Electrode modified with nitrogen-doped graphene quantum dots supported in chitosan for triclocarban monitoring

Electrochemical Sensing Platform Based on Carbon Dots for the Simultaneous Determination of Theophylline and Caffeine in Tea

A simple and selective method for the determination of caffeine (CAF) and theophylline (THEO) has been developed for a glassy carbon electrode (GCE) modified with a composite including carbon dots (CDs) and chitosan (CS). To our knowledge, there are no previous studies that analyze a CDs-modified GCE for the presence of CAF and THEO. The electrochemical behavior of a GCE modified with a CDs-CS composite was studied in acidic medium by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Considering the sensor analytical parameters, the same linear concentrations range was found for CAF and THEO ranging from 1 × 10-5 to 5 × 10-3 mol L-1 with the same detection limit (LOD) of 1 × 10-6 mol L-1. The reproducibility and repeatability data were satisfactory in terms of RSD%. Moreover, the storage stability was evaluated, evidencing good results whatever the experimental conditions used. The developed sensor was applied for the simultaneous determination of CAF and THEO in tea and drug, and results were compared with those obtained with HPLC-ESI-MS in SIR mode as an independent method optimized on purpose. The electrochemical sensor presents the undoubled advantages in terms of cheapness, portability, and ease of use, since it does not require skilled personnel.

Subppb level monitoring and UV degradation of triclosan pollutants using ZnO multipod and Ag nanocomposites

A unique nanomaterial platform was developed for trace detection and efficient degradation of triclosan (TCS). A facile spectroscopic technique for surface-enhanced Raman scattering (SERS)-supported identification and ultraviolet (UV) degradation of TCS using a SERS template based on silver spherical nanoparticle (AgNP)-modified ZnO multipods (ZnO@Ag) is reported. Core-shell composite materials of ZnO multipods with a dimension of around 3 μm and AgNPs with an average diameter of ∼27 nm was designed not only as a substrate for TCS degradation up to ∼92% upon UV irradiation (λ = 365 mm, 300 μW/cm²) but also as a monitoring platform sensitive to TCS at a detection limit as low as 10^-9 M (≈0.3 ppb). Herein, the first investigation into ZnO@Ag bimetallic composites is established for both the SERS-based detection and UV-assisted degradation of environmental TCS pollutants. The calibration curve was estimated to be linear at R² > 0.97. The validated technology was successfully used to determine the antibacterial agent and TCS in distilled or river water. The advantages of the ZnO@Ag template are highlighted over conventional detection and excellent degradation.

Modified and Optimized Glass Electrode for pH Measurements in Hydrated Ethanol Fuel

One of the quality control parameters of ethanol fuel is pH, established by the Brazilian standard ABNT NBR 10891, whose scope is specific for hydrated ethanol fuel, and by the American standard ASTM D 6423, which focuses on anhydrous ethanol fuel. This study presented a modified and optimized structure using a single solvent, both for the glass electrode and the external reference electrode, to minimize the presence of the liquid junction potential for measuring the pH of hydrated ethanol fuel. The Box-Behnken design enabled us to determine the optimal condition expected for the new measurement system, which was compared with the systems proposed by the standard references and the turning range of acid-base indicators using parametric and nonparametric tests. The results revealed that the pH values obtained by the different systems are statistically different, and that only the values obtained by this proposal are suitable for the pH range found by the indicators. The optimized electrode presented an adequate response sensitivity to the Nernst equation, having an operational behavior adequate for the modified and optimized glass electrode for pH measurements in hydrated ethanol fuel.

Electrochemical sensing of fentanyl as an anesthesia drug on NiO nanodisks combined with the carbon nanotube-modified electrode

Fentanyl was successfully determined in the current effort based on hexagonal NiO nanodisks (HG-NiO-NDs) fabricated by the hydrothermal protocol. The synergism of HG-NiO-NDs with multiwall carbon nanotubes (MWCNTs), large specific surface area, and active material enabled the electrochemical sensor to show potent electrochemical behavior. Admirable performance was found for the fentanyl measurement by the MWCNT and HG-NiO-ND-modified pencil graphite electrode (MWCNT/HG-NiO-ND/PGE). The correlation of oxidation currents with the pH value, concentration, and sweep rate of supporting electrolytes was determined for the optimization of conditions to detect fentanyl. The surfaces of modified and unmodified electrodes were characterized as well. The diffusion-control processes were confirmed on the basis of anodic peak findings. The results also revealed a two-electron transfer process. The linear range was obtained to be 0.01–800.0 μM for the fentanyl concentrations on the developed electrode, with the sensitivity of 0.1044 μA/mM/cm2. The limit of detection (S/N = 3) was 6.7 nM. The results indicated the ability of the modified electrode to fabricate non-enzymatic fentanyl sensor applications.

Electrochemical Determination of Morin in Natural Food Using a Chitosan-Graphene Glassy Carbon Modified Electrode

This report presents a new application for the chitosan-graphene glassy carbon electrode (Ch-G/GCE) system in the determination of the hydroxyflavonoid morin (MR), one of the flavonoids with the highest favorable activity for people, due to its natural properties by square-wave voltammetry (SWV). The anodic peak current for MR was observed at 0.50 V with an increase of 73% compared with the glassy carbon electrode unmodified. The surface areas of Ch-G/GCE, Ch/GCE and GCE evaluated by cyclic voltammetry were 0.140, 0.053 and 0.011 cm², respectively. Additionally, an increase greater than 100% compared to the electrode without modification was observed. The detection limit was 0.30 µmol/L for MR, and the relative standard deviations (RSDs) were 1.8% (n = 6). Possible interferences as quercetin, rutin, and applications in real samples were also evaluated with very acceptable results.

Preparation of Multicolour Solid Fluorescent Carbon Dots for Light-Emitting Diodes Using Phenylethylamine as a Co-Carbonization Agent

Carbon dots (CDs), as a new type of photoluminescent nanomaterial, have attracted extensive attention in various fields because of their unique luminescence properties. However, CDs will exhibit fluorescence quenching in the solid state or aggregate state, which limits their application. In this paper, a unique strategy is proposed to regulate solutions to achieve multicolour fluorescence of CDs in the solid state. We report the successful preparation of orange, green and blue solid fluorescent CDs using citric acid, urea and phenylethylamine as precursors and methanol, ethanol and water as solvents, respectively. The solid-state fluorescence of CDs may be caused by the linkage of the phenylethyl structure to the surface of CDs during formation, which effectively disperses the CDs and prevents π–π interactions between graphitized nuclei. Meanwhile, multicolour solid fluorescent CDs are realized by adjusting the solvent in the preparation process. Based on the excellent fluorescence properties of CDs, orange, green and blue light-emitting diodes (LEDs) are prepared. A white LED (WLED) can be obtained by mixing the three colours of solid fluorescent CDs, which shows the application potential of CDs in display lighting equipment.

MWCNTs-CTAB and HFs-Lac Nanocomposite-Modified Glassy Carbon Electrode for Rutin Determination

Rutin is a flavonoid glycoside compound, which is mainly transported via the blood circulation system in the human body. The monitoring of the blood concentration of rutin is of great significance in many fields such as pharmacology and pharmacokinetics. In this work, a biosensor based on multi-walled carbon nanotubes (MWCNTs), cetyltrimethylammonium bromide (CTAB), hydroxyl fullerenes (HFs), and laccase (Lac) nanocomposite-modified glassy carbon electrodes was constructed. The modified materials were characterized with a transmission electron microscope (TEM), cyclic voltammograms (CV), and electrochemical impedance spectroscopy (EIS). CTAB is used to disperse MWCNTs and improve hydrophilicity and biocompatibility of MWCNTs, while the use of Lac can enhance the oxidation of catechol structure in rutin, thus significantly improving the sensitivity and selectivity of the modified electrode. Linear sweep voltammetry (LSV) studies showed that the determination linear ranges of rutin were 0.1 µmol L⁻¹ to 2 µmol L⁻¹ and 2 µmol L⁻¹ to 11 µmol L⁻¹, with the determination limits of 30 nmol L⁻¹ and 95.5 nmol L⁻¹, respectively. The proposed biosensor can be used to detect rutin tablets and serum samples with high recovery, which indicates a good accuracy of this method, and the results are consistent with those measured by the traditional ultra-high performance liquid chromatography (UHPLC) method. Hence, this biosensor has potential practical application value in rutin drug quality testing and clinical blood drug concentration monitoring.

Occurrence and Fate of Triclosan and Triclocarban in Selected Wastewater Systems across Durban Metropolis, KwaZulu-Natal, South Africa

Triclosan (TCS) and triclocarban (TCC) are antimicrobial agents that have been used in personal care and consumer products in the past decades. In this study, influent, effluent, and sludge samples collected in selected wastewater treatment plants across the Durban metropolis were qualitatively and quantitatively investigated. It was revealed that the concentration of TCS ranged from 1.906 to 73.462 µg/L, from 1.732 to 6.980 µg/L, and from 0.138 to 2.455 µg/kg in influent, effluent, and sludge samples, respectively. The concentrations of TCC were found to be between 0.320 and 45.261 µg/L, <LOQ−1.103 µg/L, and from 0.107 to 8.827 µg/kg in the influent, effluent, and sludge samples, respectively. Higher concentrations of TCS as compared with TCC were observed in the aqueous samples. However, the concentrations of TCC in the sludge samples were significantly higher than the level of TCS. More water solubility of TCS could be responsible for the observed trend in the influent and effluent samples, while the trend observed in the sludge could be due to the more hydrophobicity character of TCC. The results of this study indicated that substantial amounts of TCS and TCC are been removed during the treatment process which could be a major reason for the decline in the levels recorded in the effluent samples, therefore, reducing the amount of the TCS and TCC that would eventually end up in the surface rivers. Qualitative analyses of the samples indicated the presence of caffeine, tert-butylhydroquinone, chloroxylenol, phenol, 4-(1,1,3,3-tetramethyl butyl), and dimethyl-bisphenol A. Further investigative ecological risk assessment studies are crucial due to the potential threat the contaminants may pose to aquatic lives and humans.

An upgraded 2D nanosheet-based FRET biosensor: insights into avoiding background and eliminating effects of background fluctuations

We demonstrated a new class of 2D nanosheet-based FRET biosensor utilizing vertically oriented MoS₂ nanosheets on a magnetic nanocarrier. Compared with the non-separated biosensor under identical conditions, this upgraded one can avoid the background signal of the system and eliminate the effects of background fluctuations, which produces more excellent detection methods.