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Optical waveguide biosensors

Sloper, Andrew Nigel; (1991) Optical waveguide biosensors. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

This thesis describes a novel method for the fabrication of monomode planar waveguides, and their application to the development of evanescent field fluorescence immunosensors. Previous workers, monitoring fluorescence by multiple internal reflection methods have achieved sensitivities that are sufficient for the detection of some of the analytes for which immunosensors are sought. However, there remain many analytes of clinical interest which require higher sensitivities than have so far been demonstrated. Higher sensitivities could be obtained if thin-film optical waveguides could be used. These can enhance the strength of the evanescent field and reduce its penetration, and enable a greater interaction of the light with the sample through the continuous interrogation of the interface by a propagating waveguide mode. Furthermore, they may permit the future development of more sophisticated enhancements through the incorporation of integrated optical structures. A technique has been developed for the fabrication of inexpensive planar thin-film waveguides, by the solution deposition of tri-valent metal phosphates. Compositions containing Fe, In, Ga, Al, V, Cr Y, and lanthanide elements have been deposited as continuous hard glassy films by spin- coating followed by a low temperature bake. Indium phosphate films were identified as the most appropriate waveguides for the fabrication of evanescently excited fluorescence immunosensors. An eight fold increase in sensitivity was obtained by using thin-film waveguides as opposed to multiple internal reflections. A sandwich fluorescence immunoassay for the hormone hCG in serum was used as the model analyte system. In the development of this technique, methods of controlling and improving the waveguide characteristics were examined. This included the investigation of methods of varying the refractive index, reducing propagation losses and controlling film thickness. Since the sensors are required to work in a chemical or biochemical environment, the durability of the films was examined. Many biosensors require the adsorption or covalent immobilisation of proteins at a surface. The attachment of proteins to these materials was examined and a surface loading equivalent to that for a conventional glass surface was achieved. Methods of patterning these materials were investigated to evaluate the potential for the development of more sophisticated structures, such as internally referenced or multiple analyte sensors. The films may be patterned by embossing or, with the exception of films containing Cr, by standard photolithography.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Optical waveguide biosensors
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Applied sciences; Monomode planar waveguides
URI: https://discovery.ucl.ac.uk/id/eprint/10113021
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