Highly-dispersed copper microparticles on the active gold substrate as an amperometric sensor for glucose

Abstract: A bimetallic electrode composed of copper microparticles dispersed onto a gold surface (Au/Cu) has been investigated as an amperometric sensor using glucose as a model compound. Such a sensing electrode has been prepared by electrochemical deposition of Cu-0 from 50 mM CU2+ and subsequent potential cycling in an alkaline medium. The morphology of the copper deposit has been examined by scanning electron microscopy. The effects of copper loading, scan rate, hydroxide concentration, and applied potential on the electrocatalytic oxidation of glucose have been also investigated. Long-term electrode stability, background current, sensitivity, and linear range of the Au/Cu electrode have been assessed for constant-potential amperometric detection (DC) at +0.550 and +0.350 V, and in pulsed-potential amperometric detection (PAD). When used as an amperometric sensor in the DC mode at an applied potential of +0.350 V, the bimetallic electrode yields a detection limit of 0.8 pmol glucose (S/N=3) with a linear dynamic range of four orders of magnitude. Comparable results have been obtained when the bimetallic sensing electrode was used in the DC mode at +0.550 V and in the PAD mode. Good mechanical stability under forced flow hydrodynamic conditions was also found upon changing the detection mode from DC to PAD and vice versa, making the multifunctional amperometric sensor very attractive for analytical applications in flowing streams. (C) 1997 Elsevier Science B.V

A new probe of Bonding states in Intermetallic compounds

Abstract: This paper reports an investigation of a set of Ti-Al-based alloys by X-ray photoelectron spectroscopy. A new method for interpretation of the X-ray photoelectron spectrum allows a peak-shape parameter kappa to be defined, which links the intrinsic energy loss,structure associated with a given line in the spectrum to atomic number. This parameter enables quantitative interpretation of steps in background intensity which are related to the number of final state configurations available to the photoexcited atom or ion. We have investigated the extent to which aluminium orbitals interact with the 3d transition metal structure of titanium by comparing the values of kappa for the pure metals with those for the titanium and aluminium peaks in the intermetallic compound. We conclude that this gives direct evidence for bond overlap in these alloys. The results on kappa were then compared with the Auger parameters which are also related to the relaxation process following the photoemission and therefore indicative of the charge transfer mechanism occurring between Al and Ti. In undertaking this study, which required the preparation of the intermetallic compounds for spectroscopic analysis, we have had to investigate various means of sample preparation. In particular we have developed a means by which the bulk metal structure can be exposed and transferred with minimal oxidation using an in situ milling device

An X-ray Photoelectron Study of Valence Charge in Transition Metal Aluminides

In an earlier paper we proposed a new method for interpretation of background structure in X-ray photoelectron (XP) spectra and showed that this could be used to study bonding states in intermetallic compounds using, as an example, a particular Ti—Al alloy. In this paper we have applied this method to study a set of aluminides: Me—Al alloys, where Me represents a transition metal: Ti, V, Fe, Ni or Nb. The method for background interpretation is based on a peak-shape parameter k, which links the intrinsic energy loss structure, associated with a given line in the XP spectrum, to the atomic number. This parameter is thus related to the number of final state configurations available to the photoexcited atom or ion and we show, now, how the value for aluminium varies across a series of compounds with the transition metals. The results for k are accompanied by measurement of the Auger parameters which may be indicative of the charge transfer occurring between Al and Me and thus are also influenced by the final state configuration. The approximate proportionality found between these two parameters gives confirmation that k may be a sensitive probe of the final state and bonding effects and confirms the extent to which aluminium orbitals interact with the 3d transition metal structure of vanadium, iron and nickel, and the 4d of Nb. This is in full accord with the results obtained from the TiAl alloy. Complementary information was obtained by comparing the values of k for the pure metals with those for the vanadium, iron, nickel, niobium and aluminium peaks in the intermetallic compound. XP spectra have been obtained from the alloys and these are also presented in the paper. As a result of this work it is concluded that the final state features of the spectra result from charge transfer between sp and sd valence bands

CsPbBr3 deposited by laser ablation: effects of post-growth aging, oxygen adsorption and annealing on film properties

All-inorganic perovskites are widely investigated as a new generation of materials thanks to their superior optoelectronic properties and better stability than hybrid organic-inorganic perovskites. In particular, cesium lead bromide (CsPbBr3) exhibits advantageous properties for numerous applicative fields (photovoltaics, light-emitting diodes, photodetectors, lasing, field effect transistors, and ionizing radiation detectors). The performance of CsPbBr3 being critically dependent on the deposition technique, proper understanding and optimization of the fabrication process are demanding. Despite the well-known potentiality of the Pulsed Laser Deposition (PLD) technique in depositing films with complex stoichiometry, a very limited number of literature studies report on the successful deposition of CsPbBr3 films by PLD. Recently, the authors disclosed the impact of the uneven masses of Cs, Pb, and Br on the film stoichiometry and guidelines to recover the desired composition. Herein, we exploit stoichiometric mechano-chemically synthesized targets to deposit, by nanosecond-PLD (lambda = 248 nm, tau = 20 ns, room temperature, fluence of 1 J/cm(2)), CsPbBr3 films to be studied following time aging, thermal heating and exposure to high relative humidity. Even in the presence of the characteristic absorption peak at similar to 520 nm, the freshly deposited film shows no photoluminescence. Photoluminescence is switched on by thermal annealing (at 250 and 350 degrees C) or after a few days (at least 15) of exposure to air and it persists over time. Films present interesting morphology evolution and oxygen adsorption following heating

Nuove frontiere nello studio della materia vivente: dalle opsine agli attameri.

Il trasferimento e l’integrazione di informazione fra discipline scientifiche molto diverse è sempre foriero di progresso. Questo seminario si propone di illustrare le caratteristiche della materia vivente, coniugando gli strumenti della fisica tradizionale con quelli della biologia e della chimica. Il fine è quello di aprire nuove strade, inventare nuove strategie e, nel far questo, da una parte si progredisce nella ricerca specifica, dall’altro si approda a visioni nuove, prospettive inesplorate che allargano gli orizzonti della scienza in generale

Multi-spectroscopic approach to explore the technological features of medieval gilded and enamelled glasses from Melfi (PZ)

Gilded and enamelled glasses of Islamic style, coming from a 13th century landfill in Melfi castle, a Swabian emperor Frederick II fortress, were subjected to a multi-techniques approach in order to explore the complex and very fascinating ancient production technology of gilding and enamelling on glass. Non-destructive μ-Raman spectroscopy was employed on the most important and well-preserved objects, optical (OM) and electron (SEM) microscopies were used to investigate the sections stratigraphy of tiny fragments sampled from the borders of the already damaged objects. In order to provide the chemical analyses of the bodies and the enamels, energy dispersive X-rays spectroscopy (EDS) and X-rays photoelectron spectroscopy (XPS) were also employed. The body of the objects proved to be made of silica-soda-lime glass, while the enamels of lead-rich glass (“soft enamels”) and coloured by lapis lazuli and cobalt for blue, hematite and minium for red, lead-tin yellow for green and calcium phosphate for white. The gilding was found to be applied on a red enamel basis. The presence of carbon inside the gildings and the detection of two different gold signals by XPS suggested the hypothesis of the use of the so-called “liquid gold”. This study gave thus an important contribution to the understanding of the production of this class of rare and precious objects, also confirming that the materials and technological procedures are consistent with the Islamic tradition, probably due to the presence of Islamic artisans at the court of Frederick II

Functionalization of gold screen printed electrodes with bacterial photosynthetic reaction centers by laser printing technology for mediatorless herbicide biosensing

The development of an amperometric biosensor for herbicide detection, using bacterial reaction centers (RC) as biorecognition element, is presented. RC immobilization on gold screen printed electrodes was achieved by LIFT, a powerful physisorption-based immobilization technique that enhances the intimate contact between the protein and the electrode surface. As a result, stable photocurrents driven by direct electron transfer at the donor side were observed, both in the presence and in the absence of a quinone substrate in solution. The addition of quinone UQ(0) increased the photocurrents, while the UQ(0)-free system showed higher sensitivity to the herbicide terbutryn, a model inhibitor, acting as photocurrent attenuator. In spite of its simple design, the performances achieved by our mediatorless device are comparable or superior to those reported for analogous RC-based photoelectrochemical cells, in terms of both terbutryn sensing and photocurrent generation

Stabilizing Wide Bandgap Triple-Halide Perovskite Alloy through Organic Gelators

Engineering the chemical composition of metal-halide perovskites via halide mixing allows a facile bandgap modulation but renders perovskite materials prone to photoinduced halide segregation. Triple-halide alloys containing Cl, I, and Br were recently reported as a means to stabilize Cs(y)FA(1-y)Pb(BrxI1-x)(3) perovskite under illumination. Herein, these triple-halide alloys are found to be intrinsically less stable with respect to the reference I-Br in ambient conditions. By exploiting the influence of low-molecular-weight organic gelators on the crystallization of the perovskite material, a triple-halide alloy with improved moisture tolerance and thermal stability at temperatures as high as 120 degrees C is demonstrated. The hydroxyl-terminated organic gelators are found to aggregate into nanoscale fibers and promote the gelation of the solvent inducing the formation of a 3D network, positively interfering with perovskite solidification. The addition of a tiny amount of organic gelators imparts a more compact morphology, higher crystallinity, and compositional stability to the resulting triple-halide polycrystalline films, making them more robust over time without compromising the photovoltaic performance. Overall, this approach offers a solution toward fabrication of active perovskite materials with higher energy gap and improved stability, making these triple-halide alloys truly exploitable in solar cells