Plants and some types of bacteria demonstrate an elegant means to capitalize on the superabundance of solar energy that reaches our planet with their energy conversion process called photosynthesis. Seeking to harness Nature's optimization of this process, we have devised a biomimetic photonic energy conversion system that makes use of the photoactive protein complex Photosystem I, immobilized on the surface of nanoporous gold leaf (NPGL) electrodes, to drive a photoinduced electric current through an electrochemical cell. The intent of this study is to further the understanding of how the useful functionality of these naturally mass-produced, biological light-harvesting complexes can be integrated with nonbiological materials. Here, we show that the protein complexes retain their photonic energy conversion functionality after attachment to the nanoporous electrode surface and, further, that the additional PSI/electrode interfacial area provided by the NPGL allows for an increase in PSI-mediated electron transfer with respect to an analogous 2D system if the pores are sufficiently enlarged by dealloying. This increase of interfacial area is pertinent for other applications involving electron transfer between phases; thus, we also report on the widely accessible and scalable method by which the NPGL electrode films used in this study are fabricated and attached to glass and Au/Si supports and demonstrate their adaptability by modification with various self-assembled monolayers. Finally, we demonstrate that the magnitude of the PSI-catalyzed photocurrents provided by the NPGL electrode films is dependent upon the intensity of the light used to irradiate the electrodes.
The long‐term success of photosynthetic organisms has resulted in their global superabundance, which is sustained by their widespread, continual mass‐production of the integral proteins that photocatalyze the chemical processes of natural photosynthesis. Here, a fast, general method to assemble multilayer films composed of one such photocatalytic protein complex, Photosystem I (PSI), onto a variety of substrates is reported. The resulting films, akin to the stacked thylakoid structures of leaves, consist of a protein matrix that is permeable to electrochemical mediators and contain a high concentration of photoelectrochemically active redox centers. These multilayer assemblies vastly outperform previously reported monolayer films of PSI in terms of photocurrent production when incorporated into an electrochemical system, and it is shown that these photocatalytic properties increase with the film thickness. These results demonstrate how the assembly of micron‐thick coatings of PSI on non‐biological substrates yields a biohybrid ensemble that manifests the photocatalytic activity of the film’s individual protein constituents, and represent significant progress toward affordable, biologically‐inspired renewable energy conversion platforms.
Photosystem I (PSI) has drawn widespread interest for use in biomimetically inspired energy conversion devices upon extracting it from plants or cyanobacteria and assembling it at surfaces. Here, we demonstrate that a critically dense monolayer of spinach-derived PSI must be formed on an electrode surface to achieve optimal photocurrents, and we introduce a new method for preparing these dense PSI monolayers that reduces the time required for assembly by approximately 80-fold in comparison to that for adsorption from solution. This method consists of applying a vacuum above the aqueous PSI solution during assembly to concentrate PSI and precipitate it into a thick layer onto the surface of various self-assembled monolayers or directly onto the electrode surface. Rinsing with water yields a dense monolayer of PSI that draws approximately 100 nA/cm2 of light-induced current from the gold electrode in the presence of appropriate mediators.
We report the surface-initiated ring-opening metathesis polymerization (SI-ROMP) of 5-(perfluoro-n-alkyl)norbornenes (NBFn) to grow partially fluorinated polymer films of tunable thicknesses ranging from tens of nanometers to micrometers on gold substrates. The perfluoroalkyl chains range in length (n) from 4 to 10 carbons, representing 67-83% of the molecular weight of the repeat unit. The growth rate of the film depends on the perfluoroalkyl chain length, with longer chains enabling faster surface-initiated growth and greater ultimate thicknesses. These films exhibit hydrophobic and oleophobic surface properties and provide effective barriers to the diffusion of aqueous ions. The critical surface tensions of the films exhibit a minimum for a fluorocarbon chain of 8 (pNBF8) and range from 9 to 19 mN/m. The morphologies of the pNBFn films consist of densely packed 20-30 nm clusters that differ in the concentration of fluorocarbon chains in the outer few nanometers of the film.
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