Laser Induced Plasmas: A Light source for Biological Spectroscopy

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