Chalcogenopyrylium dye functionalised gold nanoparticles for use as red-shifted SERS nanotags

  • Amy Morrison

Student thesis: Doctoral Thesis

Abstract

Surface enhanced Raman spectroscopy (SERS) in the near infrared (NIR) is a largely unexplored area in Raman spectroscopy, particularly at laser excitation wavelengths greater than 1100 nm. This thesis explores the use of a 1280 nm Raman spectrometer for NIR Raman active nanotag design and application. The NIR region of the electromagnetic spectrum is of specific interest due to the absorption and scattering properties in biological matter throughout this optical window. Research described in chapter 3 of this thesis highlights the use of a relatively novel class of chalcogenopyrylium (CP) dye molecules, which in combination with the broad extinction profile of large gold nanoparticles (AuNPs) provide an intense SERS response upon 1280 nm laser excitation, previously unachievable with commercially available Raman reporter molecules at this excitation wavelength. However, the structural design of these dyes specifically relating to their SERS performance is unreported. The relationship between CP dye molecule binding orientation, determined via sum frequency generation vibrational spectroscopy (SFG-VS), and their SERS response was investigated deducing that due to the polarisation throughout the backbone of the CP dye molecule, an optimal SERS response was achieved when the CP dye molecule is as perpendicular to the NP surface as possible. Due to the increasing technological advances surrounding counterfeit and fraudulent goods, investigation into the design of a nanotag that could be selectively detected by only those with the knowledge of how to detect it could be incredibly advantageous in the fight against consumer goods piracy and in the secure labelling of important documents.Chapter 4 of this thesis reports the design of such a nanotag using an already established CP dye as the Raman reporter and a novel, purposefully designed, CP based dye blocking molecule (BM) which is able to block or mask the SERS signal from the Raman reporter at 785 nm laser excitation, only providing a SERS response, from the nanotag, upon excitation with a 1280 nm laser source. This resulted in the ability to obtain a SERS response with a 1280 nm Raman spectrometer that was not achieved at 785 nm laser excitation, by either complete signal elimination or by masking from the BM itself. This could provide the ability to invisibly tag and detect items of vital importance in which no one else, unless equipped with this nanotag, 1280 nm Raman spectrometer and system knowledge could or should be able to identify. In order for biomedical research to advance away from dated, bulkier, fixed instrumentation, performance of handheld instrumentation, capable of being adapted into a clinical environment, needs to be explored. Previous group work has investigated the performance of CP dye based nanotags at depth through biological tissues by use of spatially offset Raman spectroscopy (SORS). As SORS is a technique which will acquire a Raman measurement at a pre-determined depth, work was also carried out in order to deduce the depth at which a conventional 785 nm Raman spectrometer could detect these nanotags in tissue samples. However, the ability to probe through biological barriers using further red-shifted excitation wavelengths has not yet been studied.Chapter 5 of this thesis reports and compares the depth, in tissue samples, at which CP dye based nanotags can be detected using portable conventional handheld Raman spectrometers of laser excitation wavelengths: 785, 1064 and 1280 nm. Recent reports have emerged, in the literature, employing CP dye based nanotags in a variety of biological applications including localisation within and detection of cancerous tumours, cell-based cancer models and in ex vivo multiplexing platforms, however, to date their cytotoxicity has gone unreported. Chapter 6 of this thesis examines the cytotoxicity of five CP based dye n
Date of Award12 Sep 2019
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorDuncan Graham (Supervisor) & Karen Faulds (Supervisor)

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