The development and utilization of new energy sources has been extensively studied in the world. Here, we report the development of flexible self-supported metal-free electrodes based on non-oxidized graphene multilayer (MLG) paper containing the lead iodide nanoparticles (PbI2-NPs). The PbI2-NPs was obtained and characterized by X-ray diffraction (XDR) and Raman spectroscopy. Supercapacitor containing the PbI2-NPs in MLG electrodes was fabricated by a simple method and characterized using atomic force microscopy (AFM), cyclic voltammetry (CV) and galvanostatic charge-discharge techniques. The results show a flexible supercapacitor fashion reaching capacitance values of 154 F/g with high prospects in electronic area. Energy and power densities obtained for the pure MLG supercapacitor were 3.40 µWh cm-2 and 0.73 mW cm-2, respectively. Regarding to PbI2-NPs/MLG capacitor the energy and power density obtained were 3.50 Wh kg-1 and 1.10 kW kg-1. The results herein presented open the possibility to new energy storage devices using PbI2-NPs and MLG flexible supercapacitor configuration.

The use of FTO samples as an extended gate field effect transistor biosensor is presented. The FTO samples were produced by spray pyrolysis technique. The cleaning process is shown to have a fundamental importance for the final sensitivity of the samples when multiple re-usage is adopted. The role of electrical resistivity and morphology of the films are investigated. The influence of pH sequence of measurements from 2 to 12 is presented. Both increasing and decreasing the pH values sequence of measurements are compared. Electrical, morphological, time evolution and electrochemical experiments are correlated in the main discussion. A physical-chemical model is presented to explain the main mechanisms of charge adsorption and desorption. Parameters not commonly reported in the literature are proven to have fundamental importance in sensors behavior and characterization.

Fluorine-doped tin oxide (SnO2:F) was investigate as the sensitive part of a pH sensor in the extended-gate field effect transistors (EGFET) device, which provided a linear response for pH range from 2 to 12; the sensitivity was 37 mV.pH-1 for experiments performed in absence of light. Neutral pH, leads to a transistor’s electric current remained practically constant, suggesting that pH 7 correspond to the isoelectric point of the SnO2:F samples. For acid and alkaline pH, the power law varied along time and stabilized at about 10 min. UV-vis light did not alter the results. The transistor’s electric current increased with the operating temperature increases. Once that small change in the operating conditions can alter the results, the physical mechanisms underlying the sensing process must be clearly understood. It is essential to monitor transient response and measurements conditions.

In this present study, the investigation about pH sensorial properties of WO3, via sol-gel, was evaluated by Voltammetry and Extended Gate Field Effect Transistor techniques. The X-ray diffractogram indicates the presence of a lamellar structure, d = 0.69 nm, resulting in WO3.2H2O. From Scanning Electron Microscopy of WO3.2H2O was observed a process corresponding to the delamination which consists of irregular stacking with rounded platelets. The WO3.2H2O was investigated as a pH sensor in the pH range 2–12, by the EGFET and Voltametry techniques presenting a sensitivity of 52 mV/pH and 60 mV/pH, respectively. These results can indicate that both Voltammetry and EGFET techniques present values close to the theoretical limit (59.2 mV/pH) as well as the material is a promising candidate for applications as a pH sensor and as disposable biosensor in the future.

O oscilador salino consiste em dois containers alinhados que são preenchidos por duas soluções distintas, exibindo oscilações de potencial elétrico quando liberado. Essas oscilações ocorrem devido à diferença de densidade apresentada pelos fluídos e promovem variação no fluxo de íons, levando a variações no potencial eletrico entre os reservatórios. Muitos sistemas biológicos podem ser entendidos por este modelo. Neste trabalho, o oscilador salino foi investigado usando soluções de sulfato de cobre, CuSO4, e cloreto de sódio, NaCl, alterando parâmetros como o diâmetro e comprimento do capilar, diâmetro do compartimento interno e quantidade de íons indesejados no reservatório principal (agua destilada e deionizada). O sistema mostrou-se muito útil para aulas de graduação.

The saline oscillator consists of two aligned containers that are filled in by a pair of different solutions, exhibiting electrical potential oscillations when released. These oscillations occur due to a difference of mass density presented by the fluids and they cause varying ions flow, leading to electrical potential variations between both reservoirs. Many biological systems can be understood by this model. In this work, the saline oscillator was investigated using copper sulfate, CuSO4, and sodium chloride, NaCl, solutions, changing parameters as the diameter and length of the capillary, diameter of the internal compartment and amount of unwanted ions in the main reservoir (distillated and deionized water). The system is shown to be very useful in undergraduate teaching classes.

The angiogenic properties of natural rubber were evaluated in this work. We have used the chick chorioallantoic membrane assay (CAM) as a model to investigate the influence of the heating on biological activity in rubber membranes and in non rubber fraction as well. Results showed that natural rubber membranes can induce vascularization. It was observed that angiogenesis activity was maximum when membranes were heated in temperatures between 65ºC and 85ºC, considering a range from 55ºC to 105ºC. The same behavior was observed for non rubber fraction and it indicates that this serum fraction may be responsible for angiogenesis. When infrared spectroscopy was performed in the cast films of non rubber fraction samples, as a function of heating, no structural changes was observed. The results obtained shown that natural rubber latex films produced by casting induce the vessel growth in the CAM and it can be considered as a potential biomaterial.