Electrochemical sensing using micro- and nanostructured poly(ferrocenylsilane)s

Abstract

In this thesis, we look for ways to use the polymer poly(ferrocenylsilane) in sensor applications. Drying a mix of PFS-Vinylimidazole with polyacrylic acid (PAA) results in a partially phase-separated layer. We have visualised this using electron microscopy (SEM) and X-ray scattering (SAXS). When the dried layer is exposed to ammonia, a porous membrane is formed. The size of the pores in the membrane can be influenced by oxidation and reduction of the PFS. We investigated fully oxidised and fully reduced membranes using electron microscopy (SEM) and X-rays (SAXS). Furthermore, we developed an electrochemical cell which allows us to carry out in-situ SAXS measurements. Using this cell, we cannot only observe the two extreme membrane states, but also the transition between them. Finally, we found that each redox state of the membrane has a unique impedance spectrum. Subsequently, we attempted to use the porous PFS membrane to fabricate a sensor. The applicability of the porous membrane was tested for ascorbic acid, Fe3+, hydrogen peroxide and enzymatic sensors. We obtained some encouraging results, but the stability of the membrane, the slow response and the limited conductibility complicate matters. There is a lot left to be desired in the reproducibility and reliability of sensors based on a porous PFS layer. Alternatively, in an attempt to construct a photonic sensor, we tested three types of PFS for use in two-photon-lithography. All three variants were suitable, but a number of obstacles was encountered. These obstacles and possible solutions were addressed in detail. Additionally, we discovered that the technology used for fabricating porous membranes can also be used to make porous micro particles. The first step herein is the fabrication of PFS/PAA micro particles. We managed to do this by means of a simple microfluidic device: a T-junction that forms droplets of polymer solution in PDMS oil. Because the polymer solvent mixes with the PDMS oil, it slowly vacates the droplets, leaving behind a PFS/PAA particle. After drying and ammonia treatment, porous PFS/PAA particles are obtained. Finally, a reference-electrode-free pH and conductivity sensor based on indium-tin-oxide (ITO) electrodes was developed.