A highly sensitive non-enzymatic glucose sensor based on bimetallic Cu–Ag superstructures

Advances of Transition Metal-Based Electrochemical Non-enzymatic Glucose Sensors for Glucose Analysis: A Review

Glucose concentration is a crucial parameter for assessing human health. Over recent years, non-enzymatic electrochemical glucose sensors have drawn considerable attention due to their substantial progress. This review explores the common mechanism behind the transition metal-based electrocatalytic oxidation of glucose molecules through classical electrocatalytic frameworks like the Pletcher model and the Hydrous Oxide-Adatom Mediator model (IHOAM), as well as the redox reactions at the transition metal centers. It further compiles the electrochemical characterization techniques, associated formulas, and their ensuing conclusions pertinent to transition metal-based non-enzymatic electrochemical glucose sensors. Subsequently, the review covers the latest advancements in the field of transition metal-based active materials and support materials used in non-enzymatic electrochemical glucose sensors in the last decade (2014-2023). Additionally, it presents a comprehensive classification of representative studies according to the active metal catalysts components involved.

Advancing Diabetes Management: The Future of Enzyme-Less Nanoparticle-Based Glucose Sensors-A Review

BACKGROUND

Glucose is vital for biological processes, requiring blood sugar levels to be maintained between 3.88 and 6.1 mmol/L, especially during fasting. Elevated levels signal diabetes, a global concern affecting 537 million people, necessitating effective glucose-monitoring devices.

METHOD

Enzyme-based sensors, though selective, are sensitive to environmental factors. Nonenzymatic sensors, especially those with nanoparticles, offer stability, high surface area, and cost-effectiveness. Existing literature supports their immediate glucose oxidation, showcasing exceptional sensitivity.

RESULTS

This review details nonenzymatic sensors, highlighting materials, detection limits, and the promise of nanoparticle-based designs, which exhibit enhanced sensitivity and selectivity in glucose detection.

CONCLUSION

Nanoparticle-based sensors, as reviewed, show potential for glucose monitoring, overcoming enzyme-based limitations. The conclusion suggests future directions for advancing these sensors, emphasizing ongoing innovation in this critical research area.

Glucose and UA sensing based on Cu nanoparticle decorated Nif/GO flexible electrode

A novel, green, and facile approach has been developed to construct an ultrasensitive flexible enzyme-less electrochemical sensor on the basis of chitosan and graphene oxide composites decorated with Cu nanoparticles supported on nickel foam (Nif/Cs/GO@Cu), in which GO functions as the intermediate between Nif and Cu nanoparticles. The Nif/Cs/GO@Cu sensing platform was successfully fabricated by the drop casting method to load Cs/GO onto Nif followed by an additionally electrodeposition to support Cu nanoparticles on Nif/Cs/GO. Impressively, the Nif/Cs/GO@Cu exhibited much higher electrocatalytic activity for glucose and UA oxidation as compared to that of Nif or Nif@Cu. For glucose and UA at about 0.6 V and 0.1 V (vs. Ag/AgCl), linearity could be obtained in the concentration ranges 5 µM-4 mM and 5-345 µM; the sensitivities were 16 and 2.5 µA µM-1 cm-2, and the detection limits 83 nM and 0.3 µM, respectively. The improved performance of the composite electrode was ascribed to the synergistic effect of Cu nanoparticles, Nif and GO, in which GO provides high electron conductivity and large surface area to prevent the agglomeration of Cu nanoparticles; Cu nanoparticles and Nif offer abundant active sites towards analytes oxidation. Additionally, the method was applied to determine both analytes successfully in blood serum samples with excellent recovery and also opens up an attractive route to potential applications of the flexible nickel foam-based electrochemical sensor.

Growth of nanostructured Cu3Al alloy films by magnetron sputtering for non-enzymatic glucose-sensing applications

Enzymatic glucose sensors usually exhibit excellent sensitivity and selectivity but suffer from poor stability due to the negative influence of temperature and humidity on enzyme molecules. As compared to enzymatic glucose sensors, non-enzymatic counterparts are generally more stable but are facing challenges in concurrently improving both sensitivity and selectivity of a trace amount of glucose molecules in physiological samples such as saliva and sweat. Here, a novel non-enzymatic glucose sensor based on nanostructured Cu₃Al alloy films has been fabricated by a facile magnetron-sputtering followed by controllable electrochemical etching approach. Since the metal Al is more reductive than Cu, by selectively etching aluminum in the Cu₃Al alloys, nanostructured alloy films were obtained with increased surface contact area and electrocatalytic active sites which resulted in enhanced glucose-sensing performance. Thus, non-enzymatic glucose sensors based on nanostructured Cu₃Al alloy films not only exhibited a high sensitivity of 1680 μA mM^-1 cm^-2 but also achieved a reliable selectivity to glucose without interference by other species in physiological samples. Consequently, this study sparked the potential for the development of non-enzymatic biosensors for the continuous monitoring of blood glucose levels with high sensitivity and impressive selectivity for glucose molecules.

Catalytic Modification of Porous Two-Dimensional Ni-MOFs on Portable Electrochemical Paper-Based Sensors for Glucose and Hydrogen Peroxide Detection

Rapid and accurate detection of changes in glucose (Glu) and hydrogen peroxide (H₂O₂) concentrations is essential for the predictive diagnosis of diseases. Electrochemical biosensors exhibiting high sensitivity, reliable selectivity, and rapid response provide an advantageous and promising solution. A porous two-dimensional conductive metal-organic framework (cMOF), Ni-HHTP (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene), was prepared by using a one-pot method. Subsequently, it was employed to construct enzyme-free paper-based electrochemical sensors by applying mass-producing screen-printing and inkjet-printing techniques. These sensors effectively determined Glu and H₂O₂ concentrations, achieving low limits of detection of 1.30 μM and 2.13 μM, and high sensitivities of 5573.21 μA μM^-1 cm^-2 and 179.85 μA μM^-1 cm^-2, respectively. More importantly, the Ni-HHTP-based electrochemical sensors showed an ability to analyze real biological samples by successfully distinguishing human serum from artificial sweat samples. This work provides a new perspective for the use of cMOFs in the field of enzyme-free electrochemical sensing, highlighting their potential for future applications in the design and development of new multifunctional and high-performance flexible electronic sensors.

Tea-polyphenol green fabricating catkin-like CuAg for electrochemical H2O2 detection

Green fabrication of unique structural nanoparticles has always been of increasing interest in many fields. Herein, a facile and green strategy of fabricating catkin-like CuAg nanocomposites using tea-polyphenols as reduction agent is reported. As-prepared nanocomposites have been characterized by a series of analysis. Physical characterizations show the synthesised of nanocomposites whose catkin-like special morphology. The electrochemical detection hydrogen peroxide (H2O2) results show that, catkin-like CuAg nanocomposites have good sensitivity, stability and anti-interference and it could detect without any additional mediator or enzyme. Specifically, it shows good H2O2 sensitivity of 2.55 μA mM-1cm-2 with range of 0.1-120 mM. Therefore, the catkin-like CuAg nanocomposites prepared by an environmental-friendly synthetic strategy, would provide a good reference for other green syntheses in the future.

Biosynthesis of Bimetallic Cu-Ag Nanocomposites and Evaluation of their Electrocatalytic, Antibacterial and Anti-Cancerous Activity

Bimetallic nanocomposites have evolved into a significant smart material in the recent past. Owing to the growing interest, we herein report the biosynthesis of bimetallic silver doped copper (Cu-Ag) nanocomposites using green methods by utilizing aqueous extract of Carica papaya leaves. The optical property and the surface morphology of the nanoparticles were determined by using various analytical techniques like Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDAX) and Transmission Electron Microscopy (TEM). The redox behaviour of the bimetallic nanocomposites was studied using Cyclic Voltammetry (CV) with platinum electrode in 0.1M KCl solution at different scan rates and concentrations. The FTIR revealed the presence of active components of the leaf extract which played the roles of surfactants, stabilizing, capping, and reducing agents. Similarly, SEM with EDAX exhibited the presence of spherically agglomerated Cu-Ag nanocomposites and TEM images revealed a particle size of 20 nm. The gradual increase in peak current was observed in CV with increase in the scan rates and concentrations apparently. The bimetallic nanocomposites showed potential anti-bacterial, anti-cancerous activity and the reports are provided in detail.

Wearable Bioelectronics for Chronic Wound Management

Chronic wounds are a major healthcare issue and can adversely affect the lives of millions of patients around the world. The current wound management strategies have limited clinical efficacy due to labor-intensive lab analysis requirements, need for clinicians' experiences, long-term and frequent interventions, limiting therapeutic efficiency and applicability. The growing field of flexible bioelectronics enables a great potential for personalized wound care owing to its advantages such as wearability, low-cost, and rapid and simple application. Herein, recent advances in the development of wearable bioelectronics for monitoring and management of chronic wounds are comprehensively reviewed. First, the design principles and the key features of bioelectronics that can adapt to the unique wound milieu features are introduced. Next, the current state of wound biosensors and on-demand therapeutic systems are summarized and highlighted. Furthermore, we discuss the design criteria of the integrated closed loop devices. Finally, the future perspectives and challenges in wearable bioelectronics for wound care are discussed.

3D printing polycaprolactone micro-nano copper scaffolds with a high antibacterial performance for potential sewage treatment

Effective application of micro-nano copper particles in elimination of the pathogenic microorganisms in the water remains a challenge. In this study, an optimum structural design was adopted in mathematical models to improve the efficiency of sewage filtration, and polycaprolactone/copper scaffold (PCs) was fabricated through a 3D printing method. The result shows that the micro-nano copper particles were physically embedded into the polycaprolactone scaffolds. In addition, the antibacterial efficiency of PCs against E. coli and S. aureus was up to 100% and the antibacterial performance could be remained in sewage filtration (copper: polycaprolactone = 1:2). The results suggest that PCs is a good candidate for application in the sewage treatment.

Controlled synthesis of Cu-Sn alloy nanosheet arrays on carbon fiber paper for self-supported nonenzymatic glucose sensing

Nanoalloy shows significant advantages and broad application prospects in chemical catalysis, due to the possessed high specific surface energy and abundant active sites can greatly promote their catalytic performance. In this work, morphology-controlled Cu-Sn alloy nanosheet arrays supported on carbon fiber paper (CP) substrate (Cu-Sn/CP) have been developed by a facile one-step electrodeposition technique at room temperature for the first time. Benefiting from the large active surface area, considerable ion transport channels and strong synergistic catalytic effect between Cu and Sn, the as-prepared Cu-Sn/CP served as a self-supported electrode for efficient nonenzymatic glucose sensing. Under optimized conditions, Cu-Sn/CP electrode offers wide linear ranges of 0.0005-2.0 mM and 2.0-10.0 mM, respectively. The detection limit is as low as 0.061 μM (S/N = 3). Cu-Sn/CP electrode also exhibited excellent selectivity and stability. Additionally, the proposed sensor is proven to be suitable for the detection of glucose in human serum samples.

Trimetallic AuPtCo Nanopolyhedrons with Peroxidase- and Catalase-Like Catalytic Activity for Glow-Type Chemiluminescence Bioanalysis

Chemiluminescence (CL) with stable and glowing light emission is vital for the accurate detection of biomarkers. Moreover, the catalyst plays an important role in CL systems. Herein, the trimetallic AuPtCo nanopolyhedrons with peroxidase- and catalase-like catalytic activities are readily synthesized via a one-step reduction method. After reaction with the substrate ABEI and oxidant H₂O₂, the AuPtCo nanozyme can catalyze the CL emission in a flash type. Interestingly, it has been found that the biofunctionalization of the AuPtCo surface can endow the catalytic interface with a slow-diffusion effect, thereby prolonging the emission of glow-type CL. On this basis, two biofunctionalized AuPtCo nanocomposites, named as AuPtCo@Cys and AuPtCo@Ab, are prepared, achieving sensitive and selective detection of H₂O₂ and lipoprotein-associated phospholipase A₂ (Lp-PLA₂), respectively. Further, the proposed glow-type CL assays are successfully applied for the determination of H₂O₂ and Lp-PLA₂ in female vaginal discharge and human serum samples, respectively, which exhibit good correlation with the clinical results. Overall, the trimetallic AuPtCo nanozyme-based glow-type CL analysis has demonstrated as a powerful and robust tool for biomarker analysis, which holds great promise in clinical applications.

Non-Enzymatic Glucose Sensors Involving Copper: An Electrochemical Perspective

Non-enzymatic glucose sensors based on the use of copper and its oxides have emerged as promising candidates to replace enzymatic glucose sensors owing to their stability, ease of fabrication, and superior sensitivity. This review explains the theories of the mechanism of glucose oxidation on copper transition metal electrodes. It also presents an overview on the development of among the best non-enzymatic copper-based glucose sensors in the past 10 years. A brief description of methods, interesting findings, and important performance parameters are provided to inspire the reader and researcher to create new improvements in sensor design. Finally, several important considerations that pertain to the nano-structuring of the electrode surface is provided.

Developments of the Electroactive Materials for Non-Enzymatic Glucose Sensing and Their Mechanisms

A comprehensive review of the electroactive materials for non-enzymatic glucose sensing and sensing devices has been performed in this work. A general introduction for glucose sensing, a facile electrochemical technique for glucose detection, and explanations of fundamental mechanisms for the electro-oxidation of glucose via the electrochemical technique are conducted. The glucose sensing materials are classified into five major systems: (1) mono-metallic materials, (2) bi-metallic materials, (3) metallic-oxide compounds, (4) metallic-hydroxide materials, and (5) metal-metal derivatives. The performances of various systems within this decade have been compared and explained in terms of sensitivity, linear regime, the limit of detection (LOD), and detection potentials. Some promising materials and practicable methodologies for the further developments of glucose sensors have been proposed. Firstly, the atomic deposition of alloys is expected to enhance the selectivity, which is considered to be lacking in non-enzymatic glucose sensing. Secondly, by using the modification of the hydrophilicity of the metallic-oxides, a promoted current response from the electro-oxidation of glucose is expected. Lastly, by taking the advantage of the redistribution phenomenon of the oxide particles, the usage of the noble metals is foreseen to be reduced.

Monitoring the mechanism of anti-cancer agents to inhibit colorectal cancer cell proliferation: Enzymatic biosensing of glucose combined with molecular docking

Glucose, a major energy source in cellular metabolism, has a significant role in cell growth. The increase in glucose uptake is a distinguishing hallmark in cancer cells. A key step in glucose utilization is the transport of glucose to the cancer cells for supplying their additional energy. The glucose transporter (or GLUT) family is a membrane protein which facilitates the uptake of glucose in most cancer cell types. Given the increased glucose level in cancer cells and the regulatory role of GLUTs in glucose uptake, it is required to combine both experimental and theoretical studies to develop new methods to monitor cell proliferation. Herein, for the first time, a new strategy was proposed to evaluate the cell proliferation of HT-29 based on glucose consumption in the presence of resveratrol (RSV) as an anticancer agent. A hybrid nanocomposite of carbon nanofibers and nitrogen-doped graphene quantum dots was used to design an enzymatic sensor for the selective and sensitive determination of glucose in cancer cells. The results obtained from the voltammetric technique were compared with the conventional colorimetric assay. A good correlation was observed between the proliferation rate and glucose utilization by cancer cells. As it was observed, RSV induces a decrease in glucose consumption, indicating lower glucose uptake efficiency for HT-29 cells. Molecular docking studies reveal that RSV can block the interaction of glucose with the GLUT family. This is one of the possible mechanisms for the decrease of glucose level followed by the reduction of cell proliferation in the presence of RSV. Compared with traditional methods, in vitro electrochemical techniques benefit from simple, nontoxic, sensitive and low-cost detection assays and hence serve as a novel tool to pursue the growth inhibition of cancer cell in response to anti-cancer agents.

Highly Deformable Fabric Gas Sensors Integrating Multidimensional Functional Nanostructures

Highly strain-endurable gas sensors were implemented on fabric, which was taken from a real T-shirt, employing a sequential coating method. Multidimensional, functional nanostructures such as reduced graphene oxide, ZnO nanorods, palladium nanoparticles, and silver nanowires were integrated for their realization. It was revealed that the fabric gas sensors could detect both oxidizing and reducing gases at room temperature with differing signs and magnitudes of responses. Noticeably, the fabric gas sensors could normally work even under large strains up to 100%, which represents the highest strain tolerance in the gas sensor field. Furthermore, the fabric gas sensors turned out to bear harsh bending and twisting stresses. It was also demonstrated that the sequential coating method is an effective and facile way to control the size of the fabric gas sensor.

Ag nanosheets grown on Cu nanowire-based flexible films for sensitive non-enzymatic glucose sensors

Cu nanowire (Cu NW) and Ag nanosheet (Ag NS) bimetallic nanocomposites were fabricated on a flexible polyethylene terephthalate (PET) slice for non-enzymatic glucose sensing via a facile two-step approach, vacuum filtration, and galvanic displacement. Low-cost Cu NW-based conductive films were employed as the conductive substrates to substitute the traditional glassy carbon electrodes or indium tin oxide electrodes. The highly stable Ag NSs grow directly on the surface of Cu NWs without additional binders. The AgNO₃ concentration and displacement time were adjusted to control the consumption of Cu NWs and the growth of Ag nanostructures. With the large load of Ag and the great connection of Cu NWs, a high sensitivity of 2033 μA mM^-1cm^-2, a fast amperometric response of 2 s, a wide linear range of 0.0015-4.02 mM, and a satisfactory result in human serum analysis were obtained by this novel Ag NS/Cu NW/PET sensor. Especially the sensitivity of the sensor was over four-fold higher than that of pure Cu NWs/PET, benefiting from the synergistic effect of bimetals. Furthermore, the Ag NS/Cu NW/PET sensor demonstrated a stable amperometric signal against mechanical bending. The material holds promise to use to fabricate flexible electrochemical devices.

Flexible Free-Standing CuxO/Ag2O (x = 1, 2) Nanowires Integrated with Nanoporous Cu-Ag Network Composite for Glucose Sensing

To improve glucose electrocatalytic performance, one efficient manner is to develop a novel Cu-Ag bimetallic composite with fertile porosity and unique architecture. Herein, the self-supported electrode with Cu_xO/Ag₂O (x = 1, 2) nanowires grown in-situ on a nanoporous Cu-Ag network (Cu_xO/Ag₂O@NP-CuAg) has been successfully designed by a facile two-step approach. The integrated hierarchical porous structure, the tip-converged Cu_xO/Ag₂O nanowires combined with the interconnected porous conductive substrate, are favorable to provide more reactive sites and improve ions or electrons transportation. Compared with monometallic Cu₂O nanowires integrated with nanoporous Cu matrix (Cu₂O@NP-Cu), the bimetallic Cu_xO/Ag₂O@NP-CuAg composites exhibit the enhanced electrocatalytic performance for glucose. Moreover, the higher sensitivity of ~1.49 mA mM⁻¹ cm⁻² in conjunction with a wider linear range of 17 mM for the Cu_xO/Ag₂O@NP-CuAg electrode anodized for 10 min are attributed to the synergistic effect of porous structure and bimetallic Cu_xO/Ag₂O nanowires. Particularly, the integrated Cu_xO/Ag₂O@NP-CuAg composites possess good flexibility, which has been reported for the first time. Accordingly, the Cu_xO/Ag₂O@NP-CuAg with excellent glucose electrocatalytic performance and good flexibility is promising to further develop as a candidate electrode material of glucose sensors.

A bio-inspired highly selective enzymatic glucose sensor using a red blood cell membrane

Red blood cell membrane (RBCM) was coated onto the enzymatic glucose sensor. The permeability of RBCM was optimized by controlling the thickness. Intriguingly, the sensor was highly accurate, despite the existence of various interfering molecules.

Large area, one step synthesis of NiSe2 films on cellulose paper for glucose monitoring in bio-mimicking samples for clinical diagnostics

There is an urgent need to develop low cost electrochemical sensors wherein the sensor can be disposed after recording data, thereby eliminating the issue of inaccuracy arising from repeated sensing measurements, which plagues most conventional electrochemical sensors. This work is the first demonstration of a NiSe₂ based disposable, one time use electrochemical glucose sensor in bio-mimicking real samples wherein NiSe₂ was hydrothermally grown NiSe₂ on a biodegradable cellulose paper. Both physicochemical (x-ray diffraction, x-ray photoelectron spectroscopy, field emission scanning electron microscope) and electrochemical (impedance spectroscopy and cyclic voltammetry (CV)) characterization techniques confirmed the growth and presence of NiSe₂ on a cellulose paper. Electrochemical techniques like CV and amperometric (i-t) were utilized for the selective and sensitive oxidation of glucose. The results suggests that the proposed NiSe₂ sensor is effective in a linear range of 0.1-1 mM with fast response time (3.9 s), low detection limit (24.8 ± 0.1 μM) and high sensitivity (0.25 A M^-1 cm^-2) at a potential applied (E _app = 0.55 V versus Ag∣AgCl). Prior to the real sample analyses i.e. glucose detection in human urine, the fabricated NiSe₂ sensor was tested for selectivity towards glucose in co-existing interferences (dopamine, ascorbic acid, uric acid, urea, sodium chloride, fructose, lactose and cysteine). Finally, glucose in artificial blood serum and urine samples was demonstrated with the fabricated NiSe₂ sensor and the results are comparable to the conventional laboratory methods. The present methodology presents a novel possibility towards the design of next generation, affordable point-of-care devices for a broad range of clinical diagnostics.

Study of the growth mechanisms of nanoporous Ag flowers for non-enzymatic glucose detection

Highly sensitive and selective non-enzymatic glucose detection was developed using nanoporous Ag flowers on a Ni substrate. The cyclic scanning electrodeposition (CSE) method was used to fabricate Ag flowers on a Ni substrate in an alkaline electrolyte. The nanoporous Ag flowers were then formed by repeated CSE in NaOH. The growth mechanisms of the nanoporous Ag flowers were systematically studied, and these mechanisms can be extended to the formation of other metal, bimetal or metal oxide. The synthesized three-dimensional nanoporous Ag flowers on the Ni substrate were used in the electro-oxidation of glucose, demonstrating a wide linear range (0.1 μM to 1 mM), fast response time (<2 s), low detection limit of 0.1 μM (S/N = 3) and a high sensitivity to detect glucose in the presence of uric acid (UA) and ascorbic acid (AA) at the level of their physiological concentrations. Apart from the nanoporous Ag flowers, the formation of a NiO thin layer on the Ni substrate during CSE also contributed to the high selectivity. This work indicates the potential for developing a fast, sensitive, selective and stable electrochemical sensor for diabetes diagnosis.