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.     

Novel Solid‐Contact Ion‐Selective Microelectrodes for Localized Potentiometric Measurements

The design and properties of novel type of solid‐contact ionophore‐based ion‐selective microelectrodes are reported. The microelectrode is based on an insulated needle‐shaped metallic wire with an exposed apex. The ion‐to‐electron transducer is made of poly(3‐octylthiophene‐2,5‐diyl) and placed between an ion‐selective membrane and the metallic tip. The ion‐selective polyvinyl chloride‐based membrane is deposited atop the layer of conductive polymer. The length of the ion‐sensitive part of the electrode is less than 10 μm. pH and Mg²⁺‐selective microelectrodes were constructed and tested showing stable potential and fast response that are essential properties for the practical application of microelectrodes for localized scanning measurements.     

A new Zn(II)-selective potentiometric sensor based on 4-tert-butylcalix[4]arene in PVC matrix

Poly(vinyl chloride) (PVC) based membranes containing 4-tert-butylcalix[4]arene (I) as an electroactive material alongwith anion excluder sodiumtetraphenylborate (NaTPB) and plasticizer tri-butylphosphate (TBP) have been developed to fabricate a new zinc-selective sensor. Out of various compositions, the best performance was exhibited by the membrane having I, NaTPB, TBP and PVC in the ratio 8:5:100:200 (w/w). The sensor works well in the concentration range 9.8 × 10⁻⁶ to 1.0 × 10⁻¹ mol dm⁻³ with a near-Nernstian slope of 28.0 ± 1.0 mV/decade of activity. The detection limit is down to 5.0 × 10⁻⁷ mol dm⁻³. The working pH range of this sensor is 2.5–4.3 and it works well in partially non-aqueous medium up to 15% (v/v) (methanol, ethanol and acetone). It exhibits a fast response time of 30 s and could be used for more than four months without any considerable change in response characteristics. It has excellent selectivity for Zn(II) over other mono-, bi- and trivalent cations which have been reported to cause interference in the working of other sensors. It has been successfully used as an indicator electrode in the potentiometric titration of Zn(II) against EDTA and also to estimate zinc ions in industrial waste waters.     

First approach to the use of liquid crystal elastomers for chemical sensors

Liquid crystalline thin films elastomers that are able to bind pesticides have been developed. The synthesis involves grafting mesogen and crosslinkable groups on a polysiloxane chain in the presence of a template molecule. The molecular imprinted material is obtained after thin film deposition, UV crosslinking and washing. Experiments of readsorption of pesticide are presented. Development of a multisensor platform based on thermal and capacitive sensors is described and tests of deposition of the polymer film are presented.     

A selective colorimetric chemosensor for lanthanide ions

The synthesis and complexing properties of a calix[4]arene derivate (6) carrying two spirobenzopyran moieties are described. The addition of lanthanide ions resulted in significant UV-vis spectral shifts (68-84 nm) in visible region. It indicates that the synthetic receptor can recognize lanthanide ions by naked eyes over other cations including Na⁺, K⁺, Mg²⁺, Ca²⁺, Fe³⁺, Cu²⁺ and Zn²⁺. The mechanism of recognition was studied with ¹H NMR, UV-vis spectra and emission spectra. The receptor may be applied to sense lanthanide ions.     

Automatic and adaptive calibration of 3D field sensors

Embedded sensors are an emerging trend in mobile consumer devices. Calibration of the sensors in this environment can be prohibitively difficult for the user. We propose an automatic calibration algorithm that can be used for any three-dimensional sensor sensing some external field. In particular, it is suitable for calibrating a three-axis magnetometer. The algorithm is based on recursive fitting of an ellipsoid to collected samples from the sensor. It can adaptively update the calibration parameters and is completely invisible to the user.     

Modeling the Electrochemical Response of Mesoporous Materials Toward Its Application to Biomolecular Detection

The performance of an electrochemical sensor based on the ability of a probe to cross a mesoporous membrane partially blocked by an analyte is predicted using a numerical model. The system comprehends a membrane placed close to the working electrode and the signal is generated by applying square wave voltammetry. The digital simulation allows comparing the responses for different situations regarding the way in which the membrane is blocked by the sample. The developed model is compared with experimental results. The effect of the sizes of the pore, analyte and probe on the system response is evaluated.     

Electrocatalysis and Amperometric Detection of the Reduced Form of Nicotinamide Adenine Dinucleotide at Toluidine Blue/Zinc Oxide Coated Electrodes

Thin toluidine blue (TBO) and zinc oxide (ZnO) hybrid films have been grown on glassy carbon electrode (GCE) and indium tin oxide coated (SnO₂) glass electrodes by using cyclic voltammetry (CV). Scanning electron microscopy (SEM) images revealed spherical and beads‐like shape of highly oriented TBO/ZnO hybrid films. Energy dispersive spectrometry (EDS) results declared that the films composed mainly of Zn and O. Moreover, TBO/ZnO hybrid films modified electrode is electrochemically active, dye molecules were not easily leached out from the ZnO matrix and the hybrid films can be considered for potential applications as sensor for amperometric determination of reduced nicotinamide adenine dinucleotide (NADH) at 0.0 V. A linear correlation between electrocatalytic current and NADH concentration was found to be in the range between 25 μM and 100 μM in phosphate buffer. In addition, we observed that dopamine, ascorbic acid and uric acid are not interference in amperometric detection of NADH in this proposed method. In addition, TBO/ZnO hybrid film modified electrode was highly stable and its response to the NADH also remained relentless.     

Amperometric glucose sensor using tetrathiafulvalene in Nafion gel as electron shuttle

An amperometric mediated sensor for glucose has been contrived by using bovine serum albumin and glutaraldehyde to immobilize glucose oxidase on a Nafion-tetrathiafulvalene (TTF) modified electrode. It is further coated by Nafion. The inner Nafion membrane can prevent leaking of tetrathiafulvalene; the outer Nafion film serves as a barrier to electroactive anionic interferents such as ascorbate and urate and protects the biosensor from fouling agents. The experiment shows that TTF⁺ and TTF²⁺ can oxidize the reduced flavin adenine dinucleotide (FADH₂) of glucose oxidase. The biosensor responds to glucose in less than 50 s and its calibration curve is linear from 3.0 × 10⁻⁴ to l.0 × 10⁻² M.     

Determination of Phenolic Compounds Based on the Tyrosinase‐ Single Walled Carbon Nanotubes Sensor

An amperometric sensor to phenolic compound was successfully constructed by immobilizing tyrosinase on the SWNTs modified glassy carbon (GC) electrode, which was covered with Nafion film. The sensitivity of the tyrosinase‐SWNTs sensor to phenol was 155 μA/mM. The tyrosinase‐SWNTs sensor also had good response to catechol, p‐chlorophenol and m‐cresol. Furthermore, benzoic acid could be detected based on the inhibition to tyrosinase activity.