Infrared spectroscopic detection of charged particles

The motivation of this thesis is to develop and investigate the merits of infrared spectroscopic based methods that could be used as a detector/identifier in biological detection systems. The selection of infrared spectroscopy is based on several recent studies [1-3] which have shown that the application of chemometrics with infrared spectra provide a means of identification of intact spores at the species level. The methods described in this thesis are based on Attenuated Total Reflection (ATR) because of the requirement of detection of spores in water. It is noted that in our work we use benign Bacillus globigii spores as a stimulant of the target Bacillus anthracis spores for obvious health and safety reasons.;Chapter 1 is an introduction to the background information related to the project and Chapter 2 describes the general experimental procedures. The use of ATR requires the development of methods that lead to concentration of the spores onto the surface of internal reflection elements (IRE). In chapter 3, an electrostatic method for concentrating Bacillus globigii spores on the surface of a ZnSe IRE is described. The IRE was coated with alumina using two approaches and it was shown that negatively charged spores adsorbed onto the positively charged alumina coating. The charge on the alumina and spores are pH dependent and it is shown that the amount of spores adsorbed on the alumina/IRE passed through a maximum near a pH value of 5. The maximum occurred at this pH because of a compromise between the attractive force for spore-alumina interaction and the repulsive force for spore-spore interactions. Two main drawbacks to this approach are that detection is a mass transport limited process and that reuse of the coated IRE was not possible.;In chapter 4, an electric field assisted ATR was developed to address the drawbacks with the approach used in Chapter 3. In this method, no coating of the IRE is required. Adsorption of the spores does not occur when a suspension containing spores is flowed through the cell. However, it is shown that application of the electric field under no flow conditions leads to a rapid adsorption of the negatively charged spores on the IRE. The spores adsorb through Van der Wall's forces and are not removed by reversing the field direction. Nevertheless, the spores could be easily and rapidly removed by the shear forces occurring with simply flowing in a new sample. Three key advantages of the E-field ATR method are; (1) no coating of the IRE is required, (2) adsorption is rapid under an applied field and (3) a cleaning step requires simply flowing in a new sample.;In conducting the experiments using the electric field ATR we realized that this method could be applied to detection of other charged particulates and that it may be possible to obtain information on particle-particle and particle-surface interactions. The work in chapter 5 explores this possibility in which the packing arrangement of kaolin particle on a ZnSe IRE under an applied electric field is investigated. It is shown that, under certain conditions, the packing geometry of kaolin on the surface can be altered by applying an electric field. In particular, polarized IR spectroscopic measurement and AFM show that under an applied electric field and no flow conditions, a deposited layer of kaolin rearranges such that the kaolin in contact with the fluid layer adopts a flatter orientation on the surface. This seeds the epitaxial deposition of a highly dense layer of kaolin when the flow is restarted under an applied electric field. The work in chapter 5 demonstrates the potential use of electric field for controlling filter cake formation which, in turn, could find use in the coating industry. (Abstract shortened by UMI.)...