Non-enzymatic sensing of glucose using screen-printed electrode modified with novel synthesized CeO2@CuO core shell nanostructure

An electrochemical sensor for the determination of environmentally hazardous fungicide pyrimethanil in water and fruit samples

We developed a facile electroanalytical system for the rapid and sensitive detection of pyrimethanil through the modification of carbon paste electrode surface using the as-fabricated europium doped feather-type CuO nanoflowers (FT-Eu3+-CuO NF sensor). The peak current of pyrimethanil oxidation was elevated by the sensor due to the integration of appreciable electrochemical features of the modifier, which indicates the high ability of the modified electrode to enhance the sensitivity of pyrimethanil detection. The pyrimethanil sensor under the optimized setting had a broad linear dynamic range (0.001-800.0 μM) and a narrow limit of detection (0.18 nM). The practical applicability of the as-fabricated electrode was verified by sensing pyrimethanil in real samples; it also exhibited commendable specificity, stability and reproducibility.

Non-enzymatic amperometric glucose sensing on CuO/mesoporous TiO2 modified glassy carbon electrode

The present study illustrates the fabrication of a glucose sensing electrode based upon binary composite of copper oxide and mesoporous titanium dioxide on glassy carbon (CuO/TiO2/GCE). The X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis evidently showed the phase pure monoclinic CuO nanoparticles and anatase TiO2. N2 adsorption-desorption analysis verified the mesoporosity in TiO2 with specific surface area greater than 105 m2 g-1. Electrochemical impedance spectroscopic analysis proved the remarkable decrease in the charge transfer resistance and facilitation of electron transfer process on the fabricated electrode. The optimum weight ratio of CuO to TiO2 was 1 : 1, and the optimum potential was 0.6 V vs. saturated calomel electrode. The chronoamperometric measurements displayed a detection limit of 1.9 μM, and sensitivities of 186.67 μA mM-1 cm-2 and 90.53 μA mM-1 cm-2 in two linear ranges of 0.05 to 5.2 mM and 5.2 to 20 mM, respectively. The amperometric analysis further showed good reproducibility, high specificity and outstanding stability of the modified electrode.

Focus Review on Nanomaterial-Based Electrochemical Sensing of Glucose for Health Applications

Diabetes management can be considered the first paradigm of modern personalized medicine. An overview of the most relevant advancements in glucose sensing achieved in the last 5 years is presented. In particular, devices exploiting both consolidated and innovative electrochemical sensing strategies, based on nanomaterials, have been described, taking into account their performances, advantages and limitations, when applied for the glucose analysis in blood and serum samples, urine, as well as in less conventional biological fluids. The routine measurement is still largely based on the finger-pricking method, which is usually considered unpleasant. In alternative, glucose continuous monitoring relies on electrochemical sensing in the interstitial fluid, using implanted electrodes. Due to the invasive nature of such devices, further investigations have been carried out in order to develop less invasive sensors that can operate in sweat, tears or wound exudates. Thanks to their unique features, nanomaterials have been successfully applied for the development of both enzymatic and non-enzymatic glucose sensors, which are compliant with the specific needs of the most advanced applications, such as flexible and deformable systems capable of conforming to skin or eyes, in order to produce reliable medical devices operating at the point of care.

Integration of nanomaterial sensing layers on printable organic field effect transistors for highly sensitive and stable biochemical signal conversion

Organic field effect transistor (OFET) devices are one of the most popular candidates for the development of biochemical sensors due to their merits of being flexible and highly customizable for low-cost large-area manufacturing. This review describes the key points in constructing an extended-gate type OFET (EGOFET) biochemical sensor with high sensitivity and stability. The structure and working mechanism of OFET biochemical sensors are described firstly, emphasizing the importance of critical material and device engineering to higher biochemical sensing capabilities. Next, printable materials used to construct sensing electrodes (SEs) with high sensitivity and stability are presented with a focus on novel nanomaterials. Then, methods of obtaining printable OFET devices with steep subthreshold swing (SS) for high transconductance efficiency are introduced. Finally, approaches for the integration of OFETs and SEs to form portable biochemical sensor chips are introduced, followed by several demonstrations of sensory systems. This review will provide guidelines for optimizing the design and manufacturing of OFET biochemical sensors and accelerating the movement of OFET biochemical sensors from the laboratory to the marketplace.

Salivary Glucose Detection with Laser Induced Graphene/AgNPs Non-Enzymatic Sensor

The tailoring of novel nanomaterials for sensitive glucose detection through a non-enzymatic mechanism is currently under intensive research. Here, we present a laser-induced graphene (LIG) electrode decorated with silver nanoparticles (AgNPs) as a catalytic element for the direct electrooxidation of glucose. The AgNPs were synthesized through cyclic voltammetry using LIG as a template, resulting in a porous tridimensional assembly with anchored nanostructures. The characterization corroborated the formation of LIG/AgNPs composite with distinctive peaks attributed to Ag₂O and AgO interaction with glucose. The proposed non-enzymatic sensors were successfully applied for non-enzymatic amperometric detection, exhibiting a linear range from 1 to 10 mM in the first peak (+0.7 V) and a narrow range from 1 to 2 mM with higher sensitivity of 52.2 mA/mM and improved LOD of 45 μM in the second peak (+0.55 V). The applicability of the LIG/AgNPs sensor was evaluated with spiked artificial saliva in a PoC format using a smartphone potentiostat, showing an average recovery rate of 91%. The analysis was performed in a portable, mobile, and low-cost fashion using a simulated non-invasive sample, with promising results in clinical ranges.

Construction of a binder-free non-enzymatic glucose sensor based on Cu@Ni core-shell nanoparticles anchored on 3D chiral carbon nanocoils-nickel foam hierarchical scaffold

Bimetallic nanostructures composited with carbonaceous materials are the potential contenders for quantitative glucose measurement owing to their unique nanostructures, high biomimetic activity, synergistic effects, good conductivity and chemical stability. In the present work, chemical vapors deposition technique has been employed to grow 3D carbon nanocoils (CNCs) with a chiral morphology on hierarchical macroporous nickel foam (NF) to get a CNCs/NF scaffold. Following, bimetallic Cu@Ni core-shell nanoparticles (CSNPs) are effectively coupled with this scaffold through a facile solvothermal route in order to fabricate a binder-free novel Cu@Ni CSNPs/CNCs/NF hybrid nanostructure. The constructed free-standing 3D hierarchical composite electrode guarantees highly efficient glucose redox activity due to core-shell synergistic effects, enhanced electrochemical active surface area, excellent electrochemical stability, improved conductivity with better ion diffusivity and accelerated reaction kinetics. Being a non-enzymatic glucose sensor, this electrode achieves highly swift response time of 0.1 s, ultra-high sensitivity of 6905 μA mM^-1 cm^-2, low limit of detection of 0.03 μM along with potential selectivity and good storage stability. Moreover, the proposed sensor is also tested successfully for the determination of glucose concentration in human serum samples under good recovery ranging from 96.6 to 102.1 %. The 3D Cu@Ni CSNPs/CNCs/NF composite electrode with unprecedented catalytic performance can be utilized as an ideal biomimetic catalyst in the field of non-enzymatic glucose sensing.

Recent progress of phytogenic synthesis of ZnO, SnO2, and CeO2 nanomaterials

A critical investigation on the fabrication of metal oxide nanoparticles (NPs) such as ZnO, SnO₂, and CeO₂ NPs synthesized from green and phytogenic method using plants and various plant parts have been compiled. In this review, different plant extraction methods, synthesis methods, characterization techniques, effects of plant extract on the physical, chemical, and optical properties of green synthesized ZnO, SnO₂, and CeO₂ NPs also have been compiled and discussed. Effect of several parameters on the size, morphology, and optical band gap energy of metal oxide have been explored. Moreover, the role of solvents has been found important and discussed. Extract composition i.e. phytochemicals also found to affect the morphology and size of the synthesized ZnO, SnO₂, and CeO₂ NPs. It was found that, there is no universal extraction method that is ideal and extraction techniques is unique to the plant type, plant parts, and solvent used.

Review on recent progress in metal-organic framework-based materials for fabricating electrochemical glucose sensors

Diabetes is a type of disease that threatens human health, which can be diagnosed based on the level of glucose in the blood. Recently, various MOF-based materials have been developed as efficient electrochemical glucose sensors because of their tunable pore channels, large specific surface area well dispersed metallic active sites, etc. In this review, the significance of glucose detection and the advantages of MOF-based materials for this application are primarily discussed. Then, the application of MOF-based materials can be categorized into two types of glucose sensors: enzymatic biosensors and non-enzymatic sensors. Finally, insights into the current research challenges and future breakthrough possibilities regarding electrochemical glucose sensors are considered.

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.

Green-synthesized CeO2 nanoparticles for photocatalytic, antimicrobial, antioxidant and cytotoxicity activities

Cerium oxide nanoparticles (CeO2 NPs) are a sought-after material in numerous fields due to their potential applications such as in catalysis, cancer therapy, photocatalytic degradation of pollutants, sensors, polishing agents. Green synthesis usually involves the production of CeO2 assisted by organic extracts obtained from plants, leaves, flowers, bacteria, algae, food, fruits, etc. The phytochemicals present in the organic extracts adhere to the NPs and act as reducing and/or oxidizing agents and capping agents to stabilize the NPs, modify the particle size, morphology and band gap energy of the as-synthesized materials, which would be advantageous for numerous applications. This review focuses on the green extract-mediated synthesis of CeO2 NPs and discusses the effects on CeO2 NPs of various synthesis methods that have been reported. Several photocatalytic, antimicrobial, antioxidant and cytotoxicity applications have been evaluated, compared and discussed. Future prospects are also suggested.

Nickel sulfide nanoworm network architecture as a binder-free high-performance non-enzymatic glucose sensor

Nickel sulfide nanoworm (Ni₃S₂ NW) network architecture was directly grown on the poly (3,4-ethylenedioxythiophene)-reduced graphene oxide hybrid films (PEDOT-rGO HFs) modified on glassy carbon electrode (GCE), acting as a binder-free sensor for high-performance non-enzymatic glucose monitoring. The sensor exhibited the satisfactory sensitivity (2123 μA mM^-1 cm^-2), wide linear range (15~9105 μM), low detection limit (0.48 μM), and rapid response time (< 1.5 s) at a potential of 0.5 V (vs. SCE) in 0.1 M NaOH and possessed good selectivity, reproducibility, and stability. The enhanced electrocatalytic activity of the sensor towards glucose oxidation was attributed to the particular morphology, satisfying hydrophilic nature, strong combination between Ni₃S₂ NWs, PEDOT-rGO, and bare GCE. Moreover, it can be used for assaying glucose in human serum samples without dilution, indicating potential for clinical diagnostic applications. Graphical abstract Nickel sulfide nanoworms (Ni₃S₂ NWs)/poly (3,4-ethylenedioxythiophene)-reduced graphene oxide hybrid films (PEDOT-rGO HFs) were used to construct a binder-free high-performance non-enzymatic glucose sensor with satisfactory sensitivity, wide linear range, low detection limit, good selectivity, amazing reproducibility, and stability.

Ultrasensitive electrochemical detection of neuron-specific enolase based on spiny core-shell Au/CuxO@CeO2 nanocubes

As a specific biomarker, neuron-specific enolase (NSE) is an essential clinical indicator for diagnosing small cell lung cancer. In this paper, a sandwich-type electrochemical immunosensor was designed for the quantitative detection of NSE. AuPt nanoblock spherical nanoarchitectonics (AuPt NSNs), a bimetallic nanoparticle with a rugged morphology, were utilized as the substrate, which could enhance the electronic conduction and increase the immobilization capacity of the primary antibody (Ab₁). Moreover, through a simple hydrothermal method, Au/Cu_xO@CeO₂ was prepared as a spiny core-shell nanocube with cerium dioxide (CeO₂) and gold nanoparticles (Au NPs) loading. The combination of Cu₂O, CuO, and CeO₂ showed favorable catalytic activity toward hydrogen peroxide (H₂O₂). Furthermore, the deposition of Au NPs on the spiny surface structure enhanced the specific surface area and biocompatibility, thereby rendering it more effective for loading the second antibody (Ab₂). As the label material, the Au/Cu_xO@CeO₂ achieved signal amplification and sensitive detection with the immunosensor. Under optimal conditions, the designed immunosensor possessed a broad linear range of 50 fg mL^-1 to 100 ng mL^-1 and a limit of detection of 31.3 fg mL^-1, along with satisfactory performance in sensitivity, selectivity, and stability.

Printed Electrochemical Biosensors: Opportunities and Metrological Challenges

Printed electrochemical biosensors have recently gained increasing relevance in fields ranging from basic research to home-based point-of-care. Thus, they represent a unique opportunity to enable low-cost, fast, non-invasive and/or continuous monitoring of cells and biomolecules, exploiting their electrical properties. Printing technologies represent powerful tools to combine simpler and more customizable fabrication of biosensors with high resolution, miniaturization and integration with more complex microfluidic and electronics systems. The metrological aspects of those biosensors, such as sensitivity, repeatability and stability, represent very challenging aspects that are required for the assessment of the sensor itself. This review provides an overview of the opportunities of printed electrochemical biosensors in terms of transducing principles, metrological characteristics and the enlargement of the application field. A critical discussion on metrological challenges is then provided, deepening our understanding of the most promising trends in order to overcome them: printed nanostructures to improve the limit of detection, sensitivity and repeatability; printing strategies to improve organic biosensor integration in biological environments; emerging printing methods for non-conventional substrates; microfluidic dispensing to improve repeatability. Finally, an up-to-date analysis of the most recent examples of printed electrochemical biosensors for the main classes of target analytes (live cells, nucleic acids, proteins, metabolites and electrolytes) is reported.

Recent Advances in Nanomaterial-Enabled Wearable Sensors: Material Synthesis, Sensor Design, and Personal Health Monitoring

Wearable sensors have gained much attention due to their potential in personal health monitoring in a timely, cost-effective, easy-operating, and noninvasive way. In recent studies, nanomaterials have been employed in wearable sensors to improve the sensing performance in view of their excellent properties. Here, focus is mainly on the nanomaterial-enabled wearable sensors and their latest advances in personal health monitoring. Different kinds of nanomaterials used in wearable sensors, such as metal nanoparticles, carbon nanomaterials, metallic nanomaterials, hybrid nanocomposites, and bio-nanomaterials, are reviewed. Then, the progress of nanomaterial-based wearable sensors in personal health monitoring, including the detection of ions and molecules in body fluids and exhaled breath, physiological signals, and emotion parameters, is discussed. Furthermore, the future challenges and opportunities of nanomaterial-enabled wearable sensors are discussed.

Green preparation of core-shell Cu@Pd nanoparticles with chitosan for glucose detection

Although core-shell structure is favored by many applications, preparing it with green way is rarely been reported. Herein, a core-shell structured Cu@Pd-CS nanocomposite is greenly fabricated utilizing a natural chitosan and applied to glucose detection. As-obtained Cu@Pd-CS nanoparticles were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (XRD). When applied to glucose detection, the Cu@Pd-CS exhibits good stability, sensitivity and anti-interference. Moreover, it has a good linear relationship in glucose concentrations range of 0.1-1 mM with the sensitivity of 1.53 μA mM^-1 cm^-2 and 1-10 mM with the sensitivity of 23.00 μA mM^-1 cm^-2. This work proves the practicability of building metal-based core-shell structure nanoparticles with green resources and glucose detection application.

Fabrication of magnetic iron oxide-supported copper oxide nanoparticles (Fe3O4/CuO): modified screen-printed electrode for electrochemical studies and detection of desipramine

The present investigation examines a sensitive electrochemical technique to detect desipramine through Fe₃O₄/CuO nanoparticles (NPs). Fe₃O₄/CuO NPs were synthesized via a coprecipitation procedure, and the products were characterized via energy disperse spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and vibrating sample magnetometer. The voltage–current curve and differential pulse voltammetry examinations of Fe₃O₄/CuO-modified screen-printed electrode (Fe₃O₄/CuO/SPE) were followed by the determination of electro-catalytic activities toward desipramine oxidation in a phosphate buffer solution (pH = 7.0). In addition, the value of diffusion coefficient (D = 3.0 × 10⁻⁶ cm² s⁻¹) for desipramine was calculated. Then, based on the optimum conditions, it was observed that the currents of the oxidation peak were linearly proportionate to the concentration of desipramine in the broad range between 0.08 and 400.0 μM and LOD of 0.03 μM (S/N = 3). Finally, our new sensor was successfully utilized to detect desipramine in the real samples, with reasonable recovery in the range of 97.2% to 102.7%.

The present investigation examines a sensitive electrochemical technique to detect desipramine through Fe₃O₄/CuO nanoparticles.

Ultrasonic synthesis of CuO nanoflakes: A robust electrochemical scaffold for the sensitive detection of phenolic hazard in water and pharmaceutical samples

Hydroquinone (HQ), a phenolic compound is expansively used in many industrial applications and due to the utilization of HQ, water pollution tragedies frequently found by the improper handling and accidental outflows. When HQ is adsorbed directly through the skin that create toxic effects to human by affecting kidney, liver, lungs, and urinary tract and hence, a highly selective and sensitive technique is required for its quantification. Herein, we have developed the ultrasonic synthesis of copper oxide nanoflakes (CuO-NFs) using ultrasonic bath (20 kHz, 100 W) and successfully employed for the sensitive detection of the environmental hazardous pollutant HQ. The formed CuO-NFs were confirmed by X-ray diffraction, field emission scanning electron microscopy (FE-SEM), FT-IR spectroscopy and UV-visible spectroscopy and fabricated with the screen-printed carbon electrode (SPCE). The SEM images exhibited the uniform CuO-NFs with an average width of 85 nm. The linker-free CuO-NFs fabricated electrode showed the appropriate wide range of concentrations from 0.1 to 1400 µM and the limit of detection was found to be 10.4 nM towards HQ. The fabricated sensor having long term stability and sensitivity was successfully applied for the environmental and commercial real sample analysis and exhibited good recovery percentage, implying that the SPCE/CuO-NFs is an economically viable and benign robust scaffold for the determination of HQ.

In situ formation of metal-organic framework derived CuO polyhedrons on carbon cloth for highly sensitive non-enzymatic glucose sensing

Metal-organic frameworks (MOFs) are considered promising templates for the fabrication of nanostructured materials with high porosities and high surface areas, which are important parameters for enhanced performance in sensing applications. Here, a facile in situ synthetic strategy to construct MOF-derived porous CuO polyhedrons on carbon cloth (CC) is reported. Uniform Cu(OH)2 nanorods are first synthesized on carbon cloth, followed by the conversion of Cu(OH)2 nanorods into porous CuO polyhedrons via a copper-based MOF, Cu-BTC, as the intermediate species. When evaluated as a glucose sensing electrode, the as-fabricated CuO polyhedrons/CC composite exhibits a high sensitivity of 13 575 μA mM-1 cm-2 with a fast response time (t90) of 2.3 s and a low detection limit of 0.46 μM. This work exemplifies the rational fabrication of porous nanostructures on conductive substrates for enhanced performance in glucose detection.

Synthesis of wearable and flexible NiP0.1-SnOx/PANI/CuO/cotton towards a non-enzymatic glucose sensor

Ni-SnO_x, PANI and CuO nanoparticles were synthesized on cotton fabric through chemical methods to make a new flexible high-performance non-enzymatic glucose sensor. FESEM, XRD, XPS, EDS and ATR analysis were employed to characterize the structure and the morphology of the nanomaterials. The high electrochemical performance of nickel and copper oxide and hydroxide on a conductive template leads to fabrication of a wearable and flexible cotton electrode with an excellent electrocatalytic activity to oxidize glucose. This hybrid system on the fabric as an electrode indicates a detection limit of 130 nM with wide linear range of 0.001-10 mM. The sensitivity was measured to be 1625 and 1325 μA mM^-1 cm^-2 for the ranges of 0.001-1 and 1-10 mM, respectively. Long-term stability, appropriate selectivity and reusability for many times make possibility for utilizing the fabricated sensor in the practical applications. The fabric is a wide linear range electrode with low detection limit to sense glucose concentration in the body fluids as well as the human blood that can be presumably suggested for designing other similar flexible types of sensor.

MOMSense: Metal-Oxide-Metal Elementary Glucose Sensor

In this paper, we present a novel Pt/CuO/Pt metal-oxide-metal (MOM) glucose sensor. The devices are fabricated using a simple, low-cost standard photolithography process. The unique planar structure of the device provides a large electrochemically active surface area, which acts as a nonenzymatic reservoir for glucose oxidation. The sensor has a linear sensing range between 2.2 mM and 10 mM of glucose concentration, which covers the blood glucose levels for an adult human. The distinguishing property of this sensor is its ability to measure glucose at neutral pH conditions (i.e. pH = 7). Furthermore, the dilution step commonly needed for CuO-based nonenzymatic electrochemical sensors to achieve an alkaline medium, which is essential to perform redox reactions in the absence of glucose oxidase, is eliminated, resulting in a lower-cost and more compact device.

Three-Dimensional CeO2 Woodpile Nanostructures To Enhance Performance of Enzymatic Glucose Biosensors

Fabrication of detection elements with ultrahigh surface area is essential for improving the sensitivity of analyte detection. Here, we report a direct patterning technique to fabricate three-dimensional CeO₂ nanoelectrode arrays for biosensor application over relatively large areas. The fabrication approach, which employs nanoimprint lithography and a CeO₂ nanoparticle-based ink, enables the direct, high-throughput patterning of nanostructures and is scalable, integrable, and of low cost. With the convenience of sequential imprinting, multilayered woodpile nanostructures with prescribed numbers of layers were achieved in a "stacked-up" architecture and were successfully fabricated over large areas. To demonstrate application as a biosensor, an enzymatic glucose sensor was developed. The sensitivity of glucose sensors can be enhanced simply by increasing the number of layers, which multiplies surface area while maintaining a constant footprint. The four-layer woodpile nanostructure of CeO₂ glucose sensor exhibited enhanced sensitivity (42.8 μA mM^-1 cm^-2) and good selectivity. This direct imprinting strategy for three-dimensional sensing architectures is potentially extendable to other electroactive materials and other sensing applications.

pH-regulated synthesis of CuOx/ERGO nanohybrids with tunable electrocatalytic oxidation activity towards nitrite sensing

CuO_x/ERGO nanohybrids with diverse morphologies prepared by pH-regulated synthesis display tunable electrocatalytic ability towards nitrite sensing.

Mesoporous cerium oxide-coated upconversion nanoparticles for tumor-responsive chemo-photodynamic therapy and bioimaging

A hollow structured biophotocatalyst comprising an UCNP core and mesoporous cerium oxide shell was constructed to realize oxygen self-efficient photodynamic therapy upon 980 nm laser irradiation under multiple imaging guidance.