Redox reaction characteristics of ferritin-immobilized onto poly(l-lysine)-modified indium oxide electrodes

Fluorescent Phthalocyanine Assembly Distinguishes Chiral Isomers of Different Types of Amino Acids and Sugars

The functions of some natural supramolecular architectures, such as ribosomes, are dependent on the recognition of different types of chiral biomolecules. However, the recognition of different types of chiral molecules (multiobject chiral recognition), such as amino acids and sugars, by independent and identically artificial supramolecular assembly, was rarely achieved. In this article, simple amphiphilic achiral phthalocyanine was found to form supramolecular chiral assemblies with charged water-soluble polymers upon host-guest interactions at the air/water interface. Among these systems, one identical phthalocyanine/poly(l-lysine) assembly not only can distinguish enantiomers of different amino acids but also can recognize several epimers of monose. The chiral recognitions were achieved by comparing either the steady-state fluorescence intensity or fluorescence quenching rate of phthalocyanine/poly(l-lysine) assemblies, before and after interaction with different small chiral molecules. It was demonstrated that the interactions between poly(l-lysine) and different small chiral molecules could change the aggregation of phthalocyanines. And the sensitivity of fluorescence and the excellent multiobject chiral recognition properties of the phthalocyanine/poly(l-lysine) assembly are dependent on the subtle molecular packing mode and the cooperation of different noncovalent interactions.

Organic field-effect transistor memory devices using discrete ferritin nanoparticle-based gate dielectrics

Organic field-effect transistor (OFET) memory devices made using highly stable iron-storage protein nanoparticle (NP) multilayers and pentacene semiconductor materials are introduced. These transistor memory devices have nonvolatile memory properties that cause reversible shifts in the threshold voltage (Vth ) as a result of charge trapping and detrapping in the protein NP (i.e., the ferritin NP with a ferrihydrite phosphate core) gate dielectric layers rather than the metallic NP layers employed in conventional OFET memory devices. The protein NP-based OFET memory devices exhibit good programmable memory properties, namely, large memory window ΔVth (greater than 20 V), a fast switching speed (10 μs), high ON/OFF current ratio (above 10(4)), and good electrical reliability. The memory performance of the devices is significantly enhanced by molecular-level manipulation of the protein NP layers, and various biomaterials with heme Fe(III) /Fe(II) redox couples similar to a ferrihydrite phosphate core are also employed as charge storage dielectrics. Furthermore, when these protein NP multilayers are deposited onto poly(ethylene naphthalate) substrates coated with an indium tin oxide gate electrode and a 50-nm-thick high-k Al2 O3 gate dielectric layer, the approach is effectively extended to flexible protein transistor memory devices that have good electrical performance within a range of low operating voltages (<10 V) and reliable mechanical bending stability.

Electrically bistable properties of layer-by-layer assembled multilayers based on protein nanoparticles

Electrochemical properties of redox proteins, which can cause the reversible changes in the resistance according to their redox reactions in solution, are of the fundamental and practical importance in bioelectrochemical applications. These redox properties often depend on the chemical activity of transition metal ions as cofactors within the active sites of proteins. Here, we demonstrate for the first time that the reversible resistance changes in dried protein films based on ferritin nanoparticles can be caused by the externally applied voltage as a result of charge trap/release of Fe(III)/Fe(II) redox couples. We also show that one ferritin nanoparticle of about 12 nm size can be operated as a nanoscale-memory device, and furthermore the layer-by-layer assembled protein multilayer devices can be extended to bioinspired electronics with adjustable memory performance via molecular level manipulation.

The Mössbauer and magnetic properties of ferritin cores

BACKGROUND

Mössbauer and magnetization measurements, singly or in combination, extract detailed information on the microscopic or internal magnetism of iron-based materials and their macroscopic or bulk magnetization. The combination of the two techniques affords a powerful investigatory probe into spin relaxation processes of nanosize magnetic systems. The ferritin core constitutes a paradigm of such nano-magnetic system where Mössbauer and magnetization studies have been broadly combined in order to elucidate its composition, the initial steps of iron nucleation and biomineralization, particle growth and core-size distribution. In vivo produced and in vitro reconstituted wild-type and variant ferritins have been extensively studied in order to elucidate structure/function correlations and ferritin's role in iron overloading or neurodegenerative disorders.

SCOPE OF REVIEW

Studies on the initial stages of iron biomineralization, biomimetic synthetic analogues and ferrous ion retention within the ferritin core are presented. The dynamical magnetic properties of ferritin by Mössbauer and magnetization measurements are critically reviewed. The focus is on experiments that reveal the internal magnetic structure of the ferritin core. Novel magnetic measurements on individual ferritin molecules via AFM and nanoSQUID investigations are also mentioned.

MAJOR CONCLUSIONS

A complex two-phase spin system is revealed due to finite-size effects and non-compensated spins at the surface of the anti-ferromagnetic ferritin core. Below the blocking temperature surface spins participate in relaxation processes much faster than those associated with collective magnetic excitations of interior spins.

GENERAL SIGNIFICANCE

The studies reviewed contribute uniquely to the elucidation of the spin-structure and spin-dynamics of anti-ferromagnetic nanolattices and their possible applications to nano/bio-technology.