Through barrier detection using surface enhanced spatially offset Raman spectroscopy

  • Fay Nicolson

Student thesis: Doctoral Thesis

Abstract

In the fields of security and biomedical imaging there is a significant need to non-invasively probe through barriers, e.g. plastic, glass or tissue. Raman spectroscopy provides a means to solving this challenge since it provides a unique chemical fingerprint without the need to destroy the sample. In spite of this, conventional Raman can be limited by sample volume and thickness, often failing to probe beneath the surface or through samples obscured by an opaque barrier.Spatially offset Raman spectroscopy provides a means of overcoming the limitation associated with conventional Raman spectroscopy since it is capable of providing a unique chemical fingerprint of the analyte understudy, even when obscuring barriers such as plastic or tissue are present. Furthermore, by combining the depth penetration benefits of SORS with the signal enhancing capabilities of SERS, SESORS is capable of achieving sample interrogation at even greater depth.Therefore, the focus of this research is to probe through barriers, specifically plastic and tissue, using both handheld CR and SORS instruments. The ability of both techniques to detect Raman and SERS analytes through barriers is explored and compared for applications involving security and biomedicine.The use of conventional Raman and SORS to detect ethanol through varying thicknesses of plastic is investigated. Raman signals from an ethanol solution through plastic was detected through thicknesses of up to 21 mm using SORS in combination with multivariate analysis. SORS was compared to conventional Raman, where through barrier detection of ethanol took place through depths up to 9 mm.Using a handheld SORS spectrometer, the detection of ex vivo breast cancer tumour models containing SERRS active nanotags through 15 mm of porcine tissue is demonstrated. In addition, SERRS-active nanotags were tracked through porcine tissue to depths of up to 25 mm. To date, this is the largest thickness that SERRS nanotags have been tracked through using a backscattering approach.This unprecedented performance is due to the use of red-shifted chalcogenpyrylium-based Raman reporters to demonstrate the novel technique of surface enhanced spatially offset resonance Raman spectroscopy (SESORRS) for the first time. The same ex vivo tumour models are also used to demonstrate a multiplexed imaging system through depths of 10 mm using back scattering SESORRS.The benefit of using red-shifted chalcogenpyrylium based Raman reporters for probing through large thicknesses of plastic and tissue barriers using SERS is also highlighted. Raman signals were collected from SERRS active nanotags through plastic thicknesses of up to 20 mm. The detection of SERRS-active nanotags taken up into ex vivo tumour models through depths of 5 mm of tissue is also shown.The advantages of applying multivariate analysis for through barrier detection when discriminating analytes with similar spectral features as the barrier is also clearly demonstrated.Finally, resonant chalcogenpyrylium nanotags were used to demonstrate the benefit of using a resonant Raman reporter for superior low-level limits of detection using SESORS. Nanotags containing chalcogenpyrylium dye were observed at concentrations as low as 1 pM through 5 mm of tissue. This is compared to the non-resonant small molecule Raman reporter BPE which could only be detected at concentrations of 11 pM.Calculated limits of detection suggest that these SERRS nanotags can be detected at concentrations as low as 104 fM using SESORRS.
Date of Award1 Apr 2018
LanguageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorKaren Faulds (Supervisor) & Duncan Graham (Supervisor)

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