Development and application of evanescent wave cavity ring-down spectroscopy as a probe of biologically relevant interfaces

Abstract

The application of a hybrid instrument combining Evanescent Wave Cavity Ring-Down Spectroscopy (EW-CRDS) with electrochemical and fluidic methods is described. The electrochemical/fluidic methods were used to induce a surface process, the effects of which were subsequently monitored in situ and in real time with exquisite spectral sensitivity and excellent temporal resolution by EW-CRDS. The well-defined manner in which the surface processes were initiated allowed the extraction of kinetic rate constants by fitting the EW-CRDS data to mathematical models of the surface process coupled to convection-diffusion. The investigations described include: the study of the thermodynamics and kinetics of the adsorption of tris(bipyridine)ruthenium(II) ([Ru(bpy)3]2+) to polypeptide films using EW-CRDS with chronoamperometry; the real-time electrochemistry of cytochrome c immobilised on silica by EW-CRDS with chronoamperometry; the kinetics of adsorption and DNA-assisted desorption of 5,10,15,20-tetra(N-methylpyridinium-4-yl)porphyrin at the silica-water interface using EW-CRDS with an impinging jet flow cell; and the monitoring the adsorption of cationic phospholipid vesicles at the silica-aqueous interface and the interaction of 5,10,15,20-Tetraphenyl-21H, 23H-porphine-p,p′,p″,p′′′-tetrasulfonic acid tetrasodium hydrate with the resulting bilayer also using EW-CRDS with an impinging jet flow cell. The work described in this thesis provides a platform on which EW-CRDS can be used to study dynamics at biointerfaces, such as the association of ions, peptides, proteins and drugs with phospholipid bilayers, the electron transfer between redox enzymes in a biomimetic environment, and the lateral diffusion of protons, ions and proteins at biomembranes. Such studies are essential to the understanding of many important cellular processes in addition to the development and optimisation of a number of bio-inspired technologies