Isacco Gualandi

Electrocatalytic oxidation of salicylic acid by a cobalt hydrotalcite-like compound modified Pt electrode

In this paper a study of the electrocatalytic oxidation of salicylic acid (SA) at a Pt electrode coated with a Co/Al hydrotalcite-like compound (Co/Al HTLC coated-Pt) film is presented. The voltammetric behaviour of the modified electrode in 0.1M NaOH shows two different redox couples: Co(II)/Co(III) and Co(III)/Co(IV). The electrocatalysis occurs at the same potential of the latter couple, showing that Co(IV) centers act as the oxidant. The CV investigation demonstrates that the process is controlled both by mass and charge transfer and that the Co(IV) centers involved in the oxidation are two for each SA molecule. The estimated value of the catalytic constant is 4×10(4) M(-1) s(-1). The determination of salicylic acid was performed both by DPV and chronoamperometry. The linearity ranges and the LOD values resulted 1×10(-5) to 5×10(-4), 5×10(-7) to 1×10(-4), 6×10(-6) and 2×10(-7) M, respectively. The Co/Al HTLC electrode has been used for SA determination in BAYER Aspirina® and the obtained results are consistent with an independent HPLC analysis.

Physical and Electrochemical Properties of PEDOT:PSS as a Tool for Controlling Cell Growth

UNLABELLED Conducting polymers are promising materials for tissue engineering applications, since they can both provide a biocompatible scaffold for physical support of living cells, and transmit electrical and mechanical stimuli thanks to their electrical conductivity and reversible doping. In this work, thin films of one of the most promising materials for bioelectronics applications, poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) ( PEDOT PSS), are prepared using two different techniques, spin coating and electrochemical polymerization, and their oxidation state is subsequently changed electrochemically with the application of an external bias. The electrochemical properties of these different types of PEDOT PSS are studied through cyclic voltammetry and spectrophotometry to assess the effectiveness of the oxidation process and its stability over time. Their surface physical properties and their dependence on the redox state of PEDOT PSS are investigated using atomic force microscopy (AFM), water contact angle goniometry and sheet resistance measurements. Finally, human glioblastoma multiforme cells (T98G) and primary human dermal fibroblasts (hDF) are cultured on PEDOT PSS films with different oxidation states, finding that the effect of the substrate on the cell growth rate is strongly cell-dependent: T98G growth is enhanced by the reduced samples, while hDF growth is more effective only on the oxidized substrates that show a strong chemical interaction with the cell culture medium.

Textile Organic Electrochemical Transistors as a Platform for Wearable Biosensors

The development of wearable chemical sensors is receiving a great deal of attention in view of non-invasive and continuous monitoring of physiological parameters in healthcare applications. This paper describes the development of a fully textile, wearable chemical sensor based on an organic electrochemical transistor (OECT) entirely made of conductive polymer (PEDOT:PSS). The active polymer patterns are deposited into the fabric by screen printing processes, thus allowing the device to actually “disappear” into it. We demonstrate the reliability of the proposed textile OECTs as a platform for developing chemical sensors capable to detect in real-time various redox active molecules (adrenaline, dopamine and ascorbic acid), by assessing their performance in two different experimental contexts: i) ideal operation conditions (i.e. totally dipped in an electrolyte solution); ii) real-life operation conditions (i.e. by sequentially adding few drops of electrolyte solution onto only one side of the textile sensor). The OECTs response has also been measured in artificial sweat, assessing how these sensors can be reliably used for the detection of biomarkers in body fluids. Finally, the very low operating potentials (<1 V) and absorbed power (~10−4 W) make the here described textile OECTs very appealing for portable and wearable applications.

Selective detection of dopamine with an all PEDOT:PSS Organic Electrochemical Transistor.

An all PEDOT:PSS Organic Electrochemical Transistor (OECT) has been developed and used for the selective detection of dopamine (DA) in the presence of interfering compounds (ascorbic acid, AA and uric acid, UA). The selective response has been implemented using a potentiodynamic approach, by varying the operating gate voltage and the scan rate. The trans-conductance curves allow to obtain a linear calibration plot for AA, UA and DA and to separate the redox waves associated to each compound; for this purpose, the scan rate is an important parameter to achieve a good resolution. The sensitivities and limits of detection obtained with the OECT have been compared with those obtained by potential step amperometric techniques (cyclic voltammetry and differential pulse voltammetry), employing a PEDOT:PSS working electrode: our results prove that the all-PEDOT:PSS OECT sensitivities and limits of detection are comparable or even better than those obtained by DPV, a technique that employs a sophisticate potential wave and read-out system in order to maximize the performance of electrochemical sensors and that can hardly be considered a viable readout method in practical applications.

A simple all-PEDOT:PSS electrochemical transistor for ascorbic acid sensing

An ascorbic acid (AA) sensor was developed by employing an organic electrochemical transistor (OECT) based only on PEDOT:PSS as a conductive material. The device was prepared by spin coating using the CLEVIOS™ PH 1000 suspension (PEDOT:PSS) masking the gate and the channel areas with tape. The device was electrically characterized while the doping level of the PEDOT:PSS in the channel was controlled using both the gate electrode and the potentiostat. It was demonstrated that the current that flows in channel (Id) is controlled by the concentration of oxidized sites in the examined potential range. AA reacts with the conductive polymer leading to the extraction of charge carriers from the channel, and thus resulting in a decrease of the absolute value of Id. It was observed that Id linearly depends on the logarithm of the AA concentration between 10-6 and 10-3 M. The OECT response to AA was studied by varying the gate voltage or the PEDOT:PSS thickness. The performance of the device for optimized conditions shows a limit of detection equal to 10-8 M and a sensitivity of 4.5 ± 0.1 × 10-6 A decade-1.

A new electrochemical sensor for OH radicals detection

A new, cheap modified electrode for indirect detection of OH radical is described. A glassy carbon (GC) electrode was modified with a polyphenol film prepared by oxidative potentiostatic electropolymerization of 0.05 M phenol in 1M H2SO4. The film having a thickness of ~10nm perfectly covered the GC surface and inhibited the charge transfer of many redox species. The degradation of the polyphenol film, that was induced by OH radicals generated by Fenton reaction or by H2O2 photolysis, is the analytical signal and it was evaluated by cyclic voltammetry and chronoamperometry using the redox probe Ru(NH3)6(3+). Some simulations of the kinetics of the reactions occurring in the solution bulk and near the electrode surface were carried out to fully understand the processes that lead to the analytical signal. The modified electrode was used to evaluate the performances of different TiO2-based photocatalysts and the results were successfully compared with those obtained from a traditional HPLC method that is based on the determination of the hydroxylation products of salicylic acid.

ANALYTICAL PROFILING OF SELECTED ANTIOXIDANTS AND TOTAL ANTIOXIDANT CAPACITY OF GOJI (LYCIUM SPP.) BERRIES

&NA; Goji berries and derived products represent a relevant source of micronutrients, most of which are natural antioxidants and contribute to the high nutritional quality of these fruits. Three brands of dried goji berries have been analysed by a multidisciplinary approach to get an insight into both their content of selected antioxidants and their antioxidant capacity (AC). The former goal has been achieved by developing a liquid chromatographic method coupled to mass spectrometry and combined to a fast solid phase extraction. Several significant representative antioxidant compounds belonging to the following classes: flavonoids, flavan‐3‐ols, phenolic acids, amino acids and derivatives, and carotenoids have been taken into account. Quercetin and rutin were found to be the predominant flavonoids, chlorogenic acid was the most abundant phenolic acid and zeaxanthin was the major carotenoid. The AC of the goji berries has been evaluated by four analytical methods in order to estimate the contributions of different reactions involved in radicals scavenging. In particular, AC has been determined using 3 standardised methods (DPPH, ABTS, ORAC) and a recently proposed electrochemical method, which measures the scavenging activity of antioxidants towards OH radicals generated both by hydrogen peroxide photolysis and the Fenton reaction. The results obtained from chemical composition and antioxidant capacity assays confirm the high nutritional and commercial value of goji berries and highlight that the three brands do not exhibit significant differences. Graphical abstract Figure. No caption available. HighlightsThe nutritional features of goji berries were assessed.An original SPE‐LC–MS/MS method was developed and validated to determine 23 antioxidants.Goji berries antioxidant activity was tested by using multiple antioxidant assay strategies.Modified electrochemical sensor detecting radicals by degradation of a polyphenol film deposited on a glassy carbon electrode was implemented.A relationship between antioxidant capacity and content of antioxidants has been investigated.

Carbazole-terpyridine donor–acceptor luminophores

With the aim to combine two versatile molecular units that are widely utilized in materials and coordination chemistry, bischromophoric electron donor–acceptor carbazole–terpyridine systems (Cbz–Tpy) have been synthesized and characterized. The connecting bridge between the two moieties is constituted by phenylene (1), methylene phenylene (2) and ethynylene phenylene (3), which allow tuning of the intercomponent electronic interactions. Electrochemical studies evidence that oxidation and reduction processes occur on the Cbz and Tpy units, respectively, suggesting the possibility of internal charge transfer states located at about 3.10 eV, which is confirmed by photophysical investigations. The absorption spectra of 1 and 3 show a tail above 300 nm, indicating that these conjugated systems exhibit low-energy transitions with charge-transfer character, as confirmed by theoretical studies. At 298 K, 1–3 show a complex pattern of fluorescence profiles as a function of solvent (toluene, dichloromethane, acetonitrile), often with double emissions attributed to transitions localized on individual chromophores or associated to internal charge-transfer processes. The variability of the spectral position affords multiple colours, including white (e.g.3 in acetonitrile). Definitive rationalization and assignment of transitions of 1–3 is obtained through singlet and triplet luminescence spectra at 77 K and by means of DFT and TD-DFT methods using the hybrid functional PBE0 and the long range corrected functional CAM-B3LYP with the polarizable continuum model. This work opens the route to versatile materials based on the Tpy–Cbz motif exhibiting luminescence all across the visible spectral region that can be controlled through electronic conjugation, solvent polarity, temperature, functionalization and cation binding.

Role of Fe in the oxidation of methanol electrocatalyzed by Ni based layered double hydroxides: X-ray spectroscopic and electrochemical studies

Ni/Al and Ni/Fe layered double hydroxides (LDHs) were electrosynthesized on Pt electrodes to be used as catalysts for the development of methanol fuel cells. The electrochemical characterization and the electrocatalytic activity of the two LDHs towards methanol electro-oxidation in alkaline conditions were investigated. Furthermore, the role of Fe on the electronic and structural properties of the LDHs was investigated performing X-ray Absorption Spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). By the means of these techniques the materials were studied just electrosynthesized and after potentiostatic oxidation. The percentage of Ni active sites in the Ni/Fe LDH was higher than that of Ni/Al LDH, leading to a more efficient catalytic effect towards methanol oxidation in terms of current recorded at any potential value. Furthermore, methanol oxidation occurred at a lower potential for the same current density in the case of Ni/Fe LDH. The electrocatalytic performance displayed by the Ni/Fe LDH suggested the occurrence of a synergic effect between Ni and Fe sites, even if Fe is not directly involved in the redox process, and this evidence was confirmed by XAS and XPS experiments.

Electrodeposition of PEDOT perchlorate as an alternative route to PEDOT:PSS for the development of bulk heterojunction solar cells

Bulk heterojunction (BHJ) solar cells were fabricated employing different poly(3,4-ethylenedioxythiophene) (PEDOT) buffers: one deposited by electrochemical potentiostatic synthesis (perchlorate as counterion) and the other by casting a commercial polymer (polystyrene sulfonate, PSS, as counterion) on indium tin oxide (ITO) electrodes. The experimental conditions to electrosynthesize the PEDOT film and control its thickness were successfully investigated. [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) was used as electron acceptor in the blend. As electron donor, either the regioregular poly(3-hexylthiophene) (P3HT) or a polythiophene copolymer, functionalized with a porphyrin derivative to improve the absorption of the layer in the visible range, was employed. The morphologies of the PEDOT and the photoactive layers were extensively investigated by atomic force microscopy. The performances of all devices were tested evaluating the power conversion efficiencies which resulted comparable when either PEDOT:ClO4 or PEDOT:PSS was used as buffer layer. That proves electrochemical deposition of PEDOT can represent a good alternative to casting for the production of solar cells, since it is less expensive and permits an excellent control of the layer thickness.