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Amperometric nanobiosensors are crucial time and cost effective analytical tools for the detection of a wide range of bioanalytes, viz. glucose present in complex environments at very low concentrations. Although the excellent analytical performance of nanobiosensors is undoubted, their exact molecular structure often remains unclear. Here, by combining advanced nanoanalytical approaches with theoretical modeling, we conducted a comprehensive study towards the investigation of the molecular structure of a hybrid GOx/Nafion/Pd-NPs layer deposited by electroplating from the multicomponent electrolyte solution on the surface of screen printed electrodes modified with graphene oxide. Specifically, we revealed that Pd2+ cations were adsorbed on GOx amino acid residues, forming the GOx·nPd2+ enzymatic complex. The highest adsorption energy of Pd2+ cations on GOx was found during their interaction with the side chains of basic amino acids and methionine. In addition, we showed and fully validated the end-structure of the one-step designed GOx/Nafion/Pd-NPs nanobiosensor as a structural model mainly composed of GOx and water molecules incorporated into the metal-polymer scaffold. Our approach will thus serve as a guideline for the study of molecular interactions occurring in complex systems and will contribute to the design of the next generation of hybrid nanobiosensors. The proposed mechanism, driving the self-assembly of the hybrid layer, will allow us to construct modular enzymatic nanoanalytical devices with tailored sequences in the future.

Indium tin oxide (ITO) has extensively used as an electrode in diverse application areas of electrochemistry, displays, photovoltaics, and catalysts. Herein, terpyridine-modified ITO and thioterpyridine-functionalized Au-modified ITO electrodes were prepared and evaluated for electrochemical redox behaviors and conversion rates of Ce(III)/Ce(IV) ions, and recycling recovery rates on the newly developed electrode by cyclic voltammetry and amperometry. Scanning electron microscopy, X-ray photoelectron spectroscopy, Ultraviolet photoelectron spectroscopy, X-ray diffraction crystallography, and fluorescence spectroscopy were employed for the physiochemical properties of the demonstrated electrodes before and after electrochemistry. The interfacial energy level was examined by ultraviolet photoelectron spectroscopy for ITO-Au and ITO-Au-STpy. Density functional theory calculations were performed to examine complexation between the functionalized ligand and Ce(III)/Ce(IV) ions by obtaining molecular orbital energy levels and thermodynamics. Thermal CO oxidation catalytic activity was tested for Ce-electrodeposited ITO electrode. In addition, electrochemical CO2 reduction performance was evaluated for Au-modified ITO electrode with and without thioterpyridine-functionalization.

In this work, platinum nanoparticles (Pt) decorated on a spinel group, zinc cobalt oxide (ZnCo2O4) 3-D flower was intended to detect caffeine electrochemical sensor. Pt particles were used to enhance the performance of hydrothermally prepared 3-D ZnCo2O4 flower. So Pt nanoparticles were decorated on each thin nanosheet of self-assembled 3-D flower-like ZnCo2O4. The thin transparent nanosheet of the ZnCo2O4 flower will benefit electrochemical sensors by simplifying its ion exchange. Therefore, Pt@ZnCo2O4 shows an excellent electrochemical conductivity, which promotes the caffeine-based sensor's rapid electrochemical oxidation. Using amperometric i-t at an applied potential of 1.45 V, Pt@ZnCo2O4 modified electrode shows widespread of two linear ranges (0.05 to 265.55 μM and 295.55 to 757.55 μM) with a low detection limit (0.0114 and 0.01657 μM) and high sensitivity (3.419 and 1.862 μA μM−1 cm−2). Moreover, good results were obtained for the real-time detection of caffeine in sugar-free cola beverage and energy drink samples. Henceforth, the developed method could be an ideal way to detect caffeine in real samples.

The present work investigates the fabrication and performance studies of nanoscale metal cluster loaded Multi-Walled Carbon Nanotubes (MWNTs) based amperometric cholesterol biosensors. By a simple chemical reduction method Pt/ MWNTs, Au/MWNTs, and Pt-Au/MWNTs nanocomposites are prepared. Metal-decorated MWNTs are characterized by using X-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy (TEM). Amperometric biosensors are fabricated by depositing cholesterol oxidase (COx) enzyme on nanocrystalline metal/MWNTs modified GCE. Performance studies of these fabricated biosensors are conducted by using cyclic voltammetry and amperometry. The fabricated Au/MWNT based biosensor is best suited for the determination of cholesterol with a response time of 15 s, linear range from 2 µM to 1.4 mM, and limit of detection (S/N = 3) of 0.5 µM.

Herein, N-doped porous carbon nano-polyhedron embedded with Co3O4 (Co3O4-NPCN) was reported for the electro-catalytic oxidation and amperometric detection of l -cysteine. Co3O4-NPCN was synthesized by the two-step redox calcination of zeolitic imidazolate framework (ZIF). Surface morphology characterization revealed that Co3O4-NPCN displayed a uniform size and rhombic dodecahedral shape. Structure and composition analysis found that Co3O4-NPCN was a N-doped carbon polyhedral matrix with hollow and porous structure, and Co3O4 nano-spheres were evenly distributed into the polyhedral matrix. Due to the hollow and porous structure, N-doped carbon matrix and embedded Co3O4 nano-spheres, Co3O4-NPCN performed a remarkable electro-catalysis towards the oxidation of l -cysteine at a very low potential of 0.10 V. A diffusion-controlled l -cysteine oxidation process was observed at Co3O4-NPCN prepared electrode. Accordingly, amperometric method was established for l -cysteine detection with a very fast current response in 2 s, wide linear range of 0.05 μM- 5.2 mM and low detection limit of 6.9 nM. Besides, notable selectivity, repeatability, reproducibility and long-term stability were also achieved. Moreover, Co3O4-NPCN sensor was successfully applied to the l -cysteine detection in human serum samples indicating the practical application of the as-developed sensor.

Serotonin (SRT), one among the neurotransmitters, is mainly responsible for physiological functions in human body. The effect of changes and intake of SRT can influence higher impact of peoples, thus sensing such compound with more effective and simple technique will be an extreme significance. Zeolite imidazole framework among MOF was constructed with the correlation of multiwall carbon nanotubes (ZIF-67/MWCNT) as sensor material via simple co-precipitation method. The rationally designed ZIF-67/MWCNT was evaluated for physico-chemical properties analyzed with XRD, XPS and the morphological structures were identified with FESEM. Cyclic voltammetry (CV) and amperometric (IT) technique was initiated for electrochemical detection of SRT. The ZIF-67/MWCNT exhibited a dodecahedron shape and larger surface area as agreed from BET analysis. The electrochemical results obtained at the interfacial site of ZIF-67/MWCNT proved to be more competent with excellent selectivity. SRT was electrochemically detected in human blood serum and urine as real sample analysis. The linear range was 0.049 μM to 800 μM with a lower LOD-7 nM. Moreover, the attained sensitivity was 5.613 µA µM−1 cm2 with excellent repeatability and reproducible behavior. The highly conducting matrix ZIF-67/MWCNT with abundantly accessible sites and higher surface area has gained significant results towards SRT detection.

Formaldehyde (FA) is a carcinogenic substance that can be found in various foods. A portable, highly sensitive, and rapid sensor comprising a flow injection amperometric analysis system and an enzy...

The design and development of new catalysts with low cost, high selectivity, and sensitivity for the electrochemical sensor applications is of huge interest. In this report, novel zinc tetra [4-[2-(1H-benzimidazol-2-yl) phenoxy]] phthalocyanine (ZnTBImPc) is prepared in a pure state with 87% yield. The characterization of the ligands and complex is carried out by combination of techniques like elemental analysis, ultraviolet–visible (UV–Vis), Fourier-transform infrared spectroscopy (FTIR), mass spectral, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and electrochemical techniques. FTIR is useful in monitoring the progress of the reaction. The benzimidazole moiety of ZnTBImPc undergoes electropolymerization and thin, uniform polymeric layer deposits on the glassy carbon surface. The polymeric film was characterized by impedance spectra and charge transfer studies. The fabricated polymeric film electrode is applied for voltammetric sensing of ammonia which showed linear characteristics in 0.1 to 1.0 µM concentration range. The LOD was 30 nM with sensitivity of 237.25 µA µM−1 cm−2. The efficiency and sensitivity of ammonia oxidation at the poly(ZnTBImPc) are compared with the composite hybrid electrode of poly(ZnTBImPc) and carbon nanoparticle (CNP). The amperometric sensing of ammonia showed linear behavior in 50 to 500 nM concentration range. The RDE experiment revealed that the number of electrons involved in the ammonia oxidation is nearly 3. The polymeric electrode was subjected to the interference studies to evaluate the selectivity of the fabricated electrode and found that the co-existing molecules do not show interference during the detection of ammonia. Schematic representation of electro-oxidation and detection of ammonia

Flexible skin patch biosensors are promising for the noninvasive determination of physiological parameters in perspiration for fitness and health monitoring. However, various prerequisites need to be met for the development of such biosensors, including the creation of a flexible conductive platform, bending/contact stability, fast electrochemical kinetics, and immobilization of biomolecules. Here, we describe a conducting polymer-reinforced laser-irradiated graphene (LIG) network as a heterostructured three-dimensional (3D) transducer for flexible skin patch biosensors. LIG with a hierarchically interconnected graphene structure is geometrically patterned on polyimide via localized laser irradiation as a flexible conductive platform, which is then reinforced by poly(3,4-ethylenedioxythiophene) (PEDOT) as a conductive binder (PEDOT/LIG) with improved structural/contact stability and electrochemical kinetics. The interconnected pores of the reinforced PEDOT/LIG function as a 3D host matrix for high loading of "artificial" (Prussian blue, PB) and natural enzymes (lactate oxidase, LOx), forming a compact and heterostructured 3D transducer (LOx/PB-PEDOT/LIG) for lactate biosensing with excellent sensitivity (11.83 mu A mM-1). We demonstrated the fabrication of flexible skin patch biosensors comprising a custom-built integrated three-electrode system achieve amperometric detection of lactate in artificial sweat over a wide physiological linear range of 0-18 mM. The advantage of this facile and versatile transducer is further illustrated by the development of a folded 3D wristband lactate biosensor and a dual channel biosensors for simultaneous monitoring of lactate and glucose. This innovative design concept of a heterostructured transducer for flexible biosensors combined with a versatile fabrication approach could potentially drive the development of new wearable and skin-mountable biosensors for monitoring various physiological parameters in biofluids for noninvasive fitness and health management. Funding Agencies|Swedish Research CouncilSwedish Research CouncilEuropean Commission [VR-2015-04434]

Background The ratio of fPSA/tPSA in the "grey zone" of tPSA with the concentration range between 4 ng/ml and 10 ng/ml is significant for diagnosis of prostate cancer, and highly efficiency quantification of the ratio of fPSA/tPSA remain elusive mainly because of their extremely low concentration in patients' peripheral blood with high biosample complexity. Methods We presented an interdigitated spiral-based MXene-assisted organic electrochemical transistors (isMOECTs) biosensor for highly sensitive determination of fPSA/tPSA. The combination of MXene and the interdigitated multiple spiral architecture synergistically assisted the amplification of amperometric signal of biosensor with dual functionalizations of anti-tPSA and anti-fPSA. Results The ultrasensitivity of the biosensor was enhanced by tunable multiple spiral architecture and MXene nanomaterials; and the sensor exhibited improved detection limit of tPSA and fPSA down to 0.01 pg/ml and acceptable performance of selectivity, repeatability and stability. Moreover, the isMOECTs displayed area under the curve (AUC) value of 0.8138, confirming the potential applications of isMOECTs in clinics. Conclusions The merits of isMOECTs biosensor demonstrated the reliability of MXene-assisted organic electrochemical transistor biosensor with multiple interdigitated spiral for ultrasensitive quantification of fPSA/tPSA, suggesting potential current and future point-of-care testing applications. Graphical Abstract

We report the synthesis of a new non-enzymatic H2O2 electrochemical sensor based on the Bi2S3/g-C3N4 core-shell nanocomposite. The Bi2S3/g-C3N4 nanocomposite was synthesized via the solvothermal process. It was characterized by XRD and TEM to identify its phase and to determine its morphology. The response of Bi2S3/g-C3N4 nanocomposite to hydrogen peroxide was investigated using the cyclic voltammetry and amperometry techniques. The obtained results show that the association of g-C3N4 nanosheets with Bi2S3 nanorods enhances the electrochemical behavior and the overall performance of the sensor. Indeed, we noted an enhanced electrochemical signal of the Bi2S3/g-C3N4 core-shell nanocomposite shown by the appearance of a H2O2 oxidation peak at around 0.26 V. Moreover, the modified Bi2S3/g-C3N4 electrode sensor demonstrated a wide linear range for H2O2 from 0.5 to 950 μM with a sensitivity of 1011 μA mM-1cm-2 and a detection limit of 78 nM. These performances are much better than those for Bi2S3 and g-C3N4 taken separately. The improved electrocatalytic activity of the sensor towards hydrogen peroxide oxidation is mainly attributed to the morphology of the core-shell nanostructure leading to the enrichment of electroactive sites for the catalytic reaction of H2O2. Additionally, the proposed sensor was successfully tested in skimmed milk and human urine samples. The novelty of this work is the simple way to synthesis Bi2S3/g-C3N4 core-shell nanostructure and its use as a H2O2 sensor, which paves the way for the synthesis of new nanomaterial heterostructures used as electrochemical sensors for detecting other molecules.

In this article, we introduce the principle of scanning electrochemical microscopy (SECM) and its applications as a powerful electrochemical method for material characterization. The principle of SECM is based on the use of a micrometer- or nanometer-sized ultramicroelectrode as the scanning chemical probe of electrons, ions, and molecules that are transferred across the interface between a target solid material and an electrolyte solution as well as air/liquid and liquid/liquid interfaces and membranes. In comparison to traditional electrochemical methods, SECM is much higher in spatial resolution and mass transport to find its advantages in the chemical imaging of a heterogeneously reactive material surface and the quantitative study of interfacial reaction dynamics. The unique capability of imaging an interfacial reactivity renders SECM complementary to other scanning probe microscopy techniques and also combinable with them to yield multidimensional images of the material surface. In this article, various operation modes of SECM are introduced and followed by examples of practical measurements based on imaging, approach curve, voltammetry, and amperometry. Present limits of the technique in both theory and experiment are briefly discussed. In addition, numerical and analytical approaches to data analysis as well as experimental protocols for tip fabrication and characterization are described. Keywords: scanning electrochemical microscopy (SECM); ultramicroelectrode (UME); chemical imaging; interface; heterogeneous electron transfer; electrode material; nanomaterial

A Ni-MOF-based novel electrochemical sensor was synthesized with high surface area of 1381 m2/g, significant porosity of 1.14–9.6 nm and average particle size of 80 nm. The final products was developed for the detection of glucose with high sensitivity and accuracy. The amperometric response of the electrode toward glucose was achieved at a steady state in 3 s. The linear range, detection limit, and sensitivity of the developed electrode toward glucose was 1–1600 µM, 0.76 µM (S/N = 3) and 2859.95 µA mM−1 cm−2 (R2 = 0.9966), respectively. Compared with the non-enzymatic sensors, the developed electrode exhibited a lower detection limit and higher sensitivity, which are promising criteria for the development of a chemical sensor.

A highly sensitive amperometric Prussian blue-based hydrogen peroxide sensor was developed using 3D pyrolytic carbon microelectrodes. A 3D printed multielectrode electrochemical cell enabled simultaneous highly reproducible Prussian blue modification on multiple carbon electrodes. The effect of oxygen plasma pre-treatment and deposition time on Prussian blue electrodeposition was studied. The amperometric response of 2D and 3D sensors to the addition of hydrogen peroxide in μM and sub-μM concentrations in phosphate buffer was investigated. A high sensitivity comparable to flow injection systems and a detection limit of 0.16 μM was demonstrated with 3D pyrolytic carbon microelectrodes at stirred batch condition.

This study used a new approach to fabricate a glucose detection system based on nano-engineered biomaterials. The fabrication steps included strategic synthesis, integration and stabilization of biological and metal nanoparticles in superabsorbent hydrogel gum matrix. The design of the high-performance electrochemical biosensor platform includes copper-micro mesh grid electrode modified with polymer phase comprising of silver nanoparticles surface coroneted with Ceratonia silique locust bean gum (LBG), Tamarindus indica seed-shell nanoparticles and glucose oxidase (GOx). Fundamental assessment of catalytic properties of the nanobiocomposite films on copper grid probe were performed by cyclic voltammetry, amperometry, differential pulse voltammetry. Probes showed good repeatability, reproducibility, selectivity, and long-term stability. The GOx was well-immobilized and stabilized by C. siliqua nano-matrix, with 85% and 98% activity retention when stored at different condiions for 6 month and 3 months, respectively. The fabricated grid-platform exhibited linear response in a wide range of glucose concentration, with detection limit of 1.0 nM (S/N = 3) and sensitivity 38.7 mA nM−1 cm−2. The bionanomaterial-based sensor was successfully applied for ultra-low glucose detection in artificial salivary samples. The designed sensor, perhaps with further modifications, has potential for the next generation of sensing platform in various biological fluids especially for non-invasive glucose detection for diabetic patients.

In the present work, a novel method for the green synthesis of CeAlO3 (CAO) polycrystalline powder through deep eutectic solvents (DES) was carried out by hydrothermal method. The carbon nitride (CN) was synthesized directly by fractional thermal polymerisation process. The combination of CeAlO3 with CN provides an excellent sensing platform for developing highly sensitive and stable electrocatalyst for non-enzymatic glucose (GLU) oxidation. The structural, morphological and electrochemical analysis of CeAlO3/CN (CAO/CN) shows the successful synthesis without any impurities. The synergistic effects of pyridinic-N, pyrrolic-N and graphitic-N are highly influencing and playing a prominent role in sensory performances of the prepared CAO/CN nano-electrocatalyst towards GLU sensing. The limit of detection (LOD) at CAO/CN modified glassy carbon electrode (CAO/CN/GCE) was calculated to be 0.86 nM in the linear concentration range of 0.01–1034.5 µM by amperometric method. The anti-interference, reproducibility, repeatability and stability analysis suggest the promising performance of the fabricated electrode towards GLU detection. The real time application of CAO/CN/GCE was evaluated towards GLU sensing in human blood, saliva and sweat, a satisfactory result was obtained. Therefore, the CAO/CN/GCE has a great application prospect as a highly efficient catalyst material for highly sensitive and efficient non-enzymatic glucose sensor.

In this study, we have introduced a three-dimensional polyaniline hydrogel (3D-PANIH) with incorporated Cu nanoparticles (CuNPs), which allows for facile fabrication of an electrochemical sensor for sensitive determination of nitrite. The value of this nanocomposite has been highlighted through the comparison of sensing property of the fabricated sensor with most other nitrite sensors reported recently. The sensing property of the sensor based on CuNPs/3D-PANIH nanocomposite was investigated by cyclic voltammetry and amperometric current–time. The electrochemical kinetics reveals that nitrite electrooxidation involves two electrons and two protons in an electrode reaction. The electrochemical sensor presented substantially enhanced electrocatalytic oxidation of nitrite in acidic medium, with an excellent sensitivity of 139.3 μA mM−1 cm−2, a low detection limit of 0.07 μM, and a broad linear range (0.2–4300 μM). From a broader perspective, the present work may exploit the opportunities for a novel electrochemical sensing platform based on 3D-PANIH.

An electrochemical biosensor for the detection of glucose is realized by immobilizing glucose oxidase (GOx) enzyme onto titanium dioxide nanotube arrays by a coupling encapsulation process. We present details of a robust fabrication technique that results in a durable and reproducible sensor characteristics. The TiO2 nanotube arrays are grown directly on a titanium substrate by a potentiostatic anodization process in a water and ethylene-glycol mixture solution, which contains ammonium fluoride. An electropolymerization process was also performed to enhance interfacial adhesion between GOx and TiO2 nanotubes. Detection of glucose concentrations was achieved with a linear response in the range of 0.01 to 0.2 mM. Investigation of enhanced sensitivity by increasing the count, the length, and the cross-section of the nanotubes was also carried out. Surface morphologies of Ti substrate were examined by scanning electron microscopy to optimize the anodization process and thus the TiO2/Ti nanotube dimensions. We utilized a time-based amperometric response for the quantitative determination of hydrogen peroxide concentration through electro-reduction reaction with a bare TiO2/Ti nanotube-array electrodes, thus providing a reference for the determination of glucose levels with a GOx-coated TiO2/Ti nanotube array electrodes. Detection levels down to 5.2 μM were recorded.

Achieving real-time, continuous and long-term monitoring of dopamine (DA) in vivo is essential for revealing brain functions and preventing and treating neurogenic diseases. However, it remains challenging to achieve a low limit of detection (LOD) and high neuron-compatibility at the same time for the current microsensors, resulting in the failure of long-term and accurate detection of DA in vivo. A DA-sensing fiber was achieved by the potentiometric method to possess a low LOD of 5 nM, 1–3 orders of magnitude lower than amperometry and differential-pulse voltammetry. The sensing fiber showed a wide linear range from 5 to 185 nM that well matched the DA concentration (26–40 nM) in vivo. After implantation, the sensing fiber showed no influence on the firing rates of neurons with the potentiometric test, indicating high neuron-compatibility. It was then integrated with electrophysiology to simultaneously monitor DA variation and electrical signal in the brain, with stable monitoring of DA change in vivo for 8 weeks. The sensing fiber was flexible and stably worked after hundreds of bending, and it showed high sensitivity even after protein adsorption, thus offering a reliable tool for neuroscience.

The growth of CZTS thin films by electrodeposition has numerous advantages in terms of controlling the deposition parameters. However, the electrochemical cells in conventional potentiostat are small and require precise adjustment. Electrodeposition is feasible by controlling solely the current without using a reference electrode and hence an expensive potentiostat. The cost and surface area limitations can be overcome by utilizing the simple two-electrodes cell and a current source. Therefore, in this study, CZTS thin films were amperometrically deposited on various substrates using our novel two-electrode electrochemical cell setup. The structural, morphological, compositional, optoelectronic properties of the electrodeposited CZTS thin films have been precisely investigated by adjusting the deposition current. Stoichiometry measurements reveal that the chemical composition and hence crystallinity of thin films strongly depend on the applied current. The critical deposition current for Zn-rich films was found to be between 0.97 and 0.98 mA/cm2.

We report a novel amperometric sensor for aqueous phosphate ions in freshwater systems based on the reductive square wave voltammetry of molybdate (VI) anions immobilized within a chitosan matrix deposited on a glassy carbon electrode. A sensitivity of 4.4±0.1 μA/μM was realized together with a LOD of 0.15 μM. The sensor was insensitive to chloride and nitrate ions below threshold concentration of 1.0 mM respectively. Analytical measurements were successfully made in authentic samples of tap and pond water.

Background Type I diabetes occurs when the pancreas can only make limited or minimal insulin. Patients with type 1 diabetes need effective approaches to manage diabetes and maintain their blood-glucose concentration. Recently, continuous glucose monitoring (CGM) has been used to help control blood-glucose levels in patients with type 1 diabetes. Patients with type 2 diabetes may also benefit from CGM on multiple insulin injections, basal insulin, or sulfonylureas. Enzyme-free glucose detection in a neutral environment is the recent development trend of CGM. Materials and Methods Pt/Au alloy electrodes for enzyme-free glucose detection in a neutral environment were formed by electrochemically depositing Pt/Au alloy on a thin polycarbonate (PC) membrane surface with a uniformly distributed micro-hemisphere array. The PC membranes were fabricated using semiconductor microelectromechanical manufacturing processes, precision micro-molding, and hot embossing. Amperometry was used to measure the glucose concentration in PBS (pH 7.4) and artificial human serum. Results The Pt/Au nanoalloy electrode had excellent specificity for glucose detection, according to the experimental results. The device had a sensitivity of 2.82 μA mM−1 cm−2, a linear range of 1.39–13.9 mM, and a detection limit of 0.482 mM. Even though the complex interfering species in human blood can degrade the sensing signal, further experiments conducted in artificial serum confirmed the feasibility of the proposed Pt/Au nanoalloy electrode in clinical applications. Conclusion The proposed Pt/Au nanoalloy electrode can catalyze glucose reactions in neutral solutions with enhancing sensing performance by the synergistic effect of bimetallic materials and increasing detection surface area. This novel glucose biosensor has advantages, such as technology foresight, good detection performance, and high mass production feasibility. Thus, the proposed neutral nonenzymatic glucose sensor can be further used in CGMs., Graphical Abstract

In this work, we demonstrate effective microwave synthesis of quaternary nanocomposites containing graphene, directing polymer PANI nanoparticles, and LaNiMoSe2. We describe the use of LaNiMoSe2-G-PANI composite materials to devise an amperometric sensor for detection of HCl, HNO3, and NH3. Specialized electrodes were coated with LaNiMoSe2-G-PANI as an active sensor material using a cyclic voltammogram. The results show the excellent capacity of PANI for joining of the functionalized GO species. With various fixations, it is important to distinguish HCl, HNO3, and NH3, even within the sight of oxygen as an obstruction species. The LaNiMoSe2-G-PANI electrode can be used to identify various HCl, HNO3, and NH3 concentrations in the range of 50–1000 ppm, with the bottom limit of 50 ppm imposed by the cyclic voltammogram. To measure sensitivity and selectivity, we used electrodes coated with the LaNiMoSe2-G-PANI composite at locations containing HCl, HNO3, and NH3, without pretreatment. LaNiMoSe2-G-PANI as an active sensing material showed excellent detection ability with reproducibility.

This study demonstrates a facile ultrasonication-assisted synthesis of gold nanoparticles (AuNPs) decorated ultrathin graphitic carbon nitride nanosheets (g-C3N4) composite as an efficient electrocatalyst material. The as-prepared g-C3N4/AuNPs composite material's structural morphology was characterized using an X-ray diffractometer, field-emission scanning electron microscopy, and transmission electron microscopy. The prepared nanomaterial was applied to fabricate g-C3N4/AuNPs composite modified screen-printed carbon electrode (SPE) sensor for the sensitive electrochemical detection of caffeic acid (CA) in various food samples. The electrocatalytic properties and interfacial electron movement behavior of the g-C3N4/AuNPs/SPE was examined using electrochemical techniques, including cyclic voltammetry, chronoamperometry, differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy. Under the optimized experimental conditions, g-C3N4/AuNPs/SPE exhibited rapid response and sensitive detection of CA in both amperometric and voltammetric techniques. Excellent linear ranges and detection limits were achieved between the CA's concentration ranging from 0.5 to 155 nM for DPV with the detection limit (LOD) of 0.1 nM and 2.5–1025 nM CA for amperometric technique with LOD of 0.5 nM. The g-C3N4/AuNPs/SPE sensor was successfully applied to quantify the amount of CA in various food samples, and the obtained results were promising over conventional and recently reported methods. Thus, the developed sensor can be applied in routine food quality control and food analysis laboratories for quick and sensitive quantification of CA in foods.

In the present research, we have reported the applicability of multiwall carbon nanotube–doped polypyrrole-carbon black (MWCNTs/PPy-C) as a potential nitrite sensor. Sophisticated characterization tools including X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, infrared spectroscopy, and transmission electron microscopy were systematically employed to characterize the as-fabricated electrocatalyst. The electro-catalytic and sensing performance were evaluated using cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and amperometric (i-t) techniques. The as-fabricated sensor electrode shows remarkable electrocatalytic activity towards nitrite ion electro-oxidation. The nitrite oxidation using the proposed catalyst follows a diffusion-controlled process with kinetic parameters having electron transfer coefficient (α) as 0.50 and the standard rate constant (k0) as 5.488 $$\times$$ 10−3 cm s−1. The MWCNTs/PPy-C modified sensor electrode exhibited excellent sensitivity of 0.1558 µAµM−1 cm−2 over the dynamic concentration range (0.50–10.50 mM) (for linear sweep voltammetry: LSV) and 0.1171 µAµM−1 cm−2 over the concentration range (5–9500 µM) (for amperometry: i-t characteristics). The detection limit was calculated to be 2.30 µM and 3.06 µM (S/N = 3) for LSV and i-t technique, respectively. Furthermore, the proposed sensor electrode exhibited good selectivity towards nitrite ion detection in the existence of common interfering metal ions and biomolecules as well as demonstrated excellent operational stability, reproducibility, and repeatability. Therefore, such developed electrocatalyst demonstrates a promising sensor material for the competent detection of nitrite ions by the electrochemical method.

The rapid and accurate detection of hydrogen peroxide (H2O2) has recently been a fascinating research topic in electrochemical sensing. Herein, spinel CuMn2O4 nanoflakes were synthesized through coprecipitation and pyrolysis methods and then drop-coated onto the surface of a bare glassy carbon electrode (GCE), successfully generating an enzymatic-free electrochemical sensor (CuMn2O4/GCE) for good amperometric detection ability of H2O2. In comparison with the reported spinel AB2O4-based electrocatalysts in a phosphate buffer solution, the CuMn2O4/GCE sensor exhibits a high sensitivity of 3.420 A M–1 cm–2 and a low detection limit of 12 nM. This excellent sensing performance is mainly derived from the inherent porous structure and the large electrochemical active area of spinel CuMn2O4 nanoflakes, as well as the synergistic effect between Cu and Mn that facilitates electron transfer and increases active sites. Especially, the high contents of Cu+ and Mn3+ ions in the nanocatalyst are useful for promoting the capture and reduction of trace H2O2. In addition, the CuMn2O4/GCE sensor presents a satisfactory recovery in monitoring H2O2 derived from rat serum, commercial milk, and disinfectors, indicating its potential applications in related environmental, food, and biological fields.

Heavy metal pollution is posing a severe health risk on living organisms. Therefore, significant research efforts are focused on their detection. Here, we developed a sensing platform sensor for the selective detection of lead(II) acetate. The sensor is based on self-assembled polyethyleneimine-functionalized carbon nanotubes (PEI-CNTs) and graphene oxide films deposited onto gold interdigitated electrodes. The graphene-based nanostructure showed a resistive behavior, and the fabricated layer-by-layer film was used to detect Pb(II) acetate in an aqueous solution by comparison of three electrochemical methods: impedance spectroscopy, amperometry, and potentiometry stripping analysis. The results obtained from different methods show that the detection limit was down to 36 pmol/L and the sensitivity up to 4.3 μAL/μmol, with excellent repeatability. The detection mechanism was associated with the high affinity of heavy metal ions with the functional groups present in the PEI-CNTs and GO, allowing high performance and sensitivity. The achieved results are important for the research toward integrated monitoring and sensing platforms for Pb(II) contamination in drinking water.

This paper is focused on the specifics of amperometric oxygen (O2) measurements in biological media (cultivation media, reaction mixtures, media designed for isolated cellular and subcellular structures) and other complex media using Clark-type electrodes. Specifically, the impact of the qualitative and quantitative composition of liquid media on the readings of Clark electrodes is considered. Using sucrose, sorbitol, NaCl and phosphate buffer as examples, it has been shown that, provided the content of dissolved O2 is constant, an increase in the content of concomitant to O2 substances in the test medium results in an increase of the signal of the Clark electrode located in this medium. On the basis of the obtained and published data, the effect of the qualitative and quantitative composition of media on the readings of Clark electrodes is evaluated. In its turn, the very effect of media composition on Clark electrodes readings can be explained by the fact that in reality Clark electrodes measure the activity of dissolved O2, which usually increases with an increase in the content of concomitant to O2 substances. Since Clark electrodes measure the activity rather than the true O2 content in media and the ratio between the activity and true O2 content is often unknown, the issue regarding the calibration of Clark electrodes has been also considered in this study. It is noted that the methods of adding known amount of O2 to liquid media (the Hill reaction, catalase reaction, or injection of a micro portion of water saturated with pure O2), which were applied in this work to demonstrate the effect of media composition on the Clark electrode readings, can be used to calibrate the Clark electrodes in units of the true O2 content, and, thus, to take into account the influence of the media content on the readings of these O2-sensors when it is necessary. It is suggested that the calibration based on the addition of an O2-saturated micro-portion of water or, if necessary, O2-saturated micro-portion of another suitable liquid to the medium with the Clark electrode is, due to its almost unlimited applicability and other advantages, the most satisfactory way of calibration. The introduction of this calibration method into scientific practice can make quantitative O2-measurements with Clark electrodes more accurate in many difficult cases.

A non-enzymatic glucose-sensing material composed of α-nickel hydroxide nanosheets grown on reduced graphene oxide sheets (α-Ni(OH)2-rGO) is fabricated by a straightforward co-precipitation method. The morphology and composition of the α-Ni(OH)2-rGO are analyzed by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, thermogravimetric analyzer, and X-ray photoelectron spectroscopy. The characterization results show that the content of Ni(OH)2 in the α-Ni(OH)2-rGO composites is about 82.77 wt%. The introduction of rGO can effectively prevent α-Ni(OH)2 from agglomeration. The thickness of the α-Ni(OH)2 sheets grown vertically on the rGO is less than 10 nm, and they are interwoven to form a porous network structure. Then, the α-Ni(OH)2-rGO/NiF (Nickel Foam)-sensing electrode is prepared with NiF as the substrate. The sensing mechanism and detection property of the α-Ni(OH)2-rGO/NiF-sensing electrode are researched through cyclic voltammetry (CV) and amperometry. The test results demonstrate that α-Ni(OH)2-rGO/NiF-sensing electrode has excellent glucose-sensing performance. Its linear detection range is as wide as 0.5–22.5 mM, and the sensitivity is as high as 95.5 μAmM−1 cm−2, which is obviously much better than previously studied glucose-sensing materials. Moreover, it is found that the prepared sensing electrode has excellent anti-interference and stability. After repeated measurements, the anodic peak current is only 6% lower than the initial current. More importantly, the sensing electrode also showed a good detection ability for actual samples, which fully confirms that α-Ni(OH)2-rGO/NiF-sensing electrode has good practical application potential.

A two-step process was used to prepare a nickel-polyaniline nanocomposite (Ni (NPs)-PANI). The first step consisted of the electrodeposition of polyaniline (PANI) in the form of thin films on fluorine-doped tin oxide (FTO) substrates from a solution of aniline, lithium perchlorate, and sulfuric acid at a pH of 0.5. In the next step, the obtained Ni (NPs) were deposed in this polyaniline films. The structural, morphological, and electrocatalytic properties of the prepared nanocomposites were then investigated. X-ray diffraction (XRD) confirmed the cubic structure of the nanocomposites, and Fourier-transform infrared spectroscopy (FTIR) indicated the existence of nickel and polyaniline in the prepared nanocomposites. Morphological analysis carried out through SEM revealed that the nanocomposites exhibit uniform dispersion of nickel nanoparticles into the polyaniline matrix. Amperometry and cyclic voltammetry were employed to investigate the electrocatalytic glucose oxidation behavior of the nanocomposite electrode in the alkaline medium. The prepared nickel-polyaniline nanocomposite electrode exhibited high sensitivity (278.8 µA mM−1 cm−2) in a range from 0.02 to 1 mM at a sufficiently fast response time of 3 s and a low glucose detection limit of 1 µM (S/N = 3). A cost-effective and straightforward synthesis procedure to prepare Ni (NPs)-PANI nanocomposite would make this material an efficient glucose sensor with appropriate stability, higher reproducibility, and excellent sensitivity.

Diabetes is a common chronic disease, so it is particularly important to develop a convenient, fast, and highly sensitive non-enzymatic glucose sensor. In this work, a high sensitivity, low cost sensor was prepared on the substrate of printed circuit board. The nickel cobaltate (NiCo2O4) spherical nanomaterials were synthesized by facile hydrothermal and calcining methods. The working electrode was modified by NiCo2O4 nanospheres and the cation exchange resin in turn. Nafion cation exchange film can help to reduce the interference caused by surface-active compounds cyclic voltammetry- amperometric method was used to study the electrocatalytic performance of the sensor at room temperature. The sensor modified by NiCo2O4 nanospheres showed good sensor performance for glucose, including excellent sensitivity ( $3449.14~\mu \text{A}$ mM $^{-1}$ cm $^{-2}$ ), wide linear range ( $1~\mu \text{M}$ to 100 mM), and low detection limit ( $0.376~\mu \text{M}$ ). In addition, it has high selectivity, repeatability and stability. The sensor proposed in this work has been successfully applied to the detection of glucose in urine, and the results are consistent with the actual glucose concentration in urine.

This study proposes the development of an electrochemical sensor based on fabrication of a glassy carbon electrode (GCE) with Fe3O4-polyaniline (Fe3O4-PANI) nanocomposite, which was further used for enzyme-less detection of 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous medium. Spectroscopic studies, microstructural studies, and elemental analysis established the formation of Fe3O4 nanoparticles with polyaniline coating. The fabricated Fe3O4-PANI-GCE was characterized by electrochemical techniques like cyclic voltammetry and electrochemical impedance spectroscopy. The electrochemical response of 2,4-D on Fe3O4-PANI-GCE was evaluated by performing cyclic voltammetry and amperometry experiments. The synergistic effect of the composite causes the superior electrochemical behavior of Fe3O4-PANI-GCE toward the detection of 2,4-D. Amperometric measurements exhibited a linear concentration range from 1.35 to 2.7 μM. The sensitivity and detection limit were evaluated from the amperometric responses, which were found to be 4.62 × 10-7 μA μM-1 cm-2 and 0.21 μM, respectively. The electrochemical sensing response could be attributed to adsorption of 2,4-D onto the Fe3O4-PANI-modified GCE (Fe3O4-PANI-GCE) surface. Fe3O4-PANI-GCE is found to be a simple, low-cost, and biocompatible non-enzymatic sensor for detection of 2,4-D in aqueous medium at ambient temperature.

The remarkable development of nanotechnology and nanoscience has greatly promoted the vigorous development of the field of nanomaterials. This study explores a porous cuboid Ni/NiO composite nanomaterial obtained by calcining NiC2O4·2H2O under a N2 environment. The composite affords direct electrochemical activity and good electrocatalytic properties. Compared to uncalcined precursor, the porous Ni/NiO obtained after calcination exhibited higher catalytic activity for glucose oxidation with higher sensitivity. Moreover, because of its regular cube structure the as-synthesized Ni/NiO exhibited improved electrochemical stability. Such porous Ni/NiO nanocubes represent promising glucose catalyst with high sensitivity and selectivity, improved stability and fast amperometric response.

In this study, a simple approach is established to fabricate NiCoSe4 nanorods grown onto carbon nanofiber (CNF) skeletons by combining electrospinning and a hydrothermal process. We achieved the rapid and ultrasensitive electrocatalytic sensing of tryptophan (Trp) in 0.1 M KOH by using intrinsically metallic NiCoSe4 anchored on CNFs as an alternative working electrode material. Benefiting from the large surface area due to rich defect active sites and the high electrocatalytic behavior of NiCoSe4 with CNF, the fabricated sensor exhibits a lower electron-transfer resistance of Rct 92 Ω with respect to the CNF–NiCo and CNFs electrodes. The results of voltammetric technique confirmed that the CNF–NiCoSe4-GCE showed higher anodic peak intensity and a lower anodic potential for Trp detection than CNFs-GCE and CNF–NiCo-GCE electrodes since the integration of sp2 carbon on the surface of the CNFs and bimetallic selenides improves the sensing performance. The amperometric I-t curve showed a linear response in the Trp concentration range of 5–95 nM and a detection limit of 0.68 nM at low potential of 0.4 V vs. Hg/HgO. The CNF–NiCoSe4-GCE was successfully utilized for the electrocatalytic monitoring of Trp from human serum, milk, and tomato juice samples with a recovery of 95.4–105.5%.

In this study, we demonstrate a facile approach for the synthesis of strontium tungstate (G-SrWO4) using Pomelo leaf extract via the sonochemical method. The electrocatalytic performance of G-SrWO4 solubilized Nafion (Nf) (G-SrWO4/Nf) modified GC electrode was evaluated for uric acid (UA) detection. The characteristic properties of the prepared G-SrWO4 nanocomposite were analyzed by techniques like XRD, FT-IR, FESEM, EDX, HR-TEM, SEAD, XPS, and TGA analysis. The G-SrWO4/Nf modified GC electrode displayed excellent electrocatalytic performance in UA sensing. The amperometric studies revealed that the G-SrWO4/Nf modified GC electrode performed admirably by attaining a wide linear range response of UA 0.001 μM to 0.5 μM with a limit of detection 33ppm and sensitivity of 486 μAμM−1cm−2. Meanwhile, the G-SrWO4/Nf modified GC electrode exhibited good selectivity, rapid and stable response towards UA. The practical applicability of the sensor was successfully tested by performing UA detection in the urine and serum samples with acceptable recovery results.

Here, fundamental aspects affecting template-assisted engineering of oxidase-associated peroxide oxidation co-catalysis of the modeled microanalytical system based on the hybrid palladium nanoparticles (Pd-NPs) with tailored functional properties were studied. By an accurate tuning and validation of the experimental setup, a modular Pd-NPs-doped one-pot/one-electrode amperometric nanobiosensor for advanced multiplex analyte detection was constructed. The specific operational conditions (electrochemical read-out mode, pH, regeneration procedure) of the modular one-pot/one-electrode nanobiosensor allowed a reliable sensing of L -lactate (with linear dynamic range, LDR = 500 µM – 2 mM, R2 = 0.977), D -glucose (with LDR = 200 µM – 50 mM, R2 = 0.987), hydrogen peroxide (with LDR = 20 µM – 100 mM, R2 = 0.998) and glutaraldehyde (with LDR = 1 – 100 mM, R2 = 0.971). In addition, mechanistic aspects influencing the performance of Pd-NPs-doped one-pot/one-electrode for multiplex analyte sensing were studied in detail. The designed one-pot/one-electrode amperometric nanobiosensor showed a thin layer electrochemical behavior that greatly enhanced electron transfer between the functional hybrid layer and the electrode. Finally, a specific regeneration procedure of the hybrid one-pot/one-electrode and algorithm towards its usage for modular biocatalysis were developed. The reported strategy can readily be considered as a guideline towards the fabrication of commercialized nanobiosensors with tailored properties for advanced modular biocatalysis.

In the present study, Malva sylvestris leaf extracts was used as a reducing agent for the synthesis of NiO NPs. They were characterized by FT-IR, XRD, and SEM studies. The synthesis of NiO NPs was monitored by different ratios of nickel nitrate solution and extract by using of SEM technique. The average particle size of NiO NPs was 35 nm which is consistent with the particle size calculated by XRD Scherer equation. Also, the carbon paste electrode modified with NiO NPs (NiO NPs/MCPE) was prepared by mixing of NiO NPs and graphite powder. Then, the electrochemical oxidation of cephalexin at the surface of this electrode was investigated using the cyclic voltammetric and amperometric techniques. The presence of NiO NPs markedly enhances the electrocatalytic activity. Under the selected conditions, the anodic peak current was linearly dependent on the concentration of cephalexin in the range of 2.5–35 µM and 65–1.23 × 103 µM by the amperometric method. The detection limit (S/N = 3) was also estimated to be 1.30 µM. This modified electrode was a simple, rapid and effective sensor that was successfully applied to determine cephalexin in the pharmaceutical samples.

The fabrication of a network of glucose oxidase-horseradish peroxidase/tin oxide (GOx-HRP/SnO2), immobilized onto a glassy carbon electrode (GCE) and its utilization as a biosensor for glucose detection is reported. The network established with GOx-HRP/SnO2 possess high sensitivity and stability by performing the electrocatalytic features in the sensing of glucose. The turbidity of fabrication had been scanned and analyzed using UV-vis spectroscopy. The morphology and composition of the fabricated GOx-HRP/SnO2 networks were characterized by scanning electron microscopy (SEM). Cyclic voltammetry and amperometry were employed to study the electrochemical properties of the proposed biosensor. The effect of applied electrode potential and pH were systemically investigated. The biosensor responds to glucose at work potential values between −400 mV, and exhibited a lower detection limit (0.025 mM) and long linear range (0.25 to 7.0 mM), and was resistant to common interferences.

In this paper, a novel trehalose sensor based on micro/nano-Ni foam modified with graphene oxidated (GO) and a non-linear data analysis model was proposed. A three-electrode electrochemical detection system, GO-modified Ni foam material as the working electrode, Ag/AgCl (saturated KCl) electrode as the reference electrode, and Pt electrode as the counter electrode, was utilized as a detecting system. Trehalose with different concentrations was measured by cyclic voltammetry (CV) and amperometric i-t curve (i-t) methods. Results showed that the sensitivity of the proposed sensor was 1.66 ± 0.07 mA cm−2 Mm−1, and the detecting limit was 37.1 μM (S/N = 3). The sensitivity of the unmodified Ni foam electrode was 0.23 ± 0.01 mA cm−2 mM−1, and the detecting limit was 52.3 μM (S/N = 3). Results demonstrated that GO-modified Ni foam electrode presented higher sensitivity and lower detecting limit than unmodified Ni foam electrode. Control experiments indicated that they presented specific responses to trehalose. It has some advantages including quick response, high sensitivity, and low detection limit.

New modified electrode materials, based on a combination of hybrid nanocomposites such as magnetic nanoparticles, inorganic polymer (SiO2) and different types of organic polymers, were studied. Thr...

The constant development and improvement of microelectromechanical systems (MEMS) have been given a great opportunity to develop new reliable microsystems devices for biomedical research. This article presents a locally addressable 2-D arrayed indium–tin oxide microelectrode platform with integrated thin-film transistors (TFTs) for biological and chemical sensing. Microelectrode arrays (MEAs) using TFT have the advantage of being transparent with a high density of microelectrodes on a large surface. In vitro 2-D electrical measurements on 28 parallel-connected lines selected from a 22 500 MEA were successfully performed with heart cells for the first time. Observation of cell contraction was performed simultaneously with an inverted microscope. Voltammetry and amperometry measurements were also demonstrated using the transparent microelectrodes as working electrodes and an integrated Ag/AgCl reference electrode. Due to its unique features, we believe that the TFT platform can provide more understanding of the key communication between heart cells, and large-scale cardiovascular and nervous systems. As a result, the platform offers unique access to versatile lab-on-a-chip devices that integrate many measurement techniques on one chip for the study of cell cultures, tissues, and organoids.