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Electrospray Ionization from an Adjustable Gap between two Silicon Chips
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.ORCID iD: 0000-0003-3548-217X
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2009 (English)In: Journal of Mass Spectrometry, ISSN 1076-5174, E-ISSN 1096-9888, Vol. 44, no 2, 171-181 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, a silicon chip - based electrospray emitter with a variable orifice size is presented. The device consists of two chips, with a thin beam elevating from the center of each of the chips. The chips are individually mounted to form an open gap of a narrow, uniform width between the top areas of the beams. The electrospray is generated at the endpoint of the gap, where the spray point is formed by the very sharp intersection between the crystal planes of the < 100 > silicon chips. Sample solution is applied to the rear end of the gap from a capillary via a liquid bridge, and capillary forces ensure a spontaneous imbibition of the gap. The sample solution is confined to the gap by means of a hydrophobic treatment of the surfaces surrounding the gap, as well as the geometrical boundaries formed by the edges of the gap walls. The gap width could be adjusted between 1 and 25 μm during electrospray experiments without suffering from any interruption of the electrospray process. Using a peptide sample solution, a shift toward higher charge states and increased signal-to-noise ratios was observed when the gap width was decreased. The limit of detection for the peptide insulin (chain B, oxidized) was approximately 4 nM. We also show a successful interfacing of the electrospray setup with capillary electrophoresis.

Place, publisher, year, edition, pages
2009. Vol. 44, no 2, 171-181 p.
Keyword [en]
Adjustable gap, Chip, Electrospray ionization, Emitter, Mass spectrometry, Nozzle
National Category
Analytical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-8438DOI: 10.1002/jms.1478ISI: 000264013300002PubMedID: 18946877Scopus ID: 2-s2.0-59949093565OAI: oai:DiVA.org:kth-8438DiVA: diva2:13757
Note
QC 20100913. Uppdaterad från Manuskript till Artikel (20100913)Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Mass Spectrometry with Electrospray Ionization from an Adjustable Gap
Open this publication in new window or tab >>Mass Spectrometry with Electrospray Ionization from an Adjustable Gap
2008 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

In this thesis the fabrication and analytical evaluation of two new electrospray emitters utilized for mass spectrometry analysis is presented. The emitters are based on a new concept, where the spray orifice can be varied in size. The thesis is based on two papers.

All present-day nanoelectrospray emitters have fixed dimensions. The range of the applicable flow rate for such an emitter is therefore rather limited and exchange of emitters may be necessary from one experiment to another. Optimization of the signal of the analyte ions is also limited to adjustments of the applied voltage or the distance between the emitter and the mass spectrometer inlet. Furthermore, clogging can occur in emitters with fixed dimensions of narrow orifice sizes. In this thesis, electrospray emitters with a variable size of the spray orifice are proposed. An open gap between two thin substrates is filled with sample solution via a liquid bridge from a capillary. Electrospray is generated at the end point of the gap, which can be varied in width.

In Paper I, electrospray emitters fabricated in polyethylene terephthalate have been evaluated. Triangular tips are manually cut from the polymer film. The tips are mounted to form a gap between the edges of the tips. The gap wall surfaces are subjected to a hydrophilic surface treatment to increase the wetting of the gap walls.

In Paper II, silicon electrospray chips with high precision are fabricated and evaluated. A thin beam, elevated from the bulk silicon chip is fabricated by means of deep reactive ion etching. The top surfaces of the beams of two chips act as a sample conduit when mounted in the electrospray setup. An anisotropic etching step with KOH of the intersecting <100> crystal planes results in a very sharp spray point. The emitters were given a hydrophobic surface treatment except for the hydrophilic gap walls.

For both emitter designs, the gap width has been adjusted during the experiments without any interruption of the electrospray. For a continuously applied peptide mixture, a shift towards higher charge states and increased signal to noise ratios could be observed when decreasing the gap width. The limit of detection has been investigated and the silicon chips have been interfaced with capillary electrophoresis.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. v, 36 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:24
Keyword
Electrospray ionization, mass spectrometry, nanoelectrospray, ESI, MS, chip, emitter, gap, liquid bridge, nozzle, peptides
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:kth:diva-4747 (URN)978-91-7178-926-6 (ISBN)
Presentation
2008-05-29, E2, KTH, Lindstedtsvägen 3, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101108Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2010-11-08Bibliographically approved
2. New methods for sensitive analysis with nanoelectrospray ionization mass spectrometry
Open this publication in new window or tab >>New methods for sensitive analysis with nanoelectrospray ionization mass spectrometry
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, new methods that address some current limitations in nanoelectrospray mass spectrometry (nESI-MS) analysis are presented. One of the major objectives is the potential gain in sensitivity that can be obtained when employing the proposed techniques.

In the first part of this thesis, a new emitter, based on the generation of electrospray from a spray orifice with variable size, is presented. Electrospray is generated from an open gap between the edges of two individually mounted, pointed tips. The fabrication and evaluation of two different types of such emitters is presented; an ESI emitter fabricated from polyethylene terephtalate (Paper I), and a high-precision silicon device (Paper II). Both emitters were surface-treated in a selective way for an improved wetting of the gap and to confine the sample solution into the gap.

In the second part of this thesis, different methods for improved sensitivity of nESI-MS analysis have been developed. In Paper III, a method for nESI-MS analysis from discrete sample volumes down to 1.5 nL is presented, using commercially available nESI needles. When analyzing attomole amounts of analyte in such a small volume of sample, an increased sensitivity was obtained, compared to when analyzing equal amounts in conventional nESI-MS analysis. To be able to analyze smaller sample volumes, needles with a narrower orifice and a higher flow resistance were needed. This triggered the development of a new method for fabrication of fused silica nESI needles (Paper IV). The fabrication is based on melting of a fused silica capillary by means of a rotating plasma, prior to pulling the capillary into a fine tip. Using the described technique, needles with sub-micrometer orifices could be fabricated. Such needles enabled the analysis of sample volumes down to 275 pL, and a further improvement of the sensitivity was obtained. In a final project (Paper V), nESI-MS was used to study the aggregation behavior of Aβ peptides, related to Alzheimer’s disease. An immunoprecipitation followed by nESI-MS was employed. This technique was also utilized to study the selectivity of the antibodies utilized.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. vii, 70 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2010:41
Keyword
mass spectrometry, electrospray ionization, nanoelectrospray ionization, adjustable gap, emitter, miniaturization, improved sensitivity, nanoliter/picoliter sample volumes, Alzheimer’s disease, amyloid-beta (Aβ)
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:kth:diva-25917 (URN)978-91-7415-751-2 (ISBN)
Public defence
2010-11-26, K1, Teknikringen 56, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20101112Available from: 2010-11-12 Created: 2010-11-04 Last updated: 2010-11-12Bibliographically approved

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