Determination of Fluoxetine in Weight Loss Herbal Medicine Using an Electrochemical Sensor Based on rGO-CuNPs

The rising popularity of herbal medicine as a weight loss remedy, fueled by misleading propaganda, raises concerns about the manufacturing processes and potential inclusion of controlled substances such as fluoxetine (FLU). The objective of this work is to develop and evaluate the performance of an electrochemical device by modifying a glassy carbon electrode (GC) with a nanocomposite based on reduced graphene oxide (rGO) and copper nanoparticles (CuNPs) for detecting FLU in manipulated herbal medicines. Scanning electron microscopy (FEG-SEM) and cyclic voltammetry (CV) were applied for morphological and electrochemical characterization and analysis of the composite's electrochemical behavior. Under optimized conditions, the proposed sensor successfully detected FLU within the range of 0.6 to 1.6 µmol L-1, showing a limit of detection (LOD) of 0.14 µmol L-1. To determine the presence of FLU in herbal samples, known amounts of the analytical standard were added to the sample, and the analyses were performed using the standard addition method, yielding recoveries between -2.13 and 2.0%.

Electrochemical monitoring of levofloxacin using a silver nanoparticle-modified disposable device based on a lab-made conductive ink

The emergence of bacteria genetically resistant to first- and second-generation fluoroquinolones has resulted in increased consumption of levofloxacin (LEV) in human and veterinary medicine. In this regard, the development of low cost and good sensitivity electrochemical devices has been highly required. Thus, in this work, we propose the development of a disposable electrochemical device (DED) using a lab-made conductive ink based on graphite powder and nail polish immobilized on a rigid polyvinyl chloride support (transparent sheet). Additionally, a simple and quick protocol for the electrodeposition of silver nanoparticles was used in order to improve the electroanalytical performance of the sensor (2.75-fold). A differential pulse voltammetry (DPV) method was optimized and the sensor was applied for LEV monitoring in pharmaceutical formulation samples, synthetic urine and simulated body fluid. The method showed a wide linear working range ranging from 0.5 to 50 μmol L^-1 and a detection limit of 68.3 nmol L^-1. Furthermore, the precision was adequate (RSD < 4.7%), while the accuracy was evaluated through spiked samples with percent recovery ranging from 93 to 103%. The sensor was also shown to be selective for LEV against other electroactive antibiotic species, thus demonstrating suitable characteristics for electroanalytical applications.

Unveiling mutation effects on the structural dynamics of the main protease from SARS-CoV-2 with hybrid simulation methods

The main protease of SARS-CoV-2 (called M^pro or 3CL^pro) is essential for processing polyproteins encoded by viral RNA. Several M^pro mutations were found in SARS-CoV-2 variants, which are related to higher transmissibility, pathogenicity, and resistance to neutralization antibodies. Macromolecules adopt several favored conformations in solution depending on their structure and shape, determining their dynamics and function. In this study, we used a hybrid simulation method to generate intermediate structures along the six lowest frequency normal modes and sample the conformational space and characterize the structural dynamics and global motions of WT SARS-CoV-2 M^pro and 48 mutations, including mutations found in P.1, B.1.1.7, B.1.351, B.1.525 and B.1.429+B.1.427 variants. We tried to contribute to the elucidation of the effects of mutation in the structural dynamics of SARS-CoV-2 M^pro. A machine learning analysis was performed following the investigation regarding the influence of the K90R, P99L, P108S, and N151D mutations on the dimeric interface assembling of the SARS-CoV-2 M^pro. The parameters allowed the selection of potential structurally stable dimers, which demonstrated that some single surface aa substitutions not located at the dimeric interface (K90R, P99L, P108S, and N151D) are able to induce significant quaternary changes. Furthermore, our results demonstrated, by a Quantum Mechanics method, the influence of SARS-CoV-2 M^pro mutations on the catalytic mechanism, confirming that only one of the chains of the WT and mutant SARS-CoV-2 M^pros are prone to cleave substrates. Finally, it was also possible to identify the aa residue F140 as an important factor related to the increasing enzymatic reactivity of a significant number of SARS-CoV-2 M^pro conformations generated by the normal modes-based simulations.

γ-Cyclodextrin-graphene quantum dots-chitosan modified screen-printed electrode for sensing of fluoroquinolones

An innovative electrochemical approach based on screen-printed carbon electrodes (SPCEs) modified with graphene quantum dots (GQDs) functionalized with γ-cyclodextrin (γ-CD) and assembled to chitosan (CHI) is designed for the assessment of the total content of fluoroquinolones (FQs) in animal source products. For the design of the bionanocomposite, carboxylated graphene quantum dots synthesized from uric acid as precursor were functionalized with γ-CD using succinic acid as a linker. Physic-chemical and nanostructural characterization of the ensuing nanoparticles was performed by high-resolution transmission scanning microscopy, dynamic light scattering, Z potential measurement, Fourier transformed infrared spectroscopy and X-ray diffraction. Electrochemical properties of assembled bionanocomposite like potential difference, kinetic electronic transfer constant and electroactive area among other parameters were assessed by cyclic voltammetry and differential pulse voltammetry using potassium ferricyanide as redox probe. The oxidation behaviour of four representative quinolones with distinctive structures was studied, obtaining in all cases the same number of involved e^- (2) and H⁺ (2) in their oxidation. These results led us to propose a single and consistent oxidation mechanism for all the checked analytes. The γ-CD-GQDs-CHI/SPCE sensor displayed a boosted electroanalytical performance in terms of linear range (4-250 µM), sensibility (LOD = 1.2 µM) and selectivity. This electrochemical strategy allowed the determination of FQs total amount in complex processed food like broths, bouillon cubes and milkshakes at three concentration levels (150, 75 and 37.5 µM) for both equimolar and different ratio FQs mixtures with recovery values ranging from 90 to 106%.

Facile Synthesis of Copper-Coated-Reduced-Graphene-Oxide and Its Application as a Highly Sensitive Electrochemical Sensor for Hydroquinone

A facile step-by-step approach for synthesizing copper nanoparticles (CuNPs) loaded on the wrinkled surface of reduced-graphene-oxide (Cu/rGO) was conducted using a reductant at room temperature. Multiple characterization methods were applied to specify the morphology and composition of the nanocomposites. The scanning electron microscope and transmission electron microscope of Cu/rGO show that spherical CuNps were dispersed uniformly on the surface of rGO. In addition, the characteristic peaks of Cu and carbon in energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses spectra proved that Cu/rGO nanocomposites were synthesized. Soon afterwards, a new hydroquinone electrochemical sensor was prepared with Cu/rGO and a glassy carbon electrode. The sensor was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Hydroquinone was detected by differential pulse voltammetry using the composite electrode. Under the optimal condition, the linear response range was from 0.05 μM to 90 μM; the detection limit is 0.02 μM (S/N = 3) for hydroquinone. The electrochemical sensor exhibited high sensitivity in practical environmental water sample detection.

Determination of Paracetamol on Electrochemically Reduced Graphene Oxide-Antimony Nanocomposite Modified Pencil Graphite Electrode Using Adsorptive Stripping Differential Pulse Voltammetry

A simple, highly sensitive, accurate, and low-cost electrochemical sensor was developed for the determination of over-the-counter painkiller, paracetamol (PC). The enhanced sensing capabilities of the developed sensor were fabricated by the single-step modification of disposable pencil graphite electrodes (PGEs) with the simultaneous electrochemical reduction in graphene oxide and antimony (II) salts. For this purpose, an electrochemically reduced graphene oxide-antimony nanoparticle (ERGO-SbNP) nanocomposite material was prepared by trapping metallic nanoparticles between individual graphene sheets in the modification of PGEs. Structural characterization by FTIR and Raman spectroscopy was employed to confirm the presence of oxygen functional groups and defects in the conjugated carbon-based structure of GO. Morphological differences between the modified PGEs were confirmed by HRTEM and HRSEM for the presence of nanoparticles. The modified electrodes were further electrochemically characterized using CV and EIS. The electrooxidation of PC on an ERGO-SbNPs-PGE was achieved by adsorptive stripping differential pulse voltametric analysis in 0.1 mol·L^-1 phosphate buffer solution at pH = 7.0. The optimum current response was used to record a detection limit of 0.057 µmol·L^-1 for PC. The electrochemical sensor was further used in real sample analysis for a commercially available pharmaceutical tablet (500 mg PC), for which the percentage recovery was between 99.4% and 100.8%.

Graphene-based electrochemical sensors for antibiotic detection in water, food and soil: A scientometric analysis in CiteSpace (2011-2021)

The residues of antibiotics in the environment pose a potential health hazard, so highly sensitive detection of antibiotics has always appealed to analytical chemists. With the widespread use of new low-dimensional materials, graphene-modified electrochemical sensors have emerged as an excellent candidate for highly sensitive detection of antibiotics. Graphene, its derivatives and its composites have been used in this field of exploration in the last decade. In this review, we have not only described the field using traditional summaries, but also used bibliometrics to quantify the development of the field. The literature between 2011 and 2021 was included in the analysis. Also, the sensing performance and detection targets of different sensors were compared. We were able to trace not only the flow of research themes, but also the future areas of development. Graphene is a material that has a high potential to be used on a large scale in the preparation of electrochemical sensors. How to design a sensor with selectivity and low cost is the key to bring this material from the laboratory to practical applications.

A Novel Method for the Detection of SARS-CoV-2 Based on Graphene-Impedimetric Immunosensor

Due to the SARS-CoV-2 pandemic, there has been an increase in the search for affordable healthcare devices for mass testing and rapid diagnosis. In this context, this work described a new methodology for SARS-CoV-2 detection based on an impedimetric immunosensor developed using the advantageous immobilization of antibodies in the reduced graphene oxide (rGO). The rGO was obtained by chemical synthesis from the commercial graphene oxide (GO), and the materials were morphologically, electrochemically and visually characterized. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques were used to evaluate the fabrication steps of the immunosensor. The electrochemical immunoassay was considered for SARS-CoV-2 spike protein RBD detection using a impedimetric immunosensor and redox couple ([(Fe(CN)6)]3-/4-) as a probe. The immunosensor was effectively developed and applied in the detection of SARS-CoV-2 spike protein RBD in saliva samples.

Impacts of COVID-19 pandemic on the wastewater pathway into surface water: A review

With global number of cases 106 million and death toll surpassing 2.3 million as of mid-February 2021, the COVID-19 pandemic is certainly one of the major threats that humankind have faced in modern history. As the scientific community navigates through the overwhelming avalanche of information on the multiple health impacts caused by the pandemic, new reports start to emerge on significant ancillary effects associated with the treatment of the virus. Besides the evident health impacts, other emerging impacts related to the COVID-19 pandemic, such as water-related impacts, merits in-depth investigation. This includes strategies for the identification of these impacts and technologies to mitigate them, and to prevent further impacts not only in water ecosystems, but also in relation to human health. This paper has critically reviewed currently available knowledge on the most significant potential impacts of the COVID-19 pandemic on the wastewater pathway into surface water, as well as technologies that may serve to counteract the major threats posed, key perspectives and challenges. Additionally, current knowledge gaps and potential directions for further research and development are identified. While the COVID-19 pandemic is an ongoing and rapidly evolving situation, compiling current knowledge of potential links between wastewater and surface water pathways as related to environmental impacts and relevant associated technologies, as presented in this review, is a critical step to guide future research in this area.

Colloidal chemical bottom-up synthesis routes of pnictogen (As, Sb, Bi) nanostructures with tailored properties and applications: a summary of the state of the art and main insights

Adjusting the colloidal chemistry synthetic parameters for pnictogen nanostructures leads to a fine control of their physical properties and the resulting performance in applications. Image adapted from Slidesgo.com.