Everson T.S.G. da Silva

Simple on-plastic/paper inkjet-printed solid-state Ag/AgCl pseudoreference electrode.

A miniaturized, disposable, and low cost Ag/AgCl pseudoreference electrode based on inkjet printing has been developed. Silver ink was printed and chlorinated with bleach solution. The reference electrodes obtained in this work showed good reproducibility and stability during at least 30 min continuous measurement and even after 30 days storage without special care. Moreover, the strategy used in this work can be useful for large scale production of a solid-state Ag/AgCl pseudoreference electrode with different designs and sizes, facilitating the coupling with different electrical/electrochemical microsensors and biosensors.

Direct laser writing of micro-supercapacitors on thick graphite oxide films and their electrochemical properties in different liquid inorganic electrolytes

In this article we demonstrate a simple approach to fabricate interdigitated in-plane electrodes for flexible micro-supercapacitors (MSCs). A nanosecond ultraviolet laser treatment is used to reduce and pattern the electrodes on thick graphite oxide (GO) freestanding films. These laser-treated regions obtained by direct writing provide the conducting channels for electrons in the capacitors. The electrochemical performance of the MSCs was evaluated in the presence of two different electrolytes and they exhibit characteristics of nearly electrical double layer capacitors. The MSCs have areal capacitances as 2.40, 2.23 and 1.62μF/cm2 for NaOH, Na2SO4 and KCl electrolytes respectively, for measurements performed at the scan rate of 50mV/s. They retain ∼93.1% of their initial capacitances after 3500 cycles (scan rate=80mV/s) in NaOH electrolyte. The proposed laser treatment approach enables facile and fast fabrication of flexible MSCs without the need for tedious processing methods such as photolithographic micro-patterning and deposition of porous carbon or metallic current collectors.

Microwave-assisted synthesis of palladium nanoparticles intercalated nitrogen doped reduced graphene oxide and their electrocatalytic activity for direct-ethanol fuel cells

Palladium nanoparticles decorated reduced graphene oxide (Pd-rGO) and palladium nanoparticles intercalated inside nitrogen doped reduced graphene oxide (Pd-NrGO) hybrids have been synthesized by applying a very simple, fast and economic route using microwave-assisted in-situ reduction and exfoliation method. The Pd-NrGO hybrids materials show good activity as catalyst for ethanol electro oxidation for direct ethanol fuel cells (DEFCs) as compared to Pd-rGO hybrids. The enhanced direct ethanol fuel cell can serve as alternative to fossil fuels because it is renewable and environmentally-friendly with a high energy conversion efficiency and low pollutant emission. As proof of concept, the electrocatalytic activity of Pd-NrGO hybrid material was accessed by cyclic voltammetry in presence of ethanol to evaluate its applicability in direct-ethanol fuel cells (DEFCs). The Pd-NrGO catalyst presented higher electro active surface area (∼6.3 m2 g-1) for ethanol electro-oxidation when compared to Pd-rGO hybrids (∼3.7 m2 g-1). Despite the smaller catalytic activity of Pd-NrGO, which was attributed to the lower exfoliation rate of this material in relation to the Pd-rGO, Pd-NrGO showed to be very promising and its catalytic activity can be further improved by tuning the synthesis parameters to increase the exfoliation rate.

Insight into the Electro-Oxidation Mechanism of Glucose and Other Carbohydrates by CuO-Based Electrodes

In this work, a new hypothesis for the electrocatalytic behavior of CuO electrodes is presented. Different from the established mechanism, here we discuss why CuIII species do not participate in the oxidation mechanism of carbohydrates. We show that hydroxyl ion adsorption and the semiconductive properties of the material play a more significant role in this process. The relationship between the flat band potential and the potential that begin oxidation suggests that the concentration of vacancies in the charge region acts upon the reactivity of the adsorbed hydroxyl ions through a partial charge transfer reaction. In the presence of carbohydrate molecules, the electron transfer is facilitated and involves the transfer of electrons from the adsorbed hydroxyl ions to the CuO film. This mechanism is fundamentally relevant since it helps the understanding of several experimental misleads. The results can also lead to obtaining better catalysts, since improvements in the material should focus on enhancing the semiconductive properties rather than the CuII/CuIII redox transition. The results shed light on different aspects of carbohydrate molecules oxidation that could lead to novel applications and possibly a better description of other semiconductor mechanisms in electrocatalysis.

A novel approach for electroanalytical determinations employing discharge of pseudocapacitor by electroactive species

In this paper, we introduce a novel approach for the detection of electroactive analytes by using oxidant species accumulated in pseudocapacitors surface. We demonstrated that pseudocapacitors can be quickly discharged when in contact with electroactive species. Thus, the variation of potential can be monitored during the discharging process and correlated with the analyte concentration. Based on this, two electroanalytical methods were proposed: continuous discharging detection and pulsed discharging detection. As a proof of concept, these methods were employed for glucose, fructose and sucrose detection using an ion chromatograph containing an electrochemical detector. Copper|cupric oxide in alkaline medium was used as the pseudocapacitive system. The obtained results proved to be very promising and the analytical curves showed good linearity in both methods. In addition, this novel approach for the detection of saccharides based on potential variation as a result of the discharging of the pseudocapacitor in contact with the analyte is very attractive because it does not require current reading. Therefore, our approach can be applied to other pseudocapacitive systems, opening new possibilities for several electroanalytical applications.

Corrigendum to “A novel approach for electroanalytical determinations employing discharge of pseudocapacitor by electroactive species” [Analytica Chimica Acta 1006 (2018) 1–9]

The purpose of this Corrigendum is to cite and comment on an important reference that brings some support to the ideas developed in this paper and should be chronologically inserted into the history of advances in this area.

Microemulsions as an alternative approach for analytical determination of graphene oxide's reduction degree

A novel method for quantitative determination of reduction degree of graphene oxide (GO) that combines simplicity and rapidity with analytical performance is presented. This approach relies on the effect of the analyte to the thermodinamic stabilization of microemulsions (MEs). Such phenomenon was expressed by the minimum volume fraction of amphipile required (in this case, the analyte of interest GO) to form ME.

CHAPTER 2:Innovative Tools with Miniaturized Devices for Food Biosensing

Screening for biological and chemical contaminants and monitoring of nutrients are some of the crucial challenges for quality assessment of food and consumer safety. Although conventional techniques provide high specificity and selectivity, these methods are normally time consuming, expensive, need trained staff to carry out the tests in a centralized laboratory, and are not always compatible with all the stages of food production and the distribution chain. To overcome those limitations, a lot of effort has been made recently to develop simple, low-cost, and sensitive miniaturized devices. Thus, in this chapter we present some of the aspects of miniaturized systems used in food biosensing, from the construction of these platforms to application in food analysis, as well as the perspective and future directions of these technologies.