Date on Master's Thesis/Doctoral Dissertation
Physics and Astronomy
Mendes, Sergio B.
Committee Co-Chair (if applicable)
Davis, Christopher L.
Zamborini, Francis Patrick
Keynton, Robert S.
Molecular crystals; Molecular structure; Molecular association
Two optical analytical tools were developed for studying molecular assemblies at solid/liquid interfaces. Electro-active single-mode integrated optical waveguide (EA-SM-IOW) technology was developed as a platform for spectroelectrochemical investigations on redox adsorbates at the sub-monolayer level. With an optimized ultra-thin indium tin oxide film combined with a single-mode integrated optical waveguide, for the first time, a more than 14,000 times higher sensitivity (compared to conventional potential-modulated transmittance) was achieved. From optical signals, this technique was able to reconstruct electrochemical information of redox adsorbates, including the formal potential and the electron transfer rate. A few major advantages were achieved with the developed EA-SM-IOW technology. I) As low as 10−15 mol/cm2 electrochemically active surface coverage of redox species could be detected; II) A new analytical methodology was developed to combine optical impedance spectroscopy (OIS) with electrochemical impedance measurements to retrieve the electron transfer rate of redox process. This approach bypasses specific knowledge of every electrical element in the electrochemical flow cell; and III) The novel technique of OIS based on EA-SM-IOW platform was applied to examine the electron transfer processes of cytochrome c proteins under different environments that the surface densities were well below the limits of detection in conventional techniques. For molecular assemblies without a convenient absorbance band, a complementary analytical tool, coupled plasmon waveguide resonance (CPWR), was developed to detect surface binding events through changes in the real part of the refractive index and shown to be superior to the surface plasmon resonance (SPR), which has been considered as a gold standard technique. The advantages of CPWR included. I) When compared to SPR theoretically, the designed CPWR sensor was featured more than 30 times better resolution for the bulk solution changes and approximately 2 times superior for probing molecular surface adsorption; II) The smaller (and better) resolution of CPWR was demonstrated experimentally for the first time; and III) The CPWR was applied in an angle-multiplexed configuration to measure the fluorescence decay of a Ru-complex molecular assembly in the nano-second time scale. These two outstanding optical analytical tools provide unprecedented information and reach new detection limits that are expected to enable novel fundamental investigations and technological applications in molecular assemblies.
Han, Xue, "Novel analytical tools for studies in molecular assemblies : I. Electro-active single-mode integrated optical waveguides ; II. Coupled plasmon waveguide resonances." (2014). Electronic Theses and Dissertations. Paper 1743.