Hierarchical Cu@CuxO nanowires arrays-coated gold nanodots as a highly sensitive self-supported electrocatalyst for L-cysteine oxidation

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.

Recent innovations in the technology and applications of low-dimensional CuO nanostructures for sensing, energy and catalysis

Low-dimensional copper oxide nanostructures are very promising building blocks for various functional materials targeting high-demanded applications, including energy harvesting and transformation systems, sensing and catalysis. Featuring a very high surface-to-volume ratio and high chemical reactivity, these materials have attracted wide interest from researchers. Currently, extensive research on the fabrication and applications of copper oxide nanostructures ensures the fast progression of this technology. In this article we briefly outline some of the most recent, mostly within the past two years, innovations in well-established fabrication technologies, including oxygen plasma-based methods, self-assembly and electric-field assisted growth, electrospinning and thermal oxidation approaches. Recent progress in several key types of leading-edge applications of CuO nanostructures, mostly for energy, sensing and catalysis, is also reviewed. Besides, we briefly outline and stress novel insights into the effect of various process parameters on the growth of low-dimensional copper oxide nanostructures, such as the heating rate, oxygen flow, and roughness of the substrates. These insights play a key role in establishing links between the structure, properties and performance of the nanomaterials, as well as finding the cost-and-benefit balance for techniques that are capable of fabricating low-dimensional CuO with the desired properties and facilitating their integration into more intricate material architectures and devices without the loss of original properties and function.

Nanomaterial-based electrochemical sensors for detection of amino acids

Amino acids are the building blocks of proteins and muscle tissue. They also play a significant role in physiological processes related to energy, recovery, mood, muscle and brain function, fat burning and stimulating growth hormone or insulin secretion. Accurate determination of amino acids in biological fluids is necessary because any changes in their normal ranges in the body warn diseases like kidney disease, liver disease, type 2 diabetes and cancer. To date, many methods such as liquid chromatography, fluorescence mass spectrometry, etc. have been used for the determination of amino acids. Compared with the above techniques, electrochemical systems using modified electrodes offer a rapid, accurate, cheap, real-time analytical path through simple operations with high selectivity and sensitivity. Nanomaterials have found many interests to create smart electrochemical sensors in different application fields e.g. biomedical, environmental, and food analysis because of their exceptional properties. This review summarizes recent advances in the development of nanomaterial-based electrochemical sensors in 2017-2022 for the detection of amino acids in various matrices such as serum, urine, blood and pharmaceuticals.

Intelligent multicolor nano-sensor based on nontoxic dual fluoroprobe and MOFs for colorful consecutive detection of Hg2+ and cysteine

Ultrasensitive detection of Hg²⁺ in aquatic ecosystems is of great significance due to its high toxicity and ubiquity in water. Herein, using a one-step in-situ synthesis method, blue fluorescent carbon dots (CDs), red fluorescent InP/ZnS quantum dots (InPQDs), and MOFs (ZIF-8) integrated multicolor nano-sensor CDs/InPQDs@ZIF-8 was constructed for consecutive visual detection of Hg²⁺ and Cys. The InPQDs can act as the response unit for Hg²⁺ and Cys, with the limit of detection (LOD) of 8.68 and 37.96 nM, respectively. Significantly, the low detection limit combines with good specificity and accuracy of the nano-sensor meet the requirement for the safety monitoring and control of Hg²⁺ in drinking and environmental water. Moreover, the color recognition and processing software installed on smart phone can realize the real-time and rapid sensing of Hg²⁺ and Cys. A logic gate circuit was also devised, providing the possibilities for the application of the nano-sensor in the field of intelligent devices. As far as we know, this was the first example to apply InPQDs to the continuous multicolor visual detection of Hg²⁺ and Cys, which provided reference for the construction of environmentally-friendly dual emission fluorescent sensors for hazardous substance monitoring.

Ultrathin graphdiyne nanosheets confining Cu quantum dots as robust electrocatalyst for biosensing featuring remarkably enhanced activity and stability

There is an urgent need for developing electrochemical biosensor based on the acetylcholinesterase (AChE) inhibition to real-time analysis of organophosphorus pesticides (OPs), but it is suffered from the sluggish electrode kinetics and high oxidation potential toward signal species. Herein, a nanocomposite of ultrafine Cu quantum dots (QD) uniformly loaded on three-dimensional ultrathin graphdiyne (GDY) nanosheets (denoted as Cu@GDY) was synthesized via a one-step strategy, which showing high-density of active sites with persistent stability. Then an AChE biosensor based on Cu@GDY was fabricated to detect OPs, and the results revealed that the Cu@GDY nanocomposite can significantly amplifies electrochemical signal and reduces the oxidation potential for OPs. The strong interaction between active site of Cu@GDY and thiocholine signal species caused rapid analyte aggregation and decreased the reaction activation energy of thiocholine electro-oxidation. Benefiting from the excellent catalytic activity of Cu@GDY nanocomposite and reasonable regulation of enzyme inhibition kinetics, the biosensor achieved rapid and sensitive detection of OPs with a detection limit of 1 μg L^-1 for paraoxon. Furthermore, the biosensor demonstrated great reproducibility, good stability and high recovery rate for OPs detection in real samples. Cu@GDY based sensor also displayed high catalytic activities and good selectivity to the non-enzymatic detection of glucose in alkaline medium. Cu@GDY offers a versatile and promising platform for sensors and biosensors featuring remarkably enhanced activity and stability, and can be applied to many other fields as desirable electrocatalyst.

Mo and Zn-Dual doped CuxO nanocrystals confined High-Conductive Cu arrays as novel sensitive sensor for neurotransmitter detection

The development of sensitive and selective sensors using facile and low-cost methods for detecting neurotransmitter molecules is a critical factor in the health care system in regard to early diagnosis. In this research, an electrocatalyst derived from Mo,Zn dual-doped Cu_xO nanocrystals-based layer coating over one-dimensional copper nanowire arrays (Mo,Zn-Cu_xO/CuNWs) was successfully designed using a facile electrodeposition approach and used as an electrochemical sensor for non-enzymatic dopamine (DA) neurotransmitter detection. The synergistic effect caused by the dual-doping effect along with its excellent conductivity produced a large electroactive surface area and an improved hetero-charge transfer, thereby boosting DA sensing ability with a low limit detection of 0.32 µM, wide-range of detection (0.5 µM - 3.9 mM), long-term stability (5 weeks), and high selectivity in phosphate buffer solution (pH 7.4). Also, the sensor accurately determined DA in real blood serum-spiked solutions. The achieved results evidenced that the Mo,Zn-Cu_xO/CuNWs derived sensor is highly suitable for DA detection. Therefore, it also opens new windows for the development of low-cost, accurate, high-performance, and stable sensors for other neurotransmitter sensing for the purposes of better health care and early diagnosis.

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.

Design, Fabrication and Applications of Electrospun Nanofiber-Based Surface-Enhanced Raman Spectroscopy Substrate

Surface-enhanced Raman spectroscopy (SERS) is an advanced and powerful analysis tool. Due to the advantages of high sensitivity, high resolution, and nondestructive testing, it has been widely used in physics, chemistry, material science and other fields. In recent years, substantial progress has been made in developing flexible platforms for the design and fabrication of SERS substrates. One important kind of the flexible platforms is based on electrospun nanofibers. Electrospun nanofibers not only have unique advantages such as easy preparation, high porosity and large specific surface area, but also can increase the number of hotspots when combined with precious metal nanomaterials, thereby enhancing the SERS signal and expanding the application scope. In this review, we firstly focus on two strategies for the fabrication of metal nanostructure decorated in/on the electrospun nanofibers, namely in-situ and ex-situ. Then the applications of these SERS substrates in the fields of quantitative analysis, monitoring chemical reactions and recyclable detection are introduced in detail. Finally, the challenges as well as perspectives are presented to offer a guideline for the future exploration of these SERS substrates. We expect that it will provide new inspiration for the development of electrospun nanofiber-based SERS substrates.

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.

Strongyloidiasis Serological Analysis with Three Different Biological Probes and Their Electrochemical Responses in a Screen-Printed Gold Electrode

(1) Background: The validation of biological antigens is the study's utmost goal in biomedical applications. We evaluated three different probes with single and multiple epitopes through electrochemical detection of specific IgG in serum for human strongyloidiasis diagnosis. (2) Methods: Screen-printed gold electrodes were used and probes consisting of two single-epitope synthetic peptides (D3 and C10) with different sequences, and a multi-epitope antigen [detergent phase (DP)-hydrophobic membrane proteins]. Human serum samples from three populations were used: Strongyloides stercoralis positive, positive for other parasitic infections and negative controls. To test the immobilization of probes onto a screen-printed gold electrode and the serum IgG detection, electrochemical analyses were carried out through differential pulse voltammetry (DPV) and the electrode surface analyses were recorded using atomic force microscopy. (3) Results: The electrochemical response in screen-printed gold electrodes of peptides D3 and C10 when using positive serum was significantly higher than that when using the DP. Our sensor improved sensitivity to detect strongyloidiasis. (4) Conclusions: Probes' sequences are critical factors for differential electrochemical responses, and the D3 peptide presented the best electrochemical performance for strongyloidiasis detection, and may efficiently substitute whole antigen extracts from parasites for strongyloidiasis diagnosis in electrochemical immunosensors.

In Situ Observation of Metal to Metal Oxide Progression: A Study of Charge Transfer Phenomenon at Ru-CuO Interfaces

Surface charge and charge transfer between nanoclusters and oxide supports are of paramount importance to catalysis, surface plasmonics, and optical energy harvesting areas. At present, high-energy X-rays and theoretical investigation are always required to determine the chemical state changes in the nanoclusters and the oxide supports, as well as the underlying transfer charge between them. This work presents the idea of using chrono-conductometric measurements to determine the chemical states of the Ru nanoclusters on CuO supports. Both icosahedral and single-crystal hexagonal close-packed Ru nanoclusters were deposited through gas-phase synthesis. To study the charge transfer phenomenon at the interface, a bias was applied to cupric oxide nanowires with metallic nanocluster decoration. In situ conductometric measurements were performed to observe the evolution of Ru into RuO_x under heating conditions. Structural elucidation techniques such as transmission electron microscopy, X-ray photoelectron spectroscopy, and Kelvin probe force microscopy were employed to study the corresponding progression of structure, chemical ordering, and surface potential, respectively, as Ru(0) was oxidized to RuO_x on the supporting oxide surface. Experimental and theoretical investigation of charge transfer between the nanocluster and oxide support highlighted the importance of metallic character and structure of the nanoclusters on the interfacial charge transfer, thus allowing the investigation of surface charge behavior on oxide-supported catalysts, in situ, during catalytic operation via conductometric measurements.