Ana C. Tavares

Electrochemical impedance immunosensor based on gold nanoparticles-protein G for the detection of cancer marker epidermal growth factor receptor in human plasma and brain tissue.

A sensitive label-free impedimetric immunosensor for the detection of cancer biomarker epidermal growth factor receptor (EGFR) was developed with a limit of detection as low as 0.34 pg mL(-1) in PBS and 0.88 pg mL(-1) in human plasma. The gold nanoparticles were electrodeposited to modify the gold surface and to increase the electrochemical active area by a factor of approximately 3, i.e. by 68%. Protein G was used as scaffold for well oriented EGFR antibodies immobilization. Under optimal experimental parameters, the impedance changes were used for the detection of EGFR with a wide dynamic range of 1 pg mL(-1)-1 μg mL(-1). The immunosensor showed an excellent reproducibility and selectivity against biomarkers, murine double minute 2 and platelet derived growth factor receptor. The excellent analytical performance of the EGFR immunosensor in terms of selectivity, sensitivity and low detection limit might be attributed to the synergetic effect between the Au nanoparticles and the protein G scaffold. The matrix effect from mouse brain tissue homogenate was also studied and the immunosensor showed excellent recoveries ranging from 98.3% to 115% and RSD of 1.55-6.17. Finally, our developed strategy could open new avenues for clinical screening and prognosis of tumors.

Ni+RuO2 co-deposited electrodes for hydrogen evolution

RuO2 particles were co-deposited with Ni onto smooth or rough Ni supports from Ni baths of different compositions, expediently named Watts, Chloride and Thiosulfate baths. Electrodeposits were characterised by means of cyclic voltammetry, X-ray diffraction, SEM and EDX. The electrocatalytic activity of the layers for H2 evolution from alkaline solutions was determined by quasi-stationary polarisation curves. Activity increases with RuO2 in the Ni deposit up to a limiting value. Sulphur is co-deposited from thiosulfate baths, and its presence clashes with the effect of RuO2. Co-deposition from Watts baths proved the most effective. Stability tests showed that Ni+RuO2 co-deposits are stable under condition of constant as well as intermittent electrolysis. However, in the latter case stability turned out to depend on the content of RuO2 in the layer.

Effect of the partial replacement of Ni or Co by Cu on the electrocatalytic activity of the NiCo2O4 spinel oxide

Abstract A comparative study of Ni 1− x Cu x Co 2 O 4 and NiCo 2− y Cu y O 4 systems derived from the NiCo 2 O 4 spinel oxide by the partial replacement of Ni or Co by Cu respectively, has been performed. The two systems have been prepared by thermal decomposition of aqueous nitrate solutions, on nickel supports, at 623 K. The influence of the amount of copper on the electrode performance towards the oxygen evolution process is studied. Steady state measurements followed by Tafel analysis has been done. The electrochemical results have been correlated with the surface composition of the electrodes by means of X-ray photoelectron spectroscopy.

Label-free impedimetric immunosensor for ultrasensitive detection of cancer marker Murine double minute 2 in brain tissue.

The detection of cancer biomarkers is as important tool for the diagnosis and prognosis of cancer such as brain cancer. Murine double minute 2 (MDM2) has been widely studied as prognostic marker for brain tumor. Here we describe development of a new sensitive label free impedimetric immunosensor for the detection of MDM2 based on cysteamine self assembled monolayers on a clean polycrystalline Au electrode surface. The amine-modified electrodes were further functionalized with antibody using homobifunctional 1,4-phenylene diisothiocyanate (PDITC) linker. The assembly processes of the immunosensor had been monitored with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques using Fe(CN)(6)(3-/4-) solution as redox probe. The impedance changes upon binding of MDM2 protein to the sensor surface was utilized for the detection of MDM2. The increase in relative electron-transfer resistance (ΔR/R(0)%) values was linearly proportional to the concentration of tumor marker MDM2 in the wide dynamic range of 1pg/ml-1μg/ml. The limit of detection was 0.29pg/ml in phosphate buffer saline (PBS) and 1.3pg/ml in mouse brain tissue homogenate, respectively. The immunosensor showed a good performance in comparison with ELISA for the analysis of the MDM2 in the cancerous mouse brain tissue homogenates. Moreover, the immunosensor had a good selectivity against epidermal growth factor receptor (EGFR) protein, long-storage stability and reproducibility. It might be become a promising assay for clinical diagnosis and early detection of tumors.

Selection and Identification of DNA Aptamers against Okadaic Acid for Biosensing Application

This work describes the selection and identification of DNA aptamers that bind with high affinity and specificity to okadaic acid (OA), a lipophilic marine biotoxin that accumulates in shellfish. The aptamers selected using systematic evolution of ligands by exponential enrichment (SELEX) exhibited dissociation constants in the nanomolar range. The aptamer with the highest affinity was then used for the fabrication of a label-free electrochemical biosensor for okadaic acid detection. The aptamer was first immobilized on the gold electrode by a self-assembly approach through Au-S interaction. The binding of okadaic acid to the aptamer immobilized on the electrode surface induces an alteration of the aptamer conformation causing a significant decrease in the electron-transfer resistance monitored by electrochemical impedance spectroscopy. The aptasensor showed a linear range for the concentrations of OA between 100 pg/mL and 60 ng/mL with a detection limit of 70 pg/mL. The dissociation constant of okadaic acid with the aptamer immobilized on the electrode surface showed good agreement with that determined using fluorescence assay in solution. Moreover, the aptasensor did not show cross-reactivity toward toxins with structures similar to okadaic acid such as dinophysis toxin-1 and 2 (DTX-1, DTX-2). Further biosensing applications of the selected aptamers are expected to offer promising alternatives to the traditional analytical and immunological methods for OA detection.

XPS and voltammetric studies on Ni1-xCuxCo2O4 spinel oxide electrodes

Abstract Spinel oxide electrodes of Ni 1− x Cu x Co 2 O 4 (0.00≤ x ≤0.75) layers were prepared by thermal decomposition of the corresponding nitrate solutions on Ni mesh at 350°C. The surface analysis was carried out by XPS and shows that the oxides surface is rich in copper for all the studied compositions, and when x ≤0.10 an enrichment in nickel was also observed. The surface electrochemical properties were studied by cyclic voltammetry and correlated with XPS data.

A facile synthesis of Fe3O4 nanoparticles/graphene for high-performance lithium/sodium-ion batteries

In this study, a facile, simple, and inexpensive co-precipitation method is used to fabricate diamond-like Fe3O4 nanoparticle/graphene composites for use as lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) electrode materials. In our synthesis, high-temperature treatment and complicated procedures and apparatus are avoided. Physical characterizations reveal that the as-prepared product is composed of a large fraction of diamond-like Fe3O4 nanoparticles uniformly distributed on thin graphene nanosheets. Compared to bare Fe3O4 and most of the previously reported studies, the as-obtained Fe3O4/graphene composite exhibits greatly enhanced electrochemical properties for both LIBs and SIBs, including excellent reversible capacity, superior cyclability and good rate performance. Specifically, when tested as an anode for LIBs, the Fe3O4/graphene composite shows specific capacity of 1430 mA h g−1 after 100 cycles at 200 mA g−1. The initial discharge capacity tested in SIBs is 855 mA h g−1, and after 40 cycles, the discharge capacity stabilizes at ∼210 mA h g−1 for 250 cycles. The excellent performance can be attributed to the greatly improved electrical conductivity, large surface area and excellent stability of the electrode material.

Nano-engineered electro-responsive drug delivery systems

Stimuli-responsive drug delivery systems can release therapeutic agents when actuated by an appropriate stimulus, whether endogenous or exogenous. Interestingly, exogenous stimuli are completely dissociated from the patients physiology and can be precisely controlled externally in magnitude, in space, and in time. They can therefore constitute more reproducible means of controlling the release of therapeutics from appropriately responsive delivery systems. One stimulus which has long attracted attention is the application of an electric potential, and most electro-responsive drug delivery systems reported to date have been based on intrinsically conducting polymers. These systems, however, are limited by slow drug release and low drug loading. These challenges are currently driving the development of new electro-responsive delivery systems with higher responsiveness and drug loading, by implementing concepts of nano-engineering into their structure. This review will focus on this exciting and most recent direction taken in this field by first discussing drug delivery from electro-responsive films containing nano-scaled features, and then nanoscale dispersed/colloidal electro-responsive drug delivery systems, such as nanoparticles, micelles, and vesicular structures.

Oxygen evolution on NiCo2−xRhxO4 spinel system

The oxygen evolution process on NiCo2−xRhxO4 (0 ⩽ x ⩽ 0.5) spinel system was studied in 5 mol dm−3 KOH aqueous solution at room temperature. The electrodes electrocatalytical activity was analysed in terms of Tafel slope, exchange current density and overpotential values. The experimental results show that the performance of the electrodes is significantly improved by the presence of rhodium, mainly due to the increase of surface and electroactive areas.

Zn-TiO2 and ZnNi-TiO2 Nanocomposite Coatings: Corrosion Behaviour

This work presents the corrosion behaviour of the as-prepared of Zn-TiO2 and ZnNi-TiO2 films in neutral Na2SO4 solution and a first attempt to correlate with their composition, morphology and structure. The films were prepared by galvanostatic pulse method onto steel electrodes, at room temperature. The X-ray diffraction study revealed that the ZnNi alloy consists of a homogenous Ni5Zn21 phase and that the preferred crystallographic orientation of Zn deposits changes in the presence of TiO2. The SEM results show that the morphology of the metallic coating is function of the metal phase composition and become more porous in the presence of 1.5 wt% TiO2.The corrosion parameters for the nanocomposite coatings were compared with those of pure Zn and ZnNi electrodeposits, and the ZnNi-TiO2 nanocomposite coating shows the less cathodic corrosion potential.