CeO2-based heterostructure nanocomposite for electrochemical determination of l-cysteine biomolecule

Laser-induced 2D/0D graphene-nanoceria freestanding paper-based films for on-site hydrogen peroxide monitoring in no-touch disinfection treatments

A one-shot CO2 laser-based strategy to generate conductive reduced graphene oxide (rGO) decorated with nanoceria (nCe) is proposed. The 2D/0D rGO-nCe films, integrated as catalytic sensing layers in paper-based sensors, were employed for on-site monitoring of indoor fogging treatments against Listeria monocytogenes (Lm), a ubiquitous pathogenic bacterium. The rGO-nCe laser-assisted synthesis was optimized to preserve the rGO film morphological and electron-transfer features and simultaneously integrate catalytic nCe. The films were characterized by microscopical (SEM), spectroscopical (EDX, Raman, and FTIR), and electrochemical techniques. The most performing film was integrated into a nitrocellulose substrate, and the complete sensor was assembled via a combination of xurography and stencil printing. The rGO-nCe sensor's catalytic activity was proved toward the detection of H2O2, obtaining sensitive determination (LOD = 0.3 µM) and an extended linear range (0.5-1500 µM). Eventually, the rGO-nCe sensor was challenged for the real-time continuous monitoring of hydrogen peroxide aerosol during no-touch fogging treatment conducted following the EU's recommendation for biocidal product use. Treatment effectiveness was proved toward three Lm strains characterized by different origins, i.e., type strain ATCC 7644, clinical strain 338, and food strain 641/6II. The sensor allows for discrimination and quantification treatments at different environmental biocidal amounts and fogging times, and correlates with the microbiological inhibition, promoting the proposed sensor as a useful tool to modulate and monitor no-touch treatments.

Microplastic contaminants detection in aquatic environment by hydrophobic cerium oxide nanoparticles

Microplastics (MPs) poses a significant threat to ecosystems and human health, demanding immediate attention. The reported research work offers an effective and low cost method towards the detection of toxic MPs. In this study, hydrophobic cerium oxide nanoparticles (CeO2 NPs) are synthesized and applied as promising electrode material for the detection of two different types of MPs, i.e. polyethylene (PE) and polypropylene (PP). Through electrochemical analyses, such as cyclic voltammetry (CV) and linear sweep voltammetry (LSV), hydrophobic CeO2 NPs modified glassy carbon electrode (GCE) based sensor demonstrated remarkable sensitivity of ∼0.0343 AmLmg-1cm-2 and detection limit of ∼0.226 mgmL-1, with promising correlation coefficient (R2) towards the detection of PE (∼27-32 μm). Furthermore, hydrophobic CeO2 NPs modified GCE exhibited promising stability and reproducibility towards PE (∼27-32 μm), suggesting the promising potential of hydrophobic CeO2 NPs as electrode materials for an electrochemical microplastics detection.

Recent Advances in Electrochemical Sensors for Sulfur-Containing Antioxidants

Sulfur-containing antioxidants are an important part of the antioxidant defense systems in living organisms under the frame of a thiol-disulfide equilibrium. Among them, l-cysteine, l-homocysteine, l-methionine, glutathione, and α-lipoic acid are the most typical representatives. Their actions in living systems are briefly discussed. Being electroactive, sulfur-containing antioxidants are interesting analytes to be determined using various types of electrochemical sensors. Attention is paid to the chemically modified electrodes with various nanostructured coverages. The analytical capabilities of electrochemical sensors for sulfur-containing antioxidant quantification are summarized and discussed. The data are summarized and presented on the basis of the electrode surface modifier applied, i.e., carbon nanomaterials, metal and metal oxide nanoparticles (NPs) and nanostructures, organic mediators, polymeric coverage, and mixed modifiers. The combination of various types of nanomaterials provides a wider linear dynamic range, lower limits of detection, and higher selectivity in comparison to bare electrodes and sensors based on the one type of surface modifier. The perspective of the combination of chromatography with electrochemical detection providing the possibility for simultaneous determination of sulfur-containing antioxidants in a complex matrix has also been discussed.

A Novel Nanocomposite Based on Triazine Based Covalent Organic Polymer Blended with Porous g-C3N4 for Photo Catalytic Dye Degradation of Rose Bengal and Fast Green

Metal free visible light active photocatalysts of covalent organic polymers (COPs) and polymeric graphitic carbon nitride (g-C₃N₄) are interesting porous catalysts that have enormous potential for application in organic pollutant degradation. Imine condensation for COPs, and thermal condensation for g-C₃N₄ were used to produce the catalysts. FT-IR, Raman, NMR, UV-Vis Spectroscopy, X-ray diffraction, and scanning electron microscopy studies were used to investigate the structural, optical, and morphological features of the metal free catalysts. We have constructed COPs with a π-electron deficient (Lewis acidic) triazine core and π -electron rich (Lewis basic) naphthalene and anthraquinone rings coupled by -O and -N donors in this study. Furthermore, the prepared Bulk-g-C₃N₄ (B-GCN) was converted to porous g-C₃N₄ (P-GCN) using a chemical oxidation process, and the generated P-GCN was efficiently mixed with the COP to create a novel nanocomposite for photocatalytic application. Using the anthraquinone-based COP and P-GCN (1:1 ratio, PA-GCN) catalyst, the highest photodegradation efficiencies for the polymeric graphitic carbon nitride of 88.2% and 82.3% were achieved using the Fast green (FG) and Rose bengal (RB) dyes, respectively. The rate constant values of 0.032 and 0.024/min were determined for FG and RB degradation, respectively. Higher activity may be related to the incorporation of COP and PA-GCN, which act significantly well in higher visible light absorption, have superior reactive oxygen generation (ROS), and demonstrate an excellent pollutant-catalyst interaction.

Review of the Design of Ruthenium-Based Nanomaterials and Their Sensing Applications in Electrochemistry

In this review, ruthenium nanoparticles (Ru NPs)-based functional nanomaterials have attractive electrocatalytic characteristics and they offer considerable potential in a number of fields. Ru-based binary or multimetallic NPs are widely utilized for electrode modification because of their unique electrocatalytic properties, enhanced surface-area-to-volume ratio, and synergistic effect between two metals provides as an effective improved electrode sensor. This perspective review suggests the current research and development of Ru-based nanomaterials as a platform for electrochemical (EC) sensing of harmful substances, biomolecules, insecticides, pharmaceuticals, and environmental pollutants. The advantages and limitations of mono-, bi-, and multimetallic Ru-based nanocomposites for EC sensors are discussed. Besides, the relevant EC properties and analyte sensing approaches are also presented. On the basis of these insights, we highlighted recent results for synthesizing techniques and EC environmental pollutant sensors from the perspectives of diverse supports, including graphene, carbon nanotubes, silica, semiconductors, metal sulfides, and polymers. Finally, this work overviews the modern improvements in the utilization of Ru-based nanocomposites on the basis for electroanalytical sensors as well as suggestions for the field's future development.

Voltammetric Electrochemical Behavior of Carbon Paste Electrode Containing Intrinsic Silver for Determination of Cysteine

In this paper, the electrochemical behavior of cysteine is described, using carbon paste electrodes (CPEs) modified with ternary silver-copper sulfide containing intrinsic silver at two pH values (pH 3 and 5). Experiments have revealed that presence of cysteine has a large impact on the electrochemical behavior of modified CPEs. Observed phenomena take place in solution, as well as at the surface of the modified CPEs, and can be applied for electroanalytical purposes. Based on the electrochemical behavior observed in the examined system, differential pulse voltammetry (DPV) was selected as an electroanalytical method for determination of cysteine. The effects of the various parameters on the electroanalytical signal, such as the amount of electroactive material, electroanalytical parameters, pH etc., were investigated using differential pulse voltammograms. The results indicated that electrochemical signal characterized with well-defined cathodic peak at 0.055 V vs. Ag/AgCl (3 M) in acetic buffer solution at pH 5 can be used for indirect electrochemical determination of cysteine. The optimization procedure revealed that the most sensitive and stabile electrode was that containing 5% modifier. The DPV response of the electrode, in the presence of cysteine, showed two different linear concentration ranges of 0.1 to 2.5 μM, and 5.6 to 28 μM. The explanation of the origin of two linear ranges is proposed. The lower concentration range was characterized by remarkable sensitivity of the 11.78 μA μM–1, owing to the chosen indirect method of determination. The calculated limit of detection (LOD), as well as limit of quantification (LOQ) were 0.032 and 0.081 μM, respectively. The influence of interfering agents on the electroanalytical response was examined, and low or no interference on the DPVs was observed. The proposed method was validated and applied for the determination of cysteine in pharmaceutical preparations with satisfactory recoveries in the range of 97 to 101.7%.

Electrochemical Amino Acid Sensing: A Review on Challenges and Achievements

The rapid growth of research in electrochemistry in the last decade has resulted in a significant advancement in exploiting electrochemical strategies for assessing biological substances. Among these, amino acids are of utmost interest due to their key role in human health. Indeed, an unbalanced amino acid level is the origin of several metabolic and genetic diseases, which has led to a great need for effective and reliable evaluation methods. This review is an effort to summarize and present both challenges and achievements in electrochemical amino acid sensing from the last decade (from 2010 onwards) to show where limitations and advantages stem from. In this review, we place special emphasis on five well-known electroactive amino acids, namely cysteine, tyrosine, tryptophan, methionine and histidine. The recent research and achievements in this area and significant performance metrics of the proposed electrochemical sensors, including the limit of detection, sensitivity, stability, linear dynamic range(s) and applicability in real sample analysis, are summarized and presented in separate sections. More than 400 recent scientific studies were included in this review to portray a rich set of ideas and exemplify the capabilities of the electrochemical strategies to detect these essential biomolecules at trace and even ultra-trace levels. Finally, we discuss, in the last section, the remaining issues and the opportunities to push the boundaries of our knowledge in amino acid electrochemistry even further.

Highly active catalyst using zeolitic imidazolate framework derived nano-polyhedron for the electro-oxidation of l-cysteine and amperometric sensing

Herein, N-doped porous carbon nano-polyhedron embedded with Co₃O₄ (Co₃O₄-NPCN) was reported for the electro-catalytic oxidation and amperometric detection of l-cysteine. Co₃O₄-NPCN was synthesized by the two-step redox calcination of zeolitic imidazolate framework (ZIF). Surface morphology characterization revealed that Co₃O₄-NPCN displayed a uniform size and rhombic dodecahedral shape. Structure and composition analysis found that Co₃O₄-NPCN was a N-doped carbon polyhedral matrix with hollow and porous structure, and Co₃O₄ nano-spheres were evenly distributed into the polyhedral matrix. Due to the hollow and porous structure, N-doped carbon matrix and embedded Co₃O₄ nano-spheres, Co₃O₄-NPCN performed a remarkable electro-catalysis towards the oxidation of l-cysteine at a very low potential of 0.10 V. A diffusion-controlled l-cysteine oxidation process was observed at Co₃O₄-NPCN prepared electrode. Accordingly, amperometric method was established for l-cysteine detection with a very fast current response in 2 s, wide linear range of 0.05 μM- 5.2 mM and low detection limit of 6.9 nM. Besides, notable selectivity, repeatability, reproducibility and long-term stability were also achieved. Moreover, Co₃O₄-NPCN sensor was successfully applied to the l-cysteine detection in human serum samples indicating the practical application of the as-developed sensor.

Selective and Sensitive ZnO Quantum Dots Based Fluorescent Biosensor for Detection of Cysteine

In the present article, a novel and effective ZnO quantum dots-based fluorescent probe has been developed for the detection of cysteine in different solutions. Firstly, melamine-based fluorescent pre-probe was successfully synthesized via condensation reaction and, then ZnO quantum dots (QDs) were homogenously dispersed into this solution. This fluorescent probe was used for the detection of cysteine in different solutions such as bovine serum albumin and tap water. ZnO QDs were characterized using XRD, nano-particle size analyzer, and FE-SEM techniques. The size of the ZnO QDs was calculated as 28.03±9.86 nm, and 31.95±10.02 nm from Scherrer's equation and nano-particle size analyzer, respectively. The developed fluorescent probe was exhibited a highly selective and sensitive response to the detection of cysteine. Also, the proposed fluorescent probe has a larger Stokes shift value (236 nm). The limit of detection and linear range of ZnO QDs-based fluorescent biosensor were found as 0.642 μM and 0.1-600 μM, respectively. ZnO quantum dot-based fluorescent sensor for L-cysteine.