A sensor based on silver nanoparticles synthesized on carbon graphite sheets for the electrochemical detection of nitrofurazone: Application: Tap water,commercial milk and human urine

Nitrofurazone is a nitrofuran-family synthetic chemical that has been used to treat bacterial infections since 1993. Silver nanoparticles synthesized by the thermal technique on graphite carbon sheets under optimal conditions were used to develop a highly sensitive electrochemical sensor. The main experimental characteristics are optimized to assure that this sensor functions correctly. Scanning electron microscope, X-ray diffraction, infrared spectroscopy were used to determine the chemical composition and morphology of the prepared pastes. With a maximal reduction peak of La nitrofurazone observed at ?0.57V/Ag-NPs@CPE versus Ag/AgCl, this sensor demonstrated good electrocatalytic activity for the reduction of La nitrofurazone. The influence of phosphate buffer solution pH indicates that the numbers of protons and electrons in the reaction at the surface of our constructed sensor were the same. The LOD and LOQ were calculated to be 1.2 × 10^?8 M and 1.3 × 10^?7 M, respectively. Using the differential pulse voltammetry technique, the calibration curve was established in the concentration range of 10^?4 M to 2 × 10^?7 M. Our Ag-NPs@CPE sensors were evaluated in order to detect nitrofurazone in real contaminated samples tap water, commercial milk, and human urine, in particular. The electroanalysis results show a very high recovery rate of more than 96% on average, permitting us to determine that our sensors are functional under optimum working conditions.     

Green Carbon Materials for the Analysis of Environmental Pollutants

Green carbon materials (GCMs) have attracted great attention as they have unique mechanical, optical, and electrical properties that make them suitable for the development of the next generation of miniature, low-power, and mobile sensors. In this review paper, an attempt has been made to explore green carbon materials where their synthesis methods, conjugation with other types of nanomaterials to form nanocomposites, thus combining different properties into one single novel material, and environmental analysis applications are detailed. Green carbon materials have great significance in the analysis of environmental pollutants because they increase the effective area of an electrode, improve the rate of electron transfer between the analytes and the electrode, and help in catalysis, which in turn increases the efficacy of an electrochemical reaction, absorption, detection, and elimination. Moreover, functionalized green carbon materials when used in sensors for fast, economic environmental pollutant analysis are found to be highly sensitive to monitoring heavy metals and other polluting impurities in air, water sources, soils, etc. This review covers research and advancements in a broad span from 2013 to 2021, and some of the leading and fascinating research articles from the early years of the century have also been incorporated.     

Electrochemically Induced Formation of Surface‐Attached Temperature‐Responsive Hydrogels. Amperometric Glucose Sensors with Tunable Sensor Characteristics

Employing thermally responsive hydrogels, the design of an amperometric glucose sensor is proposed. The properties of the biosensor can be modulated upon changing the temperature. Homo‐ and copolymers of N‐isopropylacrylamide (NIPAm) and oligo(ethylene glycol) methacrylate (OEGMA) were prepared by electrochemically induced polymerization thus yielding surface‐attached hydrogels. The growth of the films as well as the change in the film thickness in dependence from the temperature were investigated by means of an electrochemical quartz crystal microbalance (EQCM). The layer thickness in the dry state ranged from 20 to 120 nm. The lower critical solution temperature (LCST) of the hydrogel increases with increasing content of the more hydrophilic OEGMA. Hence, the swelling in aqueous electrolyte is composition dependent and can be adjusted by selecting a specific NIPAm to OEGMA ratio. All homo‐ and copolymer films showed good biocompatibility and no fouling could be observed during exposing the surfaces to human serum albumin. For amperometric glucose detection, glucose oxidase was entrapped in the films during electrochemically‐induced polymerization. Both the apparent Michaelis constant (K$\rm{{_{M}^{app}})}$ and the apparent maximum current (i$\rm{{_{max}^{app}})}$ as determined by amperometry could be adjusted both by the film composition as well as the operation temperature.     

Highly Sensitive and Selective Voltammetric Sensor Fullerene Modified Glassy Carbon Electrode for Determination of Cefitizoxime in Solubilized System

The usefulness of fullerene modified glassy carbon electrode in mediating the reduction of cefitizoxime in solubilized system has been demonstrated. Due to the unique structure and extraordinary properties, fullerene shows higher catalytic efficiency towards cefitizoxime reduction. The kinetic parameters, electron transfer coefficient (α) and rate constant (K₀) across the modified electrode are 0.37 and 0.1081/s respectively. The proposed square‐wave voltammetric method is linear over the concentration range 1.2–10.3 µg/mL. The limit of detection (LOD) is found 0.27 ng/mL. High sensitivity and selectivity together with low detection limit of the electrode response make it suitable for the determination of cefitizoxime.     

Electrogenerated Chemiluminescence Sensor Based on Tris(2,2′‐bipyridine)ruthenium(II)‐Immobilized Natural Clay and Ionic Liquid

A novel electrogenerated chemiluminescence (ECL) sensor based on natural clay and ionic liquid was fabricated. Tris(2,2′‐bipyridine)ruthenium(II) (Ru(bpy)₃²⁺) was immobilized on natural clay surface through simple adsorption. An ECL sensor was prepared by mixing Ru(bpy)₃²⁺‐incorporated clay, graphite powder and an ionic liquid (1‐butyl‐3‐methylimidazolium hexafluorophosphate) as the binder. The electrochemical behavior and ECL of the immobilized Ru(bpy)₃²⁺ was investigated. It was observed that the ECL of immobilized Ru(bpy)₃²⁺ was activated by the ionic liquid. The proposed ECL sensor showed high sensitivity to tri‐n‐propylamine (TPrA) and the detection limit was found to be 20 pM. In addition, the ECL sensor displayed good stability for TPrA detection and long‐term storage stability.     

Distinguishing Among Gases with a Semiconductor Sensor Depending on the Frequency Modulation of a Cyclic Temperature

A gas‐sensing system based on a dynamic nonlinear response shows enhanced selectivity of the sensor response toward sample vapors. A cyclic temperature composed of fundamental and 1.5‐th harmonics was applied to a SnO₂ semiconductor gas sensor and the resulting conductance of the sensor was evaluated by a polynomial approximation. The dynamic nonlinear responses to the samples were further characterized by the addition of 1.5‐th harmonic perturbation as a frequency modulation. These characteristic sensor responses under frequency modulation were considered theoretically based on a reaction‐diffusion model for the semiconductor surface.     

Integrated-optic temperature sensors based on guided-mode radiation in polymer waveguide

Optical temperature sensors consisting of low-loss polymer waveguides with a glass lower cladding are demonstrated. The refractive index of the optical polymer is precisely controlled to have a certain initial refractive index contrast with the glass substrate used for lower cladding. Depending on the initial index contrast, the operating temperature ranges of the sensors are determined. The polymer devices are fabricated by spin-coating and UV curing, which could be replaced by the cost-effective imprinting or injection molding process. The sensor exhibits a monotonic decrease of the transmission intensity corresponding to the temperature increase, which enables straightforward reading of temperature from the measured optical power.     

H2S-sensing properties of Pt-doped mesoporous indium oxide

Pt-doped mesoporous indium oxide (In₂O₃) has been successfully obtained by a simple and effective in situ nanocasting method. The resultant samples were characterized by XRD, FE-SEM, TEM, N₂ physisorption, XPS and EDX. The gas sensing properties for hydrogen sulfide (H₂S) of the Pt-doped mesoporous In₂O₃ specimens were also examined. The results exhibit those In₂O₃ specimens possess much higher response to H₂S even at low concentration of 2 ppm and a lower optimum working temperature of 150 °C. A possible mechanism was also provided to explain the improvement of the sensing properties.     

Sensitive and Facile Determination of Catechol and Hydroquinone Simultaneously Under Coexistence of Resorcinol with a Zn/Al Layered Double Hydroxide Film Modified Glassy Carbon Electrode

A stable dihydroxybenzene sensor was fabricated by electrochemical deposition of Zn/Al layered double hydroxide film on glassy carbon electrode (LDHf/GCE). The sensitive and facile electrochemical method for the simultaneous determination of catechol (CA) and hydroquinone (HQ) under coexistence of resorcinol (RE) has been achieved at the LDHf/GCE in phosphate buffer solution (pH 6.5). Under the optimized conditions, the differential pulse voltammetry response of the modified electrode to CA (or HQ) shows a linear concentration range of 0.6 μM to 6.0 mM (or 3.2 μM to 2.4 mM) with a correlation coefficient of 0.9987 (or 0.9992) and the calculated limit of detection is 0.1 μM (or 1.0 μM) at a signal‐to‐noise ratio of 3. In the presence of 50 μM isomer, the linear concentration ranges for CA and HQ are 3.0 μM to 1.5 mM and 12.0 μM to 0.8 mM, respectively. The detection limits are 1.2 μM and 9.0 μM. Further, the proposed method has been performed to successfully detect dihydroxybenzene isomers in analysis of real samples, such as water and tea.     

Polyaniline Film Based Amperometric pH Sensor Using A Novel Electrochemical Measurement System

A polyaniline based amperometric pH sensor has been developed using a novel electrochemical measurement system. A polyaniline film (PANI) coated pencil graphite electrode (PGE) is connected in series between the working and counter electrodes of a potentiostat, and immersed in the solution together with a reference electrode. When an external potential is applied, the resulting current varies with the solution pH, which provides the basis for the amperoemtric pH sensor. Equations describing the measurement principle are presented. Based on pH dependent emeraldine salt–emeraldine base transition of PANI film, the pH sensor exhibits high stability, accuracy, selectivity, sensitivity and a short time.