1,721,039 research outputs found
Facing the Didactic Emergency During Covid-19 Pandemic in an Analytical Chemistry Laboratory
No full textThe active learning environment adopted in an undergraduate course of instrumental analysis was completely rethought and reshaped to accomplish the strict lockdown conditions during the most severe period of pandemic (from march 2020) when all the didactic activities (lessons and laboratory) were fully online and during the less severe condition of the following year, when a blended online learning approach allowed to attend in presence the lab activities but to frequent only online the class didactic activity. The instrumental analysis course has been since several years structured on a problem/project-based learning (PrPBL) cycle, consisting in a part of experimental project accomplished by the students, a subsequent laboratory activity, where the procedures defined by the students are applied to the specific problem to be solved, and a final restitution from each group to the whole class. The pandemic forced us to implement in the learning cycle both asynchronous and synchronous online strategy to keep the PrPBL approach and the active interaction between the students. The extensive use of simulated data and of breakthrough rooms (allowed in Teams® application) was found a highly effective way to reach satisfactory learning results, comparable with, and in some case better than, the ones obtain in conventional teaching mode. In this work we present how the online PrPBL approach was developed and applied to a lab experience concerning a conductimetric titration
Electrochemical characterisation of electrodes modified with a Co/Al hydrotalcite-like compound
No full textThe electrochemical behaviour of electrodes modified with a Co/Al-NO3 hydrotalcite-like compound was investigated by voltammetric techniques and electrochemical impedance spectroscopy in aqueous solution. The latter technique was used in order to study the electronic and ionic transport, both inside and on the surface of the material. The behaviour of the modified electrode was studied at different OH− concentrations (pH 11–12.8) and at different temperatures, with the aim to calculate the activation energies of the electronic conduction and charge-transfer processes.
The electronic conductivity of the bulk material is dependent on the CoIII/CoII ratio and results the limiting parameter of the overall redox process. The same result was previously obtained for the Ni based hydrotalcite, but the latter material showed a better electrical conductivity
Transient-doped organic electrochemical transistors working in current-enhancing mode as sensing devices for low concentration of oxygen dissolved in solution
Full text linkDissolved oxygen in cell culture media represents an interesting parameter worth monitoring, especially at very low concentrations. Indeed, cells grow faster and live longer in hypoxic conditions, and recent studies relate stronger tumor malignancy, recurrence, and progression with reduced oxygen levels. Standard techniques for dissolved oxygen evaluation rely either on optical investigations or on electrochemical methods. The former requires complex protocols and expensive instrumentations, while for the latter, the presence of a silver/silver chloride electrode hinders the device miniaturization and induces cytotoxic effects. In this work, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (Pedot:Pss)-based Organic Electrochemical Transistors (OECTs) are presented as dissolved oxygen sensors. The catalytic activity of the Pedot chains is exploited for the transduction since oxygen reduction reactions, occurring at the polymer/electrolyte interface, induce Pedot:Pss to switch from the less conductive neutral state (off) to the more conductive oxidized one (on). This transient-doping effect enhances OECT current output, which presents a high signal to noise ratio (i.e., >102-103). The transistor architecture allows for high output/input signal power amplification (i.e., >15 dB-22 dB) and excellent sensitivities [328 ± 11 mV/dec and -0.38 ± 0.02 mA/dec for transfer and Ids(t), respectively], together with a low detection limit (0.9 μM, which represents the 0.07% of oxygen partial pressure). Finally, the here reported OECT sensors are demonstrated to work also in a real-life complex biological environment. This work paves the way for reliable, real-time oxygen monitoring in in vitro cell cultures for various relevant applications, such as investigating the influence of hypoxia conditions on cell lines or tumors
An XPS investigation on glucose oxidase and Ni/Al hydrotalcite interaction
No full textIn this work, a Ni/Al hydrotalcite (HT) was used as glucose oxidase (GOx) immobilizer. Small-area and angle-resolved X-ray photoelectron spectra were recorded on HTs electrosynthesized on Pt in the absence and in the presence of GOx, and compared with those obtained for a Pt surface, modified with the electrosynthesized HT, on which a drop of GOx solution was deposited. The simultaneous electrodeposition of HT + GOx resulted in a compact deposit, thicker than the XPS sampling depth (>10 nm), that is not homogeneous in the lateral and in-depth composition. The presence of GOx can be deduced comparing the N1s spectra of HT and HT + GOx: in the latter, the N1s component at 400 eV binding energy (BE) is predominant whilst, depending on the analyzed point, a small or no contribution from the component at 407.2 eV, due to nitrate, is revealed. Angle-resolved XPS provides evidence on the in-depth composition of anions, cations and GOx. The results highlight the crucial role played by nickel in GOx immobilization. On the basis of the results, it can be suggested that enzyme activity is unevenly distributed and is localized in small areas, where Ni concentration is higher
Electrochemical characterization of self assembled monolayers on flexible electrodes
No full textSelf assembled assembled monolayers of amine- and carboxylic acid terminated thiols have been chemisorbed on gold electrodes deposited on flexible polyethylene terephthalate substrates. These devices, being flexible, low cost, and highly resistant could find application in several fields such as the design of implantable biomedical devices and disposable light-weight sensors.
Four different molecules have been investigated, namely cysteamine, 12-mercaptododecanoic acid, aminothiophenol, and 3-mercaptopropionic acid, each bearing either an amino or a carboxylic terminal group and different chain lengths. These molecules have been chosen since the SAM they can form could find application as such or constitute the basis for a further modification step. The modified surfaces have been characterized by electrochemical techniques and the surface pK(a) values of the terminal groups have been estimated by impedance titration
[Ni/Al-Cl]-based hydrotalcite electrodes as amperometric sensors: Preparation and electrochemical study
No full textA study has been carried out to develop electrochemical devices based on the hydrotalcite (HT) [Ni/Al-Cl] suitable for the amperometric determination of oxidisable species. The amperometric sensors have been tested on methanol, mannitol and glucose substrates. The measured signal is an electrocatalytic current due to the oxidation of Ni(II) centres present in the brucite layers of HT to Ni(III) or NI(IV). Different kinds of electrodes have been studied in terms of chemical and mechanical stability, lifetime, and simple regenerability of the surface. Cyclic voltammetry has been used to evaluate the electrochemical responses. The best performances have been achieved when HT particles were entrapped into an epoxy resin and the electrical contact was guaranteed by a carbon-based material. (C) 2001 Elsevier Science Ltd. All rights reserved
Electrochemical characterisation of Ni/Al-X hydrotalcites and their electrocatalytic behaviour
No full textSome 'conductive' hydrotalcites containing nickel as divalent cation and Cl-, SO42- or CO32- as interlayer anion, have been synthesised and membranised with different types of polymeric matrices to modify glassy carbon electrodes. The mechanism responsible of the conductive properties has been deeply investigated by voltammetric techniques using both a stationary and a rotating disk electrode, demonstrating that the interlayer anion does not affect significantly the electrochemical behaviour of the material. The electrocatalytic properties have been also studied pointing out the key role of the steric hindrance of the oxidisable substrate. In particular, mono- and polyhydric compounds have been taken into account. As to the electrocatalytic efficiency, the nature of the interlayer anion and, hence, the dimension of the interlayer spacing, is important in determining the sensitivity of the measurement since it can affect the analyte diffusion inside the hydrotalcite structure. © 2002 Published by Elsevier Science Ltd
Organic-based sensor for chemical detection in aqueous solution
No full textWe present a flexible, pentacene-based field-effect device, for the detection of chemical species in aqueous solution. The sensor consists in a double-gate transistor, where the detection is achieved by exploiting the charge sensing capabilities of the floating-gate terminal. To provide the pH -sensitivity, the floating gate is functionalized with thioamine groups as such groups protonize proportionally to the concentration of H3O+ ions in solution. With respect to the existing organic-based devices for pH monitoring, our sensor does not require a counterelectrode and the organic semiconductor is not affected by the contact with the monitored solutio
Nickel hexacyanoferrate membrane as a coated wire cation-selective electrode
No full textNickel hexacyanoferrates containing alkali metal cations as counter ions were used to prepare ion-selective electrodes for potentiometric sensing of intercalated species in the coated wire electrode (CWE) configuration. All the electrodes developed display a quasi-Nernstian response towards potassium ion, whereas the highest sensitivity is generally achieved when Cs+ is the counter cation in the sensing material. The selectivity constants of the electrodes were calculated by the matched potential method considering K+ as the primary ion. The selectivity order is Cs+ > K+ > Na+ > Li+ and reflects the effective dimension of the hydrated cations
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