Graphene Based Nanofibrous Scaffold for Embedding Bacteriorhodopsin for Bioengineered Memory Application

The photoactive protein, Bacteriorhodopsin (bR), is being implemented into optical memory applications, most notably for its photochemical and thermal stability. Due to this photochemical stability, bR can remain in one of two stable photostates, bR (ground state) and Q (elevated state), which are used to designate binary bits ‘0’ and ‘1’. The challenge with this phenomenon is that the Q photo state has a low quantum yield, meaning that bR will not absorb enough photons to undergo photoisomerization. To increase the quantum yield of the photocycle, a molecular dynamics simulation involving graphene monolayer and crystal structure of the bR protein was performed to study the adsorption and preservation of the photostates of bR, where it was found that graphene has a potential to increase the quantum yield. However, a major challenge is to have a porous surface with even distribution of graphene nanoparticles to employ it as a scaffold to anchor the bR protein. The porosity of the surface would help anchor the protein onto the surface and the distribution of graphene nanoparticles would ensure proper chemical interactions. Such a porous surface is achieved through electrospinning where nanofibrous scaffold of poly vinyl alcohol (PVA) with graphene nanoparticles is utilized to immobilize the bR protein. Four different scaffolds on aluminum and Indium Titanium Oxide (ITO) surfaces are fabricated with and without graphene having PVA as a common matrix with optimized electrospinning parameters including flow rate, nozzle collector distance, voltage between nozzle and collector, viscosity of the polymer solution and type and configuration of the collector. It is found that the synthesized nanofibers have average diameters of ~200nm with graphene monolayers embedded within the nanofibrous scaffolds. The resulting scaffolds are characterized using scanning electron microscopy (SEM), profilometry and electrochemical impedance spectroscopy (EIS) to quantify its physical and electrical properties and are compared to the control PVA-bR scaffolds without graphene. The distribution of the purple membrane discs containing bR embedded within the nanofibers is also quantified based on the fiber diameter, porosity and collector surface. The synthesized scaffolds are also tested using lasers with wavelengths ranging from 380nm to 640nm to drive the bR molecules to the branched photostates to demonstrate their use as a bioengineered memory device.