Surface enhanced Raman scattering (SERS) is a useful tool for the detection of metal ions due to the characteristic vibrational spectra that can be produced. Complexing different metal ions to a single ligand in solution can uniquely alter the SERS spectrum of that ligand, with the changes being specific to each individual metal ion. This approach has been used to research a nanoparticle-based sensor that can detect a number of metalions using SERS for environmental monitoring purposes. Research commenced by studying the small Raman reporter molecules, 4-mercaptobenzoic acid (4-MBA) and 4-mercaptopyridine (4-MPY), which were functionalised onto the surface of AgNPs. Upon addition of different metal ions, the AgNPs would aggregate resulting in an increased SERS response and characteristic frequency shifts in certain bands, which allowed discrimination of different species. The potential of 2,2'-bipyridyl (bipy) as a chelating ligand for the SERS detection of multiple metal ions has also been investigated. It has been shown that coordination of six different metal ions to this ligand produces characteristic changes throughout the entire spectral region, and therefore the presence of a metal ion can be identified with greater confidence. Not only that, the sensitivity is also greatly improved, with both Zn(II)and Cu(II) capable of being detected below the World Health Organisation (WHO) recommended limits of 0.22 and 0.6 ppm, respectively. Finally, the characteristic changes produced in the SERS spectrum of salen by Ni(II), Cu(II), Co(II) and Mn(II) is discussed. Although a smaller range of species can be detected compared to bipy, detection limits are significantly improved and changes produced by the different metal ions are arguably more pronounced. This approach has also been applied to real environmental freshwater samples in order to determine whether it is suitable for environmental sampling. A contaminated water sample known to contain elevated levels of Mn(II) was tested and it has been demonstrated that this method is indeed capable of detecting high levels of metal ions in natural freshwater samples.
|Date of Award||18 May 2017|
- University Of Strathclyde
|Sponsors||University of Strathclyde & NERC (Natural Environment Research Council)|
|Supervisor||Duncan Graham (Supervisor) & Karen Faulds (Supervisor)|