Roberto A. S. Luz

Nanomaterials for Biosensors and Implantable Biodevices

The study of biological recognition elements and their specific functions has enabled the development of a new class of electrochemical modified electrodes called biosensors. Since the development of the first biosensor almost 50 years ago, biosensors technology have experienced a considerable growth in terms of applicability and complexity of devices. In the last decade this growth has been accelerated due the utilization of electrodes-modified nanostructured materials in order to increase the power detection of specific molecules. Other important feature can be associated with the development of new methodologies for biomolecules immobilization. This includes the utilization of several biological molecules such as enzymes, nucleotides, antigens, DNA, aminoacids and many others for biosensing. Moreover, the utilization of these biological molecules in conjunction with nanostructured materials opens the possibility to develop several types of biosensors such as nanostructured and miniaturized devices and implantable biosensors for real time monitoring. Based on recent strategies focused on nanomaterials for electrochemical biosensors development, these topics has presented recent methodologies and tools used until nowadays and the prospects for the future in the area.

Modulation of the catalytic activity of porphyrins by lipid-and surfactant-containing nanostructures

The structural factors modulating porphyrin activity encompass pyrrole and equatorial ligands, as well as the central metal and the number and structure of their axial ligands. Of equal importance is the microenvironment provided by apoproteins, solvents and membranes. Porphyrins are often used to construct supramolecular structures with different applications. The modulation of activity of the porphyrins has been frequently achieved by mimicking nature, i.e., by the provision of different microenvironments for these molecules. The association of porphyrins to surfactant- and lipid-containing nanostructures has changed the activity of these compounds to mimic different enzymes such as SOD, cytochrome P450, peroxidases and others. In determined conditions, the reactive forms of the porphyrins are high-valence states of oxo-metal-πcations and oxo-metal produced by the reaction with peroxides and peracids. The modulation of porphyrin activity by surfactant- and lipid-containing nanostructures has also been achieved for hemeproteins, as the lipid nanostructures affect the conformation of proteins.

Organização supramolecular da ftalocianina de cobalto(II) e seu efeito na oxidação do aminoácido cisteína

The interest in the chemistry of cobalt (II) tetrasulfonated phthalocyanine (PcTsCo) comes mainly from its macrocycle-ligand structure combined with their special chemical characteristics, such as high solubility, well-defined redox reactions and remarkable optical absorption in the visible region. In this work, we use layer-by-layer technique in order to assemble CoTsPc and poly(allylaminehydrochloride) (PAH) in hybrid supramolecular system. The electronic spectroscopy and cyclic voltammetry techniques were utilized to study PAH/CoTsPc multilayers growth and the cysteine catalytic oxidation. PAH/CoTsPc showed high electrochemical stability and worthwhile to mention is the remarkable influence of supramolecular arrangement on the final redox properties of the system.

Highly stable magnetite modified with chitosan, ferrocene and enzyme for application in magneto-switchable bioelectrocatalysis

Magnetic fields have been used in Bioelectrochemistry to carry enzymes or redox mediators immobilized on magnetite (Fe3O4) to the electrodes surface, providing a switchable control of faradaic current from biocatalysis. In this work, it is reported an advance in the magnetic control of bioelectrochemical reactions, by construction of a system containing simultaneously a magnetic particle (for controlled driving), an enzyme (for biocatalysis) and a redox mediator (for mediation of electron transfer). The advance was attained by synthesis of a new material (Fe3O4-Chi-Fc/GOx) that consists of Fe3O4 particles modified with insoluble ferrocene (Fc) and chitosan (Chi) cross-linked with glucose oxidase (GOx). When this material was used in electrochemical studies, an increase of 70% was observed in the catalytic current of glucose oxidation when 0.24 T was applied perpendicularly to electrode plane. This is the first time that a control of the bioelectrocatalytic process was achieved using enzyme, mediator and magnetite in a unique system switched by a magnetic field.

Gold nanoparticle-mediated electron transfer of cytochrome c on a self-assembled surface

The presence of gold nanoparticles (AuNPs) at the protein/electrode interface has a significant impact on the electrodic microenvironment, and allows the optimization of the activity catalysis as well as electrochemical properties. Here, we report a novel and accurate methodology to observe AuNP mediated electron transfer mechanism from Cytochrome c (Cyt c) to a polycrystalline gold surface. Poly(allylamine hydrochloride) molecules (PAH) were used as spacers between Cyt c and the electrode surface, and the electron rate constant within the PAH layer was measured in the presence and absence of AuNPs. Based on cyclic voltammetric experiments and Marcus theory, a four-fold increase in the electron rate constant was observed in the presence of AuNPs, and the reorganization energy was estimated to be 0.49 eV. Furthermore, AuNPs decreased the effective distance between the redox center of Cyt c and the electrode surface by 20%. These results suggest that the electron transfer properties of Cyt c based protein electrodes are significantly enhanced in the presence of the AuNPs.

Biofuel Cells: Bioelectrochemistry Applied to the Generation of Green Electricity

Several studies published in the last decade have pointed to the use of enzymes and microorganisms in biocatalytic reactions to generate electricity. Enzymes and living organisms can be used in modified electrodes to build the so-called biofuel cells (BFCs). However, a deep understanding of the structure and biocatalytic properties after enzyme immobilization is still lacking because they are immobilized in the solid state and outside of their natural environment. Thus, based on biological molecules and nanostructure materials applied to BFCs, these current topics shall be reviewed here, and prospects for future development in these areas will be presented as well. Moreover, immobilization methodologies and enzyme stability systems that result in BFCs will also be presented. Finally, BFC power density and catalyst support will be widely discussed in this book chapter.