Introduction: Polypyrrole (Ppy) is a very widely used soft electrically conductive biomaterial with applications in biomedical engineering. In the past cyclic voltammetry (CV) has extensively been used to synthesize Ppy films with and without carbon-based nanoparticles to improve the rigidity of the composite material by doping it with carbon allotropes. Furthermore, electrochemical impedance spectroscopy (EIS) can be easily utilized to measure the impedance and hence application specific electrical conductivity of the Ppy nanocomposites. The objective of this research is to optimize the CV parameters to synthesize a Ppy scaffold containing graphene and/ or carbon nanotubes with and without the protein, bacteriorhodopsin.
Materials and
Methods: A Pyrrole solution is used in the dispersion and it consists of DI water, pyrrole, and sodium sulfate as the salt for synthesizing the polypyrrole film. The pyrrole solution is made using a bath sonicator and a hot plate. Once the dispersion is complete, the solution is a light yellow color. The film is created from this solution through Cyclic voltammetry which uses the applied potential, scan rate and number of cycles to synthesize the film. There are three electrodes, the working electrode , counter electrode, and reference electrode. The working electrode is where the film coats.This occurs because the ions and pyrrole monomers in the solution are attracted to the working electrode. We utilized a three-electrode system, a graphite plate working electrode (WE), a Silver/ Silver Chloride (Ag/AgCl2) reference electrode (RE), and a platinum Counter electrode (CE). Throughout this project different parameters and alterations were made producing different results based on the amount of sodium sulfate in solution, continuous versus intermediate cycles, and variations in the scan rate.
Results, Conclusions, and Discussions: The cyclic voltammetry parameters that produced the best result and the synthesis of a film was a scan rate of 50 mv/s, 250 intermittent cycles, and a voltage difference of -220 mV to 480 mV. The film appeared to be flat with minor bubbling at certain points. When the film was being extracted from the carbon plate, curling of the film occurred. Under the microscope, the side that was closest to the electrodes, rather than facing the solution, showed presence of salt crystals as was evident from EDAX analysis. The film had a thickness range of 28-33 micron while a scan rate of 100 mv/s 100 cycles did not produce large enough film. So we utilized the first set of parameters and in the next step added the bacteriorhodopsin (BR) in the form of a purple membrane to the solution to see if it attaches to the carbon plate and becomes part of the film. The motivation behind using this protein is that it is sensitive to light making it an ideal biological macromolecule for a number of biomedical applications including biological memory storage. The processes of reaction kinetics and mass transport are also investigated to better understand the interface between multiwalled carbon nanotubes (MWNT) and BR and that between BR and Ppy. The synthesized films containing BR and MWNT are also analyzed using the SEM to understand the morphology of the composite material and more importantly to locate the BR and MWNT on the Ppy film. In conclusion, we are able to synthesize the Ppy film with and without MWNT and BR and it is found that utilizing SEM and EDAX, it is possible to locate the MWNT and BR molecules over the Ppy film. This is an ongoing research that seeks to also come up with a reliable technique to use the visible light to store and read data in the form of BR conformations off of the MWNT/Ppy as well as Graphene/ Ppy scaffolds, which will further be integrated in bioelectronic devices.
Acknowledgements (Optional): We thank Fairfield University for the INSPIRE travel grant and the school of Engineering and Computing for providing the necessary resources.
