Interfacing poly(p-anisidine) with photosystem I for the fabrication of photoactive composite films.

Photosystem I (PSI) is an intrinsically photoactive multi-subunit protein that is found in higher order photosynthetic organisms. PSI is a promising candidate for renewable biohybrid energy applications due to its abundance in nature and its high quantum yield. To utilize PSI's light-responsive properties and to overcome its innate electrically insulating nature, the protein can be paired with a biologically compatible conducting polymer that carries charge at appropriate energy levels, allowing excited PSI electrons to travel within a composite network upon light excitation. Here, a substituted aniline, 4-methoxy-aniline (para-anisidine), is chemically oxidized to synthesize poly(p-anisidine) (PPA) and is interfaced with PSI for the fabrication of PSI-PPA composite films by drop casting. The resulting PPA polymer is characterized in terms of its structure, composition, thermal decomposition, spectroscopic response, morphology, and conductivity. Combining PPA with PSI yields composite films that exhibit photocurrent densities on the order of several µA cm-2 when tested with appropriate mediators in a 3-electrode setup. The composite films also display increased photocurrent output when compared to single-component films of the protein or PPA alone to reveal a synergistic combination of the film components. Tuning film thickness and PSI loading within the PSI-PPA films yields optimal photocurrents for the described system, with ∼2 wt% PSI and intermediate film thicknesses generating the highest photocurrents. More broadly, dilute PSI concentrations show significant importance in achieving high photocurrents in PSI-polymer films.

Photoactive and conductive biohybrid films by polymerization of pyrrole through voids in photosystem I multilayer films.

The combination of conducting polymers with electro- and photoactive proteins into thin films holds promise for advanced energy conversion materials and devices. The emerging field of protein electronics requires conductive soft materials in a composite with electrically insulating proteins. The electropolymerization of pyrrole through voids in a drop-casted photosystem I (PSI) multilayer film enables the straightforward fabrication of photoactive and conductive biohybrid films. The rate of polypyrrole (PPy) growth is reduced by the presence of the PSI film but is insensitive to its thickness, suggesting that rapid diffusion of pyrrole through the voids within the PSI film enables initiation at vacant areas on the gold surface. The base thickness of the composite tends to increase with time, as PPy chains propagate through and beyond the PSI film, coalescing to exhibit a tubule-like morphology as observed by scanning electron microscopy. Increasing amounts of PPy greatly increase the capacitance of the composite films in a manner almost identical to that of pure PPy films grown from unmodified gold, consistent with a high polymer/aqueous interfacial area and a conductive composite film. While PPy is not photoactive here, all composite films, including those with large amounts of PPy, exhibit photocurrents when irradiated by white light in the presence of redox mediator species. Optimization of the Py electropolymerization time is necessary, as increasing amounts of PPy lead to decreased photocurrent density due to a combination of light absorbance by the polymer and reduced accessibility of redox species to active PSI sites.