Poly Vinyl Alcohol and Carbon Nanotube Based Scaffolds for Engineered Biosensors

Biosensors are analytical devices that can turn biological responses into electrical signals which can be very useful in the diagnostics of numerous diseases. This work looks into the fabrication of an impedance based biosensor using electrospun Poly Vinyl Alcohol (PVA) and Carbon nanotubes (CNTs) to be used in conjunction with bacteriorhodopsin contained in a purple membrane. Dispersions of PVA are created with and without CNTs in deionized (DI) water, which are then utilized to synthesize porous electrospun nanofibrous scaffolds with fiber diameters ranging from 150nm to 250nm. The detection technique utilized for the fabricated biosensor is through the quantification of electrochemical impedance via the Electrochemical Impedance Spectroscopy (EIS). The parameters for both electrospinning and EIS are carefully optimized to achieve porous nanofibrous scaffolds having expected fiber diameter, porosity and impedance. The parameters which are optimized for the electrospinning process include the flow rate, collection distance, voltage, viscosity of the polymer CNT solution, and the type and configuration of the collector. Similarly, the parameters for the EIS include optimum potential of the applied small ac signal in mV, frequency range, electrolyte concentration and the type of electrodes and their configuration. This careful optimization of the parameters would enable the fabrication and the dynamic response of the designed biosensor to be able to hold its integrity through the entire process of characterization and testing. Two different forms of CNTs are used, which are single-walled carbon nanotubes (SWNTs), and multi-walled carbon nanotubes (MWCNTs). The two different SWNTs used in this study have a (6, 5) chirality and also mixed metallic and semiconducting chirality to assess the differences in the biosensor performance based on the type of SWNT and its comparison to the MWNTs. The synthesized scaffolds are also characterized through atomic force microscopy (AFM) and scanning electron microscopy (SEM), and compared to control samples without CNTs. The synthesized scaffolds are then tested for performance through the detection of a light sensitive protein bacteriorhodopsin (BR), which is a membrane protein found in Archaea, most notably Halobacteria. The primary function of the protein is in its use as a proton pump across the cell membrane and its novel characteristic to detect light of different wavelengths make it attractive for application in optical memory. Although this is a specific example, these scaffolds can accommodate different types of analyte for biosensors in many applications.