Marcelo Nakamura

Conduction and photoelectrochemical properties of monomeric and electropolymerized tetraruthenated porphyrin films

The influence of the preparation method on the structure, conduction and photoelectrochemical properties of monomeric and polymeric tetraruthenated porphyrin films on ITO glass and nanocrystalline TiO2 has been investigated. The films were characterized by STM, MAC mode SFM, cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and combined electro-/photoelectrochemical techniques. The electronic diffusion coefficient D(e)C(m)2 of the films differed by three to four orders of magnitude depending on the procedure employed for the deposition process. The photoelectrochemical properties were evaluated either: by depositing the films directly on transparent ITO electrodes, under an applied bias potential and presence of O2 as electron acceptor; or by depositing the porphyrin material on nanocrystalline TiO2 in a Grätzel-type cell. In the first case the porphyrin films exhibited a typical p-type semiconductor behavior described by a Schottky junction model, while in the second the films behaved as a sensitizer of an n-type semiconductor. The photoelectrochemical properties of the porphyrin films and their performance as sensitizer in Grätzel-type cells were found to be strongly dependent on the conductivity and packing characteristics of the material. Semi-empirical calculations were performed by modified MM2 and ZINDO/S methods, in order to simulate the packing and electronic structures of the tetraruthenated porphyrin.

Hyperspectral dark-field microscopy of gold nanodisks

The light scattering properties of hexagonal and triangular gold nanodisks were investigated by means of Cytoviva hyperspectral dark-field microscopy, exploring the huge enhancement of the scattered waves associated with the surface plasmon resonance (SPR) effect. Thanks to the high resolution capability of the dark-field microscope, the SPR effect turned it possible to probe the individual nanoparticles directly from their hyperspectral images, extrapolating the classical optical resolution limit, and providing their corresponding extinction spectra. Blue spectral shifts involving the in-plane dipolar modes were observed for the hexagonal gold nanodisks in relation to the triangular ones, allowing their spectroscopic differentiation in the dark-field images.

Thermodynamic stabilization of nanostructured alpha-Ni1−xCox(OH)2 for high efficiency batteries and devices

The exceptional stability of FTO electrodes modified with Ni1−xCox(OH)2 in the alpha polymorphic phase was assigned to Co(II) substitution in the Ni(II) reticule, decreasing the basal plane distances and the average grain size, as confirmed by careful analyses of their X-ray diffractograms and thermal behavior as a function of the cobalt content. That phenomenon can be assigned to thermodynamic rather than kinetic factors, reflected by much higher dehydration/dehydroxilation temperatures, as expected for the stabilization of the mixed alpha-phase hydroxides in detriment of the oxides, opening real perspectives for application of alpha-Ni1−xCox(OH)2 in high efficiency batteries and devices.

Effect of cations/polycations on the efficiency of formation of a hybrid bilayer membrane that mimics the inner mitochondrial membrane

We aim in this study to characterize the effect of cations and polycations on the formation of hybrid bilayer membranes (HBMs), especially those that mimic the inner mitochondrial membrane (IMM), with a proper composition of phosphatidylcholine (PC), phosphatidylethanolamine (PE) and cardiolipin (CL) adsorbed on an alkanethiol monolayer. HBMs are versatile membrane mimetics that show promising results in sensor technology. Its formation depends on the fusion of vesicles on hydrophobic surfaces, a process that is not well understood at the molecular level. Our results showed to which extend and in which condition the presence of cations and polycations facilitate the formation of HBMs. The required time for lipid layer formation was reduced several times and the lipid layer reaches the expected thickness of 19.5±1.8 Ǻ, in contrast to only 2±1.5 Ǻ usually observed in the absence of cations. In the presence of specific concentrations of spermine and Ca(2+) the amount of adsorbed phospholipids on the thiol layer increased nearly 70% compared to that observed when Na(+) was used at concentrations 10 times higher. Divalent cations and polycations adsorb specifically on the lipid headgroups destabilizing the hydration forces, facilitating the process of vesicle fusion and formation of lipid monolayers. The concepts and conditions described in the manuscript will certainly help the development of the field of membrane biosensors.

Correction: Bovine glutamate dehydrogenase immobilization on magnetic nanoparticles: conformational changes and catalysis

Correction for ‘Bovine glutamate dehydrogenase immobilization on magnetic nanoparticles: conformational changes and catalysis’ by Caterina G. C. Marques Netto et al., RSC Adv., 2016, 6, 12977–12992.

Efficient electrochemical biosensors for ethynylestradiol based on the laccase enzyme supported on single walled carbon nanotubes decorated with nanocrystalline carbon quantum dots

A new hybrid nanomaterial based on single-walled carbon nanotubes incorporating nanocrystalline carbon quantum dots (SWCNT/C-dots) was developed and characterized by means of high resolution transmission electron microscopy, atomic force microscopy, Raman spectroscopy and electrochemical techniques. A glassy carbon electrode modified with SWCNT/C-dots exhibited an enhanced electrocatalytic response for 17α-ethynylestradiol, reflecting an increase of the active area of the hybrid material, promoted by the C-dots. However, the best activity was observed for laccase immobilized on CGE/SWCNT/C-dots, suggesting that the nanocrystalline C-dots improve the electron transport between the substrate, SWCNTs and the copper ions in the enzyme active sites. Such an association provided a very efficient bioelectrochemical sensor for the 17α-ethynylestradiol endocrine interfering agent, with a detection limit of 4.0 nmol L−1 in real samples.

Electrocatalytic activity in sensing of nitrite by films produced by electropolymerization of [Fe(Br-ph-tpy)2]2+

Abstract Nitrite is a preservative agent broadly used in the food industry. Its excessive consumption can cause several diseases including cancer. Thus, the development of sensors for nitrite is indispensable for strict nitrite level control in industrialized products and consequently for human welfare. Herein, is presented a study of the modification of electrodes by electropolymerization of [Fe(Br-ph-tpy)2](PF6)2 and its use as electroactive films in sensing of nitrite. The films were characterized by cyclic voltammetry, electrochemical quartz crystal microbalance, atomic-force microscopy and they were employed in electroanalytical experiments. The film obtained by electropolymerization exhibited some fibers dispersed on the substrate, reflecting the formation polymers on the surface of the electrode. The electrodes were further improved by drop casting a film of the complex on a glass carbon electrode, and then performing the electropolymerization of the complex. An increase in stability and a 41% enhancement of the electrocatalytical response for nitrite ions have been observed, in comparison with the bare electrode.