A review on recent advances in hierarchically porous metal and metal oxide nanostructures as electrode materials for supercapacitors and non-enzymatic glucose sensors

Biofouling-resistant nanomaterials for non-enzymatic glucose sensors: A critical review

Biofouling is a significant concern in sensors and diagnostic applications as it results in reduced sensitivity, selectivity, and response time, false signals or noise, and ultimately causes a reduction in the sensor lifespan. This is particularly a concern while developing non-enzymatic glucose sensors (NEGS) that can be used to fabricate implantable sensors for continuous glucose monitoring. Thus, developing advanced materials solutions in the form of nanomaterials that display inherent antifouling activity is imperative. Due to their small nanosized dimensions and tunable microstructures, nanomaterials display unique physio-chemical properties that display antifouling efficiency and thus can be applied towards developing highly stable, sensitive, and selective NEGS. Through this review, we aim to explore the recent advances in the field of antifouling nanomaterials that offer promising potential to be applied towards developing NEGS. We discuss the details of various biofouling-resistant nanomaterials, including graphene and graphene oxide, carbon nanotubes, gold nanoparticles, silver nanoparticles, metal oxide nanoparticles, and polymeric nanocomposites. Further, we highlighted the possible mechanism of action involving nanomaterials in providing antifouling features in NEGS, followed by a brief discussion of the advantages and disadvantages of using nanomaterials for antifouling in developing NEGS. Finally, we concluded the article by proposing the future prospects of this promising technology.

Transformation study and characterization of Cu-BTC MOF-derived nanoporous copper oxide

This study provides a systematic and comprehensive investigation of the transformation process of copper-based metal-organic frameworks (Cu-BTC MOFs) into nanoporous copper oxides (P-CuOx) through controlled calcination. While calcination is a well-established method for producing MOF-derived oxides, previous studies have primarily focused on their applications. Most of them often lack detailed exploration of the transformation process and decomposition mechanisms though it is crucial for achieving tunability in MOF-derived structures. Our study addresses this gap by offering valuable insights that can guide the production of various MOF-derived oxides with tunable structural and functional properties. In this report, we have meticulously analysed the combined effects of calcination parameters, including temperature (250-500 °C), heating rate (0.5-10 °C min-1), and duration (1 and 2 hours) on the phase transformation, morphological features, and optical properties of Cu-BTC during its transformation to P-CuOx. Results revealed that fine adjustments to these calcination parameters allow precise control over phase purity, surface area, and porosity, achieving a high surface area of 113 m2 g-1 for derived P-CuO. Furthermore, the P-CuOx materials exhibited strong visible-light absorption, highlighting their potential for solar energy harvesting applications. This approach opens opportunities for designing advanced materials with customized performance characteristics. The findings have broad applicability and enable the research community to fully exploit MOF-derived oxides for designing advanced materials with customized properties for diverse applications, including energy, sensing, and biomedical.

High-Performance 3D Nanostructured Silver Electrode for Micro-Supercapacitor Application

In the current energy crisis scenario, the development of renewable energy forms such as energy storage systems among the supercapacitors is an urgent need as a tool for environmental protection against increasing pollution. In this work, we have designed a novel 3D nanostructured silver electrode through an antireplica/replica template-assisted procedure. The chemical surface and electrochemical properties of this novel 3D electrode have been studied in a 5 M KOH electrolyte. Microstructural characterization and compositional analysis were studied by SEM, energy-dispersive X-ray spectroscopy, XRD technique, and Kripton adsorption at -198 °C, together with cyclic voltammetry and galvanostatic charge-discharge cycling measurements, Coulombic efficiency, cycle stability, and their leakage current drops, in addition to the self-discharge and electrochromoactive behavior, were performed to fully characterize the 3D nanostructured electrode. Large areal capacitance value of 0.5 F/cm2 and Coulombic efficiency of 97.5% are obtained at a current density of 6.4 mA/cm2 for a voltage window of 1.2 V (between -0.5 and 0.8 V). The 3D nanostructured silver electrode exhibits excellent capacitance retention (95%) during more than 2600 cycles, indicating a good cyclic stability. Additionally, the electrode delivers a high energy density of around 385.87 μWh/cm2 and a power density value of 3.82 μW/cm2 and also displays an electrochromoactive behavior. These experimental results strongly support that this versatile combined fabrication procedure is a suitable strategy for improving the electrochemical performances of 3D nanostructured silver electrodes for applications as micro-supercapacitors or in electrochemical devices.

A Porous Nanostructured ZnO Layer for Ultraviolet Sensing with Quartz Crystal Microbalance Technique

Porous films of metals and metal oxides have gained growing attention as potential materials for use in applications that require large, specific surface areas, such as sensors, supercapacitors, and batteries. In this study, a "black-metal"-like porous Zn-ZnO composite layer was grown by room temperature co-sputtering of Zn metal and ZnO:Ga (3 at/%) ceramic targets. Following deposition, a porous ZnO layer was obtained by a subsequent thermal annealing process at 400 °C in air. The morphology and structural properties of the obtained porous layered objects were analyzed. The porosity and chemical characteristics of the nanostructured ZnO layer obtained with the method herein described make it suitable to be used as a sensitivity-enhancing active layered element in quartz crystal microbalance (QCM)-based ultraviolet (UV) sensors. The prepared resonant ZnO/QCM sensors under UV radiation exhibited maximum shift up to 35 Hz for several "on-off" UV cycles, excellent response, and recovery times of 11 and 12 s, respectively.

Ultrasensitive Nonenzymatic Real-Time Hydrogen Peroxide Monitoring Using Gold Nanoparticle-Decorated Titanium Dioxide Nanotube Electrodes

An amperometric enzyme-free hydrogen peroxide (H₂O₂) sensor was developed by catalytically stabilizing active gold nanoparticles (Au NPs) of 4-5 nm on a porous titanium dioxide nanotube (TiO₂ NTs) electrode. The Au NPs were homogeneously distributed on anatase TiO₂ NTs with an outer diameter of ~102 nm, an inner diameter of ~60 nm, and a wall of thickness of ~40 nm. The cyclic voltammogram of the composite electrode showed a pair of redox peaks characterizing the electrocatalytic reduction of H₂O₂. The entrapping of Au NPs on TiO₂ NTs prevented aggregation and facilitated good electrical conductivity and electron transfer rate, thus generating a wide linear range, a low detection limit of ~104 nM, and high sensitivity of ~519 µA/mM, as well as excellent selectivity, reproducibility, repeatability, and stability over 60 days. Furthermore, excellent recovery and relative standard deviation (RSD) were achieved in real samples, which were tap water, milk, and Lactobacillus plantarum bacteria, thereby verifying the accuracy and potentiality of the developed nonenzymatic sensor.

Applications of trimetallic nanomaterials as Non-Enzymatic glucose sensors

OBJECTIVE

This article critically reviews recent research on the use of trimetallic nanomaterials for the fabrication of non-enzymatic glucose sensors (NEGS), also known as fourth-generation glucose sensors (FGGS).

SIGNIFICANCE

Diabetes is a prevalent chronic disease worldwide, and glucose monitoring is crucial for its management. However, conventional enzymatic glucose sensors suffer from several technological drawbacks, and there is a need to develop new-generation glucose sensors that can overcome these limitations. NEGS, particularly those composed of trimetallic nanocomposites, have demonstrated promising results in terms of improved shelf life, higher sensitivity, and simplicity of operation during glucose measurement.

METHODS

In this review, we discuss the different trimetallic nanomaterials developed and used by researchers in recent years for glucose detection, including their mechanisms of action. We also provide a brief discussion of the advantages and disadvantages of FGGS-based trimetallic nanomaterials, as well as the industrial challenges in this area of research.

RESULTS

Trimetallic nanomaterials for FGGS have shown excellent reproducibility and high stability, making them suitable for continuous glucose monitoring. The different types of trimetallic nanomaterials have varying sensing properties, and their performance can be tuned by controlling their synthesis parameters.

CONCLUSION

Trimetallic nanomaterials are a promising avenue for the development of FGGS, recent research has demonstrated their potential for glucose monitoring. However, there are still some challenges that need to be addressed before their widespread adoption, such as their long-term stability and cost-effectiveness. Further research in this area is needed to overcome these challenges and to develop commercially viable FGGS for diabetes management.

Non-enzymatic glucose sensors composed of trimetallic CuO/Ag/NiO based composite materials

The escalating risk of diabetes and its consequential impact on cardiac, vascular, ocular, renal, and neural systems globally have compelled researchers to devise cost-effective, ultrasensitive, and reliable electrochemical glucose sensors for the early diagnosis of diabetes. Herein, we utilized advanced composite materials based on nanoporous CuO, CuO/Ag, and CuO/Ag/NiO for glucose detection. The crystalline structure and surface morphology of the synthesized materials were ascertained via powder X-ray diffraction (P-XRD), energy dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. The electro-catalytic properties of the manufactured electrode materials for glucose electro-oxidation in alkaline conditions were probed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. Notably, the CuO/Ag/NiO electrode material exhibited exceptional performance as a non-enzymatic glucose sensor, displaying a linear range of 0.001-5.50 mM, an ultrahigh sensitivity of 2895.3 μA mM^-1 cm^-2, and a low detection limit of 0.1 μM. These results suggest that nanoporous CuO/Ag/NiO-based composite materials are a promising candidate for early diagnosis of hyperglycemia and treatment of diabetes. Furthermore, non-enzymatic glucose sensors may pave the way for novel glucometer markets.

Progress on the influence of non-enzymatic electrodes characteristics on the response to glucose detection: a review (2016–2022)

Glucose sensing devices have experienced significant progress in the last years in response to the demand for cost-effective monitoring. Thus, research efforts have been focused on achieving reliable, selective, and sensitive sensors able to monitor the glucose level in different biofluids. The development of enzyme-based devices is challenged by poor stability, time-consuming, and complex purification procedures, facts that have given rise to the synthesis of enzyme-free sensors. Recent advances focus on the use of different components: metal-organic frameworks (MOFs), carbon nanomaterials, or metal oxides. Motivated by this topic, several reviews have been published addressing the sensor materials and synthesis methods, gathering relevant information for the development of new nanostructures. However, the abundant information has not concluded yet in commercial devices and is not useful from an engineering point of view. The dependence of the electrode response on its physico-chemical nature, which would determine the selection and optimization of the materials and synthesis method, remains an open question. Thus, this review aims to critically analyze from an engineering vision the existing information on non-enzymatic glucose electrodes; the analysis is performed linking the response in terms of sensitivity when interferences are present, stability, and response under physiological conditions to the electrode characteristics.

CuO/Cu/rGO nanocomposite anodic titania nanotubes for boosted non-enzymatic glucose biosensors

Highly arranged porous anodic titania (TiO2) nanotube arrays (ATNT) were fruitfully fabricated by the anodization of Ti foil in an ammonium fluoride electrolyte.

A Review on Non-Enzymatic Electrochemical Biosensors of Glucose Using Carbon Nanofiber Nanocomposites

Diabetes mellitus has become a worldwide epidemic, and it is expected to become the seventh leading cause of death by 2030. In response to the increasing number of diabetes patients worldwide, glucose biosensors with high sensitivity and selectivity have been developed for rapid detection. The selectivity, high sensitivity, simplicity, and quick response of electrochemical biosensors have made them a popular choice in recent years. This review summarizes the recent developments in electrodes for non-enzymatic glucose detection using carbon nanofiber (CNF)-based nanocomposites. The electrochemical performance and limitations of enzymatic and non-enzymatic glucose biosensors are reviewed. Then, the recent developments in non-enzymatic glucose biosensors using CNF composites are discussed. The final section of the review provides a summary of the challenges and perspectives, for progress in non-enzymatic glucose biosensors.

Fabrication and characterization of Ti/polyaniline-Co/PbO2-Co for efficient electrochemical degradation of cephalexin in secondary effluents

The traditional interlayer of PbO₂ electrode possessed many problems, such as short service lifetime and limited specific surface area. Herein, a novel and efficient Ti/polyaniline-Co/PbO₂-Co electrode was conctructed employing cyclic voltammetry to introduce a Co-doped polyaniline interlayer and anodic electrodeposition to synthetize a β-PbO₂-Co active layer. Compared with pristine PbO₂ electrode, Ti/polyaniline-Co/PbO₂-Co exhibited more compact crystalline shape and higher active sites amounts. Pratically, the electrochemical degradation of 5 mg L^-1 cephalexin in real secondary effluents was effectively achieved by the novel anode with 87.42% cephalexin removal and 71.8% COD mineralization after 120 min of 15 mA cm^-2 electrolysis. The hydroxyl radical production and electrochemical stability were increased by 3.16 and 3.27 times respectively. The cephalexin degradation pathway was investigated by combining a density functional theory-based theoretical approach and LC-QTrap-MS/MS. The most likely cleavage point of the β-lactam ring was the O=C-N bond, whose attack would produce small molecular compounds containing the thiazole and 4, 6-thiazine rings. Further oxidation produced inorganic ions; quantitative investigations indicated the amino groups to undergo decomposition to form aqueous NH₄⁺, which was further oxidized to NO₃^-. The accumulation of NO₃^- and SO₄^2-, combined with a decrease in toxicity toward Escherichia coli, demonstrated the efficient mineralization of cephalexin on the Ti/polyaniline-Co/PbO₂-Co electrode.

Nonenzymatic Glucose Sensor Based on Porous Co3O4 Nanoneedles

Herein, porous Co3O4 nanoneedle arrays were synthesized on nickel (Ni) foam (Co3O4 NNs/NF) by one-step hydrothermal method. Some electrochemical methods were used to investigate its nonenzymatic glucose sensing performance in alkaline solution. The results show that the sensitivity of Co3O4 NNs/NF electrode to glucose is 4570 μA mM-1 cm-2. The linear range is 1 μM-0.337 mM, and the detection limit is 0.91 μM ( $S/N=3$ ). It also displays good selectivity and repeatability for glucose. The good electrochemical sensing performance of Co3O4 NNs/NF based sensor for glucose can be attributed to interconnected porous structure and large specific surface area of Co3O4.

Cyclic and Linear Sweep Voltammetric Studies of a Modified Carbon Paste Electrode with Nickel Oxide Nanoparticles toward Tamoxifen: Effects of Surface Modification on Electrode Response Kinetics

Due to the serious adverse futures of some anticancer drugs, the determination of trace amounts of these drugs by simple analytical techniques is of great interest. In this regard, knowing about the mechanism of the analyte with the sensing material plays an important role. Nickel oxide nanoparticles (NiO NPs) modified by a carbon paste electrode (NiO-CPE) showed an irreversible cyclic voltammetric (CV) behavior in the NaOH (pH 13) supporting electrolyte based on the peak separation of 311 mV. Its peak current was decreased by adding tamoxifen (TAM), confirming that TAM molecules can consume NiO before participating in the electrode reaction. For this goal, TAM can be oxidized or reduced, and the corresponding mechanisms are schematically illustrated in the text. This study focused on the kinetic aspects of the process. Based on the CV results, a surface coverage (Γ) value of 2.72 × 10^-5 mol NiO per cm² was obtained with charge transfer coefficients α_a and α_c of 0.317 and 0.563, respectively. α_a and α_c values were changed to 0.08 and 0.72 in the presence of TAM. Further, the rate constant (k _s) value was 0.021 ± 0.01 s^-1 in the presence of TAM. In linear sweep voltammetry (LSV), an α value of about 0.636 ± 0.023 and an exchange rate constant (k _o) value of about 0.097 ± 0.031 s^-1 were obtained in the absence of TAM, which changed to 0.62 ± 0.081 and 0.089 ± 0.021 s^-1 in the presence of TAM, respectively. Despite more published papers, when the TAM analyte was added to the NaOH supporting electrolyte, both anodic and cathodic peak currents of the modified NiO-CPE decreased. We suggested some reasons for this decreased peak current, and four mechanisms were illustrated for the electrode response in the presence of TAM.

Porous CeNiO3 with an enhanced electrochemical performance and prolonged cycle life (>50 000 cycles) via a lemon-assisted sol–gel autocombustion method

A symmetric device with long life span and high Coulombic efficiency has been fabricated using porous structured CeNiO3.

Conversion of Plastic Waste into Supports for Nanostructured Heterogeneous Catalysts: Application in Environmental Remediation

Plastics are ubiquitous in our society and are used in many industries, such as packaging, electronics, the automotive industry, and medical and health sectors, and plastic waste is among the types of waste of higher environmental concern. The increase in the amount of plastic waste produced daily has increased environmental problems, such as pollution by micro-plastics, contamination of the food chain, biodiversity degradation and economic losses. The selective and efficient conversion of plastic waste for applications in environmental remediation, such as by obtaining composites, is a strategy of the scientific community for the recovery of plastic waste. The development of polymeric supports for efficient, sustainable, and low-cost heterogeneous catalysts for the treatment of organic/inorganic contaminants is highly desirable yet still a great challenge; this will be the main focus of this work. Common commercial polymers, like polystyrene, polypropylene, polyethylene therephthalate, polyethylene and polyvinyl chloride, are addressed herein, as are their main physicochemical properties, such as molecular mass, degree of crystallinity and others. Additionally, we discuss the environmental and health risks of plastic debris and the main recycling technologies as well as their issues and environmental impact. The use of nanomaterials raises concerns about toxicity and reinforces the need to apply supports; this means that the recycling of plastics in this way may tackle two issues. Finally, we dissert about the advances in turning plastic waste into support for nanocatalysts for environmental remediation, mainly metal and metal oxide nanoparticles.

Non-Enzymatic Amperometric Glucose Screen-Printed Sensors Based on Copper and Copper Oxide Particles

Non-enzymatic amperometric glucose sensors have gained much attention in the past decade because of the better chemical and thermal stability and biocompatibility compared to conventional sensors based on the use of biomolecules. This study focuses on a novel copper and copper oxide-based glucose sensor synthesized by an electrodeposition technique through a rigorous protocol which reports an excellent analytical performance due to its structure and its increased active area. In addition, the linear response range, detection limit and sensitivity were 0.5–5.0 mmol L−1, 0.002 mmol L−1, 904 μA mmol−1 L−1 cm−2, respectively. Results show a reliable electrode as it is chemically stable, exhibits rapid and excellent sensitivity, and it is not significantly affected by coexisting species present in the blood samples; furthermore, it reports a maximum relative standard deviation error (RSD) of 6%, and showed long operating life as the electrode was used for thousand measurements of 4.0 mmol L−1 glucose solution during three days.

Synthesis and Characterization of Supercapacitor Materials from Soy

Renewable resources and their byproducts are becoming of growing interest for alternative energy. Here, we have demonstrated the use of Arkansas’ most important crop, soy, as a carbon precursor for the synthesis of carbonized activated materials for supercapacitor applications. Different soy products (soymeal, defatted soymeal, soy flour and soy protein isolate) were converted into carbonized carbon and co-doped with phosphorus and nitrogen simultaneously, using a facile and time-effective microwave synthesis method. Ammonium polyphosphate was used as a doping agent which also absorbs microwave radiation. The surface morphology of the resulting carbonized materials was characterized in detail using scanning electron microscopy. X-ray photoelectron spectroscopy was also performed, which revealed the presence of a heteroelemental composition, along with different functional groups at the surface of the carbonized materials. Raman spectroscopy results depicted the presence of both a graphitic and defect carbon peak, with defect ratios of over one. The electrochemical performance of the materials was recorded using cyclic voltammetry in various electrolytes including acids, bases and salts. Among all the other materials, soymeal exhibited the highest specific capacitance value of 127 F/g in acidic electrolytes. These economic materials can be further tuned by changing the doping elements and their mole ratios to attain exceptional surface characteristics with improved specific capacitance values, in order to boost the economy of Arkansas, USA.

Recent Advances in Non-Enzymatic Glucose Sensors Based on Metal and Metal Oxide Nanostructures for Diabetes Management- A Review

There is an undeniable growing number of diabetes cases worldwide that have received widespread global attention by many pharmaceutical and clinical industries to develop better functioning glucose sensing devices. This has called for an unprecedented demand to develop highly efficient, stable, selective, and sensitive non-enzymatic glucose sensors (NEGS). Interestingly, many novel materials have shown the promising potential of directly detecting glucose in the blood and fluids. This review exclusively encompasses the electrochemical detection of glucose and its mechanism based on various metal-based materials such as cobalt (Co), nickel (Ni), zinc (Zn), copper (Cu), iron (Fe), manganese (Mn), titanium (Ti), iridium (Ir), and rhodium (Rh). Multiple aspects of these metals and their oxides were explored vis-à-vis their performance in glucose detection. The direct glucose oxidation via metallic redox centres is explained by the chemisorption model and the incipient hydrous oxide/adatom mediator (IHOAM) model. The glucose electrooxidation reactions on the electrode surface were elucidated by equations. Furthermore, it was explored that an effective detection of glucose depends on the aspect ratio, surface morphology, active sites, structures, and catalytic activity of nanomaterials, which plays an indispensable role in designing efficient NEGS. The challenges and possible solutions for advancing NEGS have been summarized.