Controllable synthesis of six corner star-like Cu2O/PEDOT-MWCNT composites and their performance toward electrochemical glucose sensing

MoS2_CNTs_aerogel-based PEDOT nanocomposite electrochemical sensor for simultaneous detection of chloramphenicol and furazolidone in food samples

Toxic intermediates in food caused by chloramphenicol (CP) and furazolidone (FZ) have gained interest in research toward their detection. Hence, fast, reliable, and accurate detection of CP and FZ in food products is of utmost importance. Here, a novel molybdenum disulfide-connected carbon nanotube aerogel/poly (3,4-ethylenedioxythiophene) [MoS2/CNTs aerogel/PEDOT] nanocomposite materials are constructed and deposited on the pretreated carbon paste electrode (PCPE) by a facile eletropolymerization method. The characterization of MoS2/CNTs aerogel/PEDOT nanocomposite was analyzed by scanning electron microscopy (SEM), cyclic voltammetry, and differential pulse voltammetry. The modified MoS2/CNTs aerogel/PEDOT nanocomposite has improved sensing characteristics for detecting CP and FZ in PBS solution. For this work, we have studied various parameters like electrocatalytic activity, the effect of scan rates, pH variation studies, and concentration variation studies. Under optimum conditions, the modified electrode exhibited superior sensing ability compared to the bare and pretreated CPE. This improvement in electrocatalytic activity can be the higher conductivity, larger surface area, increased heterogeneous rate constant, and presence of more active sites in the MoS2/CNTs aerogel/PEDOT nanocomposite. The modified electrode demonstrated distinct electrochemical sensing toward the individual and simultaneous analysis of CP and FZ with a high sensitivity of 0.701 µA. µM-1 .cm-2 for CP and 0.787 µA. µM-1 .cm-2 for FZ and a low detection limit of 3.74 nM for CP and 3.83 nM for FZ with good reproducibility, repeatability, and interferences. Additionally, the prepared sensor effectively detects CP and FZ in food samples (honey and milk) with an acceptable recovery range and a relative standard deviation below 4%.

Wearable electrochemical glucose sensor of high flexibility and sensitivity using novel mushroom-like gold nanowires decorated bendable stainless steel wire sieve

Long-term high blood glucose levels brings extremely detrimental effect on diabetic patients, such as blindness, renal failure, and cardiovascular diseases. Therefore, there is an urgent need to develop highly flexible and sensitive sensors for precisely non-invasive and continuous monitoring glucose levels. Herein, we present a highly flexible and sensitive wearable sensor for non-enzymatic electrochemical glucose analysis with vertically aligned mushroom-like gold nanowires (v-AuNWs) chemically grown on stainless steel wire sieve (SSWS) as integrated electrode. Owing to the unique nanostructures and excellent catalysis of the v-AuNWs, the as-fabricated glucose sensors exhibit superior flexibility and excellent electro-catalytic capability. In detail, these sensors display rapid response towards glucose within 5 s, and the sensor constructed with v-AuNWs for growth time of 15 min shows the highest sensitivity of 180.1 μA mM-1 cm-2 within a wide linear range of 6.5 × 10-4 mM-12.0 mM and the lowest detection limit of 0.65 μM (S/N = 3). It is noteworthy that due to the good ductility of the v-AuNWs and their strong contact with the SSWS substrate, these glucose sensors exhibit no obvious response variation after repeated bending for 100 times at bending angle of 180°. Additionally, the glucose sensors display superior anti-interfering capability as well as desirable repeatability. More importantly, these glucose sensors can be attached on human skin to determine sweat glucose reliably and analyze glucose concentration in human serum in vitro.

An efficient biosensor using a functionalized microneedle of Cu2O-based CoCu-LDH for glucose detection

Glucose detection with small and micro volume sampling has recently received increasing attention in monitoring personal health. Herein, a cauliflower-type cluster of Cu2O nanoparticles (NPs) was directly deposited on the tip surface of a stainless steel acupuncture needle electrode (ANE) by electrochemical deposition, and then this pre-formed cuprous basis was used to further prepare the neatly arranged CoCu-layered double hydroxide (CoCu-LDH) nanosheets that interconnected to form nano-sized pores in the range from 100 to 500 nm. The microstructure and spectral characteristics of the surface modification materials were comprehensively characterized by FE-SEM, EDS, XRD, FT-IR and TEM. Cu2O-based CoCu-LDH composites with special morphology had been proven to accelerate the rate of electron transport and provide more available active centers, and moreover, the mixed valence of Cu/Co induced an excellent synergism for the electrocatalytic oxidation of glucose. As a result, CoCu-LDH/Cu2O/ANE as a sensitive glucose probe exhibited two wider linear ranges of 0.03-0.40 mM and 0.40-6.00 mM, with sensitivities of 116.13 μA mM-1 and 52.08 μA mM-1, respectively, and the detection limit as low as 0.46 μM (S/N = 3). The response time only took 3 s and it kept working stably in the interference of ascorbic acid (AA), dopamine (DA), uric acid (UA), and Cl-. In the stability test, the CoCu-LDH/Cu2O/ANE sensor exhibited a stable monitoring sensitivity after 15 days. Finally, the CoCu-LDH/Cu2O/ANE sensor had been successfully applied to glucose analysis in human serum, proving that our design was an attractive strategy for developing a portable, minimally invasive, and low-cost non-enzymatic electrochemical glucose sensing platform.

Wearable non-invasive glucose sensors based on metallic nanomaterials

The development of wearable non-invasive glucose sensors provides a convenient technical means to monitor the glucose concentration of diabetes patients without discomfortability and risk of infection. Apart from enzymes as typical catalytic materials, the active catalytic materials of the glucose sensor are mainly composed of polymers, metals, alloys, metal compounds, and various metals that can undergo catalytic oxidation with glucose. Among them, metallic nanomaterials are the optimal materials applied in the field of wearable non-invasive glucose sensing due to good biocompatibility, large specific surface area, high catalytic activity, and strong adsorption capacity. This review summarizes the metallic nanomaterials used in wearable non-invasive glucose sensors including zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) monometallic nanomaterials, bimetallic nanomaterials, metal oxide nanomaterials, etc. Besides, the applications of wearable non-invasive biosensors based on these metallic nanomaterials towards glucose detection are summarized in detail and the development trend of the wearable non-invasive glucose sensors based on metallic nanomaterials is also outlook.

Copper(II)-Incorporated Porphyrin-Based Porous Organic Polymer for a Nonenzymatic Electrochemical Glucose Sensor

To date, the fabrication of multifunctional nanoplatforms based on a porous organic polymer for electrochemical sensing of biorelevant molecules has received considerable attention in the search for a more active, robust, and sensitive electrocatalyst. Here, in this report, we have developed a new porous organic polymer based on porphyrin (TEG-POR) from a polycondensation reaction between a triethylene glycol-linked dialdehyde and pyrrole. The Cu(II) complex of the polymer Cu-TEG-POR shows high sensitivity and a low detection limit for glucose electro-oxidation in an alkaline medium. The characterization of the as-synthesized polymer was done by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, and ¹³C CP-MAS solid-state NMR. The N₂ adsorption/desorption isotherm was carried out at 77 K to analyze the porous property. TEG-POR and Cu-TEG-POR both show excellent thermal stability. The Cu-TEG-POR-modified GC electrode shows a low detection limit (LOD) value of 0.9 μM and a wide linear range (0.001-1.3 mM) with a sensitivity of 415.8 μA mM^-1 cm^-2 toward electrochemical glucose sensing. The interference of the modified electrode from ascorbic acid, dopamine, NaCl, uric acid, fructose, sucrose, and cysteine was insignificant. Cu-TEG-POR exhibits acceptable recovery for blood glucose detection (97.25-104%), suggesting its scope in the future for selective and sensitive nonenzymatic glucose detection in human blood.

Highly sensitive detection of glucose via glucose oxidase immobilization onto conducting polymer-coated composite polyacrylonitrile nanofibers

Current study introduces composite polyacrylonitrile - multiwall carbon nanotubes nanofibers (PAN-MWCNTs NFs) coated with conducting polymers (polypyrrole (PPy) or poly(3,4-ethylenedioxythiophene) (PEDOT)) by chemical vapor deposition for efficient glucose detection. The potential of nanofibrous assemblies and nano-conducting elements in biosensing was explored as pre-processing of NFs with MWCNTs and post-processing with CPs were both employed. These 'core-shell' conducting NFs were further employed as platforms for glucose oxidase immobilization for enzymatic detection of glucose. The performance of the biosensors was closely correlated with the concentration of immobilized enzyme and with the type of conducting polymer. The biosensors showed high sensitivities of 92.94 and 81.72 µA/mM.cm^-2 for (PAN-MWCNTs)/ PEDOT and (PAN-MWCNTs)/ PPy accompanied by low limit of detection values of 2.30 and 2.38 µM, respectively. Good operational stability was observed throughout twenty-five consecutive measurements, over 90% activity was maintained for both sensors. This study represents proof of concept for the methodology, showcasing the advantages of nanomaterial synthesis for bio-applications. The work was compared thoroughly with previously reported biosensors showing some of the best results reported to date in terms of analytical characteristics.

Participation of Lattice Oxygen in Perovskite Oxide as a Highly Sensitive Sensor for p-Phenylenediamine Detection

The harmful effects on the human body from p-phenylenediamine (PPD) in hair dyes can cause allergies and even cancer. Therefore, it is particularly important to accurately control and detect the content of PPD in our daily products and environment. Here, a small amount of non-metallic elemental P doped in perovskite oxide of SrCoO_3-δ (SC) forms a good catalytic material, SrCo_0.95P_0.05O_3-δ (SCP), for PPD detection. The improved performance compared with that of the parent SC can be attributed to three contributing factors, including a larger amount of highly oxidative oxygen species O^22-/O^-, better electrical conductivity, and more active sites on the P⁵⁺-oxygen bonds of SCP. Moreover, the lattice oxygen mechanism (LOM) with highly active species of lattice O vacancies and adsorbed -OO for electrocatalytic oxidation of PPD by the SCP/GCE (glass carbon electrode) sensor is proposed in our work. More importantly, the SCP/GCE sensor exhibits good stability, a low limit of detection, and high reliability (error < 5.78%) towards PPD determination in real samples of hair dyes, suggesting the substantial research potential for practical 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.

Label Free Glucose Electrochemical Biosensor Based on Poly(3,4-ethylenedioxy thiophene):Polystyrene Sulfonate/Titanium Carbide/Graphene Quantum Dots

The electrochemical biosensor devices based on enzymes for monitoring biochemical substances are still considered attractive. We investigated the immobilization of glucose oxidase (GOx) on a new composite nanomaterial poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS)/titanium carbide,(Ti₃C₂)/graphene quantum dots(GQD) modified screen-printed carbon electrode (SPCE) for glucose sensing. The characterization and electrochemical behavior of PEDOT:PSS/Ti₃C₂/GQD towards the electrocatalytic oxidation of GOx was analyzed by FTIR, XPS, SEM, cyclic voltammetry (CV), and differential pulse voltammetry (DPV). This composite nanomaterial was found to tend to increase the electrochemical behavior and led to a higher peak current of 100.17 µA compared to 82.01 µA and 95.04 µA for PEDOT:PSS and PEDOT:PSS/Ti₃C₂ alone. Moreover, the detection results demonstrated that the fabricated biosensor had a linear voltammetry response in the glucose concentration range 0-500 µM with a relatively sensitivity of 21.64 µAmM^-1cm^-2 and a detection limit of 65 µM (S/N = 3), with good stability and selectivity. This finding could be useful as applicable guidance for the modification screen printed carbon (SPCE) electrodes focused on composite PEDOT:PSS/Ti₃C₂/GQD for efficient detection using an enzyme-based biosensor.

E-Tongues/Noses Based on Conducting Polymers and Composite Materials: Expanding the Possibilities in Complex Analytical Sensing

Conducting polymers (CPs) are extensively studied due to their high versatility and electrical properties, as well as their high environmental stability. Based on the above, their applications as electronic devices are promoted and constitute an interesting matter of research. This review summarizes their application in common electronic devices and their implementation in electronic tongues and noses systems (E-tongues and E-noses, respectively). The monitoring of diverse factors with these devices by multivariate calibration methods for different applications is also included. Lastly, a critical discussion about the enclosed analytical potential of several conducting polymer-based devices in electronic systems reported in literature will be offered.

Electrochemical Sensors Based on Conducting Polymers for the Aqueous Detection of Biologically Relevant Molecules

Electrochemical sensors appear as low-cost, rapid, easy to use, and in situ devices for determination of diverse analytes in a liquid solution. In that context, conducting polymers are much-explored sensor building materials because of their semiconductivity, structural versatility, multiple synthetic pathways, and stability in environmental conditions. In this state-of-the-art review, synthetic processes, morphological characterization, and nanostructure formation are analyzed for relevant literature about electrochemical sensors based on conducting polymers for the determination of molecules that (i) have a fundamental role in the human body function regulation, and (ii) are considered as water emergent pollutants. Special focus is put on the different types of micro- and nanostructures generated for the polymer itself or the combination with different materials in a composite, and how the rough morphology of the conducting polymers based electrochemical sensors affect their limit of detection. Polypyrroles, polyanilines, and polythiophenes appear as the most recurrent conducting polymers for the construction of electrochemical sensors. These conducting polymers are usually built starting from bifunctional precursor monomers resulting in linear and branched polymer structures; however, opportunities for sensitivity enhancement in electrochemical sensors have been recently reported by using conjugated microporous polymers synthesized from multifunctional monomers.

Electrochemical dual signal sensing platform for the simultaneous determination of dopamine, uric acid and glucose based on copper and cerium bimetallic carbon nanocomposites

A highly sensitive electrochemical sensor for the simultaneous dual signal determination of dopamine (DA), uric acid (UA) and glucose (Glu) has been obtained using nanocomposites based on the copper and cerium bimetallic nanoparticles and carbon nanomaterials of graphene and single-walled carbon nanotubes in the presence of Tween 20 (GR-SWCNT-Ce-Cu-Tween 20) modified glassy carbon electrode. The surface morphology of the nanocomposites was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and the electrochemical behavior of the sensor was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with potassium ferricyanide as probe. In the coexistence system of DA, UA and Glu, three clear and well-isolated voltammetric peaks were obtained by CV and differential pulse voltammetry (DPV), and oxidation peak currents of DA and UA are positively correlated with their concentrations respectively, while the peak current of Glu is negatively correlated with its concentration. Linearity was obtained in the ranges of 0.1-100 µM for dopamine, 0.08-100 µM for uric acid and 1-1000 µM for glucose with DPV, and the detection limits (S/N = 3) of 0.0072 µM, 0.0063 µM, and 0.095 µM for DA, UA and Glu, respectively. The method was successfully applied to the determination of DA, UA and Glu in blood serum samples, which provided a reference for further sensor research.

Non-enzymatic electrochemical glucose sensing by Cu2O octahedrons: elucidating the protein adsorption signature

Developing an electrochemical biosensor based on Cu₂O octahedrons for rapid, sensitive and highly selective detection of glucose in real samples with an unprecedented analysis of their protein adsorption signature.

Partial sulfidation for constructing Cu2O–CuS heterostructures realizing enhanced electrochemical glucose sensing

A Cu₂O–CuS heterostructure was constructed to elucidate the relationship between heterojunctions and electrochemical glucose sensing.

A simple enzymeless approach for Paraoxon determination using imidazole-functionalized carbon nanotubes

This work describes the application of a glassy carbon electrode (GCE) modified with imidazole functionalized carbon nanotubes (CNT-H-IMZ) for Paraoxon (PX) determination in samples of commercial, fresh and 100% orange juice. Homemade multi-walled CNTs were treated according to the Hummers procedure to oxidize graphite and later chemically functionalized with imidazole groups. Modified electrodes with CNT-H-IMZ presented a high peak current of PX reduction and an electrocatalytic effect in comparison to the other electrodes. This behavior was associated with the synergistic contribution of IMZ and CNT that increases the electrochemical activity of PX. Repeatability and reproducibility studies showed that the relative peak current values did not show significant differences between them, less than 10%, and it was possible to define that the diffusional process is the mechanism that limits the electrode mass transport. After the optimization of parameters inherent to the methodology and the voltammetric technique, the proposed device presented a linear region of 1.0 to 16.0 μM^-1 (R² = 0.99), presenting LOD and LOQ as 120 and 400 nM^-1, respectively. The method proposed was successfully applied to PX determination in spiked samples.

Boosting glucose oxidation by constructing Cu–Cu2O heterostructures

An octahedral Cu–Cu₂O heterostructure with loose and porous structure was fabricated and exhibits enhanced electrocatalytic activity towards glucose oxidation.

Electrochemical Characterization of Mancozeb Degradation for Wastewater Treatment Using a Sensor Based on Poly (3,4-ethylenedioxythiophene) (PEDOT) Modified with Carbon Nanotubes and Gold Nanoparticles

Mancozeb is a worldwide fungicide used on a large scale in agriculture. The active component and its main metabolite, ethylene thiourea, has been related to health issues. Robust, fast, and reliable methodologies to quantify its presence in water are of great importance for environmental and health reasons. The electrochemical evaluation of mancozeb using a low-cost electrochemical electrode modified with poly (3,4-ethylene dioxythiophene), multi-walled carbon nanotubes, and gold nanoparticles is a novel strategy to provide an in-situ response for water pollution from agriculture. Additionally, the thermal-, electrochemical-, and photo-degradation of mancozeb and the production of ethylene thiourea under controlled conditions were evaluated in this research. The mancozeb solutions were characterized by electrochemical oxidation and ultraviolet-visible spectrophotometry, and the ethylene thiourea concentration was measured using ultra-high-performance liquid chromatography high-resolution mass spectrometry. The degradation study of mancozeb may provide routes for treatment in wastewater treatment plants. Therefore, a low-cost electrochemical electrode was fabricated to detect mancozeb in water with a robust electrochemical response in the linear range as well as a quick response at a reduced volume. Hence, our novel modified electrode provides a potential technique to be used in environmental monitoring for pesticide detection.