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- Ek, Patrik, 1980-
(author)
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New methods for sensitive analysis with nanoelectrospray ionization mass spectrometry
- 2010
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Doctoral thesis (other academic/artistic)abstract
- 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.
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| 2. |
- Benkestock, Kurt, 1961-
(author)
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Electrospray Ionization Mass Spectrometry for Determination of Noncovalent Interactions in Drug Discovery
- 2008
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Doctoral thesis (other academic/artistic)abstract
- Noncovalent interactions are involved in many biological processes in which biomolecules bind specifically and reversibly to a partner. Often, proteins do not have a biological activity without the presence of a partner, a ligand. Biological signals are produced when proteins interact with other proteins, peptides, oligonucleotides, nucleic acids, lipids, metal ions, polysaccharides or small organic molecules. Some key steps in the drug discovery process are based on noncovalent interactions. We have focused our research on the steps involving ligand screening, competitive binding and ‘off-target’ binding. The first paper in this thesis investigated the complicated electrospray ionization process with regards to noncovalent complexes. We have proposed a model that may explain how the equilibrium between a protein and ligand changes during the droplet evaporation/ionization process. The second paper describes an evaluation of an automated chip-based nano-ESI platform for ligand screening. The technique was compared with a previously reported method based on nuclear magnetic resonance (NMR), and excellent correlation was obtained between the results obtained with the two methods. As a general conclusion we believe that the automated nano-ESI/MS should have a great potential to serve as a complementary screening method to conventional HTS. Alternatively, it could be used as a first screening method in an early phase of drug development programs when only small amounts of purified targets are available. In the third article, the advantage of using on-line microdialysis as a tool for enhanced resolution and sensitivity during detection of noncovalent interactions and competitive binding studies by ESI-MS was demonstrated. The microdialysis device was improved and a new approach for competitive binding studies was developed. The last article in the thesis reports studies of noncovalent interactions by means of nanoelectrospray ionization mass spectrometry (nanoESI-MS) for determination of the specific binding of selected drug candidates to HSA. Two drug candidates and two known binders to HSA were analyzed using a competitive approach. The drugs were incubated with the target protein followed by addition of site-specific probes, one at a time. The drug candidates showed predominant affinity to site I (warfarin site). Naproxen and glyburide showed affinity to both sites I and II.
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| 3. |
- Bonn, Jonas, 1978-
(author)
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Improved Techniques for Sampling and Sample Introduction in Gas Chromatography
- 2008
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Licentiate thesis (other academic/artistic)abstract
- Sampling and sample introduction are two key steps in quantitative gas chromatography. In this thesis, a development of a previously described sampling technique as well as a novel concept for sample introduction in gas chromatography are presented. The thesis is based on two papers. Paper I describes a method for preparing physically mixed polymers for use as sorbent phases in open tubular trapping of gaseous analytes. The concept is based on mechanical disintegration and mixing of solid or liquid poly(ethylene glycol), PEG, into poly(dimethylsiloxane), PDMS, in a straightforward manner. The resulting mixture exhibits a higher affinity towards polar analytes, as compared to pure PDMS. Paper II describes a novel approach to liquid sample introduction with the split/splitless inlet, used in gas chromatography. Classical injection techniques struggle with discrimination of high boiling analytes and poor repeatability of the injected amount of analytes. The presented injection technique utilizes high voltage to obtain a spraying effect of the injected liquid. The spraying effect can be achieved with a cold needle, which is unprecedented for gas chromatographic injections. The cold needle spraying results in highly repeatable injections, free from discrimination of high boiling analytes.
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| 4. |
- Hartmann, Michael
(author)
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Microfluidic Methods for Protein Microarrays
- 2010
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Doctoral thesis (other academic/artistic)abstract
- Protein microarray technology has an enormous potential for in vitro diagnostics (IVD)1. Miniaturized and parallelized immunoassays are powerful tools to measure dozens of parameters from minute amounts of sample, whilst only requiring small amounts of reagent. Protein microarrays have become well-established research tools in basic and applied research and the first diagnostic products are already released on the market. However, in order for protein microarrays to become broadly accepted tools in IVD, a number of criteria have to be fulfilled concerning robustness and automation. Robustness and automation are key demands to improve assay performance and reliability of multiplexed assays, and to minimize the time of analysis. These key demands are addressed in this thesis and novel methods and techniques concerning assay automation, array fabrication as well as performance and detection strategies related to protein microarrays are presented and discussed. In the first paper an automated assay format, based on planar protein microarrays is described and evaluated by the detection of several auto-antibodies from human serum and by quantification of matrix metalloproteases present in plasma. Diffusion-rate limited solid phase reactions were enhanced by microagitation, using the surface acoustic wave technology, resulting in a slightly increased signal-to-noise ratio. In the second paper of the thesis, a novel multiplexed immunoassay system was developed by combining a direct immunoassay with a competitive system. This set-up allows quantification of analytes present in widely varying concentrations within a single multiplex assay. In the third paper, a new concept for sample deposition is introduced, addressing contemporary problems of contact or non-contact microarrayers in protein microarray fabrication. In the fourth paper, a magnetic bead-based detection method for protein microarrays is described as a cost-effective alternative approach to the commonly used fluorescence-based confocal scanning systems. The magnetic bead-based detection could easily be performed by using an ordinary flatbed scanner. In addition, applying magnetic force to the magnetic bead-based detection approach enables to run the detection step more rapidly. Finally, in paper five, a microfluidic bead-based immunoassay for multiplexed detection of receptor tyrosine kinases in breast cancer tissue is presented. Since the assay is performed inside a capillary, the amounts of sample and reagent material could be reduced by a factor of 30 or more when compared with the current standard protein microarray assay.
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