Suspended Polypyrrole Films Supporting Alamethicin Reconstituted Bilayer Membranes

This thesis presents a novel architecture for a sensing element fabricated from a conducting polymer and a bioderived membrane. The thin film device provides controlled, selective ion transport from a chemical concentration and produces measurable electrical signals, ion storage, and small scale actuation. A chemical gradient applied across a bioderived membrane generates ion flow through protein transporters in the presence of a gating signal. A conducting polymer undergoes ion ingress/egress in the presence of an electrical and chemical potential, which causes a change on the polymers conformal backbone. A ligand (or) voltage gated protein in the bioderived membrane results in ion transport through the bioderived membrane. Integrating the two electroactive materials provides a unique architecture which takes advantage of their similarities in ionic function to produce a device with controlled and selective ion transport. The chemoelectromechanical device is one that couples chemical, electrical, and mechanical potentials through number of ions, dielectric displacement, and strain. The prototype consists of a stacked thin conducting polymer film and bioderived membrane which form three aqueous chambers of varying ionic concentrations. The top chamber contains an electrolytic solution, and the bottom chamber contains deionized water adjacent to the conducting polymer. The current that passes through a conducting polymer for an applied electrical signal is based on the level of doping/undoping and therefore can be used as a method of sensing protein function in the sensing element. This architecture results in a sensing element applicable in real time chemical sensors, volatile organic compound detectors, and bioanalytical sensors. The conducting polymer layer is formed from polypyrrole (PPy) doped with sodium dodecylbenzenesulfonate (NaDBS), and the bilayer lipid membrane is formed from 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) reconstituted with the protein alamethicin. The magnitude of current required to span a 175 µm pore was empirically found to be 326.5 A/cm2 and is based on electrode condition, electrode surface area, pyrrole concentration, and electrical potential. A micron-scale pore through a silicon substrate is spanned by a thin PPy(DBS) layer, forming a bridge which supports the bioderived membrane. The bioderived membrane is reconstituted with alamethicin, a voltage-gated protein extracted from trichoderma viride. Ion transport experiments were performed to characterize the PPy(DBS) layer and the bioderived membrane and are represented as electrical equivalents for subsequent analysis. The equivalent impedance of polypyrrole was calculated to be 1.7847±0.1735Ωcm2 and capacitance was calculated to be 1.2673±0.1823µF/cm2. The equivalent impedance of a bioderived membrane was calculated to be 1.654±1.9894MΩcm2, capacitance was calculated to be 1.1221± 0.239µF/cm2, and alamethicin resistance was calculated to be 1.025± 0.7228MΩcm2. Thus, using impedance measurements in the conducting polymer layer, it is proposed that a scaled up sensing element can be fabricated using the suspended polypyrrole supported bioderived membrane