Scanning Electrochemical Microscopy And Surface Plasmon Resonance Spectroscopy Combined With Technology Development And Applications

Surface plasmon resonance (SPR) is an optical technique that canmonitor interfacial reactions at solid-liquid interfacese. SPR is attractiveowing to several inherent advantages, such as label-free analysis, rapidand high sensitivity. In rencent years, SPR has successfully applied toelectrochemistry field. EC-SPR offers a viable avenue to probe opticaland electrochemical properties of adsorbates and a sensitive means toquantify thickness variations of ultrathin films accompanying redoxreactions. However, in conventional EC-SPR experiments, the SPRangular shifts caused by an externally applied electrode potential couldaffect the sensitivity. It becomes difficult for EC-SPR to observe SPRangular shifts caused by conformational change of organic or evenbiological adsorbates.Two approaches to mitigate the inherent problem of EC-SPR byenhancing the sensitivity are described in this thesis. One is to establisha novel combined technique to avoid the effect of the applied electrodepotential on the variation of the surface charge density and reduce theSPR angular shifts. Another is to fabricate novel SPR substractes toenhance the small SPR responses.The combination of scanning electrochemical microscopy withsurface plasmon resonance is descibed in the thesis. An oxidant(reductant) electrogenerated at the SECM tip rapidly diffuses to the SPRsubstrate and oxidizes (reduces) the molecules affixed onto the surface.The coupled technique eliminates the SPR resonance angle changecaused by an externally applied electrode potential. The results, usingthe ferrocenyl alkanethiol and Ce(NO₃)₃ as a model system, by oxidizingferrocenylalkanethiol self-assembled monolayer with SECM-generatedCe⁴⁺, showed that the SECM-SPR coupled technique be viabel fordetermining local variations in the thin film thickness. Factors astip/substrate, tip potential affecting the SECM-SPR response are discussed. Furthermore, the approach was extended to the determinationof conformational changes of cytochrome c molecules. The accurate andreliable SECM-SPR results, which are well within those measured bysmall-angle X-ray scattering, demonstrate that the coupled technique caneffectively eliminate the 'inherent' interference.Ag films with the highest SPR response are limited to apply toEC-SPR research due to the low electrochemical stabilization. Bilayeredsilver/gold films were fabricated to achieve the sensitive EC-SPRmeasures. The result, using electrochemical deposition/stripping ofcopper as a model system, demonstrated that the bilayered silver/goldfilms produce a sharper SPR dip profile than pure Au films. Factorsaffecting the overall SPR sensitivity at the bilayered films, such as thefilm morphologh, gold/silver thickness ratio, and the adsorbate layer, were investigated. For the case of redox-induced conformation changesof cytochrome c, the SPR signal botaned at the bilayered silver/gold filmis 2.7 times as high as that at a pure gold film. It is significant for SPR tostudy electrode reactions at a very sensitive level.