In English

Single Molecule Detection using Optical Waveguide

Mathias Elmeskog
Göteborg : Chalmers tekniska högskola, 2013. 48 s.
[Examensarbete på avancerad nivå]

Molecular interactions with single molecule sensitivity is a growing field with application in pharmaceutical development and diagnostics. Existing techniques that can be used for single molecule interaction studies, such as total internal reflection fluorescence (TIRF) microscopy are often expensive and complicated to use. They also have critical limitations, for example the need of labeling with fluorophores. In this thesis a novel method based on a single mode optical waveguide is investigated for surface binding with single molecule sensitivity. A three layer planar waveguide is used where the core layer is a light carrier. The refractive index of the cladding layers are matched to that of water in order to make it compatible with measurements in a liquid environment. Mounted under a regular upright microscope, the evanescent field in the waveguide can be used for excitation of fluorophores or for monitoring the scattering intensity. In this project the latter method was used exclusively. It was shown 20 nm gold nano particles bound to, or very close to, the core layer surface of the optical waveguide could be visualized. The ability to perform real time measurements makes it possible to determine if a gold nano particle binds reversibly or irreversibly to the surface. The possibility to functionalize the core layer surface in di↵erent ways has also been studied. The concept was further developed into a biosensing technique using an antibody sandwich assay to detect amyloid-! peptides at very low concentrations. This is of interest due to amyloid-! peptides suspected role in developing plaque in brain tissue which lead to Alzheimer’s disease. To be able to detect traces of this peptide in blood plasma at an early stage could help develop techniques to inhibit or stop the development process of the disease. It was found to be possible to detect amyloid-! 1-37, 1-37 indicates the number of amino acids in the peptide, down to at least a concentration of 100 fM in the bulk solution added to the waveguide chip using the waveguide technique.

Nyckelord: Optical waveguide, evanescent field, single molecule sensitivity, surface sensitive



Publikationen registrerades 2014-03-05. Den ändrades senast 2014-03-05

CPL ID: 194445

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