Enzyme-free Electrochemical Sensor Research Articles

Probing trace of intracellularly-originated hydrogen peroxide based Pt–Cd bimetallic nanozyme on an enzyme-free electrochemical sensor

BackgroundMeasurement of endogenous cellular hydrogen peroxide (H2O2) can provide information on cellular status, and help to understand cellular metabolism and signaling processes, thus contributing to elucidation of disease mechanisms and new diagnostics/therapeutic approaches. ResultsIn this work, Pt–Cd bimetallic nanozyme was successfully prepared via the solvothermal synthetic method for sensitive detection of H2O2. The synthesized Pt–Cd bimetallic nanozyme could exhibited good electrochemical activity. Then, the materials were analyzed for the electrochemical properties and catalytic properties of H2O2 by cyclic voltammetry and chronoamperometry, respectively. Results indicated that the synthesized nanozyme had superior sensitivity (295 μA⸳mM−1⸳cm−2) and selectivity toward H2O2 with a detection limit of 0.21 μM. Further, the Pt–Cd bimetallic nanozyme displayed good electrochemical properties compared to platinum catalysts alone. The application was extended to determine the produced H2O2 from human hepatocellular carcinoma cells (HepG2) and normal hepatocyte (LO2) samples after ascorbic acid stimulation, thus enabling the early warning of cellular carcinogenesis. SignificanceThis strategy promises simple, rapid, inexpensive and effective electrochemical sensing and provides a new pathway for the synthesis of bimetallic nanozymes to construct an electrochemical sensor for the sensitive detection of H2O2.

A minimally invasive sensing system based on hydrogel microneedle patches and Au/Cu2O nanospheres modified screen-printed carbon electrode for glucose monitoring in interstitial skin fluid

Glucose monitoring in interstitial skin fluid (ISF) has become a novel approach for diabetes management. In this paper, a minimally invasive sensing system consisted of methacrylated hyaluronic acid (MeHA) based microneedle patches and Au/Cu2O nanospheres modified screen-printed carbon electrode (SPCE) was designed for glucose monitoring in the ISF of living mice. The highly swellable and biocompatible MeHA microneedle patches can effectively extract ISF from the skin, barely cause pain to the living mice. The glucose level in the extracted ISF was detected via an enzyme-free electrochemical sensor using the Au/Cu2O nanospheres as the electrocatalyst. The doping of Au into Cu2O resulted in a highly conductive and active electrocatalyst for glucose oxidation, which improved the sensing performance of glucose sensor. A wide linear range (0.02 – 6 mM), low detection limit (0.018 mM), and high sensitivity (110.38 μA mM−1 cm−2) were obtained under the optimized condition. The obtained results exhibited a comparable trend to those obtained from commercial glucometers. We have combined successfully MeHA patches for ISF extraction with enzyme-free electrochemical glucose sensor. Therefore, this novel sensing system holds great potential for diabetes management in a minimally invasive manner.

A sensitive enzyme-free electrochemical sensor based on ZnWO4@co-MNPC@MIP for specific recognition and determination of chloramphenicol in milk sample

We have carefully built a new chloramphenicol (CAP) electrochemical sensor, which takes the zinc tungstate @ cobalt magnetic nanoporous carbon @ molecularly imprinted polymer (ZnWO4@Co-MNPC@MIP) as the core. First, we successfully prepared Co-MNPC nanomaterials using an efficient one-step hydrothermal method and a direct carbonization method. Next, we recombined ZnWO4 with Co-MNPC and synthesized the completely new ZnWO4@Co-MNPC complex by using the hydrothermal method. To further improve its performance, we combined ZnWO4@Co-MNPC with a molecular imprinted polymer and coated a molecular imprinted (MIP) shell on the surface of ZnWO4@Co-MNPC by precipitation polymerization. This shell not only gives the sensor a new performance but also gives it a stronger peak current, resulting in a more accurate detection of CAP. Under optimal conditions, the ZnWO4@Co-MNPC@MIP (MMIP) electrode has a stronger CAP detection peak current than the one-component electrode, with a fairly wide linear range: 0.007–200 μM and 200–1400 μM. Even more surprisingly, the detection limit is as low as 0.0027 μM, which allows the sensor to maintain excellent selectivity and stability in the face of various interferences, making it an excellent electrochemically modified electrode. Compared to magnetic non-molecular imprint sensors (MNIPs), MMIP sensors have higher detection efficiency. After practical application, we found that the ZnWO4@Co-MNPC@MIP modified electrode was satisfactory in milk samples.

Advancements in enzyme-free electrochemical glucose sensor materials

ABSTRACT Increased health awareness has called for better health monitoring devices, resulting in continuous research and advancement in glucose sensors. Innovations in both enzymatic and enzyme-free sensors (or non-enzymatic) are revolutionising diabetes control. While enzymatic sensors offer superior sensitivity and selectivity, enzyme-free sensors are preferred for stability and affordability, advancing the quest for rapid and accurate glucose tests. Progress in the development of enzyme-free glucose sensors is being achieved by improvements in electrode materials as well as sensor design. The selection of electrode materials is crucial in these sensors for attaining optimum values of sensing time as well as accuracy. Numerous electrode materials, including graphene, carbon nanotubes, metal oxides (such as platinum and gold), and conductive polymers, have been developed and studied by researchers to be employed in glucose sensors. Among the most critical factors being considered for developing glucose sensor materials is the selectivity for glucose molecules without interference due to the presence of another molecule. This article focuses on tracing recent developments in enzyme-free glucose sensor research, highlighting efforts to overcome limitations and drive innovation in glucose monitoring technology.

Functionalization of Carbon Nanofibers with an Aromatic Diamine: Toward a Simple Electrochemical-Based Sensing Platform for the Selective Sensing of Glucose.

Despite a variety of glucose sensors being available today, the development of nonenzymatic devices for the determination of this biologically relevant analyte is still of particular interest in several applicative sectors. Here, we report the development of an impedimetric, enzyme-free electrochemical glucose sensor based on carbon nanofibers (CNFs) functionalized with an aromatic diamine via a simple wet chemistry functionalization. The electrochemical performance of the chemically modified carbon-based screen-printed electrodes (SPCEs) was evaluated by electrical impedance spectroscopy (EIS), demonstrating a high selectivity of the sensor for glucose with respect to other sugars, such as fructose and sucrose. The sensing parameters to obtain a reliable calibration curve and the selective glucose sensing mechanism are discussed here, highlighting the performance of this novel electrochemical sensor for the selective sensing of this important analyte. Two linear trends were noted, one at low concentrations (0-1200 μM) and the other from 1200 to 5000 μM. The limit of detection (LOD), calculated as the (standard error/slope)*3.3, was 18.64 μM. The results of this study highlight the performance of the developed novel electrochemical sensor for the selective sensing of glucose.

A Novel MXene@MOF@Pt NPs-Based Enzyme-Free Electrochemical Sensor for Highly Sensitive Detection of Hydrogen Peroxide Released from Living Cells

Rapid and accurate detection of hydrogen peroxide (H2O2), an important reactive oxygen species (ROS) released from living cells, is of great significance for early diagnosis of tumors. Here, a high sensitive enzyme-free electrochemical sensor for the detection of H2O2 released from living cells was constructed based on MXene@ZIF-8@Pt NPs nanocomposites. Through the characterization of physical and chemical properties, it was observed that Pt NPs with excellent catalytic activity were uniformly supported on MXene@ZIF-8, which exhibited excellent conductivity and large specific surface area. Thanks to the significantly enhanced catalytic activity derived from the successful integration of MXene, ZIF-8 and Pt NPs, under the optimal conditions, the sensing platform based on MXene@ZIF-8@Pt NPs exhibited a wide linear range from 355.4 nM to 21.75 mM, with a limit of detection as low as 120.9 nM, while showing satisfactory reproducibility and selectivity. Furthermore, the developed electrochemical sensor enables real-time monitoring of H2O2 released from living Hela cells under N-formylmethionyl-leucyl-phenylalanine stimulation. Overall, the MXene@ZIF-8@Pt NPs developed in this article will become a promising candidate in monitoring physiological processes.

A sensitive enzyme-free electrochemical sensor based on ZnWO4/γ-Fe2O3 magnetic molecularly imprinted polymer for specific recognition and determination of Chloramphenicol

A chloramphenicol (CAP) electrochemical sensor based on zinc tungstate and magnetic hematite (ZnWO4/γ-Fe2O3) magnetic molecularly imprinted polymer (ZnWO4/γ-Fe2O3/MIP) is proposed. First, ZnWO4, γ-Fe2O3 nanomaterials were synthesized by one-step hydrothermal method, and then ZnWO4, magnetic nanoparticles were combined with molecularly imprinted polymers, that is, ZnWO4/γ-Fe2O3 was coated with a molecularly imprinted (MIP) shells by precipitation polymerization method to prepare magnetic molecularly imprinted nanomaterials, and then modified on glassy carbon electrodes to construct an electrochemical sensor for the determining of CAP. The results show that under the optimal conditions, the ZnWO4/γ-Fe2O3/MIP (MMIP) modified electrode has a stronger CAP detection reduction peak current than the one-component electrode, and exhibits better electrocatalytic activity, which is an excellent electrochemically modified electrode. Compared to magnetic non-molecular imprint sensors (MNIP), MMIP sensors have higher detection efficiency. The linear range of ZnWO4/γ-Fe2O3/MIP/GCE for the detection of CAP was 0.12 ∼ 1224 μM, and the detection limit was 0.034 μM, showing excellent stability and reproducibility, and good selectivity in the presence of different interferences. ZnWO4/γ-Fe2O3/MIP/GCE was applied to the detection of CAP in milk samples with satisfactory results.

Smartphone-interfaced flow injection amperometric system for enzyme-free glucose detection using a palladium-PANI/carbon microsphere@carbon nanotubes modified electrode

Integrating a flow injection system with an electrochemical sensor controlled by a smartphone enables rapid, precise real-time monitoring and reduces analyte consumption, contamination and costs. An enzyme-free electrochemical sensor is presented for the monitoring of glucose, an important indicator of diabetes. The sensor integrates a smartphone and a flow injection amperometric system. The flow cell is fabricated from acrylic plastic and includes an electrochemical three-electrode cell that comprises a working electrode modified with a catalyst of palladium-polyaniline/carbon microspheres@carbon nanotubes (Pd-PANI/CM@CNTs/E) for the detection of glucose oxidation. In the optimal condition, the proposed system produced good analytical performances. The sensor determined glucose linearly in a range from 0.020 to 100 mM, with a sensitivity of 51.51 μA mM−1 cm−2, and a detection limit (LOD) of 0.0071 mM. The developed system also exhibited good repeatability, reproducibility, operational stability, and anti-interference properties, and accurately determined glucose levels in real human serum samples. This sensing platform provides an alternative tool for the development of a continuous glucose monitor system for clinical applications.

Enzyme-free intelligent films in electrochemistry of malathion with a binary architecture: Combined Cu2+ complexed carbon nitride nanosheets and poly(N,N-dimethylacrylamide) hydrogels

In the present work, surface and interfacial modifications have been used to successfully prepare a low-cost enzyme-free electrochemical sensor was constructed and assembled a smart binary hydrogel film of Cu@g-C3N4 NSs/PDEA (g-C3N4 NSs: graphitic C3N4 nanosheets; PDEA: poly(N,N- dimethylacrylamide). On account of g-C3N4 NSs have multiple uniform nitrogen coordination sites, making it easy to adsorb metal ions. Complexation of Cu2+ to g-C3N4 NSs enhances the electrical conductivity while increasing the specific surface area of the nanomaterials. They are used for trace monitoring of malathion. It showed good stability when detecting malathion in synthetic urine. A 4-Input/7-Output logic gate system including OR, AND and NOT is constructed using membrane electrode switching behavior for pH, temperature, SO42–, and methanol. And a 2-to-4 decoder was constructed. The complexity of non-traditional computer systems is enriched by this logic gate system about contaminants.

Spherical nickel boride nanoparticles anchored on a carbon nanofiber composite for efficient sensing of non-enzymatic hydrogen peroxide in biological samples

Spherical nickel boride nanoparticles (Ni3B NPs) were grown firmly on surface-functionalized carbon nanofibers (ƒ-CNFs) using a simple and convenient synthesis strategy and their application as enzyme-free electrochemical sensors for hydrogen peroxide (H2O2) were examined. The Ni3B NPs/ƒ-CNFs composite was characterized by the crystalline structure, surface morphology, and surface chemical states using a range of techniques. The sensing efficiency of the as-prepared composite was also examined using various voltammetry techniques. The structural and morphological characterization results showed that the Ni3B NPs could be effectively anchored in the ƒ-CNFs matrix and the average particle size of the anchored Ni3B NPs is 15.9 nm. The electrochemical studies suggested that the small Ni3B NPs could enhance the electrocatalytic activity for the reduction of H2O2 via the ƒ-CNFs because of the synergistic effects of ƒ-CNFs and Ni3B NPs. The kinetic parameters, such as the catalytic rate constant and diffusion coefficient of the Ni3B NPs/ƒ-CNFs composite modified electrode, were calculated to be 30.9 × 105 mol−1s−1 and 4.48 × 10-6 cm2s−1, respectively. Under the optimal conditions, the enzyme-free H2O2 sensor showed a more comprehensive linear range (0.083 µM – 12.6 mM and 14.2 – 39.5 mM), low detection limit (21 nM), high sensitivity (59 µA mM−1 cm−2), and negligible interference from glucose, dopamine, uric acid, and ascorbic acid. Moreover, the prepared electrode showed good repeatability, reproducibility, stability, and suitability for real sample analysis. These results highlight a method to develop high-performance sensing materials and a great candidate for practical application.

In situ decorated 2D vanadium disulphide on optimized reduced graphene oxide-based interface for highly sensitive nonenzymatic glutamate detection

2D layered transition metal dichalcogenides (TMDs) possess eccentric nanostructures, large surface areas, and unique semiconducting properties, making them exceptional for non-enzymatic applications compared to metal oxides. However, TMDs like vanadium disulfide (VS2), with peroxidase-like nanozymatic characteristics, suffer from limited electronic conductivity, restricting their use as electrochemical (EC) sensors. To address this, reduced graphene oxide (rGO) is introduced to enhance electronic conductivity and leverage the enzyme-like property of VS2. This study introduces a novel enzyme-free EC sensor, rGO/VS2 nanocomposite-based, for accurate and efficient glutamate (Glut) detection. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) demonstrated that rGO/VS2 electrodes with varying rGO to VS2 composition ratios exhibit superior EC properties compared to pure VS2 electrodes. The EC response of the rGO/VS2 modified electrode towards Glut was investigated using CV and differential pulse voltammetry (DPV). The fabricated electrode displayed a linear relationship with Glut concentration (4–300 μM) (normal levels 30–80 μM), boasting a low limit of detection (LOD) (0.056 μM) and higher sensitivity (0.797 μA/(mM·cm2)) compared to existing non-enzymatic Glut sensors. Structural and morphological characterizations employed Raman spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), and energy-dispersive X-ray spectroscopy (EDX). Furthermore, the proposed electrode's electroanalytical activity was assessed in spiked real samples, establishing its reliability and precision in Glut detection. The developed rGO/VS2-based EC sensor holds practical utility in biomedical research, clinical diagnostics, and environmental monitoring, where Glut detection is essential.

Self-assembled monolayer of poly(o-phenylenediamine)/silver core-shell hybrid-based enzyme-free impedimetric glucose sensor for blood samples.

A core-shell hybrid of poly(o-phenylenediamine)/silver was prepared by a simple single-step process and self-assembled on a glassy carbon electrode to design an enzyme-free electrochemical glucose sensor. The working electrode was fabricated by self-assembling a dimethyl sulfoxide (DMSO) solution of the prepared hybrid on a glassy carbon electrode. The electrochemical properties of the fabricated electrode were analyzed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in an aqueous potassium chloride electrolyte containing the [Fe(CN)6]3-/4- redox couple. The electrochemical sensing responses towards varying concentrations of glucose were studied by CV and EIS in the same redox electrolyte medium. The poly(o-phenylenediamine)/silver core-shell hybrid-based sensor was found to show a reliable response in the EIS experiment over the CV experiment. By analyzing the EIS sensing responses, the experimental limit of detection was determined to be 10 μL of ∼80 mg per dL glucose solution in 25 mL of 1 (M) KCl electrolyte containing the 10-3 M [Fe(CN)6]3-/4- redox couple with a sensitivity of 298 Ω mg-1 dL cm-2. Excellent selectivity towards glucose was confirmed over various bioactive interfering biomolecules like ascorbic acid, dopamine, uric acid, lactose, fructose and sucrose. The glucose content in the human blood sample was verified by the designed sensor with almost 100% recovery.

Cascaded recycling amplification mediated in situ synthesis of silver nanoclusters for the construction of sensitive and label-free electrochemical sensor

A growing number of studies have shown the crucial role of microRNA (miRNA) sensing in cancer clinical diagnosis and prognosis research. In this study, a label-free and enzyme-free electrochemical sensor was presented to achieve sensitive determination of miRNA 122, which was constructed based on in situ synthesis of silver nanoclusters (AgNCs) mediated by cascaded recycling amplification. The efficient and cascaded recycling amplification was initiated by the target miRNA 122, resulting in the release of signal probe with rich cytosine bases, which would be loaded on the sensing interface for in situ synthesis of silver nanoclusters, leading to dramatically increased current for quantitative analysis. This method achieved selective and robust miRNA 122 sensing in human serum samples with a detection limit down to 27 aM. The proposed work would provide an innovative method for determining different biomarkers, holding great potential for boosting the development of clinical diagnosis and drug investigation.

Fabrication of Ni–Mo–Nb metallic glass/micro-nano lattice composite for nonenzymatic glucose sensing

The rising global diabetic population has ignited significant interest in enzyme-free electrochemical glucose sensors. However, their widespread usage has been severely impeded by the lack of sensing probes with both high sensitivity and stability. In this work, we present a novel approach for conformally depositing a Ni–Mo–Nb metallic-glass film onto a three-dimensional printed polymer skeleton for glucose detection. The printing template is designed based on a six-membered tricapped trigonal prism (6M-TTP) structure, which is derived from a medium-range order structure motif observed in amorphous alloys. The fabricated composite combines the high electrochemical activity of Ni–Mo–Nb amorphous alloy with the stability afforded by the micro-nano lattice structure, resulting in a high sensitivity (482 ​μA mM−1cm−2), a wide linear range (0–1 ​mM and 1–5 ​mM), a low detection limit (2.94 ​μM), and good long-term stability and selectivity in alkaline solution. Our work has proposed a new avenue to fabricate complex micro-nano electrodes, potentially offering significant versatility and great promise for widespread applications in the field of electrochemistry.

Target-modulated mineralization of wood channels as enzyme-free electrochemical sensors for detecting amyloid-β species

Alzheimer's disease (AD) is an irreversible brain disorder, which has been found to be associated with neurotoxic amyloid-β oligomers (AβO). The early diagnosis of AD is still a great challenge. Herein, inspired by the hierarchical channel structure of natural wood, we design and demonstrate a low-cost and sensitive wood channel-based fluidic membrane for electrochemical sensing of AβO1-42. In this design, Zn/Cu-2-methylimidazole (Zn/Cu-Hmim) with artificial peroxidase (POD)-like activity was asymmetrically fabricated at one side of the wood channels by biomimetic mineralization and a subsequent ion exchange reaction. The strong affinity between Cu(II) and AβO1-42 enables Cu(II) species in Zn/Cu-Hmim to be extracted by AβO1-42, thus suppressing the POD-like performance via Zn/Cu-Hmim disassembly. Using Zn/Cu-Hmim to catalyze the oxidation reaction of 2,2′-diazo-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) by H2O2, the current–voltage (I–V) properties of wood channels are influenced by the generated oxidation product (ABTS•+), thus providing information useful for the quantitative analysis of AβO1-42. Importantly, the three aggregation states of Aβ1-42 (AβM1-42, AβO1-42, and AβF1-42) can also be identified, owing to the affinity difference and available reaction sites. The proposed wood membrane provides a novel, assessable, and scalable channel device to develop sensitive electrochemical sensors; moreover, the sustainable wood materials represent alternative candidates for developing channel-structured sensing platforms.

(Invited) towards Continuous Health Monitoring Platforms By Enzyme-Free Electrochemical Sensors and Triboelectric Sensors for Noninvasive Lactate Detection

Emerging wearable devices with non-invasively biosensing technics have drawn considerable attention to continuously monitor several metabolites in body fluids, such as a tear, saliva, and sweat, to diagnose human health conditions. Most importantly, wearable sensors could offer unique possibilities for online, real-time and non-invasive monitoring of health compared to traditional invasive biosensors. Among lots of analytes, lactic acid concentration in the human body exhibits a high relationship with several diseases such as acute heart diseases, hypoxia, muscle fatigue, meningitis, and cystic fibrosis, and it could also cause muscle pain in athletes. To further boost up the reproducibility and reliability of wearable biosensors to detect lactate concentration levels from human sweat, Ni-based layered double hydroxide (LDH) with various secondary transition metals (Fe and Co) was proposed as electrocatalysts in an enzyme-free electrochemical lactate sensor. According to the mechanism of lactate oxidation on the transition metal-based electrocatalyst, secondary transition metal of Co could serve as the active site for lactate oxidation and facilitate the adsorption of OH- in the alkaline electrolyte. To further increasing the active surface area for enhancing the sensitivity of Ni-based LDH, ZIF-67 derived NiCo LDH was synthesized as the electrocatalyst for non-enzymatic lactate detection. Co-based ZIF-67 served as self-sacrificial templates to fabricate hierarchically structural NiCo LDH with uniform porosity and high electrochemically active surface area to achieve outstanding electrocatalytic performance for lactate sensing. After optimizing the particle size of ZIF-67 and transformation times, ZIF-67 derived NiCo LDH reached the ultrahigh sensitivity of 83.98 μA mM- 1 cm- 2 at an applied potential of 0.55 V (vs. Ag/AgCl KCl sat’d) in the concentration range from 2 to 26 mM. On the other hand, pioneering works in biosensors for lactate detection in sweat has been encountered major challenges such as noble material usage, immobile power supply, and complicated circuit connection to realize the compact sustainable sensing systems. To solve these restrictions, herein, the self-powered molecular imprinted polymers based triboelectric sensor (MIP-TES) was designed to offer a multifunctional noninvasive approach for specific and simultaneous lactate detection. Free-standing PVDF/graphene flexible electrode modified poly(3-aminophenyl boronic acid) imprinted lactate molecule demonstrated the change of the surface properties afterlactate adsorption. MIP-modified electrode revealed the selective lactate sensing over non molecular imprinted polymers (NIP) electrode through the superior and stable signal change with variation of lactate concentration in human sweat. Moreover, MIP modified lactate sensor was further introduced in the triboelectric nanogenerator system to harvest mechanical energy from contact and separation into electrical output. The more adsorbed lactate led to lower energy barriers and decreasing electrical potential when detecting higher lactate concentration. Self-power triboelectric lactate sensor could directly power the number of LED lights without an external energy supply. Eventually, it was validated the feasible application of wearable sensors on human skin. After introducing noninvasive enzyme-free biosensors and triboelectric sensors, an innovatively continuous non-invasive health monitoring platforms can be achieved for practical applications, especially in the areas of home medical examination and wearable personal biosensors.

High-performance amperometric detection of hydroxylamine on fluorine doped tin oxide electrode modified with NiCo2O4 nanoparticles

The design and development of inexpensive, and extremely sensitive sensors for Hydroxylamine (HYA) are imperative due to its toxicity to animals, plants, and aquatic life. This work proposes a high-performance enzyme-free electrochemical sensor for HYA based on its oxidation on Nickel cobaltite (NCO) spinel-modified fluorine doped tin oxide (FTO) electrode. Hydrothermally grown irregularly shaped NCO nanoparticles (NPs) of size around 10 nm are characterized by XRD, XPS, UV–visible, BET, and TEM to evaluate the structural and morphological characteristics. NCO-modified FTO (NCO@FTO) electro-oxidizes HYA at a potential of 0.66 V vs. Ag/AgCl, delivering 1.7 times the current response than bare FTO. The rich catalytically active redox couples of Ni and Co, high conductivity, and high surface area of the NCO NPs contribute to the superior electrochemical response of NCO@FTO. As an amperometric sensor, NCO@FTO detects HYA in a wide range of 10 to 4000 µM concentration with a high sensitivity of 408 μA mM−1 cm−2. The sensor has a detection limit of 0.47 μM (S/N = 3), faster response of less than 3 s, excellent selectivity, and good stability. The practical feasibility of the proposed sensor is investigated by employing it in the monitoring of real samples. This study demonstrates NCO@FTO as an efficient low-cost sensor for HYA and extends the use of spinel metal oxides in bioanalysis.

Cobalt-based layered double hydroxide nanosheet-supported AuNPs for high performance electrochemical H2O2 detection

Enzyme-free electrochemical sensors with both high sensitivity and selectivity for H2O2 is highly desirable for biological science. During the electrochemical reduction of H2O2, the breakage of the O-O bond and subsequent stabilization of OH on the electrode are key to the performance of the electrochemical sensors. Noble metal nanoparticles could efficiently stabilize the above intermediate, but the stability of the naked nanoparticles was not satisfactory. Carbon-based supported materials are thus proposed, but lack efficient active sites for H2O2 reduction. Herein, cobalt-based layered double hydroxide-supported gold nanoparticles (AuNPs/Co-LDH) nanocomposite were fabricated as the electrode material for high-performance electrochemical H2O2 reduction in neutral media. Due to the abundant redox sites (Co2+/Co3+) and large surface area, AuNPs were formed in situ on Co-LDH with good dispersion and stability. Meanwhile, the redox sites of Co-LDH could also aid the electrochemical H2O2 reduction. A sensitivity of 406.61 μA mM−1 cm−2 and a detection limit of 0.19 μM were achieved, which outperformed most of reported nanomaterials. The above excellent electrochemical properties endow the follower-like AuNPs/Co-LDH as promising alternative to enzymes in the biological field.

Yttria-zirconia electrochemical sensor for the detection of tyrosine

A simple enzyme-free electrochemical sensor, based on modified yttria-doped zirconium oxide screen-printed carbon electrode (SPCE) has been developed for the determination of tyrosine (Tyr). Firstly, the morphology, microstructure and the electrochemical characteristics of commercial yttria-doped zirconium oxides with different yttria loading (0–40 mol. %) were reported. Cyclic voltammetry (CV) tests performed in phosphate buffer solutions (0.01 M PBS; pH = 7.4) in the absence and the presence of Tyr showed that the modified Zr8Y/SPCE (containing 8 mol. % of yttria) exhibits better electrochemical properties compared to other electrodes investigated. Finally, the Zr8Y/SPCE sensor was tested for the detection of tyrosine by using the differential pulse voltammetry (DPV) method, providing a sensitivity of 0.140 μA μM−1cm−2 and a limit of detection (LOD) of 0.1 μM (at S/N = 3). The performed study shows excellent results for tyrosine detection in a real food supplement sample. The calculated relative standard deviation (RSD) was 1.41 %. To our knowledge, this is the first device developed with a commercial yttria-doped zirconia nanomaterial for the electroanalytical determination of tyrosine.

Highly efficient electrocatalytic oxidation of hexestrol based on bismuth molybdenum oxide nanoparticle/graphene oxide nanosheets modified screen printed electrode

In this work, an enzyme-free electrochemical sensor based on orthorhombic bismuth molybdate nanoparticles decorated graphene oxide composite was developed for the detection of hexestrol. Hexestrol is a non-steroidal estrogen which causes carcinogenic and toxic effects in human body. Herein, we report the development of a modified electrochemical sensor to detect toxic hexestrol in ultralow concentrations. Bismuth molybdate particles of the bimetal oxide and transition element-based composite has used on a screen-printed carbon electrode (SPCE) to set up a Bi2MoO6/graphene oxide modified SPCE. Transmission electron microscopy, energy dispersive spectra and electrochemical strategies were utilized to confirm the composite of Bi2MoO6/GO hybrid composite. The electrochemical analysis for hexestrol at Bi2MoO6/GO composite altered SPCE were developed. Also, enhanced electrochemical sensor results have appeared by DPV strategy and hexestrol anodic reactions are exceptionally direct from 20 nM to 416.7 μM (linear range) and sensitivity of the modified sensor is 33.527 µA µM−1 cm−2. Further, the limit of detection (LOD) of the modified sensor is 2.5 nM (S/N = 3). In addition, the Bi2MoO6/GO hybrid modified SPCEs were distinguished to ascertain the hexestrol detection in pH 7.0. The bimetal oxide modified electrode also exhibited high selectivity, reproducibility, and stability. Consequently, it could give occasions to detect of bio-tests for real time applications.