Green synthesis and characterization of gold-based anisotropic nanostructures using bimetallic nanoparticles as seeds.

Nanostructured noble metals are of great interest because of their tunable optical and electronic properties. However, the green synthesis of anisotropic nanostructures with a defined geometry by the systematic nanoassembly of particles into specific shape, size, and crystallographic facets still faces major challenges. The present work aimed to establish an environmentally friendly methodology for synthesizing gold-based anisotropic nanostructures using starch-capped bimetallic silver/gold nanoparticles as seeds and hydrogen peroxide as a reducing agent.

Nanostructured Titanium Dioxide Surfaces for Electrochemical Biosensing.

TiO2 electrochemical biosensors represent an option for biomolecules recognition associated with diseases, food or environmental contaminants, drug interactions and related topics. The relevance of TiO2 biosensors is due to the high selectivity and sensitivity that can be achieved. The development of electrochemical biosensors based on nanostructured TiO2 surfaces requires knowing the signal extracted from them and its relationship with the properties of the transducer, such as the crystalline phase, the roughness and the morphology of the TiO2 nanostructures. Using relevant literature published in the last decade, an overview of TiO2 based biosensors is here provided. First, the principal fabrication methods of nanostructured TiO2 surfaces are presented and their properties are briefly described. Secondly, the different detection techniques and representative examples of their applications are provided. Finally, the functionalization strategies with biomolecules are discussed. This work could contribute as a reference for the design of electrochemical biosensors based on nanostructured TiO2 surfaces, considering the detection technique and the experimental electrochemical conditions needed for a specific analyte.

Green synthesis of starch-capped Cu2O nanocubes and their application in the direct electrochemical detection of glucose.

Glucose determination is an essential procedure in different fields, used in clinical analysis for the prevention and monitoring of diabetes. In this work, modified carbon paste electrodes with Cu2O nanocubes (Cu2O NCs) were developed to test electrochemical glucose detection. The synthesis of the Cu2O NCs was achieved by a green method using starch as the capping agent, obtaining cubic-like morphologies and particle sizes from 227 to 123 nm with increasing amounts of the capping agent, as corroborated by electron microscopy analysis. Their crystalline structure and purity were determined by X-ray diffraction. The capability of starch as a capping agent was verified by Fourier-transform infrared spectroscopy, in which the presence of functional groups of this biopolymer in the Cu2O NCs were identified. The electrochemical response to glucose oxidation was determined by cyclic voltammetry, obtaining a linear response of the electrical current as a function of glucose concentration in the range 100-700 µM, with sensitivities from 85.6 to 238.8 µA mM-1 cm-2, depending on the amount of starch used in the synthesis of the Cu2O NCs.

A Magnetic Force Microscopy Study of Patterned T-Shaped Structures.

The study of patterned magnetic elements that can sustain more than one bit of the information is an important research line for developing new routes in magnetic storage and magnetic logic devices. Previous Monte Carlo studies of T-shaped magnetic nanostructures revealed the equilibrium and evolution of magnetic states that could be found as a result of the strong configurational anisotropy of these systems. In this work, for the first time, such behavior of T-shaped magnetic nanostructures is experimentally studied. In particular, T-shaped Co nanostructures have been produced by electron beam lithography using a single step lift-off process over Si substrates. The existence of four magnetic stable states has been proven by Magnetic Force Microscopy (MFM) and the analysis was complemented by Micromagnetic Simulations. The results confirmed that even for what can be considered large structures, with µm sizes, such four stable magnetic states can be achieved, and therefore two magnetic bits of information can be stored. We also addressed how to write and read those bits.

Magnetic properties of Fe3O4 antidot arrays synthesized by AFIR: atomic layer deposition, focused ion beam and thermal reduction.

Magnetic films of magnetite (Fe3O4) with controlled defects, so-called antidot arrays, were synthesized by a new technique called AFIR. AFIR consists of the deposition of a thin film by atomic layer deposition, the generation of square and hexagonal arrays of holes using focused ion beam milling, and the subsequent thermal reduction of the antidot arrays. Magnetic characterizations were carried out by magneto-optic Kerr effect measurements, showing the enhancement of the coercivity for the antidot arrays. AFIR opens a new route to manufacture ordered antidot arrays of magnetic oxides with variable lattice parameters.

Nanometer Scale Hard/Soft Bilayer Magnetic Antidots.

The effect of arrays of nanometer scale pores on the magnetic properties of thin films has been analyzed. Particularly, we investigated the influence of the out-of-plane magnetization component created by the nanopores on the in-plane magnetic behavior of patterned hard/soft magnetic thin films in antidot morphology. Its influence on the coupling in Co/Py bilayers of few tens of nanometer thick is compared for disordered and ordered antidots of 35-nm diameter. The combination of magneto-optical Kerr effect (MOKE) and first-order reversal curve (FORC) technique allows probing the effects of the induced perpendicular magnetization component on the bilayer magnetic behavior, while magnetic force microscopy (MFM) is used to image it. We found that ordered antidots yield a stronger out-of-plane component than disordered ones, influencing in a similar manner the hard layer global in-plane magnetic behavior if with a thin or without soft layer. However, its influence changes with a thicker soft layer, which may be an indication of a weaker coupling.