Non-native Co-, Mn-, and Ti-oxyhydroxide nanocrystals in ferritin for high efficiency solar energy conversion

Protein-Nanoparticle Complex Structure Determination by Cryo-Electron Microscopy

Methods that allow the study of the structure of proteins in complex with nanomaterials promise to enhance our understanding of how biological molecules interface with inorganic materials. We used single-particle cryo-electron microscopy (cryo-EM) to demonstrate the potential for cryo-EM analysis to reveal structural details of protein-nanoparticle complexes. Two protein-nanomaterial complexes, namely, GroEL bound to platinum nanoparticles (GroEL-PtNP) and ferritin bound to an iron oxide nanoparticle, were used as model samples. For the GroEL-PtNP complex, a final reconstruction was obtained to 3.93 Å, which allowed us to fit the atomic model of GroEL into the resulting map. This sets the stage for future work and improvements on the use of cryo-EM for the study of protein-nanomaterial complexes.

Ferritin-Based Single-Electron Devices

We report on the fabrication of single-electron devices based on horse-spleen ferritin particles. At low temperatures the current vs. voltage characteristics are stable, enabling the acquisition of reproducible data that establishes the Coulomb blockade as the main transport mechanism through them. Excellent agreement between the experimental data and the Coulomb blockade theory is demonstrated. Single-electron charge transport in ferritin, thus, establishes a route for further characterization of their, e.g., magnetic, properties down to the single-particle level, with prospects for electronic and medical applications.

Permanganate-based synthesis of manganese oxide nanoparticles in ferritin

This paper investigates the comproportionation reaction of Mn^II with [Formula: see text] as a route for manganese oxide nanoparticle synthesis in the protein ferritin. We report that [Formula: see text] serves as the electron acceptor and reacts with Mn^II in the presence of apoferritin to form manganese oxide cores inside the protein shell. Manganese loading into ferritin was studied under acidic, neutral, and basic conditions and the ratios of Mn^II and permanganate were varied at each pH. The manganese-containing ferritin samples were characterized by transmission electron microscopy, UV/Vis absorption, and by measuring the band gap energies for each sample. Manganese cores were deposited inside ferritin under both the acidic and basic conditions. All resulting manganese ferritin samples were found to be indirect band gap materials with band gap energies ranging from 1.01 to 1.34 eV. An increased UV/Vis absorption around 370 nm was observed for samples formed under acidic conditions, suggestive of MnO₂ formation inside ferritin.

Tuning Ferritin's band gap through mixed metal oxide nanoparticle formation

This study uses the formation of a mixed metal oxide inside ferritin to tune the band gap energy of the ferritin mineral. The mixed metal oxide is composed of both Co and Mn, and is formed by reacting aqueous Co²⁺ with [Formula: see text] in the presence of apoferritin. Altering the ratio between the two reactants allowed for controlled tuning of the band gap energies. All minerals formed were indirect band gap materials, with indirect band gap energies ranging from 0.52 to 1.30 eV. The direct transitions were also measured, with energy values ranging from 2.71 to 3.11 eV. Tuning the band gap energies of these samples changes the wavelengths absorbed by each mineral, increasing ferritin's potential in solar-energy harvesting. Additionally, the success of using [Formula: see text] in ferritin mineral formation opens the possibility for new mixed metal oxide cores inside ferritin.