Electrochemical determination of methyl parathion using poly(malachite green)/graphene nanosheets–nafion composite film-modified glassy carbon electrode

Conducting dyes as electro-active monomers and polymers for detecting analytes in biological and environmental samples

Currently, electrochemical sensors are regarded as an efficient tool for the biological and environmental sensing. Electrochemical sensors, such as voltammetric, amperometric, and impedimetric sensors, have gained great attention due to their simplicity, sensitivity, and selectivity. The performance of these electrochemical sensors could be enhanced by surface engineered nano/micro structured materials with conducting dyes/redox species. In this review, a great focus has been put on the redox-active dyes because of their electronic, optical, electrochromic, and conductivity properties. The mechanisms of oxidation and subsequent polymerization of different redox-active dyes at the surface of electrodes have been studied. Additionally, their role in catalyzing the oxidation or reduction of the target analytes at the surfaces of electrodes has also been highlighted. The redox-active dyes were used as electrochemical probes for detecting various analytes in biological and environmental samples. Overall, redox-active dyes are considered promising conducting polymers for the assessment of many analytes such as drugs, pesticides, surfactants, and heavy metal ions.

Recent Developments in Polymer Nanocomposite-Based Electrochemical Sensors for Detecting Environmental Pollutants

The human population is generally subjected to diverse pollutants and contaminants in the environment like those in the air, soil, foodstuffs, and drinking water. Therefore, the development of novel purification techniques and efficient detection devices for pollutants is an important challenge. To date, experts in the field have designed distinctive analytical procedures for the detection of pollutants including gas chromatography/mass spectrometry and atomic absorption spectroscopy. While the mentioned procedures enjoy high sensitivity, they suffer from being laborious, expensive, require advanced skills for operation, and are inconvenient to deploy as a result of their massive size. Therefore, in response to the above-mentioned limitations, electrochemical sensors are being developed that enjoy robustness, selectivity, sensitivity, and real-time measurements. Considerable advancements in nanomaterials-based electrochemical sensor platforms have helped to generate new technologies to ensure environmental and human safety. Recently, investigators have expanded considerable effort to utilize polymer nanocomposites for building the electrochemical sensors in view of their promising features such as very good electrocatalytic activities, higher electrical conductivity, and effective surface area in comparison to the traditional polymers. Herein, the first section of this review briefly discusses the most important methods for polymer nanocomposites synthesis, such as in situ polymerization, direct mixing of polymer and nanofillers (melt-mixing and solution-mixing), sol-gel, and electrochemical methods. It then summarizes the current utilization of polymer nanocomposites for the preparation of electrochemical sensors as a novel approach for monitoring and detecting environmental pollutants which include heavy metal ions, pesticides, phenolic compounds, nitroaromatic compounds, nitrite, and hydrazine in different mediums. Finally, the current challenges and future directions for the polymer nanocomposites-based electrochemical sensing of environmental pollutants are outlined.

Adsorptive stripping voltammetric determination of Tetracycline in pharmaceutical capsule formulation using Poly(Malachite green) modified glassy carbon electrode

A selective and sensitive electrochemical method based on glassy carbon electrode modified with poly(malachite green) was developed for determination of tetracycline in pharmaceutical capsule formulation. Cyclic voltammetry and electrochemical impedance spectroscopy using [Fe(CN)6]3-/4- as a probe were used to characterize the potentiodynamiclly deposited poly(malachite green) on the surface of glassy carbon electrode. In contrast to the unmodified glassy carbon electrode, the fabricated poly(malachite green) modified glassy carbon electrode showed catalytic property towards two steps irreversible oxidation of tetracycline. Better correlation of the oxidative peak current with the scan rate than with the square root of scan rate supported by slope of 0.60 for log(current) versus log(scan rate) indicated that the oxidation reaction of tetracycline at the modified electrode was predominantly controlled by electron exchange step at the solution polymer interface. Under optimized solution pH, and accumulation parameters, the square wave adsorptive anodic striping peak current response of the modified electrode showed linear dependence on concentration of tetracycline in the range 5-100 μM with determination coefficient, method detection limit, and quantification limit of 0.99588, 1.6 μM, and 5.3 μM, respectively. The tetracycline content of a capsule sample claimed to have 250 mg/capsule was found to be 250.53 mg/capsule with 0.21% deviation. Excellent spike recovery result of 99.80%, and 98.49-99.78% recovery of tetracycline in capsule sample in the presence of 50-200% of UA, AA, and ampicillin validated the applicability of the method for determination of tetracycline in real samples with complex matrix like capsule formulations.

Highly dispersed core-shell iron nanoparticles decorating onto graphene nanosheets for superior Zn(II) wastewater treatment

This study reports the preparation of highly dispersed nanoscale zerovalent iron (nZVI) with core-shell structure decorated onto graphene nanosheets (Gr-NS) to form nZVI-Gr-NS composite. Meanwhile, its excellent performance for concentrated Zn(II) wastewater treatment is also studied. The adsorption of Zn(II) onto nZVI-Gr-NS is well simulated by the pseudo-second-order model, which indicates the adsorption is the rate-controlling step. Moreover, the adsorption isotherms of Zn(II) on the nZVI-Gr-NS can fit well with the Langmuir model. The negative thermodynamic parameters (△G^Ɵ, △H^Ɵ, △S^Ɵ) calculated from the temperature-dependent isotherms indicate that the sorption reaction of Zn(II) is an exothermic and spontaneous process. The high saturation magnetization (37.4 emu g^-1) of the nZVI-Gr-NS makes separation of nZVI-Gr-NS-bound Zn(II) easily and quickly from aqueous solution. Most importantly, nZVI-Gr-NS composites not only remove Zn(II) but also spontaneously remove As, Se, and Cu ions from real smelting wastewater samples. This study provides a good solution for heavy metal removal in real wastewater.

Ultrasensitive electrochemical detection of methyl parathion pesticide based on cationic water-soluble pillar[5]arene and reduced graphene nanocomposite

We report a rapid, sensitive and selective electrochemical sensor based on pillar[5]arene (CP5) reduced graphene (rGO) nanohybrid-modified glassy carbon electrode CP5-rGO/GCE for the trace detection of methyl parathion (MP) by differential pulse voltammetry (DPV) for the first time. Compared to beta-cyclodextrin (β-CD)-functionalized reduced graphene (rGO)-modified GCE β-CD-rGO/GCE, the proposed CP5-rGO/GCE sensor exhibits excellent electrochemical catalytic activity, rapid response, high sensitivity, good reproducibility and anti-interference ability towards MP. The recognition mechanism of β-CD/MP and CP5/MP was studied by 1H NMR. The results indicate a higher supramolecular recognition capability between CP5 and MP compared to that between β-CD and MP. The β-CD-rGO and CP5-rGO nano-composites were prepared via a wet chemistry approach. The resulting nano-composites have been characterized by thermogravimetric analysis (TGA), fourier transform infrared spectrometry (FTIR), charge transfer resistance (R ct) and zeta potential. The CP5-rGO/GCE combines the merits of CP5 and rGO, and is used for quantitative detection of MP. It has a low detection limit of 0.0003 μM (S/N = 3) and a linear response range of 0.001-150 μM for MP. This method has been used to detect MP in soil and waste water samples with satisfactory results. This study provides a promising electrochemical sensing platform and is a promising tool for the rapid, facile and sensitive analysis of MP.

How cutting-edge technologies impact the design of electrochemical (bio)sensors for environmental analysis. A review

Through the years, scientists have developed cutting-edge technologies to make (bio)sensors more convenient for environmental analytical purposes. Technological advancements in the fields of material science, rational design, microfluidics, and sensor printing, have radically shaped biosensor technology, which is even more evident in the continuous development of sensing systems for the monitoring of hazardous chemicals. These efforts will be crucial in solving some of the problems constraining biosensors to reach real environmental applications, such as continuous analyses in field by means of multi-analyte portable devices. This review (with 203 refs.) covers the progress between 2010 and 2015 in the field of technologies enabling biosensor applications in environmental analysis, including i) printing technology, ii) nanomaterial technology, iii) nanomotors, iv) biomimetic design, and (v) microfluidics. Next section describes futuristic cutting-edge technologies that are gaining momentum in recent years, which furnish highly innovative aspects to biosensing devices.

Facile and sensitive electrochemical detection of methyl parathion based on a sensing platform constructed by the direct growth of carbon nanotubes on carbon paper

Facile and sensitive methyl parathion detection was achieved based on a novel carbon nanotube/carbon paper sensor.

Online microchannel preconcentrator for carbofuran detection

A simple and rapid online microchannel preconcentrator coupled with an amperometric detection for the analysis of carbofuran using polyethylene glycol coated onto magnetic particle (PEG-magnetic particles) sorbents was developed. This simple-to-prepare microchannel preconcentrator used an external magnet to retain the PEG-magnetic particle sorbents inside the microchannel. Under optimum conditions, the system provided two linear ranges, from 0.01 to 10.0 mg L(-1) and from 10.0 to 130.0 mg L(-1) with a limit of detection of 8.7 ± 0.1 μg L(-1). The microchannel preconcentrator provided very good stability; it can be used for up to 326 consecutive injections of 5.0 mg L(-1) carbofuran with a relative standard deviation of less than 3%. The developed system provided a good microchannel-to-microchannel and a good electrode-to-electrode reproducibility (n = 6, %RSD < 1). It also provided an excellent selectivity when it was tested with two other carbamate pesticides, carbaryl and methomyl, with a 43 and 256 times higher detection sensitivity for carbofuran, respectively. The developed system was successfully applied to detect carbofuran in surface water samples obtained near vegetable plantation areas. The concentrations of carbofuran in these samples were found to be in the range of non-detectable to 0.047 ± 0.001 mg L(-1). The developed system is easy to operate and easy to couple with other analytical instruments and it could be easily adapted for the analysis of other polar organic contaminants.