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Title: Fabrication and optimisation of SERS substrates for medical diagnostics and monitoring
Author: Wijesuriya, Shavini
ISNI:       0000 0004 5914 7285
Awarding Body: Brunel University London
Current Institution: Brunel University
Date of Award: 2016
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Surface enhanced Raman spectroscopy (SERS) has great potential for design of next generation point-of-care (POC) diagnostic devices. However, its practical application in medical diagnosis is limited due to high cost of SERS substrates. The goal for this thesis was to develop affordable SERS substrates, and demonstrate their efficacy in the detection and assay of a Raman probe and diabetes biomarkers, using 514nm and 1064nm Raman spectrometers. Rapid and less energy intensive methods were optimised for manufacturing three categories of SERS substrates: 1) chemically roughened silver (Ag) metal, 2) Ag and gold (Au) nanoparticles (NPs) prepared using microemulsions, and 3) Ag and Au NPs’ coated insoluble electrospun membranes. Immersion of Ag metal for 30 seconds in ammonia (NH4OH), followed by 10 seconds in nitric acid (HNO3) produced optimum roughened Ag metal SERS substrates. For synthesis of gold (Au) and Ag NPs, microemulsion compositions were varied, and the use of sodium borohydrate (NaBH4) produced the desired larger sizes and anisotropic shapes of the NPs. Nanostructured planar SERS structures based on insoluble electrospun membranes, were prepared by covalently binding Au or Ag NPs, on electrospun poly acrylic acid-ethylene glycol (PAA-EG) fibres. Ag metal SERS substrates provided the best SERS enhancement for the Raman probe molecule, 4-methylbenzenethiol (MBT), with a detection limit of 1aM, using 514nm Raman spectrometer. The Ag metal SERS substrates were then used to demonstrate proof-of-concept for the use of SERS for assay of diabetes biomarkers. The higher laser intensity of 106nm Raman caused burning of the dry NPs’ incorporated SERS substrates; but the thermally conductivity of solid Ag in Ag metal SERS substrate allowed SERS detection of 1nM MBT. To conclude, chemically roughened Ag metal SERS substrates proved cost effective and robust for quantitative SERS detection of MBT and diabetes biomarkers both with 514nm and 1064nm Raman spectrometers.
Supervisor: Burugapalli, K. ; Balachandran, W. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Microemulsion ; Electrospinning ; Nanotechnology ; Biosensors ; Raman scattering