Structural reorganization of CuO/Cu2[Fe(CN)6] nanocomposite: characterization and electrocatalytic effect for the hydrogen peroxide reduction.

We report the study on the formation of the Cu2[Fe(CN)6] nanocomposite, which was obtained from copper oxide nanoparticles (CuO NPs) and Prussian Blue precursors. UV-vis analysis indicated that Cu2+ ions are released from CuO NPs, while Fe3+ ions are adsorbed onto the structure of CuO due to a sharp increase in zeta potential (from -30 to 0 mV) after the formation of the Cu2[Fe(CN)6]. Moreover, energy dispersive spectroscopy confirmed that Fe3+ ions are trapped in the CuO NPs structure. The CuO/Cu2[Fe(CN)6] nanocomposite exhibited the monoclinic and face-centered cubic phases that correspond to the CuO and Cu2[Fe(CN)6] components. Cyclic voltammetry (CV) for the Nanocomposite modified electrode revealed two well-defined redox couples at -0.073 ((E1/2)1) and 0.665 mV ((E1/2)2), attributed to the conversion of Cu2+ to Cu+ and CuFe2+ CuFe3+ pairs, respectively, which is similar to those in the CuO and Cu2[Fe(CN)6]components. Furthermore, the catalytic activity of the nanocomposite towards hydrogen was investigated through CV, where the reduction of H2O2 led to increased currents for the electrochemical process associated with the first redox pair. In contrast, for isolated materials (CuO NPs and Cu2[Fe(CN)6]), there was no significant increase in the current associated with either redox pair.

Diffusion of Oligonucleotides from within Iron-Cross-Linked, Polyelectrolyte-Modified Alginate Beads: A Model System for Drug Release.

An analytical model to describe diffusion of oligonucleotides from stable hydrogel beads is developed and experimentally verified. The synthesized alginate beads are Fe(3+) -cross-linked and polyelectrolyte-doped for uniformity and stability at physiological pH. Data on diffusion of oligonucleotides from inside the beads provide physical insights into the volume nature of the immobilization of a fraction of oligonucleotides due to polyelectrolyte cross-linking, that is, the absence of a surface-layer barrier in this case. Furthermore, the results suggest a new simple approach to measuring the diffusion coefficient of mobile oligonucleotide molecules inside hydrogels. The considered alginate beads provide a model for a well-defined component in drug-release systems and for the oligonucleotide-release transduction steps in drug-delivering and biocomputing applications. This is illustrated by destabilizing the beads with citrate, which induces full oligonucleotide release with nondiffusional kinetics.

New Hybrid Nanomaterial Based on Self-Assembly of Cyclodextrins and Cobalt Prussian Blue Analogue Nanocubes.

Supramolecular self-assembly has been demonstrated to be a useful approach to developing new functional nanomaterials. In this work, we used a cobalt Prussian blue analogue (PBA, Co3[Co(CN)6]2) compound and a ß-cyclodextrin (CD) macrocycle to develop a novel host-guest PBA-CD nanomaterial. The preparation of the functional magnetic material involved the self-assembly of CD molecules onto a PBA surface by a co-precipitation method. According to transmission electronic microscopy results, PBA-CD exhibited a polydisperse structure composed of 3D nanocubes with a mean edge length of 85 nm, which became shorter after CD incorporation. The supramolecular arrangement and structural, crystalline and thermal properties of the hybrid material were studied in detail by vibrational and electronic spectroscopies and X-ray diffraction. The cyclic voltammogram of the hybrid material in a 0.1 mol · L(-1) NaCl supporting electrolyte exhibited a quasi-reversible redox process, attributed to Co2+/Co3+ conversion, with an E1/2 value of 0.46 V (vs. SCE), with higher reversibility observed for the system in the presence of CD. The standard rate constants for PBA and PBA-CD were determined to be 0.07 and 0.13 s(-1), respectively, which suggests that the interaction between the nanocubes and CD at the supramolecular level improves electron transfer. We expect that the properties observed for the hybrid material make it a potential candidate for (bio)sensing designs with a desirable capability for drug delivery.

Evidence of short-range electron transfer of a redox enzyme on graphene oxide electrodes.

Direct electron transfer (DET) between redox enzymes and electrode surfaces is of growing interest and an important strategy in the development of biofuel cells and biosensors. Among the nanomaterials utilized at electrode/enzyme interfaces to enhance the electronic communication, graphene oxide (GO) has been identified as a highly promising candidate. It is postulated that GO layers decrease the distance between the flavin cofactor (FAD/FADH2) of the glucose oxidase enzyme (GOx) and the electrode surface, though experimental evidence concerning the distance dependence of the rate constant for heterogeneous electron-transfer (k(het)) has not yet been observed. In this work, we report the experimentally observed DET of the GOx enzyme adsorbed on flexible carbon fiber (FCF) electrodes modified with GO (FCF-GO), where the k(het) between GO and electroactive GOx has been measured at a structurally well-defined interface. The curves obtained from the Marcus theory were used to obtain k(het), by using the model proposed by Chidsey. In agreement with experimental data, this model proved to be useful to systematically probe the dependence of electron transfer rates on distance, in order to provide an empirical basis to understand the origin of interfacial DET between GO and GOx. We also demonstrate that the presence of GO at the enzyme/electrode interface diminishes the activation energy by decreasing the distance between the electrode surface and FAD/FADH2.