Anomalous Enhancement of Electrochemical Charge Transfer by a Ru Complex Ion Intercalator

We have found that the DNA intercalator [Ru­(bpy)2DPPZ]2+ (bpy = 2,2′-bipyridine; DPPZ = dipyrido­[3,2-a:2′,3′-c]­phenazine) causes an anomalous increase in charge transfer in electrochemical impedance spectroscopy (EIS). With a carbonaceous electrode and a 1 mM hexacyanoferrate (1 mM [Fe­(CN)6]3– and 1 mM [Fe­(CN)6]4–) mediator, we found that adding only 1 μM [Ru­(bpy)2DPPZ]2+ greatly enhanced the charge transfer between the electrode and hexacyanoferrate mediator, independently of other electrolytes or buffer components. The effect started with a one millionth amount of hexacyanoferrate. Since [Ru­(bpy)2DPPZ]2+ can intercalate with dsDNA, the effect is highly applicable for dsDNA detection or PCR monitoring. With further developments of this method, EIS sensors not requiring specific electrode modifications should be possible

Random Number Generation by a Two-Dimensional Crystal of Protein Molecules

We discuss 2D and binary self-assemblies of protein molecules using apo-ferritin and holo-ferritin, which have identical outer-shell structures but different inner structures. The assemblies do not show any phase separation but form 2D monomolecular-layer crystals. Statistical analyses showed a random molecular distribution in the crystal where the molar ratio was conserved as it was in the solution. This molecular pattern is readily prepared, but it is neither reproducible nor predictable and hence can be used as a nanometer-scale cryptographic device or an identification tag

Fabrication of ZnSe Nanoparticles in the Apoferritin Cavity by Designing a Slow Chemical Reaction System

Zinc selenide nanoparticles (ZnSe NPs) were synthesized in the cavity of the cage-shaped protein apoferritin by designing a slow chemical reaction system, which employs tetraaminezinc ion and selenourea. The chemical synthesis of ZnSe NPs was realized in a spatially selective manner from an aqueous solution, and ZnSe cores were formed in almost all apoferritin cavities with little bulk precipitation. Three factors are found to be important for ZnSe NP synthesis in the apoferritin cavity:  (1) the threefold channel, which selectively introduces zinc ion into the apoferritin cavity, (2) the apoferritin internal potential, which favors zinc ion accumulation in the cavity, and (3) the nucleation site, which nucleates ZnSe inside the cavity. The characterization of the synthesized ZnSe NPs by X-ray powder diffraction and energy-dispersive spectrometry revealed that the synthesized NPs are a collection of cubic ZnSe polycrystals. It was shown that the 500 °C heat treatment for 1 h under nitrogen gas transformed the polycrystalline ZnSe core into a single crystal, and single-crystal ZnSe NPs free of protein were obtained

In Aqua Structuralization of a Three-Dimensional Configuration Using Biomolecules

Ferritin nanoparticles ornamented with a Ti-binding peptide are versatile nanoscaled building blocks. Their specific binding ability is strong enough to position them on nanopatterned Ti regions on a Pt substrate. Furthermore, the peptides mineralization activity enables the formation of titania on the outer side of the particle, and the particle's inner nanospaces can serve as a carrier for inorganic nanodots. Making use of all these properties, here we show controlled in aqua fabrication of three-dimensional nanoscale structures. The X−Y positioning obeyed the specific binding of the peptide, while fabrication in the Z-dimension entailed stepwise formation of titania and ferritin layers by alternately applying the binding and mineralization abilities of the Ti-binding peptide. This method paves the way for in aqua fabrication of nanodevices having complicated structures and functions

Fabrication of Aligned Magnetic Nanoparticles Using Tobamoviruses

We used genetically modified tube-shaped tobamoviruses to produce 3 nm aligned magnetic nanoparticles. Amino acid residues facing the central channel of the virus were modified to increase the number of nucleation sites. Energy dispersive X-ray spectroscopy and superconducting quantum interference device analysis suggest that the particles consisted of Co−Pt alloy. The use of tobamovirus mutants is a promising approach to making a variety of components that can be applied to fabricate nanometer-scaled electronic devices

CNT Binding Peptides Selected by the Phage Display Method

Using the M13 phage display method, 236 amino acid sequences (peptide aptamers) that could specifically adsorb to CNTs were selected. These peptide aptamers had abundant hydrophobic amino acids and evenly dispersed charged amino acids. The hydrophobic amino acids were postulated to contribute to CNT adsorption, while the charged amino acids contribute to their aqueous solubility. The frequency of proline amino acids, which causes the amino acid main chain bending, was slightly higher than in nature, suggesting that some conformational constraint might be required. Four peptide aptamers with a high frequency of occurrence in the selected sequences were further studied. Hydrophobicity scores were periodic along the amino acid sequence. 3D structure predictions by PEP-FOLD3 indicated that these aptamers would take a helical structure with hydrophobic amino acid residues on one side, suggesting that the aptamers bind hydrophobically to the CNT. The adsorption of these four aptamers to the carbon electrode was confirmed by electrochemical impedance spectroscopy, which demonstrated the effectiveness of the phage display method. At the same time, it was shown that even for selected peptides, the adsorption performance varied, and verification was needed

Synthesis of CoPt and FePt₃ Nanowires Using the Central Channel of Tobacco Mosaic Virus as a Biotemplate

Synthesis of CoPt and FePt3 Nanowires Using the Central Channel of Tobacco Mosaic Virus as a Biotemplat

Functionalizable Organic Nanochannels Based on Lipid Nanotubes: Encapsulation and Nanofluidic Behavior of Biomacromolecules

The amino groups on the inner surface of the nanotube that was self-assembled from unsymmetrical bolaamphiphile, N-(2-aminoethyl)-N‘-(β-d-glucopyranosyl)-icosanediamide 1, were modified covalently with a fluorescence donor dye. This functionalization of the nanotube inner surfaces has allowed us to achieve the construction of an optical recognition system for the encapsulation of guest molecules. Fluorescence resonance energy transfer (FRET) from the fluorescence donor located on the inner surface to the ferritin labeled with fluorescence acceptor enabled us to visualize the encapsulation and nanofluidic features of the ferritin in the nanochannel shaped by the hollow cylinder structure. By using this system, we were able to estimate the diffusion constants for ferritin and gold nanoparticles in the organic nanochannels on the basis of lipid nanotubes. We have also demonstrated that the size and surface charge of the nanochannel strongly affect the encapsulation behavior toward the biomacromolecules such as DNA and spherical proteins

Electrochemical Impedimetric Real-Time Polymerase Chain Reactions Using Anomalous Charge Transfer Enhancement

We developed a new electrochemical impedimetric method for the real-time detection of polymerase chain reactions (PCR) based on our recent discovery that the DNA intercalator, [Ru­(bpy)2DPPZ]2+, anomalously enhances charge transfer between redox mediators, K4[Fe­(CN)6]/K3[Fe­(CN)6], and a carbon electrode. Three mM [Fe­(CN)6]3–/4– and 5 μM [Ru­(bpy)2DPPZ]2+ were added to the PCR solution, and electrochemical impedance spectroscopy (EIS) measurements were performed at each elongation heat cycle. The charge transfer resistance (Rct) was initially low due to the presence of [Ru­(bpy)2DPPZ]2+ in the solution. As PCR progressed, amplicon dsDNA was produced exponentially, and intercalated [Ru­(bpy)2DPPZ]2+ ions, which could be detected as a steep Rct, increased at specific heat cycles depending on the amount of template DNA. The Rct increase per heat cycle, ΔRct, showed a peak at the same heat cycle as optical detection, proving that PCR can be accurately monitored in real time by impedance measurement. This simple method will enable a cost-effective and portable PCR device

Critical Amino Acid Residues for the Specific Binding of the Ti-Recognizing Recombinant Ferritin with Oxide Surfaces of Titanium and Silicon

The interactions of ferritins fused with a Ti-recognizing peptide (RKLPDA) and their mutants with titanium oxide substrates were explored with an atomic force microscope (AFM). The amino acid sequence of the peptide was systematically modified to elucidate the role of each amino acid residue in the specific interaction. Force measurements revealed a clear correlation among the sequences in the N-terminal domain of ferritin, surface potentials, and long-range electrostatic interactions. Measurements of adhesion forces clearly revealed that hydrogen bonds take part in the specific binding as well as the electrostatic interaction between charged residues and surface charges of Ti oxides. Moreover, our results indicated that not only the charged and polar residues but also a neutral residue (proline) govern the strength of the specific binding, with the order of the residues also being significant. These results demonstrate that the local structure of the peptide governs the special arrangement of charged residues and strongly affects the strength of the bindings