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Interfacing microfluidics with information-rich detection systems for cells, bioparticles, and molecules. Anal Bioanal Chem 2022; 414:4575-4589. [PMID: 35389095 PMCID: PMC8987515 DOI: 10.1007/s00216-022-04043-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Revised: 03/01/2022] [Accepted: 03/24/2022] [Indexed: 11/16/2022]
Abstract
The development of elegant and numerous microfluidic manipulations has enabled significant advances in the processing of small volume samples and the detection of minute amounts of biomaterials. Effective isolation of single cells in a defined volume as well as manipulations of complex bioparticle or biomolecule mixtures allows for the utilization of information-rich detection methods including mass spectrometry, electron microscopy imaging, and amplification/sequencing. The art and science of translating biosamples from microfluidic platforms to highly advanced, information-rich detection system is the focus of this review, where we term the translation between the microfluidics elements to the external world “off-chipping.” When presented with the challenge of presenting sub-nanoliter volumes of manipulated sample to a detection scheme, several delivery techniques have been developed for effective analysis. These techniques include spraying (electrospray, nano-electrospray, pneumatic), meniscus-defined volumes (droplets, plugs), constrained volumes (narrow channels, containers), and phase changes (deposition, freezing). Each technique has been proven effective in delivering highly defined samples from microfluidic systems to the detection elements. This review organizes and presents selective publications that illustrate the advancements of these delivery techniques with respect to the type of sample analyzed, while introducing each strategy and providing historical perspective. The publications highlighted in this review were chosen due to their significance and relevance in the development of their respective off-chip technique.
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Feng X, Liu BF, Li J, Liu X. Advances in coupling microfluidic chips to mass spectrometry. MASS SPECTROMETRY REVIEWS 2015; 34:535-57. [PMID: 24399782 DOI: 10.1002/mas.21417] [Citation(s) in RCA: 87] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2013] [Revised: 11/07/2013] [Accepted: 11/07/2013] [Indexed: 05/26/2023]
Abstract
Microfluidic technology has shown advantages of low sample consumption, reduced analysis time, high throughput, and potential for integration and automation. Coupling microfluidic chips to mass spectrometry (Chip-MS) can greatly improve the overall analytical performance of MS-based approaches and expand their potential applications. In this article, we review the advances of Chip-MS in the past decade, covering innovations in microchip fabrication, microchips coupled to electrospray ionization (ESI)-MS and matrix-assisted laser desorption/ionization (MALDI)-MS. Development of integrated microfluidic systems for automated MS analysis will be further documented, as well as recent applications of Chip-MS in proteomics, metabolomics, cell analysis, and clinical diagnosis.
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MESH Headings
- Animals
- Chromatography, Liquid/instrumentation
- Chromatography, Liquid/methods
- Electrophoresis, Microchip/instrumentation
- Electrophoresis, Microchip/methods
- Equipment Design
- Humans
- Lab-On-A-Chip Devices
- Lipids/analysis
- Metabolomics/instrumentation
- Metabolomics/methods
- Polysaccharides/analysis
- Proteins/analysis
- Proteomics/instrumentation
- Proteomics/methods
- Spectrometry, Mass, Electrospray Ionization/instrumentation
- Spectrometry, Mass, Electrospray Ionization/methods
- Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization/instrumentation
- Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization/methods
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Affiliation(s)
- Xiaojun Feng
- Britton Chance Center for Biomedical Photonics at Wuhan National Laboratory for Optoelectronics-Hubei Bioinformatics and Molecular Imaging Key Laboratory, Systems Biology Theme, Department of Biomedical Engineering, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, China
| | - Bi-Feng Liu
- Britton Chance Center for Biomedical Photonics at Wuhan National Laboratory for Optoelectronics-Hubei Bioinformatics and Molecular Imaging Key Laboratory, Systems Biology Theme, Department of Biomedical Engineering, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, China
| | - Jianjun Li
- Human Health Therapeutics, National Research Council Canada, Ottawa, Ontario, Canada K1A 0R6
| | - Xin Liu
- Britton Chance Center for Biomedical Photonics at Wuhan National Laboratory for Optoelectronics-Hubei Bioinformatics and Molecular Imaging Key Laboratory, Systems Biology Theme, Department of Biomedical Engineering, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, China
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Hommerson P, Khan AM, de Jong GJ, Somsen GW. Ionization techniques in capillary electrophoresis-mass spectrometry: principles, design, and application. MASS SPECTROMETRY REVIEWS 2011; 30:1096-1120. [PMID: 21462232 DOI: 10.1002/mas.20313] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2009] [Accepted: 06/03/2010] [Indexed: 05/30/2023]
Abstract
A major step forward in the development and application of capillary electrophoresis (CE) was its coupling to ESI-MS, first reported in 1987. More than two decades later, ESI has remained the principal ionization technique in CE-MS, but a number of other ionization techniques have also been implemented. In this review the state-of-the-art in the employment of soft ionization techniques for CE-MS is presented. First the fundamentals and general challenges of hyphenating conventional CE and microchip electrophoresis with MS are outlined. After elaborating on the characteristics and role of ESI, emphasis is put on alternative ionization techniques including sonic spray ionization (SSI), thermospray ionization (TSI), atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), matrix-assisted laser desorption ionization (MALDI) and continuous-flow fast atom bombardment (CF-FAB). The principle of each ionization technique is outlined and the experimental set-ups of the CE-MS couplings are described. The strengths and limitations of each ionization technique with respect to CE-MS are discussed and the applicability of the various systems is illustrated by a number of typical examples.
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MESH Headings
- Electrophoresis, Capillary/instrumentation
- Electrophoresis, Capillary/methods
- Equipment Design/instrumentation
- Equipment Design/methods
- Pharmaceutical Preparations/analysis
- Pharmaceutical Preparations/chemistry
- Proteins/analysis
- Proteins/chemistry
- Spectrometry, Mass, Electrospray Ionization/instrumentation
- Spectrometry, Mass, Electrospray Ionization/methods
- Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization/instrumentation
- Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization/methods
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Affiliation(s)
- Paul Hommerson
- Department of Biomedical Analysis, Utrecht University, PO Box 80082, 3508 TB Utrecht, The Netherlands.
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Sikanen T, Franssila S, Kauppila TJ, Kostiainen R, Kotiaho T, Ketola RA. Microchip technology in mass spectrometry. MASS SPECTROMETRY REVIEWS 2010; 29:351-391. [PMID: 19514079 DOI: 10.1002/mas.20238] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Microfabrication of analytical devices is currently of growing interest and many microfabricated instruments have also entered the field of mass spectrometry (MS). Various (atmospheric pressure) ion sources as well as mass analyzers have been developed exploiting microfabrication techniques. The most common approach thus far has been the miniaturization of the electrospray ion source and its integration with various separation and sampling units. Other ionization techniques, mainly atmospheric pressure chemical ionization and photoionization, have also been subject to miniaturization, though they have not attracted as much attention. Likewise, all common types of mass analyzers have been realized by microfabrication and, in most cases, successfully applied to MS analysis in conjunction with on-chip ionization. This review summarizes the latest achievements in the field of microfabricated ion sources and mass analyzers. Representative applications are reviewed focusing on the development of fully microfabricated systems where ion sources or analyzers are integrated with microfluidic separation devices or microfabricated pums and detectors, respectively. Also the main microfabrication methods, with their possibilities and constraints, are briefly discussed together with the most commonly used materials.
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Affiliation(s)
- Tiina Sikanen
- Faculty of Pharmacy, Division of Pharmaceutical Chemistry, University of Helsinki, Helsinki, Finland.
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Zhou J, Ellis AV, Voelcker NH. Recent developments in PDMS surface modification for microfluidic devices. Electrophoresis 2010; 31:2-16. [DOI: 10.1002/elps.200900475] [Citation(s) in RCA: 599] [Impact Index Per Article: 42.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Zhang Z, Feng X, Luo Q, Liu BF. Environmentally friendly surface modification of PDMS using PEG polymer brush. Electrophoresis 2009; 30:3174-80. [PMID: 19722209 DOI: 10.1002/elps.200900132] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
A PEG-NH2-based environmentally friendly surface modification strategy was developed for PDMS microchips to prevent protein adsorption and to enhance separation performance. PEG-NH2 was synthesized using a modified synthesis procedure. A two-step grafting method was used for PDMS modification. FTIR absorption by attenuated total reflection and contact angle measurements verified the successful grafting of PEG-NH2 onto the PDMS surface. Subsequent EOF Measurements and protein adsorption studies of PEG-modified PDMS microchips revealed noticeable EOF suppression and resistance to nonspecific protein adsorption for more than 30 days. Separation of four FITC-labeled amino acids was further demonstrated with high repeatability and reproducibility. Comparison of electrophoresis of 3-(2-furoyl)quinoline-2-carboxaldehyde-labeled BSA using PDMS microchips before and after surface modification resulted in significantly improved electrophoretic performance of the PEG-modified PDMS microchips, suggesting that our PEG grafting method successfully modified PDMS surface property and prevented adsorption of proteins. We expect that this environmentally friendly surface modification method will be useful for future protein separations with long-term surface stability.
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Affiliation(s)
- Zhaowei Zhang
- The Key Laboratory of Biomedical Photonics of MOE-Hubei Bioinformatics and Molecular Imaging Key Laboratory-Division of Biomedical Photonics at Wuhan National Laboratory for Optoelectronics, Department of Systems Biology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, P. R. China
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Li FA, Huang JL, Her GR. Chip-CE/MS using a flat low-sheath-flow interface. Electrophoresis 2008; 29:4938-43. [DOI: 10.1002/elps.200800271] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Kelly RT, Tang K, Irimia D, Toner M, Smith RD. Elastomeric microchip electrospray emitter for stable cone-jet mode operation in the nanoflow regime. Anal Chem 2008; 80:3824-31. [PMID: 18419138 PMCID: PMC2692495 DOI: 10.1021/ac8000786] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Despite widespread interest in combining laboratory-on-a-chip technologies with mass spectrometry (MS)-based analyses, the coupling of microfluidics to electrospray ionization (ESI)-MS remains challenging. We report a robust, integrated poly(dimethylsiloxane) microchip interface for ESI-MS using simple and widely accessible microfabrication procedures. The interface uses an auxiliary channel to provide electrical contact for the stable cone-jet electrospray without sample loss or dilution. The electric field at the channel terminus is enhanced by two vertical cuts that cause the interface to taper to a line rather than to a point, and the formation of a small Taylor cone at the channel exit ensures subnanoliter postcolumn dead volumes. Cone-jet mode electrospray was demonstrated for up to 90% aqueous solutions and for extended durations. Comparable ESI-MS sensitivities were achieved using both microchip and conventional fused silica capillary emitters, but stable cone-jet mode electrosprays could be established over a far broader range of flow rates (from 50-1000 nL/min) and applied potentials using the microchip emitters. This attribute of the microchip emitter should simplify electrospray optimization and make the stable electrospray more resistant to external perturbations.
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Affiliation(s)
- Ryan T Kelly
- Biological Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
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Li HF, Liu J, Cai Z, Lin JM. Coupling a microchip with electrospray ionization quadrupole time-of-flight mass spectrometer for peptide separation and identification. Electrophoresis 2008; 29:1889-94. [DOI: 10.1002/elps.200700477] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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10
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Peng Y, Pallandre A, Tran NT, Taverna M. Recent innovations in protein separation on microchips by electrophoretic methods. Electrophoresis 2008; 29:157-78. [DOI: 10.1002/elps.200700347] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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11
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Koster S, Verpoorte E. A decade of microfluidic analysis coupled with electrospray mass spectrometry: an overview. LAB ON A CHIP 2007; 7:1394-1412. [PMID: 17960264 DOI: 10.1039/b709706a] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
This review presents a thorough overview covering the period 1997-2006 of microfluidic chips coupled to mass spectrometry through an electrospray interface. The different types of fabrication processes and materials used to fabricate these chips throughout this period are discussed. Three 'eras' of interfaces are clearly distinguished. The earliest approach involves spraying from the edge of a chip, while later devices either incorporate a standard fused-silica emitter inserted into the device or fully integrated emitters formed during chip fabrication. A summary of microfluidic-electrospray devices for performing separations and sample pretreatment steps before sample introduction into the mass spectrometer is also presented.
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Affiliation(s)
- Sander Koster
- Groningen Research Institute of Pharmacy, University of Groningen, Antonius Deusinglaan 1, 9713AV Groningen, The Netherlands.
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Hoffmann P, Häusig U, Schulze P, Belder D. Microfluidic glass chips with an integrated nanospray emitter for coupling to a mass spectrometer. Angew Chem Int Ed Engl 2007; 46:4913-6. [PMID: 17516595 DOI: 10.1002/anie.200605152] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Peter Hoffmann
- Institut für Analytische Chemie, Chemo- und Biosensorik, Universität Regensburg, 93040 Regensburg, Germany
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13
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Hoffmann P, Häusig U, Schulze P, Belder D. Mikrofluidische Glas-Chips mit integriertem Nanospray-Emitter zur Kopplung mit der Massenspektrometrie. Angew Chem Int Ed Engl 2007. [DOI: 10.1002/ange.200605152] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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14
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Zamfir AD. Recent advances in sheathless interfacing of capillary electrophoresis and electrospray ionization mass spectrometry. J Chromatogr A 2007; 1159:2-13. [PMID: 17428492 DOI: 10.1016/j.chroma.2007.03.115] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2006] [Revised: 03/20/2007] [Accepted: 03/29/2007] [Indexed: 01/13/2023]
Abstract
On line sheathless capillary electrophoresis (CE)-electrospray ionization (ESI) mass spectrometry is developing as a powerful method in bioanalytics as it provides high resolution, sensitivity, relatively short analysis times, and amenability to a wide class of compounds. However, unlike the popular nano liquid chromatography (nano LC) or sheath-flow CE/ESI-MS, the sheathless coupling lacks standardized designs and protocols. For this reason, sheathless CE/ESI is a subject of conceptual and technical upgrading more than any other liquid-based separation method hyphenated to MS. Here, recent innovations in sheathless CE/ESI-MS interfacing are gathered in a survey covering the 2005/2006 period. In the first part of the review, the current concepts and methods for in-laboratory production of sturdy designs based on either conductive emitters or electrodeless interfaces are described. The second part is dedicated to microchip CE platforms with externally connected emitters for sheathless coupling to ESI-MS and advanced microfluidic devices integrating CE and sheathless electrospray in a single chip substrate. The advantages, limitations and feasibility for certain applications of all these systems as well as the perspectives for their performance improvement are concurrently assessed.
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Affiliation(s)
- Alina D Zamfir
- Department of Chemistry and Biology, University of Arad, Revolutiei Blvd. 1, RO-310139 Arad, Romania.
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Li FA, Wang CH, Her GR. A sheathless poly(methyl methacrylate) chip-CE/MS interface fabricated using a wire-assisted epoxy-fixing method. Electrophoresis 2007; 28:1265-73. [PMID: 17366484 DOI: 10.1002/elps.200600552] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Using a wire-assisted epoxy-fixing method, a sheathless CE/MS interface on a poly-(methyl methacrylate) (PMMA) CE chip has been developed. The sheathless chip-CE/MS interface utilized a tapered fused-silica tip and the electrical connection was achieved through a layered coating of conductive rubber. The wire-assisted method provided facile alignment of channels between the PMMA CE chip and an external capillary sprayer without the need for micromachining. Because the wire was in the channel during fixing, the risk of channel blockage by the epoxy was avoided. This chip CE device has minimal dead volume because the interstitial spaces were filled by a fast-fixing epoxy resin. The performance of the chip-CE-ESI-MS device was demonstrated with the analysis of peptide mixtures.
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Affiliation(s)
- Fu-An Li
- Department of Chemistry, National Taiwan University, Taipei, Taiwan
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Mao X, Chu IK, Lin B. A sheath-flow nanoelectrospray interface of microchip electrophoresis MS for glycoprotein and glycopeptide analysis. Electrophoresis 2006; 27:5059-67. [PMID: 17117389 DOI: 10.1002/elps.200600349] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Microchip was coupled with MS through a stable, sensitive, and controllable sheath-flow nanoelectrospray (nES) interface for glycoprotein and glycopeptide analysis. The nano-ESI (nESI) was made with a delivery capillary, a commercial nES capillary, and a stainless steel (SS) tube which were connected together through a tee unit. High voltage for nES was applied on the SS tube and the commercial nES capillary was used as nES emitter. The delivery capillary was attached to the microchannel for delivering liquid from microchip to the nESI source. The flow rate of sheath liquid was optimized to be 100-200 nL/min which largely reduced the sample dilution. The detection limit of peptides on this microchip/MS platform was at femtomole level. Glycoprotein and glycopeptides were also successfully analyzed on the platform. All the glycoforms and glycopeptides of ribonuclease B (RNase B) were identified with this method. Some structures of the glycopeptides from RNase B were further characterized with MS/MS on the microchip, coupled with a quadrupole IT-MS.
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Affiliation(s)
- Xiuli Mao
- Dalian Institute of Chemical Physics, Chinese Academy of Scienes, Dalian, PR China
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Zhuang G, Jin Q, Liu J, Cong H, Liu K, Zhao J, Yang M, Wang H. A low temperature bonding of quartz microfluidic chip for serum lipoproteins analysis. Biomed Microdevices 2006; 8:255-61. [PMID: 16799750 DOI: 10.1007/s10544-006-9142-z] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
A low-temperature bonding method for microfabrication of quartz microfluidic chips has been developed. The bonding process involved two steps: pre-bonding and post-annealing at low temperature. The bonding quality was evaluated by measuring the shear force at bonding interface and the electrical properties of the chips. Shear force of 5.66 MPa (566 N/cm(2)) was obtained in a bonded chip after a post-annealing at 200 degrees C for 6 h. We owe the strong bonding strength to the formation of Si-O-Si bonds at the bonding interface during the post-annealing stage. The bonding procedures were not sensitive to surrounding and could be performed in a routine laboratory without clean room conditions. The performance of the fabricated microfluidic chips was tested by capillary zone electrophoresis (CZE) of serum lipoproteins with laser-induced fluorescence (LIF). The low-density (LDL) and high-density (HDL) lipoproteins in the serum was separated completely by using tricine buffer with methylglucamine.
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Affiliation(s)
- Guisheng Zhuang
- Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Science, 865 Chang Ning Road, 200050 Shanghai, China.
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Roman GT, Culbertson CT. Surface engineering of poly(dimethylsiloxane) microfluidic devices using transition metal sol-gel chemistry. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2006; 22:4445-51. [PMID: 16618201 DOI: 10.1021/la053085w] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
We report the coating of poly(dimethylsiloxane) (PDMS) microchannels using transition metal sol-gel chemistry and the subsequent characterization of the coatings. The channels were created using soft polymer lithography, and three metal alkoxide sol-gel precursors were investigated, titanium isopropoxide, zirconium isopropoxide, and vanadium triisobutoxide oxide. The metal alkoxides were diffused into the sidewalls of a PDMS channel and subsequently hydrolyzed using water vapor. This procedure resulted in the formation of durable metal oxide surfaces of titania, zirconia, or vanadia. The resulting surfaces were characterized using contact angle, X-ray photoelectron spectroscopy (XPS), Raman, transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and electroosmotic mobility (EOM) measurements. All of the metal oxide-modified PDMS surfaces were significantly more hydrophilic than native PDMS. Contact angles for the coatings were 90 degrees for PDMS-ZrO2, 61 degrees for PDMS-TiO2, and 19 degrees for PDMS-vanadia. XPS showed the presence of titania, zirconia, and vanadia on the PDMS surface. XPS spectra also showed no chemical modification of the PDMS after the in situ deposition of the particles either in the Si-O, Si-C, or C-H bonds of the PDMS. The particles deposited in situ were imaged with TEM and were found to be homogeneously distributed throughout the bulk of the PDMS. EOM measurements of the inorganic coatings were stable over a period of at least 95 days. Both cathodic and anodic EOMs could be generated depending upon buffer pH used. The points of net zero charge for PDMS-TiO2, PDMS-ZrO2, and PDMS-vanadia channels were calculated using EOM versus pH measurements and were found to be 4.1 +/- 0.25, 6.1 +/- 0.2, and 7.0 +/- 0.43, respectively. In addition to modifying PDMS channels with inorganic coatings, these inorganic coatings were derivatized with various organic functionalities including oligoethylene oxide (OEO), amino, perfluoro, or mercapto groups using silane chemistry. Contact angle measurements for perfluoro, mercapto, amino, and OEO-coated surfaces yielded contact angles of 120 degrees , 76 degrees , 45 degrees , and 23 degrees , respectively. These contact angles did not change over the period of 95 days. OEO-coated channels reduced the EOM by 50% from native PDMS-TiO2 to 0.9 +/- 0.05 x 10(-4) cm2/V.s (n = 5, 5.5% RSD).
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Affiliation(s)
- Gregory T Roman
- Department of Chemistry, Kansas State University, 111 Willard Hall, Manhattan, Kansas 66506, USA
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Iannacone JM, Jakubowski JA, Bohn PW, Sweedler JV. A multilayer poly(dimethylsiloxane) electrospray ionization emitter for sample injection and online mass spectrometric detection. Electrophoresis 2005; 26:4684-90. [PMID: 16278909 DOI: 10.1002/elps.200500498] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
An ESI emitter made of poly(dimethylsiloxane) interfaces on-chip sample preparation with MS detection. The unique multilayer design allows both the analyte and the spray solutions to reside on the device simultaneously in discrete microfluidic environments that are spatially separated by a polycarbonate track-etched, nanocapillary array membrane (NCAM). In direct spray mode, voltage is applied to the microchannel containing a spray solution delivered via a syringe pump. For injection, the spray potential is lowered and a voltage is applied that forward biases the membrane and permits the analyte to enter the spray channel. Once the injection is complete, the bias potential is switched off, and the spray voltage is increased to generate the ESI of the injected analyte plug. Consecutive injections of a 10 microM bovine insulin solution are reproducible and produce sample plugs with limited band broadening and high quality mass spectra. Peptide signals are observed following transport through the NCAM, even when the peptide is dissolved in solutions containing up to 20% seawater. The multilayer emitter shows great potential for performing multidimensional chemical manipulations on-chip, followed by direct ESI with negligible dead volume for online MS analysis.
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Affiliation(s)
- Jamie M Iannacone
- Department of Chemistry and the Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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Tuomikoski S, Sikanen T, Ketola RA, Kostiainen R, Kotiaho T, Franssila S. Fabrication of enclosed SU-8 tips for electrospray ionization-mass spectrometry. Electrophoresis 2005; 26:4691-702. [PMID: 16283694 DOI: 10.1002/elps.200500475] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
We describe a novel electrospray tip design for MS which is fabricated completely out of SU-8 photoepoxy. A three-layer SU-8 fabrication process provides fully enclosed channels and tips. The tip shape and alignment of all SU-8 layers is done lithographically and is therefore very accurate. Fabrication process enables easy integration of additional fluidic functions on the same chip. Separation channels can be made with exactly the same process. Fluidic inlets are made in SU-8 during the fabrication process and no drilling or other postprocessing is needed. Channels have been fabricated and tested in the size range of 10 microm x 10 microm-50 microm x 200 microm. Mass spectrometric performance of the tips has been demonstrated with both pressure-driven flow and EOF. SU-8 microtips have been shown to produce stable electrospray with EOF in a timescale of tens of minutes. With pressure driven flow stable spray is maintained for hours. Taylor cone was shown to be small in volume and well defined even with the largest channel cross section. The spray was also shown to be well directed with our tip design.
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Affiliation(s)
- Santeri Tuomikoski
- Microelectronics Centre, Helsinki University of Technology, Helsinki, Finland
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Thorslund S, Lindberg P, Andrén PE, Nikolajeff F, Bergquist J. Electrokinetic-driven microfluidic system in poly(dimethylsiloxane) for mass spectrometry detection integrating sample injection, capillary electrophoresis, and electrospray emitter on-chip. Electrophoresis 2005; 26:4674-83. [PMID: 16273585 DOI: 10.1002/elps.200500338] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
A novel microsystem device in poly(dimethylsiloxane) (PDMS) for MS detection is presented. The microchip integrates sample injection, capillary electrophoretic separation, and electrospray emitter in a single substrate, and all modules are fabricated in the PDMS bulk material. The injection and separation flow is driven electrokinetically and the total amount of external equipment needed consists of a three-channel high-voltage power supply. The instant switching between sample injection and separation is performed through a series of low-cost relays, limiting the separation field strength to a maximum of 270 V/cm. We show that this set-up is sufficient to accomplish electrospray MS analysis and, to a moderate extent, microchip separation of standard peptides. A new method of instant in-channel oxidation makes it possible to overcome the problem of irreversibly bonded PDMS channels that have recovered their hydrophobic properties over time. The fast method turns the channel surfaces hydrophilic and less prone to nonspecific analyte adsorption, yielding better separation efficiencies and higher apparent peptide mobilities.
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Affiliation(s)
- Sara Thorslund
- Department of Engineering Sciences, Angström Laboratory, Uppsala University, Uppsala, Sweden
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Sung WC, Makamba H, Chen SH. Chip-based microfluidic devices coupled with electrospray ionization-mass spectrometry. Electrophoresis 2005; 26:1783-91. [PMID: 15800960 DOI: 10.1002/elps.200410346] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
We present the current status of the development of microfluidic devices fabricated on different substrates for coupling with electrospray ionization-mass spectrometry (ESI-MS). Until now, much success has been gained in fabricating the ESI chips, which show better performances due to miniaturization when compared with traditional methods. Integration of multiple steps for sample preparation and ESI sample introduction, however, remains a great challenge. This review covers the main technical development of electrospray device that were published from 1997 to 2004. This article does not attempt to be exclusive. Instead, it focuses on the publications that illustrated the breath of the development and applications of microchip devices for MS-based analysis.
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Affiliation(s)
- Wang-Chou Sung
- Department of Chemistry, National Cheng Kung University, No. 1 Ta-Hsueh Road, Tainan 701, Taiwan
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Abstract
Microfluidic systems show considerable potential for use in the continuous reaction and analysis of biosamples for various applications, such as drug screening and chemical synthesis. Typically, microfluidic chips are externally connected with large-scale autosamplers to inject specific volumes of discrete samples in the continuous monitoring and analysis of multiple samples. This paper presents a novel microelectromechanical system (MEMS)-based autosampler capable of performing the discrete injection and dispensation of variable-volume samples. This microdevice can be integrated with other microfluidic devices to facilitate the continuous monitoring and analysis of multiple biosamples. By means of electroosmotic focusing and switching controlled by the direct application of electric sources on specific fluid reservoirs, a precise sample volume can be injected into the specified outlet port. Fluorescence dye images verify the performance of the developed device. An injection-and-washing scheme is developed to prevent cross-contamination during the continuous injection of different samples. This approach renders feasible the injection of several discrete samples using a single microchip. Compared to its large-scale counterparts, the developed microautosampler is compact in size, has low fabrication costs, is straightforward to control, and most importantly, is readily integrated with other microfluidic devices (e.g., microcapillary electrophoresis chips) to form a microfluidic system capable of the continuous monitoring and analysis of bioreactions. The proposed microautosampler could be promising towards realizing the micrototal analysis system (mu-TAS) concept.
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Affiliation(s)
- Chun-Wei Huang
- Department of Engineering Science, National Cheng Kung University, Tainan, Taiwan 701
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Roman GT, Hlaus T, Bass KJ, Seelhammer TG, Culbertson CT. Sol−Gel Modified Poly(dimethylsiloxane) Microfluidic Devices with High Electroosmotic Mobilities and Hydrophilic Channel Wall Characteristics. Anal Chem 2005; 77:1414-22. [PMID: 15732926 DOI: 10.1021/ac048811z] [Citation(s) in RCA: 176] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Using a sol-gel method, we have fabricated poly(dimethylsiloxane) (PDMS) microchips with SiO2 particles homogeneously distributed within the PDMS polymer matrix. These particles are approximately 10 nm in diameter. To fabricate such devices, PDMS (Sylgard 184) was cast against SU-8 molds. After curing, the chips were carefully removed from the mold and sealed against flat, cured pieces of PDMS to form enclosed channel manifolds. These chips were then solvated in tetraethyl orthosilicate (TEOS), causing them to expand. Subsequently, the chips were placed in an aqueous solution containing 2.8% ethylamine and heated to form nanometer-sized SiO2 particles within the cross-linked PDMS polymer. The water contact angle for the PDMS-SiO2 chips was approximately 90.2 degrees compared to a water contact angle for Sylgard 184 of approximately 108.5 degrees . More importantly, the SiO2 modified PDMS chips showed no rhodamine B absorption after 4 h, indicating a substantially more hydrophilic and nonabsorptive surface than native PDMS. Initial electroosmotic mobilities (EOM) of (8.3+/-0.2)x10(-4) cm2/(V.s) (RSD=2.6% (RSD is relative standard deviation); n=10) were measured. This value was approximately twice that of native Sylgard 184 PDMS chips (4.21+/-0.09)x10(-4) cm2/(V.s) (RSD=2.2%; n=10) and 55% greater than glass chips (5.3+/-0.4)x10(-4) cm2/(V.s) (RSD=7.7%; n=5). After 60 days of dry storage, the EOM was (7.6+/-0.3)x10(-4) cm2/(V.s) (RSD=3.9%; n=3), a decrease of only 8% below that of the initially measured value. Separations performed on these devices generated 80,000-100,000 theoretical plates in 6-14 s for both tetramethylrhodamine succidimidyl ester and fluorescein-5-isothiocyanate derivatized amino acids. The separation distance was 3.5 cm. Plots of peak variance vs analyte migration times gave diffusion coefficients which indicate that the separation efficiencies are within 15% of the diffusion limit.
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Affiliation(s)
- Gregory T Roman
- Kansas State University, 111 Willard Hall, Manhattan, Kansas 66506, USA
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Monton MRN, Terabe S. Recent Developments in Capillary Electrophoresis-Mass Spectrometry of Proteins and Peptides. ANAL SCI 2005; 21:5-13. [PMID: 15675508 DOI: 10.2116/analsci.21.5] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Many researchers have invested considerable efforts toward improving capillary electrophoresis (CE)-mass spectrometry (MS) systems so they can be applied better to standard analyses. This review highlights the developments in CE-MS of proteins and peptides over the last five years. It includes the developments in interfaces, sample-enrichment techniques, microfabricated devices, and some applications, largely in capillary zone electrophoresis (CZE), capillary isoelectric focusing (CIEF) and capillary isotachophoresis formats.
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Affiliation(s)
- Maria Rowena N Monton
- Graduate School of Material Science, University of Hyogo, Kamigori, Hyogo 678-1297, Japan.
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Dahlin AP, Wetterhall M, Liljegren G, Bergström SK, Andrén P, Nyholm L, Markides KE, Bergquist J. Capillary electrophoresis coupled to mass spectrometry from a polymer modified poly(dimethylsiloxane) microchip with an integrated graphite electrospray tip. Analyst 2005; 130:193-9. [PMID: 15665973 DOI: 10.1039/b414592e] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Hybrid capillary-poly(dimethysiloxane)(PDMS) microchips with integrated electrospray ionization (ESI) tips were directly fabricated by casting PDMS in a mould. The shapes of the emitter tips were drilled into the mould, which produced highly reproducible three-dimensional tips. Due to the fabrication method of the microfluidic devices, no sealing was necessary and it was possible to produce a perfect channel modified by PolyE-323, an aliphatic polyamine coating agent. A variety of different coating procedures were also evaluated for the outside of the emitter tip. Dusting graphite on a thin unpolymerised PDMS layer followed by polymerisation was proven to be the most suitable procedure. The emitter tips showed excellent electrochemical properties and durabilities. The coating of the emitter was eventually passivated, but not lost, and could be regenerated by electrochemical means. The excellent electrochemical stability was further confirmed in long term electrospray experiments, in which the emitter sprayed continuously for more than 180 h. The PolyE-323 was found suitable for systems that integrate rigid fused silica and soft PDMS technology, since it simply could be applied successfully to both materials. The spray stability was confirmed from the recording of a total ion chromatogram in which the electrospray current exhibited a relative standard deviation of 3.9% for a 30 min run. CE-ESI-MS separations of peptides were carried out within 2 min using the hybrid PDMS chip resulting in similar efficiencies as for fused silica capillaries of the same length and thus with no measurable band broadening effects, originating from the PDMS emitter.
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