Amperometric nitrite sensor based on a glassy carbon electrode modified with multi-walled carbon nanotubes and poly(toluidine blue)

Detection of respiratory inflammation biomarkers in non-processed exhaled breath condensate samples using reduced graphene oxide

In this work, we studied several important parameters regarding the standardization of a portable sensor of nitrite, a key biomarker of inflammation in the respiratory tract in untreated EBC samples. The storage of the EBC samples and electrical properties of both EBC samples and the sensor as main standardization parameters were investigated. The sensor performance was performed using differential pulse voltammetry (DPV) in a standard nitrite solution and untreated EBC samples. The storage effect was monitored by comparing sensor data of fresh and stored samples for one month at -80 °C. Results show, on average, a 20 percent reduction of peak current for stored solutions. The sensor's performance was compared with a previous EBC nitrite sensor and chemiluminescence method. The results demonstrate a good correlation between the present sensor and chemiluminescence for low nitrite concentrations in untreated EBC samples. The electrical behavior of the sensor and electrical variation between EBC samples were characterized using methods such as noise analysis, electrochemical impedance spectroscopy (EIS), electrical impedance (EI), and voltage shift. Data show that reduced graphene oxide (rGO) has lower electrical noise and a higher electron transfer rate regarding nitrite detection. Also, a voltage shift can be applied to calibrate the data based on the electrical variation between different EBC samples. This result makes it easy to calibrate the electrical difference between EBC samples and have a more reproducible portable chip design without using bulky EI instruments. This work helps detect nitrite in untreated and pure EBC samples and evaluates critical analytical EBC properties essential for developing portable and on-site point-of-care sensors.

Polyphenazine and polytriphenylmethane redox polymer/nanomaterial-based electrochemical sensors and biosensors: a review

In recent years, an increasing number of studies has demonstrated that redox polymers can be used in simple and effective electrochemical sensing platforms due to their fast electron transfer and electrocatalytic ability. To develop more sensitive and selective electrochemical (bio)sensors, the electrocatalytic properties of redox polymers and the electrical, mechanical, and catalytic properties of various nanomaterials are combined. This review aims to summarize and contribute to the development of (bio)sensors based on polyphenazine or polytriphenylmethane redox polymers combined with nanomaterials, including carbon-based nanomaterials, metal/metal oxide, and semiconductor nanoparticles. The synthesis, preparation, and modification of these nanocomposites is presented and the contribution of each material to the performance of (bio)sensor has been be examined. It is explained how the combined use of these redox polymers and nanomaterials as a sensing platform leads to improved analytical performance of the (bio)sensors. Finally, the analytical performance characteristics and practical applications of polyphenazine and polytriphenylmethane redox polymer/nanomaterial-based electrochemical (bio)sensors are compared and discussed.

Electrochemical Sensors Based on Conducting Polymers for the Aqueous Detection of Biologically Relevant Molecules

Electrochemical sensors appear as low-cost, rapid, easy to use, and in situ devices for determination of diverse analytes in a liquid solution. In that context, conducting polymers are much-explored sensor building materials because of their semiconductivity, structural versatility, multiple synthetic pathways, and stability in environmental conditions. In this state-of-the-art review, synthetic processes, morphological characterization, and nanostructure formation are analyzed for relevant literature about electrochemical sensors based on conducting polymers for the determination of molecules that (i) have a fundamental role in the human body function regulation, and (ii) are considered as water emergent pollutants. Special focus is put on the different types of micro- and nanostructures generated for the polymer itself or the combination with different materials in a composite, and how the rough morphology of the conducting polymers based electrochemical sensors affect their limit of detection. Polypyrroles, polyanilines, and polythiophenes appear as the most recurrent conducting polymers for the construction of electrochemical sensors. These conducting polymers are usually built starting from bifunctional precursor monomers resulting in linear and branched polymer structures; however, opportunities for sensitivity enhancement in electrochemical sensors have been recently reported by using conjugated microporous polymers synthesized from multifunctional monomers.

Bifunctional cyclomatrix polyphosphazene-based hybrid with abundant decorating groups: Synthesis and application as efficient electrochemical Pb(II) probe and methylene blue absorbent

HYPOTHESIS

The construction of novel functional cyclomatrix polyphosphazenes (CPPs) hybrid, which with diverse decorating groups, is a challenging task due to the structural limitation of available reaction substrates (phenols and amines).

EXPERIMENTS

Herein, a phenolic hydroxyl (OH) modified ployamide derivative (P2) was successfully prepared via novel benzoxazine-isocyanide chemistry (BIC). A kind of CPP hybrid (P3), which with abundant functional groups (amide, tertiary amine, benzoxazine and phenolic hydroxyl) was prepared subsequently by the condensation between P2 and hexachlorocyclotriphosphazene (HCCP). Chemical structure, elemental composition, morphology, porous properties and crystallinity of P3 were systematically analyzed here. The electrochemical detection of lead ion (Pb²⁺) was realized by using P3-modified glassy carbon electrode (GCE/Nafion/P3) as the working electrode. Besides this, given the unique chemical structure and morphology of P3, the selective adsorption of methylene blue (MB) by P3 was also studied here.

FINDINGS

Experimental results indicated that that P3 can act as bifunctional hybrid material to solve environmental issues.

Ultrasensitive Electrochemical Sensor Based on Polyelectrolyte Composite Film Decorated Glassy Carbon Electrode for Detection of Nitrite in Curing Food at Sub-Micromolar Level

To ensure food quality and safety, developing cost-effective, rapid and precision analytical techniques for quantitative detection of nitrite is highly desirable. Herein, a novel electrochemical sensor based on the sodium cellulose sulfate/poly (dimethyl diallyl ammonium chloride) (NaCS/PDMDAAC) composite film modified glass carbon electrode (NaCS/PDMDAAC/GCE) was proposed toward the detection of nitrite at sub-micromolar level, aiming to make full use of the inherent properties of individual component (biocompatible, low cost, good electrical conductivity for PDMDAAC; non-toxic, abundant raw materials, good film forming ability for NaCS) and synergistic enhancement effect. The NaCS/PDMDAAC/GCE was fabricated by a simple drop-casting method. Electrochemical behaviors of nitrite at NaCS/PDMDAAC/GCE were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under optimum conditions, the NaCS/PDMDAAC/GCE exhibits a wide linear response region of 4.0 × 10⁻⁸ mol·L⁻¹~1.5 × 10⁻⁴ mol·L⁻¹ and a low detection 1imit of 43 nmol·L⁻¹. The NaCS/PDMDAAC shows a synergetic enhancement effect toward the oxidation of nitrite, and the sensing performance is much better than the previous reports. Moreover, the NaCS/PDMDAAC also shows good stability and reproducibility. The NaCS/PDMDAAC/GCE was successfully applied to the determination of nitrite in ham sausage with satisfactory results.

Electrocatalytic reduction of low-concentration thiamphenicol and florfenicol in wastewater with multi-walled carbon nanotubes modified electrode

The electrocatalytic reduction of thiamphenicol (TAP) and florfenicol (FF) was investigated with multi-walled carbon nanotubes (MWCNTs) modified electrode. MWCNTs was dispersed in pure water with the assistance of dihexadecyl phosphate (DHP), and then modified on glassy carbon electrode (GCE). The electrocatalytic reduction conditions, such as bias voltage, supporting electrolyte and its initial pH, and the initial concentrations of TAP and FF, were also optimized. The experimental results indicated that the removal efficiencies of 2mgL^-1 TAP and FF in 0.1M NH₃·H₂O-NH₄Cl solution (pH 7.0) reached 87% and 89% at a bias voltage of -1.2V after 24h electrocatalytic reduction, respectively. The removal process could be described by pseudo first-order kinetic model, and the removal rate constants of TAP and FF were obtained as 0.0837 and 0.0915h^-1, respectively. The electrocatalytic reduction products of TAP and FF were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the possible reduction mechanisms were preliminarily analyzed. Electrocatalytic reduction is promising to remove low-concentration TAP and FF in wastewater with the MWCNTs modified electrode, and may cut down their toxicity through dehalogenation and carbonyl reduction.

Economical, facile synthesis of network-like carbon nanosheets and their use as an enhanced electrode material for sensitive detection of ascorbic acid

A highly sensitive electrochemical sensor for the detection of ascorbic acid (AA) was first fabricated using network-like carbon nanosheets (NCN) as an enhanced electrode modifier.