Crystal Chemistry and Physical Properties of the Nonmagnetic Kondo Compound HfAs1.7Se0.2

Single crystals of HfAs_1.7Se_0.2 are grown by chemical transport reaction and their chemical composition characterized in detail by various analytical methods. Chemical analyses and crystal structure investigations by single‐crystal X‐ray diffraction as well as powder diffraction with synchrotron radiation reveal a tetragonal PbFCl structure type with strong disorder caused by a significant arsenic deficiency (As_0.9) on the 2a site and mixed occupancy of the 2c site (As_0.8Se_0.2). HfAs_1.7Se_0.2 is a diamagnetic metal which transforms into a superconducting state at T_c=0.52 K. Similar to other PbFCl‐type arsenide selenides, the title compound displays a magnetic‐field‐independent ?AT^1/2 term in the low‐temperature electrical resistivity. This unusual term presumably originates from the electron scattering of structural two‐level systems. According to the experimental results, HfAs1.7Se0.2 appears to be a rare example of a nonmagnetic Kondo material.     

Modified Electrodes with Switchable Selectivity for Cationic and Anionic Redox Species

The modified electrode functionalized with a mixed‐polymer brush composed of poly(2‐vinylpyridine) and polyacrylic acid tethered to the surface demonstrated switchable interfacial properties discriminating negatively and positively charged redox species. The switchable electrochemical process was characterized by differential pulse voltammetry and Faradaic impedance spectroscopy. The electrochemical system was discussed as a model of an electrochemical multiplexer with two chemical redox inputs, the pH input operating as the selecting signal and one electronic output signal readable by the impedance spectroscopy in the form of the interfacial resistance. The modified electrode represents a novel component for integration with biocatalytic and biocomputing systems aiming at biochemically and electronically controlled actuators.     

Simultaneous Determination of Cr(III) and Cr(VI) by Differential Pulse Voltammetry Using Modified Screen‐Printed Carbon Electrodes in Array Mode

A new procedure for the speciation of chromium by means of differential pulse voltammetry using screen‐printed carbon electrodes (SPCEs) has been proposed. Two different modified carbon working, a Ag/AgCl reference and a carbon counter screen‐printed electrodes have been connected in array mode for the simultaneous determination of Cr(III) and Cr(VI). Mercury films or gold nanoparticles have been ground onto the SPCEs in order to improve their selectivity to each chromium species. The quantification of the peak currents observed at ?1.25 V in Hg‐SPCE and ?0.1 V in AuNPs‐SPCE were carried out. The method has been applied to the speciation of chromium in waste water from a tannery factory.     

Development of an Electrochemical Immunoassay Based on the Use of an Eight‐Electrodes Screen‐Printed Array Coupled with Magnetic Beads for the Detection of Antimicrobial Sulfonamides in Honey

In this work an electrochemical immunoassay, based on a direct competitive assay, was developed using magnetic beads as solid phase and carbon screen‐printed arrays as transducers for the detection of sulfonamides in food matrices such as honey. Magnetic beads coated with protein A were modified by immobilisation of specific antibodies and then the competition between the target analyte and the corresponding analyte‐labelled with an enzyme was carried out; after the immunosensing step, beads were captured by a magnet onto the working surfaces of a screen‐printed eight‐electrodes array for a multiple electrochemical detection. Screen‐printed eight‐electrodes arrays were chosen as transducers due to the possibility to repeat multiple analysis and to test different samples simultaneously. Alkaline Phosphatase (AP) was used as enzyme label and Differential Pulse Voltammetry (DPV) as fast electrochemical technique. Calibration curves demonstrate that the developed electrochemical immunoassay was able to detect this class of drugs in standard solutions at low concentrations (ng/mL levels). The short incubation times (25 min) and the fast electrochemical measurement (10 sec) make of these systems a possible alternative to classic ELISA tests.     

Effect of Poly(3‐octylthiophene) Doping on the Attachment and Proliferation of Osteoblasts

The effect of doping P3OT with ferric chloride on the attachment and proliferation of MC3T3‐E1 osteoblasts is reported. Cell density and area correlated strongly with doping concentration: cells were larger and exhibited better spreading as doping increased. Cells cultured on undoped P3OT showed a decrease in proliferation between 24 and 48 h followed by a recovery after 72 h. However, this trend diminished with increasing doping concentration, and disappeared completely at the highest dopant level investigated. Analysis of cell‐cell spatial distributions suggested that contact inhibition of proliferation occurred similarly on both undoped and doped P3OT. From these results, FeCl₃‐doping had no significant deleterious effect on attachment or proliferation of osteoblasts in vitro.

     

Electrochemical Preparation,Characterization, and Electrocatalytic Properties of OsPtCl6 Film Electrodes Towards Reduction of NAD+, Chloroacetic Acids,and Nitrous Oxide

Stable electroactive mixed films of osmium oxide/hexachloroplatinate, osmium oxide and platinum have been deposited on different electrode materials by cycling the electrode potential repetitively in solution containing Os³⁺ and PtCl . The film growth of was monitored by using cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The cyclic voltammetric features of modified electrode in Os³⁺ solution resembles that of surface wave, and involves ions‐exchange with Os³⁺ ions present in the solution. Based on the SEM results the modifier was considered as one‐dimensional, mixed‐valent polymeric film, and stabilized by Os^3+/2+ counter ions. Finally, the electrocatalytic activity of the modified electrode was examined toward reduction of NAD⁺, chloroacetic acids and nitrous oxide.     

Room Temperature Ionic Liquids (RTILs) and Multiwalled Carbon Nanotubes (MWCNTs) as Modifiers for Improvement of Carbon Paste Ion Selective Electrode Response; A Comparison Study with PVC Membrane

Room temperature ionic liquids (RTILs), 1‐n‐butyl‐3‐methylimidazolium tetrafluoroborate, [bmim]BF₄, and multiwalled carbon nanotubes (MWCNTs) were used for improvement of a praseodymium carbon paste ion selective sensor response. [bmim]BF₄ can be a better binder than mineral oils. MWCNTs have a good conductivity which helps the transduction of the signal in carbon paste electrode. The characteristics of these electrodes as potentiometric sensors were evaluated and compared with PVC membrane sensor. The results indicate that potentiometric sensor constructed with ionic liquid shows an increase in performance in terms of Nernstian slope, selectivity, response time, and response stability compared to Pr(III) PVC membrane sensor.     

Metallic Free Carbon Nanotube Cluster Modified Screen Printed Electrodes for the Sensing of Nicotine in Artificial Saliva

We demonstrate that metallic free carbon nanotube cluster modified screen printed electrodes provide an advantageous sensing methodology for nicotine. The electrochemical oxidation of nicotine is possible at low potentials compared to other commercially available carbon electrodes. Using the carbon nanotube cluster modified screen printed electrodes a detection range of 10 to 1000 μM is possible with a limit of detection of 2 μM. The sensing protocol is shown to be viable in artificial saliva and is promising as a portable and rapid sensor for nicotine in oral fluid (saliva) in areas such as health/life insurance, instances where smoking is banned and also as a point of care test to help improve smoking quit rates.     

Light sensitivity and potential stability of electrically conducting polymers commonly used in solid contact ion-selective electrodes

The results of a systematic study of the light sensitivity and long-term potential stability (30 days) of poly(pyrrole) (PPy), poly(3-octylthiophene) (POT), poly(3,4-ethylenedioxythiophene) (PEDOT), poly(aniline) (PANI) and plasticised poly(vinyl chloride) (PVC) containing 20% (m/m) PANI are reported. Thin films were prepared either electrochemically or by the solution casting technique. This fundamental study is of importance because conducting polymers (CP) are commonly used as ion-to-electron transduction materials in all-solid-state solid contact ion-selective electrodes. The potential stability test done in 0.1 M KCl (pH 7.5) simulates the extreme situation when the CP-based SC becomes in direct contact with water. Films prepared of a nanodispersion of PANI showed both good potential stability and insensitivity to light even under illumination with very intensive light (>10⁵ lx). In contrary, it was observed that POT is very light-sensitive. Upon illumination with intensive light, the potential responses of POT films prepared by solution casting and electropolymerisation were 315 and 590 mV, respectively. A room light sensitivity of approximately −10 to −15 mV was observed for these films. The other CPs in this study were insensitive to room light (∼150 lx), but were light-sensitive under illumination with intensive light. The potential drift of PPy(Cl) is below −10 μV/h (3–30 days), whereas the other most stable CPs in this study had a slightly higher potential drift.     

Photoelectrochemical Studies of Gold Electrodes Chemically Modified with Single‐Walled Carbon Nanotubes

Seeing the light : An electrode is assembled by linking acid‐shortened single‐walled carbon nanotubes with carboxylic groups to a gold surface modified with a cysteamine monolayer. The electrode generates a photocurrent when illuminated with visible light in the presence of an electroactive species (see picture). With an appropriate applied potential the device behaves as a photodiode.