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200030China
| | - Ting Zhang
- Department of Anesthesiology and Surgical Intensive Care UnitXinhua HospitalSchool of Medicine and School of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200092China
- State Key Laboratory of Oncogenes and Related GenesInstitute for Personalized MedicineSchool of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200030China
| | - Lei Zhao
- Department of Anesthesiology and Surgical Intensive Care UnitXinhua HospitalSchool of Medicine and School of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200092China
- State Key Laboratory of Oncogenes and Related GenesInstitute for Personalized MedicineSchool of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200030China
| | - Jinjuan Hu
- Department of Anesthesiology and Surgical Intensive Care UnitXinhua HospitalSchool of Medicine and School of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200092China
- State Key Laboratory of Oncogenes and Related GenesInstitute for Personalized MedicineSchool of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200030China
| | - Shuxin Gao
- Department of Anesthesiology and Surgical Intensive Care UnitXinhua HospitalSchool of Medicine and School of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200092China
- State Key Laboratory of Oncogenes and Related GenesInstitute for Personalized MedicineSchool of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200030China
| | - Sunfengda Song
- Department of Anesthesiology and Surgical Intensive Care UnitXinhua HospitalSchool of Medicine and School of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200092China
- State Key Laboratory of Oncogenes and Related GenesInstitute for Personalized MedicineSchool of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200030China
| | - Jiasu Xu
- Department of Anesthesiology and Surgical Intensive Care UnitXinhua HospitalSchool of Medicine and School of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200092China
- State Key Laboratory of Oncogenes and Related GenesInstitute for Personalized MedicineSchool of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200030China
| | - Li Xu
- Department of Anesthesiology and Surgical Intensive Care UnitXinhua HospitalSchool of Medicine and School of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200092China
- State Key Laboratory of Oncogenes and Related GenesInstitute for Personalized MedicineSchool of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200030China
| | - Xinyi Sun
- Department of Anesthesiology and Surgical Intensive Care UnitXinhua HospitalSchool of Medicine and School of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200092China
- State Key Laboratory of Oncogenes and Related GenesInstitute for Personalized MedicineSchool of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200030China
| | - Yi Ding
- Department of Anesthesiology and Surgical Intensive Care UnitXinhua HospitalSchool of Medicine and School of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200092China
- State Key Laboratory of Oncogenes and Related GenesInstitute for Personalized MedicineSchool of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200030China
| | - Lai Jiang
- Department of Anesthesiology and Surgical Intensive Care UnitXinhua HospitalSchool of Medicine and School of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200092China
- State Key Laboratory of Oncogenes and Related GenesInstitute for Personalized MedicineSchool of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200030China
| | - Xianting Ding
- Department of Anesthesiology and Surgical Intensive Care UnitXinhua HospitalSchool of Medicine and School of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200092China
- State Key Laboratory of Oncogenes and Related GenesInstitute for Personalized MedicineSchool of Biomedical EngineeringShanghai Jiao Tong UniversityShanghai200030China
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Alibekova Long M, Benman WKJ, Petrikas N, Bugaj LJ, Hughes AJ. Enhancing Single-Cell Western Blotting Sensitivity Using Diffusive Analyte Blotting and Antibody Conjugate Amplification. Anal Chem 2023; 95:17894-17902. [PMID: 37974303 DOI: 10.1021/acs.analchem.3c04130] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2023]
Abstract
While there are many techniques to achieve highly sensitive, multiplex detection of RNA and DNA from single cells, detecting protein content often suffers from low limits of detection and throughput. Miniaturized, high-sensitivity Western blots on single cells (scWesterns) are attractive because they do not require advanced instrumentation. By physically separating analytes, scWesterns also uniquely mitigate limitations to target protein multiplexing posed by the affinity reagent performance. However, a fundamental limitation of scWesterns is their limited sensitivity for detecting low-abundance proteins, which arises from transport barriers posed by the separation gel against detection species. Here we address the sensitivity by decoupling the electrophoretic separation medium from the detection medium. We transfer scWestern separations to a nitrocellulose blotting medium with distinct mass transfer advantages over traditional in-gel probing, yielding a 5.9-fold improvement in the limit of detection. We next amplify probing of blotted proteins with enzyme-antibody conjugates, which are incompatible with traditional in-gel probing to achieve further improvement in the limit of detection to 1000 molecules, a 120-fold improvement. This enables us to detect 100% of cells in an EGFP-expressing population using fluorescently tagged and enzyme-conjugated antibodies compared to 84.5% of cells using in-gel detection. These results suggest the compatibility of nitrocellulose-immobilized scWesterns with a variety of affinity reagents─not previously accessible for in-gel use─for further signal amplification and detection of low-abundance targets.
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Affiliation(s)
- Mariia Alibekova Long
- Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
- Bioengineering Graduate Group, University of Pennsylvania, Philadelphia, Pennsylvania, 19104, United States
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - William K J Benman
- Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
- Bioengineering Graduate Group, University of Pennsylvania, Philadelphia, Pennsylvania, 19104, United States
| | - Nathan Petrikas
- Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Lukasz J Bugaj
- Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
- Bioengineering Graduate Group, University of Pennsylvania, Philadelphia, Pennsylvania, 19104, United States
- Institute for Regenerative Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
- Abramson Cancer Center, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Alex J Hughes
- Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
- Bioengineering Graduate Group, University of Pennsylvania, Philadelphia, Pennsylvania, 19104, United States
- Institute for Regenerative Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
- Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
- Center for Soft and Living Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
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3
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Long MA, Benman W, Petrikas N, Bugaj LJ, Hughes AJ. Enhancing single-cell western blotting sensitivity using diffusive analyte blotting and antibody conjugate amplification. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.13.544857. [PMID: 37398364 PMCID: PMC10312704 DOI: 10.1101/2023.06.13.544857] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/04/2023]
Abstract
While there are many techniques to achieve highly sensitive, multiplex detection of RNA and DNA from single cells, detecting protein contents often suffers from low limits of detection and throughput. Miniaturized, high-sensitivity western blots on single cells (scWesterns) are attractive since they do not require advanced instrumentation. By physically separating analytes, scWesterns also uniquely mitigate limitations to target protein multiplexing posed by affinity reagent performance. However, a fundamental limitation of scWesterns is their limited sensitivity for detecting low-abundance proteins, which arises from transport barriers posed by the separation gel against detection species. Here we address sensitivity by decoupling the electrophoretic separation medium from the detection medium. We transfer scWestern separations to a nitrocellulose blotting medium with distinct mass transfer advantages over traditional in-gel probing, yielding a 5.9-fold improvement in limit of detection. We next amplify probing of blotted proteins with enzyme-antibody conjugates which are incompatible with traditional in-gel probing to achieve further improvement in the limit of detection to 103 molecules, a 520-fold improvement. This enables us to detect 85% and 100% of cells in an EGFP-expressing population using fluorescently tagged and enzyme-conjugated antibodies respectively, compared to 47% of cells using in-gel detection. These results suggest compatibility of nitrocellulose-immobilized scWesterns with a variety of affinity reagents - not previously accessible for in-gel use - for further signal amplification and detection of low abundance targets.
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Affiliation(s)
- Mariia Alibekova Long
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, 19104, PA, USA
- Bioengineering Graduate Group, University of Pennsylvania, Philadelphia, PA, 19104, PA, USA
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, PA, USA
| | - William Benman
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, 19104, PA, USA
- Bioengineering Graduate Group, University of Pennsylvania, Philadelphia, PA, 19104, PA, USA
| | - Nathan Petrikas
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, 19104, PA, USA
- Currently at Tempus Labs Inc., Chicago, IL, USA
| | - Lukasz J. Bugaj
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, 19104, PA, USA
- Bioengineering Graduate Group, University of Pennsylvania, Philadelphia, PA, 19104, PA, USA
- Institute for Regenerative Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
- Abramson Cancer Center, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Alex J. Hughes
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, 19104, PA, USA
- Bioengineering Graduate Group, University of Pennsylvania, Philadelphia, PA, 19104, PA, USA
- Institute for Regenerative Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
- Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, PA, 19104, USA
- Center for Soft and Living Matter, University of Pennsylvania, Philadelphia, PA, 19104, USA
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Responsive Hyaluronic Acid–Ethylacrylamide Microgels Fabricated Using Microfluidics Technique. Gels 2022; 8:gels8090588. [PMID: 36135299 PMCID: PMC9498840 DOI: 10.3390/gels8090588] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2022] [Revised: 09/08/2022] [Accepted: 09/10/2022] [Indexed: 11/16/2022] Open
Abstract
Volume changes of responsive microgels can probe interactions between polyelectrolytes and species of opposite charges such as peptides and proteins. We have investigated a microfluidics method to synthesize highly responsive, covalently crosslinked, hyaluronic acid microgels for such purposes. Sodium hyaluronate (HA), pre-modified with ethylacrylamide functionalities, was crosslinked in aqueous droplets created with a microfluidic technique. We varied the microgel properties by changing the degree of modification and concentration of HA in the reaction mixture. The degree of modification was determined by 1H NMR. Light microscopy was used to investigate the responsiveness of the microgels to osmotic stress in aqueous saline solutions by simultaneously monitoring individual microgel species in hydrodynamic traps. The permeability of the microgels to FITC-dextrans of molecular weights between 4 and 250 kDa was investigated using confocal laser scanning microscopy. The results show that the microgels were spherical with diameters between 100 and 500 µm and the responsivity tunable by changing the degree of modification and the HA concentration. Microgels were fully permeable to all investigated FITC-dextran probes. The partitioning to the microgel from an aqueous solution decreased with the increasing molecular weight of the probe, which is in qualitative agreement with theories of homogeneous gel networks.
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Abstract
Hydrogels are important structural and operative components of microfluidic systems, finding diverse utility in biological sample preparation and interrogation. One inherent challenge for integrating hydrogels into microfluidic tools is thermodynamic molecular partitioning, which reduces the in-gel concentration of molecular solutes (e.g., biomolecular regents), as compared to the solute concentration in an applied solution. Consequently, biomolecular reagent access to in-gel scaffolded biological samples (e.g., encapsulated cells, microbial cultures, target analytes) is adversely impacted in hydrogels. Further, biomolecular reagents are typically introduced to the hydrogel via diffusion. This passive process requires long incubation periods compared to active biomolecular delivery techniques. Electrotransfer is an active technique used in Western blots and other gel-based immunoassays that overcomes limitations of size exclusion (increasing the total probe mass delivered into gel) and expedites probe delivery, even in millimeter-thick slab gels. While compatible with conventional slab gels, electrotransfer has not been adapted to thin gels (50-250 μm thick), which are of great interest as components of open microfluidic devices (vs enclosed microchannel-based devices). Mechanically delicate, thin gels are often mounted on rigid support substrates (glass, plastic) that are electrically insulating. Consequently, to adapt electrotransfer to thin-gel devices, we replace rigid insulating support substrates with novel, mechanically robust, yet electrically conductive nanoporous membranes. We describe grafting nanoporous membranes to thin-polyacrylamide-gel layers via silanization, characterize the electrical conductivity of silane-treated nanoporous membranes, and report the dependence of in-gel immunoprobe concentration on transfer duration for passive diffusion and active electrotransfer. Alternative microdevice component layers─including the mechanically robust, electrically conductive nanoporous membranes reported here─provide new functionality for integration into an increasing array of open microfluidic systems.
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Affiliation(s)
- Andoni P Mourdoukoutas
- The UC Berkeley/UCSF Graduate Program in Bioengineering, University of California, Berkeley, California 94720, United States
| | - Amy E Herr
- Department of Bioengineering, University of California, Berkeley, California 94720, United States
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6
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Reaction-diffusion model to quantify and visualize mass transfer and deactivation within core-shell polymeric microreactors. J Colloid Interface Sci 2021; 608:1999-2008. [PMID: 34749148 DOI: 10.1016/j.jcis.2021.10.092] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2021] [Revised: 10/15/2021] [Accepted: 10/16/2021] [Indexed: 12/13/2022]
Abstract
HYPOTHESIS The performance of a polymeric core-shell microreactor depends critically on (i) mass transfer, (ii) catalyzed chemical reaction, and (iii) deactivation within the nonuniform core-shell microstructure environment. As such, these three basic working principles control the active catalytic phase density in the reactor. THEORY We present a high-fidelity, image-based nonequilibrium computational model to quantify and visualize the mass transport as well as the deactivation process of a core-shell polymeric microreactor. In stark contrast with other published works, our microstructure-based computer simulation can provide a single-particle visualization with a micrometer spatial accuracy. FINDINGS We show how the interplay of kinetics and thermodynamics controls the product-induced deactivation process. The model predicts and visualizes the non-trivial, spatially resolved active catalyst phase patterns within a core-shell system. Moreover, we also show how the microstructure influences the formation of foulant within a core-shell structure; that is, begins from the core and grows radially onto the shell section. Our results suggest that the deactivation process is highly governed by the porosity/microstructure of the microreactor as well as the affinity of the products towards the solid phase of the reactor.
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Tan KY, Desai S, Raja E, Etienne C, Webb B, Herr AE. Comparison of photoactivatable crosslinkers for in-gel immunoassays. Analyst 2021; 146:6621-6630. [PMID: 34591044 DOI: 10.1039/d1an01309b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
While fluorescence readout is a key detection modality for hydrogel-based immunoassays, background fluorescence due to autofluorescence or non-specific antibody interactions impairs the lower limit of detection of fluorescence immunoassays. Chemical modifications to the hydrogel structure impact autofluorescence and non-specific interactions. Benzophenone is a common photoactivatable molecule, and benzophenone methacrylamide (BPMA) has been used for cross-linking protein in polyacrylamide (PA) hydrogels. However, previous studies have suggested that the aromatic structure of benzophenone can contribute to increased autofluorescence and non-specific hydrophobic interactions with unbound fluorescent probes. Here, we synthesize diazirine methacrylamide (DZMA) as an alternative photoactivatable molecule to crosslink into PA hydrogels for in-gel protein capture for in-gel immunoassays. We hypothesize that the less hydrophobic structure of diazirine (based on previously reported predicted and experimental log P values) exhibits both reduced autofluorescence and non-specific hydrophobic interactions. We find that while equal concentrations of DZMA and BPMA result in lower protein target photocapture in the diazirine configuration, increasing the DZMA concentration up to 12 mM improves in-gel protein capture to be on par with previously reported and characterized 3 mM BPMA hydrogels. Furthermore, despite the higher concentration of diazirine, we observe negligible autofluorescence signal and a 50% reduction in immunoassay fluorescence background signal in diazirine gels compared to BPMA gels resulting in comparable signal-to-noise ratios (SNR) of the probed protein target. Finally, we test the utility of DZMA for single-cell immunoblotting in an open microfluidic device and find that protein migrates ∼1.3× faster in DZMA hydrogels than in BPMA hydrogels. However, in DZMA hydrogels we detect only 15% of the protein signal compared to BPMA hydrogels suggesting that the diazirine chemistry results in greater protein losses following electrophoretic separations. We establish that while diazirine has lower background fluorescence signal, which may potentially improve immunoassay performance, the lower capture efficiency of diazirine reduces its utility in open microfluidic systems susceptible to sample losses.
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Affiliation(s)
- Kristine Y Tan
- The UC Berkeley - UCSF Graduate Program in Bioengineering, 94720 Berkeley, CA, USA.
| | - Surbhi Desai
- Department of Research and Development, Thermo Fisher Scientific, Rockford, Illinois, USA
| | - Erum Raja
- Department of Research and Development, Thermo Fisher Scientific, Rockford, Illinois, USA
| | - Chris Etienne
- Department of Research and Development, Thermo Fisher Scientific, Rockford, Illinois, USA
| | - Brian Webb
- Department of Research and Development, Thermo Fisher Scientific, Rockford, Illinois, USA
| | - Amy E Herr
- The UC Berkeley - UCSF Graduate Program in Bioengineering, 94720 Berkeley, CA, USA. .,Department of Bioengineering, University of California, Berkeley, 94720 Berkeley, CA, USA
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Lomeli G, Bosse M, Bendall SC, Angelo M, Herr AE. Multiplexed Ion Beam Imaging Readout of Single-Cell Immunoblotting. Anal Chem 2021; 93:8517-8525. [PMID: 34106685 PMCID: PMC8499019 DOI: 10.1021/acs.analchem.1c01050] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Improvements in single-cell protein analysis are required to study the cell-to-cell variation inherent to diseases, including cancer. Single-cell immunoblotting (scIB) offers proteoform detection specificity, but often relies on fluorescence-based readout and is therefore limited in multiplexing capability. Among rising multiplexed imaging methods is multiplexed ion beam imaging by time-of-flight (MIBI-TOF), a mass spectrometry imaging technology. MIBI-TOF employs metal-tagged antibodies that do not suffer from spectral overlap to the same degree as fluorophore-tagged antibodies. We report for the first-time MIBI-TOF of single-cell immunoblotting (scIB-MIBI-TOF). The scIB assay subjects single-cell lysate to protein immunoblotting on a microscale device consisting of a 50- to 75-μm thick hydrated polyacrylamide (PA) gel matrix for protein immobilization prior to in-gel immunoprobing. We confirm antibody-protein binding in the PA gel with indirect fluorescence readout of metal-tagged antibodies. Since MIBI-TOF is a layer-by-layer imaging technique, and our protein target is immobilized within a 3D PA gel layer, we characterize the protein distribution throughout the PA gel depth by fluorescence confocal microscopy and confirm that the highest signal-to-noise ratio is achieved by imaging the entirety of the PA gel depth. Accordingly, we report the required MIBI-TOF ion dose strength needed to image varying PA gel depths. Lastly, by imaging ∼42% of PA gel depth with MIBI-TOF, we detect two isoelectrically separated TurboGFP (tGFP) proteoforms from individual glioblastoma cells, demonstrating that highly multiplexed mass spectrometry-based readout is compatible with scIB.
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Affiliation(s)
| | - Marc Bosse
- Department of Pathology, Stanford University, Stanford, California 94025, United States
| | - Sean C Bendall
- Department of Pathology, Stanford University, Stanford, California 94025, United States
| | - Michael Angelo
- Department of Pathology, Stanford University, Stanford, California 94025, United States
| | - Amy E Herr
- Chan Zuckerberg Biohub, San Francisco, California 94158, United States
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Abstract
A hydrogel is a solid form of polymer network absorbed in a substantial amount of aqueous solution. In electrophoresis, hydrogels play versatile roles including as support media, sieving matrixes, affinity scaffolds, and compositions of molecularly imprinting polymers. Recently, the study of hydrogels has been advancing with unprecedented speed, and the application of hydrogels in separation science has brought new opportunities and possible breakthroughs. A good understanding about the roles and effects of the material is essential for hydrogel applications. This review summarizes the hydrogels that has been described in various modes of electrophoretic separations, including isoelectric focusing gel electrophoresis (IEFGE), isotachophoresis (ITP), gel electrophoresis and affinity gel electrophoresis (AGE). As microchip electrophoresis (ME) is one of the future trends in electrophoresis, thought provoking studies related to hydrogels in ME are also introduced. Novel hydrogels and methods that improve separation performance, facilitate the experimental operation process, allow for rapid analysis, and promote the integration to microfluidic devices are highlighted.
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Affiliation(s)
- Chenchen Liu
- Department of Material Chemistry, Graduate School of Engineering, Kyoto University
| | - Takuya Kubo
- Department of Material Chemistry, Graduate School of Engineering, Kyoto University
| | - Koji Otsuka
- Department of Material Chemistry, Graduate School of Engineering, Kyoto University
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Rosàs-Canyelles E, Modzelewski AJ, Geldert A, He L, Herr AE. Multimodal detection of protein isoforms and nucleic acids from mouse pre-implantation embryos. Nat Protoc 2021; 16:1062-1088. [PMID: 33452502 PMCID: PMC7954398 DOI: 10.1038/s41596-020-00449-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2020] [Accepted: 10/19/2020] [Indexed: 01/29/2023]
Abstract
Although mammalian embryo development depends on critical protein isoforms that arise from embryo-specific nucleic acid modifications, the role of these isoforms is not yet clear. Challenges arise in measuring protein isoforms and nucleic acids from the same single embryos and blastomeres. Here we present a multimodal technique for performing same-embryo nucleic acid and protein isoform profiling (single-embryo nucleic acid and protein profiling immunoblot, or snapBlot). The method integrates protein isoform measurement by fractionation polyacrylamide gel electrophoresis (fPAGE) with off-chip analysis of nucleic acids from the nuclei. Once embryos are harvested and cultured to the desired stage, they are sampled into the snapBlot device and subjected to fPAGE. After fPAGE, 'gel pallets' containing nuclei are excised from the snapBlot device for off-chip nucleic acid analyses. fPAGE and nuclei analyses are indexed to each starting sample, yielding same-embryo multimodal measurements. The entire protocol, including processing of samples and data analysis, takes 2-3 d. snapBlot is designed to help reveal the mechanisms by which embryo-specific nucleic acid modifications to both genomic DNA and messenger RNA orchestrate the growth and development of mammalian embryos.
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Affiliation(s)
- Elisabet Rosàs-Canyelles
- Department of Bioengineering, University of California Berkeley, Berkeley, CA, USA
- The University of California Berkeley and University of California San Francisco Graduate Program in Bioengineering, Berkeley, CA, USA
| | - Andrew J Modzelewski
- Division of Cellular and Developmental Biology, Department of Molecular & Cell Biology, University of California, Berkeley, Berkeley, CA, USA
| | - Alisha Geldert
- Department of Bioengineering, University of California Berkeley, Berkeley, CA, USA
- The University of California Berkeley and University of California San Francisco Graduate Program in Bioengineering, Berkeley, CA, USA
| | - Lin He
- Division of Cellular and Developmental Biology, Department of Molecular & Cell Biology, University of California, Berkeley, Berkeley, CA, USA
| | - Amy E Herr
- Department of Bioengineering, University of California Berkeley, Berkeley, CA, USA.
- The University of California Berkeley and University of California San Francisco Graduate Program in Bioengineering, Berkeley, CA, USA.
- Chan Zuckerberg Biohub, San Francisco, CA, USA.
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Grist SM, Mourdoukoutas AP, Herr AE. 3D projection electrophoresis for single-cell immunoblotting. Nat Commun 2020; 11:6237. [PMID: 33277486 PMCID: PMC7718224 DOI: 10.1038/s41467-020-19738-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Accepted: 10/20/2020] [Indexed: 12/21/2022] Open
Abstract
Immunoassays and mass spectrometry are powerful single-cell protein analysis tools; however, interfacing and throughput bottlenecks remain. Here, we introduce three-dimensional single-cell immunoblots to detect both cytosolic and nuclear proteins. The 3D microfluidic device is a photoactive polyacrylamide gel with a microwell array-patterned face (xy) for cell isolation and lysis. Single-cell lysate in each microwell is "electrophoretically projected" into the 3rd dimension (z-axis), separated by size, and photo-captured in the gel for immunoprobing and confocal/light-sheet imaging. Design and analysis are informed by the physics of 3D diffusion. Electrophoresis throughput is > 2.5 cells/s (70× faster than published serial sampling), with 25 immunoblots/mm2 device area (>10× increase over previous immunoblots). The 3D microdevice design synchronizes analyses of hundreds of cells, compared to status quo serial analyses that impart hours-long delay between the first and last cells. Here, we introduce projection electrophoresis to augment the heavily genomic and transcriptomic single-cell atlases with protein-level profiling.
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Affiliation(s)
- Samantha M Grist
- Department of Bioengineering, University of California, Berkeley, USA
| | - Andoni P Mourdoukoutas
- Department of Bioengineering, University of California, Berkeley, USA
- UC Berkeley - UCSF Graduate Program in Bioengineering, Berkeley, USA
| | - Amy E Herr
- Department of Bioengineering, University of California, Berkeley, USA.
- UC Berkeley - UCSF Graduate Program in Bioengineering, Berkeley, USA.
- Chan Zuckerberg Biohub, San Francisco, CA, USA.
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12
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Moss AC, Herr AE. In-gel fluorescence detection by DNA polymerase elongation. APL Bioeng 2020; 4:046104. [PMID: 33263097 PMCID: PMC7680656 DOI: 10.1063/5.0021149] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Accepted: 10/07/2020] [Indexed: 11/14/2022] Open
Abstract
Fluorescence-based DNA readouts are increasingly important in biological research, owing to enhanced analytical sensitivity and multiplexing capability. In this study, we characterize an in-gel polymerase elongation process to understand the reaction kinetics and transport limitations, and we evaluate DNA sequence design to develop signal amplification strategies. Using fluorescently labeled nucleotides, we scrutinize polymerase elongation on single-stranded overhangs of DNA immobilized in polyacrylamide hydrogels. When polymerase elongation reactions were carried out with reactants diffused into the gels, we observed reaction completion after 2 h, indicating that the process was efficient but much slower than that predicted by models. Confocal microscopy revealed a nonuniform post-reaction fluorescence profile of the elongated DNA throughout the depth of the gel and that the time for complete fluorescence penetration was proportional to the immobilized DNA concentration. These observations suggest retarded diffusion of the polymerase, attributable to interactions between diffusing polymerase and immobilized DNA. This study will ultimately inform assay design by providing insight into the reaction completion time to ensure spatial uniformity of the fluorescence signal. In agreement with our hypothesis that incorporation of multiple labeled nucleotides per DNA strand results in an increased signal, incorporation of four labeled nucleotides resulted in a 2.3-fold increase in fluorescence intensity over one labeled nucleotide. Our results further suggest that the fluorescence signal increases with spacing between labeled nucleotides, validating the number of and spacing between labeled nucleotides as tunable parameters for signal amplification. In-gel polymerase-based fluorescence readout is promising for signal amplification when considering both transport limitations and DNA sequence design.
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Affiliation(s)
| | - Amy E. Herr
- Author to whom correspondence should be addressed:
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Mourdoukoutas AP, Grist SM, Herr AE. Rapid electrotransfer probing for improved detection sensitivity in in-gel immunoassays. ANALYTICAL METHODS : ADVANCING METHODS AND APPLICATIONS 2020; 12:4638-4648. [PMID: 33030469 PMCID: PMC7552878 DOI: 10.1039/d0ay01203c] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Protein electrotransfer in conventional western blotting facilitates detection of size-separated proteins by diffusive immunoprobing, as analytes are transferred from a small-pore sizing gel to a blotting membrane for detection. This additional transfer step can, however, impair detection sensitivity through protein losses and confound protein localization. To overcome challenges associated with protein transfer, in-gel immunoassays immobilize target proteins to the hydrogel matrix for subsequent in-gel immunoprobing. Yet, detection sensitivity in diffusive immunoprobing of hydrogels is determined by the gel pore size relative to the probe size, and in-gel immunoprobing results in (i) reduced in-gel probe concentration compared to surrounding free-solution, and (ii) slow in-gel probe transfer compared to immunocomplex dissociation. Here, we demonstrate electrotransfer probing for effective and rapid immunoprobing of in-gel immunoassays. Critically, probe (rather than target protein) is electrotransferred from an inert, large-pore 'loading gel' to a small-pore protein sizing gel. Electric field is used as a tuneable parameter for electromigration velocity, providing electrotransfer probing with a fundamental advantage over diffusive probing. Using electrotransfer probing, we observe 6.5 ± 0.1× greater probe concentration loaded in-gel in ∼82× time reduction, and 2.7 ± 0.4× less probe concentration remaining in-gel after unloading in ∼180× time reduction (compared to diffusive probing). We then apply electrotransfer probing to detect OVA immobilized in-gel and achieve 4.1 ± 3.4× greater signal-to-noise ratio and 30× reduction in total immunoprobing duration compared to diffusive probing. We demonstrate electrotransfer probing as a substantially faster immunoprobing method for improved detection sensitivity of protein sizing in-gel immunoassays.
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Affiliation(s)
- Andoni P Mourdoukoutas
- The UC Berkeley/UCSF Graduate Program in Bioengineering, University of California, Berkeley, Berkeley, California 94720, USA.
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Geldert A, Huang H, Herr AE. Probe-target hybridization depends on spatial uniformity of initial concentration condition across large-format chips. Sci Rep 2020; 10:8768. [PMID: 32472029 PMCID: PMC7260366 DOI: 10.1038/s41598-020-65563-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Accepted: 04/23/2020] [Indexed: 12/30/2022] Open
Abstract
Diverse assays spanning from immunohistochemistry (IHC), to microarrays (protein, DNA), to high-throughput screens rely on probe-target hybridization to detect analytes. These large-format 'chips' array numerous hybridization sites across centimeter-scale areas. However, the reactions are prone to intra-assay spatial variation in hybridization efficiency. The mechanism of spatial bias in hybridization efficiency is poorly understood, particularly in IHC and in-gel immunoassays, where immobilized targets are heterogeneously distributed throughout a tissue or hydrogel network. In these systems, antibody probe hybridization to a target protein antigen depends on the interplay of dilution, thermodynamic partitioning, diffusion, and reaction. Here, we investigate parameters governing antibody probe transport and reaction (i.e., immunoprobing) in a large-format hydrogel immunoassay. Using transport and bimolecular binding theory, we identify a regime in which immunoprobing efficiency (η) is sensitive to the local concentration of applied antibody probe solution, despite the antibody probe being in excess compared to antigen. Sandwiching antibody probe solution against the hydrogel surface yields spatially nonuniform dilution. Using photopatterned fluorescent protein targets and a single-cell immunoassay, we identify regimes in which nonuniformly distributed antibody probe solution causes intra-assay variation in background and η. Understanding the physicochemical factors affecting probe-target hybridization reduces technical variation in large-format chips, improving measurement precision.
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Affiliation(s)
- Alisha Geldert
- UC Berkeley - UCSF Graduate Program in Bioengineering, Berkeley, United States
| | - Haiyan Huang
- Department of Statistics, University of California Berkeley, Berkeley, California, 94720, United States
- Center for Computational Biology, University of California Berkeley, Berkeley, California, 94720, United States
| | - Amy E Herr
- UC Berkeley - UCSF Graduate Program in Bioengineering, Berkeley, United States.
- Department of Bioengineering, University of California Berkeley, Berkeley, California, 94720, United States.
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Jeeawoody S, Yamauchi KA, Su A, Herr AE. Laterally Aggregated Polyacrylamide Gels for Immunoprobed Isoelectric Focusing. Anal Chem 2020; 92:3180-3188. [PMID: 31985208 PMCID: PMC7861876 DOI: 10.1021/acs.analchem.9b04913] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Immunoprobed isoelectric focusing (IEF) resolves proteins based on differences in isoelectric point (pI) and then identifies protein targets through immunoprobing of IEF-separated proteins that have been immobilized onto a gel scaffold. During the IEF stage, the gel functions as an anti-convective medium and not as a molecular sieving matrix. During the immunoprobing stage, the gel acts as an immobilization scaffold for IEF-focused proteins via photoactive moieties. Here, we characterized the effect of gel pore size on IEF separation and in-gel immunoassay performance. We modulated polyacrylamide (PA) gel pore size via lateral chain aggregation initiated by PEG monomers. During IEF, the 2% PEG highly porous PA gel formulation offered higher resolution (minimum pI difference ∼0.07 ± 0.02) than unmodified 6%T, 3.3%C (benchmark) and 6%T, 8%C (negative control) PA gels. The highly porous gels supported a pH gradient with slope and linearity comparable to benchmark gels. The partition coefficient for antibodies into the highly porous gels (K = 0.35 ± 0.02) was greater than the benchmark (3×) and negative control (1.75×) gels. The highly porous gels also had lower immunoassay background signal than the benchmark (2×) and negative control (3×) gels. Taken together, lateral aggregation creates PA gels that are suitable for both IEF and subsequent in-gel immunoprobing by mitigating immunoprobe exclusion from the gels while facilitating removal of unbound immunoprobe.
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Affiliation(s)
- Shaheen Jeeawoody
- Department of Bioengineering , University of California Berkeley , Berkeley , California 94720 , United States
- The UC Berkeley/UCSF Graduate Program in Bioengineering , University of California Berkeley , Berkeley , California 94720 , United States
| | - Kevin A Yamauchi
- Department of Bioengineering , University of California Berkeley , Berkeley , California 94720 , United States
- The UC Berkeley/UCSF Graduate Program in Bioengineering , University of California Berkeley , Berkeley , California 94720 , United States
| | - Alison Su
- Department of Bioengineering , University of California Berkeley , Berkeley , California 94720 , United States
- The UC Berkeley/UCSF Graduate Program in Bioengineering , University of California Berkeley , Berkeley , California 94720 , United States
| | - Amy E Herr
- Department of Bioengineering , University of California Berkeley , Berkeley , California 94720 , United States
- The UC Berkeley/UCSF Graduate Program in Bioengineering , University of California Berkeley , Berkeley , California 94720 , United States
- Chan Zuckerberg Biohub , 499 Illinois Street , San Francisco , California 94158 , United States
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