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The work presented in this thesis investigates the viability using a laser induced plasmas as a high intensity, UV/VIS/IR benchtop light source for biological spectroscopic applications. It is well known that plasmas make excellent light sources due to their broadband emission throughout the UV/VIS/IR. A detailed account is given of the construction and testing of a prototype benchtop spectrometer that utilised a laser induced plasma as its light source. The parts to build this spectrometer had a total cost of £6480.49, a competitive price for an instrument capable of measuring absorbance/turbidity spectra in the wavelength range of 380 to 700 nm at a rate of up to 5 times a second and to a wavelength resolution of approximately 0.2 nm. The production of shorter wavelength is very possible using this technology but would require a much more expensive, higher repetition rate laser, which was beyond the scope of this project. A review of the physical factors influencing the emission of light from a plasma is first presented. Several noble gases were tested to optimise the intensity and short wavelength output of the plasma. The results showed that argon had the highest emission intensity light for reasonable cost. The prototype instrument can be run in two different modes, static mode and dynamic mode. In static mode, the spectrometer can determine the absorbance spectrum of samples that do not change over time such as coloured dyes. In dynamic mode that monitors the absorbance of samples whose absorbance/turbidity varies with time. The accuracy of the prototype plasma spectrometer was tested by determining the absorption spectrum of holmium oxide in perchloric acid, a standard solution often employed for spectrometer calibration and testing. The prototype spectrometer was then successfully employed to investigate the effect of heparin, in the presence of the cations Fe2+, Zn2+ and Cu2+, on the aggregation rate of the protein human lysozyme, over a range of pHs. The aggregation of lysozyme was an interesting system to monitor, as it has been proposed as a model for the formation of the fibrils found in amyloidal plaques.

The principal method of probing the structure of these films was the non-linear optical technique of Sum Frequency Generation (SFG). The experimental techniques used in this work are first introduced together with a theoretical description of SFG. There then follows an overview which describes semiconductor nanoparticle monolayers and the application of SFG to them. The work was subsequently extended to the investigation of multilayers of semiconductor nanoparticles incorporated within fatty acid films. Whilst SFG of monolayers is well understood SFG of multilayer films is not and most of this dissertation has been devoted to providing a systematic description of SFG of multilayer films adsorbed onto both metal and dielectric substrates. The observed multilayer SFG spectrum is shown to be a superposition of SFG signals coming from the surface layer, in contact with air, and the lowermost layer, in contact with the substrate. The SFG spectrum is a simple numerical addition of the two signals when gold is used as a substrate and as a subtle convolution of the two signals when a dielectric substrate is used. Through the incorporation of a single perprotonated fatty acid layer within an otherwise fully per-deuterated film it has been possible to study both the surface layer and buried interfaces. The resonant line shapes of SFG spectra obtained on gold substrates were found to depend on layer thickness, something which has been quantified experimentally and explained theoretically in terms of a nanoscale thin film interference effect. In the final part of the dissertation the capacity of SFG for studying buried interfaces has been exploited to investigate nanoparticle-induced structural changes within fatty acid multilayer films, demonstrating the versatility and potential of this novel application of SFG. It was found that, following nanoparticle formation within the fatty acid film, the surface layer remained highly ordered whilst the buried layers became disordered.