Fabrication of an ElectrochemicalL-Cysteine Sensor Based on Graphene Nanosheets Decorated Manganese Oxide Nanocomposite Modified Glassy Carbon Electrode

Alternative method for rhamnolipids quantification using an electrochemical platform based on reduced graphene oxide, manganese nanoparticles and molecularly imprinted Poly(L-Ser)

Rhamnolipids (RHLs) are promising biosurfactants with important applications in several industrial segments. These compounds are produced through biotechnological processes using the bacteria Pseudomonas Aeruginosa. The main methods of analyzing this compound are based on chromatographic techniques. In this study, an electrochemical sensor based on a platform modified with reduced graphene oxide, manganese nanoparticles covered with a molecularly imprinted poly (L-Ser) film was used as an alternative method to quantify RHL through its hydrolysis product, acid 3-hydroxydecanoic acid (3-HDA). The proposed sensor was characterized microscopically, spectroscopically and electrochemically. Under optimized experimental conditions, an analytical curve was obtained in the linear concentration range from 2.0 × 10-12 mol L-1 to 1.0 × 10-10 mol L-1. The values estimated of LOD, LOQ and AS were 8.3 × 10-13 mol L-1, 2.7 × 10-12 mol L-1and 1.3 × 107 A L mol-1, respectively. GCE/rGO/MnNPs/L-Ser@MIP exhibits excellent selectivity, repeatability, and high stability for the detection of 3-HDA. Furthermore, the developed method was successfully applied to the recognition of the hydrolysis product (3-HDA) of RHLs obtained from guava agro-waste. Statistical comparison between GCE/rGO/MnNPs/L-Ser@MIP and HPLC method confirms the accuracy of the electrochemical sensor within a 95% confidence interval.

Trace identification of cysteine enantiomers based on an electrochemical sensor assembled from CuxS@SOD zeolite

The nonchiral sensor concept based on a sodalite (SOD) zeolite loaded CuxS (CuxS@SOD) catalyst is proposed as a sensing platform for chiral cysteine (Cys) determination. Chiral Cys is analyzed by the difference of binding capacity between CuxS catalysts. The observed current in amperometric i-t curve (A i-t C) is always positive for the L-cysteine (L-Cys), while it is negative for the D-cysteine (D-Cys). Under differential pulse voltammetry (DPV) method, the characteristic current peak for the CuxS@SOD moves to right (positive potential position) with the addition of L-Cys while it moves to left (negative potential direction) with the addition of D-Cys, respectively. Cyclic voltammetry (CV) is consistent with DPV and discusses the diffusion control mechanism. In this work, the ultra-trace determination of cysteine enantiomers reaches the limit of detection (LOD) of 0.70 fM and 0.60 fM by the highly efficient CuxS catalyst restrained in the nanosized SOD zeolite cages of the opening window pores, respectively. The sensor opens up a novel potential prospect for achiral composite in the field of chiral recognition through electrochemical methods with extra-low concentration.

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.

Detection of Selenium and Nickel Metal Ion in Water Using Mn3O4-Cn-Modified Electrode

The present study reports the design of the Mn3O4-Cn electrode and its use for simultaneous detection of selenium and nickel in water. The designed electrode can be used as a convenient electrochemical device for on-site testing of Se (IV) and Ni (II) levels in affected regions. The best responses are obtained with 0.1 M phosphate buffer saline (PBS) and 5 mM Fe (CN)6 as supporting electrolyte. The scan rate and the number of cyclic repetitions have a great effect on peak shape and intensity. It is seen from our study that peak intensity is directly proportional to Se (IV) and Ni (II) concentrations in the range of 5 to 250 µg/L (correlation coefficients 0.952 and 0.984) when the optimized parameters are used. The detection limit of 0.533 µg/L Se (IV) and 0.718 µg/L for Ni (VI) with a response time of 18 s for 5–250 µg/L concentration is obtained, respectively. Enhanced analytical results for different water samples establish that the proposed method is appropriate for Se (IV) and Ni (II) detection. FESEM images confirm the Mn3O4-Cn nanocomposite formation on the electrode.

An electrochemical platform for the selective detection of azathioprine utilizing a screen-printed carbon electrode modified with manganese oxide/reduced graphene oxide

Scheme representing the electro-reduction of AZT at Mn₂O₃–rGO/SPCE.

Simple synthesis of ZnO nanoparticles on N-doped reduced graphene oxide for the electrocatalytic sensing of l-cysteine

A new kind of ZnO nanoparticle/N-doped reduced graphene oxide nanocomposite (ZnONPs/N-rGO) was synthesized through a low temperature, low-cost and one step hydrothermal process.

Surface-Renewable AgNPs/CNT/rGO Nanocomposites as Bifunctional Impedimetric Sensors

ABSTRACT

In this study, glassy carbon electrode modified by silver nanoparticles/carbon nanotube/reduced graphene oxide (AgNPs/CNT/rGO) composite has been utilized as a platform to immobilize cis-dioxomolybdenum (VI)-salicylaldehyde-histidine (MoO₂/Sal-His). The modified electrode shows two reversible redox couples for MoO₂/Sal-His. Electrocatalytic oxidation of cysteine (CySH) and electrocatalytic reduction of iodate on the surface of the modified electrode were investigated with cyclic voltammetry and electrochemical impedance spectroscopy methods. The presence of MoO₂/Sal-His on AgNPs/CNT/rGO shifted the catalytic current of iodate reduction to a more positive potential and the catalytic current of cysteine oxidation to a more negative potential. The change of interfacial charge transfer resistance (R _ct) recorded by the modified electrode was monitored for sensitive quantitative detection of CySH and iodate. Moreover, the sensor has a good stability, and it can be renewed easily and repeatedly through a mechanical or electrochemical process.

Bifunctional impedimetric sensors based on azodicarboxamide supported on modified graphene nanosheets

Herein, gold-coated graphene oxide nanosheets hybrid material (GO/AuNPs) with exceptional physical and chemical properties has been utilized as a novel platform for electrode modification. The synthetic method of GO/AuNPs involves anon-covalent functionalization of exfoliated GO with AuNPs based on the reduction of the Au(III) complex by sodium citrate. The prepared GO/AuNPs hybrid exhibits the dispersion of high density AuNPs which were densely decorated on the large surface area of GO. The GO/AuNPs modified glassy carbon (GC) electrode was employed as a sensing platform to immobilize azodicarboxamide (ACA). The morphology, structure and electrochemical performance of the sensor were characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results indicate that the modified electrode has a notable bifunctional catalytic activity. Electrocatalytic oxidations of cysteine and electrocatalytic reduction of iodate at the surface of modified electrode were investigated with different technique.

Engineered Carbon-Nanomaterial-Based Electrochemical Sensors for Biomolecules

The study of electrochemical behavior of bioactive molecules has become one of the most rapidly developing scientific fields. Biotechnology and biomedical engineering fields have a vested interest in constructing more precise and accurate voltammetric/amperometric biosensors. One rapidly growing area of biosensor design involves incorporation of carbon-based nanomaterials in working electrodes, such as one-dimensional carbon nanotubes, two-dimensional graphene, and graphene oxide. In this review article, we give a brief overview describing the voltammetric techniques and how these techniques are applied in biosensing, as well as the details surrounding important biosensing concepts of sensitivity and limits of detection. Building on these important concepts, we show how the sensitivity and limit of detection can be tuned by including carbon-based nanomaterials in the fabrication of biosensors. The sensing of biomolecules including glucose, dopamine, proteins, enzymes, uric acid, DNA, RNA, and H2O2 traditionally employs enzymes in detection; however, these enzymes denature easily, and as such, enzymeless methods are highly desired. Here we draw an important distinction between enzymeless and enzyme-containing carbon-nanomaterial-based biosensors. The review ends with an outlook of future concepts that can be employed in biosensor fabrication, as well as limitations of already proposed materials and how such sensing can be enhanced. As such, this review can act as a roadmap to guide researchers toward concepts that can be employed in the design of next generation biosensors, while also highlighting the current advancements in the field.

Selective electrochemical detection of dopamine using nitrogen-doped graphene/manganese monoxide composites

Nitrogen doping plays a critical role in regulating the electronic properties of graphene, which has shown fascinating applications in bioelectronics and biosensors.