Evan A. Gizzie

Enhanced Photocurrents of Photosystem I Films on p‐Doped Silicon

Tuning the Fermi energy of silicon through doping leads to alignment of silicon bands with the redox active sites of photosystem I. Integrating photosystem I films with p-doped silicon results in the highest reported photocurrent enhancement for a biohybrid electrode based on photosystem I.

Photosystem I-polyaniline/TiO2 solid-state solar cells: simple devices for biohybrid solar energy conversion

Novel Photosystem I (PSI) based solid-state solar cells were prepared by directly electropolymerizing polyaniline (PAni) in the presence of solubilized PSI on a TiO2 anode. These devices feature a unique bio-derived, photoactive composite layer for efficient charge separation and charge transfer from protein to electrode. This work introduces a new artificial photosynthesis platform for scalable and sustainable solar energy conversion.

Photosystem I Protein Films at Electrode Surfaces for Solar Energy Conversion

Over the course of a few billion years, nature has developed extraordinary nanomaterials for the efficient conversion of solar energy into chemical energy. One of these materials, photosystem I (PSI), functions as a photodiode capable of generating a charge separation with nearly perfect quantum efficiency. Because of the favorable properties and natural abundance of PSI, researchers around the world have begun to study how this protein complex can be integrated into modern solar energy conversion devices. This feature article describes some of the recent materials and methods that have led to dramatic improvements (over several orders of magnitude) in the photocurrents and photovoltages of biohybrid electrodes based on PSI, with an emphasis on the research activities in our laboratory.

Electrochemical Preparation of Photosystem I−Polyaniline Composite Films for Biohybrid Solar Energy Conversion

In this work, we report for the first time the entrapment of the biomolecular supercomplex Photosystem I (PSI) within a conductive polymer network of polyaniline via electrochemical copolymerization. Composite polymer-protein films were prepared on gold electrodes through potentiostatic electropolymerization from a single aqueous solution containing both aniline and PSI. This study demonstrates the controllable integration of large membrane proteins into rapidly prepared composite films, the entrapment of such proteins was observed through photoelectrochemical analysis. PSIs unique function as a highly efficient biomolecular photodiode generated a significant enhancement in photocurrent generation for the PSI-loaded polyaniline films, compared to pristine polyaniline films, and dropcast PSI films. A comprehensive study was then performed to separately evaluate film thickness and PSI concentration in the initial polymerization solution and their effects on the net photocurrent of this novel material. The best performing composite films were prepared with 0.1 μM PSI in the polymerization solution and deposited to a film thickness of 185 nm, resulting in an average photocurrent density of 5.7 μA cm(-2) with an efficiency of 0.005%. This photocurrent output represents an enhancement greater than 2-fold over bare polyaniline films and 200-fold over a traditional PSI multilayer film of comparable thickness.

Photoactive films of photosystem I on transparent reduced graphene oxide electrodes.

Photosystem I (PSI) is a photoactive electron-transport protein found in plants that participates in the process of photosynthesis. Because of PSIs abundance in nature and its efficiency with charge transfer and separation, there is a great interest in applying the protein in photoactive electrodes. Here, we developed a completely organic, transparent, conductive electrode using reduced graphene oxide (RGO) on which a multilayer of PSI could be deposited. The resulting photoactive electrode demonstrated current densities comparable to that of a gold electrode modified with a multilayer film of PSI and significantly higher than that of a graphene electrode modified with a monolayer film of PSI. The relatively large photocurrents produced by integrating PSI with RGO and using an opaque, organic mediator can be applied to the facile production of more economic solar energy conversion devices.

Construction of a Semiconductor–Biological Interface for Solar Energy Conversion: p-Doped Silicon/Photosystem I/Zinc Oxide

The interface between photoactive biological materials with two distinct semiconducting electrodes is challenging both to develop and analyze. Building off of our previous work using films of photosystem I (PSI) on p-doped silicon, we have deposited a crystalline zinc oxide (ZnO) anode using confined-plume chemical deposition (CPCD). We demonstrate the ability of CPCD to deposit crystalline ZnO without damage to the PSI biomaterial. Using electrochemical techniques, we were able to probe this complex semiconductor-biological interface. Finally, as a proof of concept, a solid-state photovoltaic device consisting of p-doped silicon, PSI, ZnO, and ITO was constructed and evaluated.

Electrochemical Detection of 2,4,6-Trinitrotoluene at Colloidal Gold Nanoparticle Film Assemblies

This work investigates citrate-capped, colloidal gold nanoparticle (AuNP) film assemblies of varying particle sizes (5–50 nm) adsorbed to bulk Au substrates to serve as platform electrochemical sensors to simultaneously detect and reduce TNT to 2,4,6-triaminotoluene (TAT) in solution. The high surface area-to-volume ratio of colloidal AuNPs offers advantages in electrocatalysis and enhanced signal transduction, while the facile immobilization onto a variety of substrates provides an adaptable and reproducible platform technology. In order to validate these AuNP film assemblies as platform sensors, square wave voltammetry is performed to enhance TNT sensitivity and optimize the signal transduction of TNT reduction. The highest sensitivity of TNT reduction is observed on 15 nm AuNP films (high nanomolar limits of detection). It is hypothesized that the 15 nm AuNP film assemblies store charge more efficiently because of their large dielectric constant compared to AuNP films of alternative sizes. It is also observed that upon assembly of the 5, 15, and 30 nm AuNPs, TNT reduction begins at more positive potentials compared to bulk Au and organic monolayer films, suggesting that these films exhibit electrocatalytic properties. The onset reduction potentials for 5, 15, and 30 nm AuNP assemblies were calculated and undergo 70 mV shifts to more positive potentials in comparison to bulk Au and organic monolayer control electrodes.