Synthesis of three dimensional nickel cobalt oxide nanoneedles on nickel foam, their characterization and glucose sensing application

Nanostructured wearable electrochemical and biosensor towards healthcare management: a review

In recent years, there has been a rapid increase in demand for wearable sensors, particularly these tracking the surroundings, fitness, and health of people. Thus, selective detection in human body fluid is a demand for a smart lifestyle by quick monitoring of electrolytes, drugs, toxins, metabolites and biomolecules, proteins, and the immune system. In this review, these parameters along with the main features of the latest and mostly cited research work on nanostructured wearable electrochemical and biosensors are surveyed. This study aims to help researchers and engineers choose the most suitable selective and sensitive sensor. Wearable sensors have broad and effective sensing platforms, such as contact lenses, Google Glass, skin-patch, mouth gourds, smartwatches, underwear, wristbands, and others. For increasing sensor reliability, additional advancements in electrochemical and biosensor precision, stability in uncontrolled environments, and reproducible sample conveyance are necessary. In addition, the optimistic future of wearable electrochemical sensors in fields, such as remote and customized healthcare and well-being is discussed. Overall, wearable electrochemical and biosensing technologies hold great promise for improving personal healthcare and monitoring performance with the potential to have a significant impact on daily lives. These technologies enable real-time body sensing and the communication of comprehensive physiological information.

Glucose nano biosensor with non-enzymatic excellent sensitivity prepared with nickel-cobalt nanocomposites on f-MWCNT

NiCo (Nickel-cobalt) nanoparticles were obtained by the chemical reduction method on functionalized multi-walled carbon nanotubes. After this process, chronoamperometry, cyclic voltammetry, and amperometric methods were used to investigate the electrochemical and electrocatalytic behavior of NiCo@f-MWCNT against glucose oxidation. In addition, the NiCo@f-MWCNT nanocomposites were analyzed by characterization techniques such as X-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Transmission Electron Microscopy (TEM), and Atomic Force Microscopy (AFM) in terms of the morphological and atomic structure of prepared nanomaterials. The sensitivity and limit of detection the non-enzymatic glucose sensor (NiCo@f-MWCNT) were calculated as 10,015 μA/mM^-1 cm^-2 0.26 μM, respectively. As a result of these studies and experiments, the NiCo@f-MWCNT nanocomposite is a really good sensor and their stability showed that the current nanomaterials expressed to be new material for the electrochemical detection of glucose.

NiCo2O4 Nano-/Microstructures as High-Performance Biosensors: A Review

Non-enzymatic biosensors based on mixed transition metal oxides are deemed as the most promising devices due to their high sensitivity, selectivity, wide concentration range, low detection limits, and excellent recyclability. Spinel NiCo2O4 mixed oxides have drawn considerable attention recently due to their outstanding advantages including large specific surface area, high permeability, short electron, and ion diffusion pathways. Because of the rapid development of non-enzyme biosensors, the current state of methods for synthesis of pure and composite/hybrid NiCo2O4 materials and their subsequent electrochemical biosensing applications are systematically and comprehensively reviewed herein. Comparative analysis reveals better electrochemical sensing of bioanalytes by one-dimensional and two-dimensional NiCo2O4 nano-/microstructures than other morphologies. Better biosensing efficiency of NiCo2O4 as compared to corresponding individual metal oxides, viz. NiO and Co3O4, is attributed to the close intrinsic-state redox couples of Ni3+/Ni2+ (0.58 V/0.49 V) and Co3+/Co2+ (0.53 V/0.51 V). Biosensing performance of NiCo2O4 is also significantly improved by making the composites of NiCo2O4 with conducting carbonaceous materials like graphene, reduced graphene oxide, carbon nanotubes (single and multi-walled), carbon nanofibers; conducting polymers like polypyrrole (PPy), polyaniline (PANI); metal oxides NiO, Co3O4, SnO2, MnO2; and metals like Au, Pd, etc. Various factors affecting the morphologies and biosensing parameters of the nano-/micro-structured NiCo2O4 are also highlighted. Finally, some drawbacks and future perspectives related to this promising field are outlined.

n-Butanol/Water Interface-Aided Physicochemical Tuning of Two-Dimensional Transition-Metal Oxides

Herein, we report a facile regulation of the interface of two immiscible solvents, n-butanol and water, to achieve the physicochemical tuning of the transition-metal oxide nickel cobaltite. The crystal nucleation and the growth of nickel cobaltite into distinct morphology are highly dependent on the orientation and the mass transfer of the reactive species through the reactive interface layer. A distinct two-dimensional flakelike (1 nm thickness) nickel cobaltite is formed at the interface of n-butanol/water in a 1:1 solvent ratio. Rather, one-dimensional needles and irregular interconnected networks are achieved, as aqueous and organic counterparts are, respectively, increased. The impact of the solvent ratio on doping metal ions (Co²⁺ and Ni²⁺) at the interstitial sites of fcc spinel structure is evident from the X-ray and electronic absorption investigations. It is presumed that the interface-assisted synthesis may provide a simple and novel way to develop and adopt various transition-metal oxides for wide applications.

A practical non-enzymatic urea sensor based on NiCo2O4 nanoneedles

We propose a new facile electrochemical sensing platform for determination of urea, based on a glassy carbon electrode (GCE) modified with nickel cobalt oxide (NiCo₂O₄) nanoneedles.

Synthesis of Co3O4/graphene nanocomposite using paraffin wax for adsorption of methyl violet in water

This study discusses the use of Co3O4 impregnated graphene (CoOIG) as an efficient adsorbent for the removal of methyl violet (MV) dye from wastewater. CoOIG nanocomposites have been prepared by pyrolyzing paraffin wax with cobalt acetate. The synthesised nanocomposite was characterised by X-ray diffraction, field emission scanning electron microscope, transmission electron microscope, Fourier transform infrared spectroscope, Raman spectroscopy, and Brunauer-Emmett-Teller isotherm studies. The above studies indicate that the composites have cobalt oxide nanoparticles of size 51-58 nm embedded in the graphene nanoparticles. The adsorption studies were conducted with various parameters, pH, temperature and initial dye concentration, adsorbent dosage and contact time by the batch method. The adsorption of MV dye by the adsorbent CoOIG was about 90% initially at 15 min and 98% dye removal at pH 5. The data were fitted in Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich and Sips isotherm models. Various thermodynamic parameters like Gibbs free energy, enthalpy, and entropy of the on-going adsorption process have also been calculated.

Three-dimensional porous self-assembled chestnut-like nickel-cobalt oxide structure as an electrochemical sensor for sensitive detection of hydrazine in water samples

Three-dimensional NiCo₂O₄ is a kind of superior sensing material owing to its high electron transfer capability, large available surface area and numbers of active sites. In this work, NiCo₂O₄ of the three-dimensional chestnut-like structure were easily achieved through a one step hydrothermal process. Afterwards, the morphology and structure were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Based on the three-dimensional porous chestnut-like NiCo₂O₄, an electrochemical sensor for hydrazine (N₂H₄) detection is fabricated. This electrochemical platform can realize good selectivity, excellent stability, high sensitivity (∼2154.4 μA mM^-1 cm^-2), and low detection limit (0.3 μM), as well as a wide linear range from 1 μM to 1096 μM. The synergistic effect of nickel-cobalt in such mixed transition metal oxides which Co in Co₃O₄ is partially replaced by Ni are beneficial for enhancing sensing properties. This study proves that three-dimensional porous chestnut-like NiCo₂O₄ is electrochemically active for catalytic performance which is particular and promising material for good application in the practical detection of N₂H₄.

Facile Synthesis of Ultrathin Nickel-Cobalt Phosphate 2D Nanosheets with Enhanced Electrocatalytic Activity for Glucose Oxidation

Two-dimensional (2D) ultrathin nickel-cobalt phosphate nanosheets were synthesized using a simple one-step hydrothermal method. The morphology and structure of nanomaterials synthesized under different Ni/Co ratios were investigated by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Moreover, the influence of nanomaterials' structure on the electrochemical performance for glucose oxidation was investigated. It is found that the thinnest nickel-cobalt phosphate nanosheets synthesized with a Ni/Co ratio of 2:5 showed the best electrocatalytic activity for glucose oxidation. Also, the ultrathin nickel-cobalt phosphate nanosheet was used as an electrode material to construct a nonenzymatic electrochemical glucose sensor. The sensor showed a wide linear range (2-4470 μM) and a low detection limit (0.4 μM) with a high sensitivity of 302.99 μA·mM^-1·cm^-2. Furthermore, the application of the as-prepared sensor in detection of glucose in human serum was successfully demonstrated. These superior performances prove that ultrathin 2D nickel-cobalt phosphate nanosheets are promising materials in the field of electrochemical sensing.

Enhanced tortuosity for electrolytes in microwave irradiated self-organized carbon-doped Ni/Co hydroxide nanocomposite electrodes with higher Ni/Co atomic ratio and rate capability for an asymmetric supercapacitor

We demonstrate a green, facile and rapid microwave-mediated process for fabricating carbon black (CB) incorporated Ni/Co hydroxide porous nanocomposites and study the effect of various mass loading of CB on supercapacitor performance. The structure and interactions between CB and Ni/Co hydroxide are characterized by using x-ray diffraction, Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy, which suggest the miniaturization of the single-phase Ni/Co hydroxide formation time. A morphology study reveals that the addition of CB into Ni/Co hydroxide develops a loose network structure with well-defined architectural pores. In addition, the nanocomposites demonstrate noticeable improvements in porosity and atomic ratio of Ni/Co with an increasing percentage of carbon, which results in a higher diffusion of electrolytes, and hence electrical conduction. The developed electrode materials exhibit a maximum specific capacitance value of 1526 Fg^-1 at current density 1 Ag^-1 with excellent cyclic stability (92% retention at 5000 cycles), energy density (76 Wh Kg^-1), power density (250 W Kg^-1) and rate capability. A solid state asymmetric supercapacitor device is fabricated and utilized to brighten a commercial LED effectively for validating real usage.

Hierarchical NiCo₂O₄ Hollow Sphere as a Peroxidase Mimetic for Colorimetric Detection of H₂O₂ and Glucose

In this work, the hierarchical NiCo₂O₄ hollow sphere synthesized via a “coordinating etching and precipitating” process was demonstrated to exhibit intrinsic peroxidase-like activity. The peroxidase-like activity of NiCo₂O₄, NiO, and Co₃O₄ hollow spheres were comparatively studied by the catalytic oxidation reaction of 3,3,5,5-tetramethylbenzidine (TMB) in presence of H₂O₂, and a superior peroxidase-like activity of NiCo₂O₄ was confirmed by stronger absorbance at 652 nm. Furthermore, the proposed sensing platform showed commendable response to H₂O₂ with a linear range from 10 μM to 400 μM, and a detection limit of 0.21 μM. Cooperated with GOx, the developed novel colorimetric and visual glucose-sensing platform exhibited high selectivity, favorable reproducibility, satisfactory applicability, wide linear range (from 0.1 mM to 4.5 mM), and a low detection limit of 5.31 μM. In addition, the concentration-dependent color change would offer a better and handier way for detection of H₂O₂ and glucose by naked eye.

Nanostructured Tip-Shaped Biosensors: Application of Six Sigma Approach for Enhanced Manufacturing

Nanostructured tip-shaped biosensors have drawn attention for biomolecule detection as they are promising for highly sensitive and specific detection of a target analyte. Using a nanostructured tip, the sensitivity is increased to identify individual molecules because of the high aspect ratio structure. Various detection methods, such as electrochemistry, fluorescence microcopy, and Raman spectroscopy, have been attempted to enhance the sensitivity and the specificity. Due to the confined path of electrons, electrochemical measurement using a nanotip enables the detection of single molecules. When an electric field is combined with capillary action and fluid flow, target molecules can be effectively concentrated onto a nanotip surface for detection. To enhance the concentration efficacy, a dendritic nanotip rather than a single tip could be used to detect target analytes, such as nanoparticles, cells, and DNA. However, reproducible fabrication with relation to specific detection remains a challenge due to the instability of a manufacturing method, resulting in inconsistent shape. In this paper, nanostructured biosensors are reviewed with our experimental results using dendritic nanotips for sequence specific detection of DNA. By the aid of the Six Sigma approach, the fabrication yield of dendritic nanotips increases from 20.0% to 86.6%. Using the nanotips, DNA is concentrated and detected in a sequence specific way with the detection limit equivalent to 1000 CFU/mL. The pros and cons of a nanotip biosensor are evaluated in conjunction with future prospects.

Recent developments in nanostructure based electrochemical glucose sensors

Diabetes is a major health problem causing 4 million deaths each year and 171 million people suffering worldwide. Although there is no cure for diabetes, nevertheless, the blood glucose level of diabetic patients should be monitored tightly to avoid further complications. Thus, monitoring of glucose in blood has become an inevitable need leading to fabrication of accurate and sensitive advanced blood sugar detection devices for clinical diagnosis and personal care. It led to the development of enzymatic glucose sensing approach. Later on, various types of nanostructures have been utilized owing to their high surface area, great stability, and cost effectiveness for the fabrication of enzymatic as well as for nonenzymatic glucose sensing approach. This work reviews on both categories, however it is not intended to discuss all the research reports published regarding nanostructure based enzymatic and nonenzymatic approaches between mid-2010 and mid-2015. We, do, however, focused to describe the details of many substantial articles explaining the design of sensors, and utilities of the prepared sensors, so that readers might get the principles behind such devices and relevant detection strategies. This work also focuses on biocompatibility and toxicity of nanomaterials as well as provides a critical opinion and discussions about misconceptions in glucose sensors.

Zinc oxide nanostructure-modified textile and its application to biosensing, photocatalysis, and as antibacterial material

Recently, one-dimensional nanostructures with different morphologies (such as nanowires, nanorods (NRs), and nanotubes) have become the focus of intensive research, because of their unique properties with potential applications. Among them, zinc oxide (ZnO) nanomaterials has been found to be highly attractive, because of the remarkable potential for applications in many different areas such as solar cells, sensors, piezoelectric devices, photodiode devices, sun screens, antireflection coatings, and photocatalysis. Here, we present an innovative approach to create a new modified textile by direct in situ growth of vertically aligned one-dimensional (1D) ZnO NRs onto textile surfaces, which can serve with potential for biosensing, photocatalysis, and antibacterial applications. ZnO NRs were grown by using a simple aqueous chemical growth method. Results from analyses such as X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that the ZnO NRs were dispersed over the entire surface of the textile. We have demonstrated the following applications of these multifunctional textiles: (1) as a flexible working electrode for the detection of aldicarb (ALD) pesticide, (2) as a photocatalyst for the degradation of organic molecules (i.e., Methylene Blue and Congo Red), and (3) as antibacterial agents against Escherichia coli. The ZnO-based textile exhibited excellent photocatalytic and antibacterial activities, and it showed a promising sensing response. The combination of sensing, photocatalysis, and antibacterial properties provided by the ZnO NRs brings us closer to the concept of smart textiles for wearable sensing without a deodorant and antibacterial control. Perhaps the best known of the products that is available in markets for such purposes are textiles with silver nanoparticles. Our modified textile is thus providing acceptable antibacterial properties, compared to available commercial modified textiles.

Nickel-Cobalt Oxide Decorated Three-Dimensional Graphene as an Enzyme Mimic for Glucose and Calcium Detection

Glucose and calcium ion play key roles in human bodies. The needlelike NiCo2O4 nanostructures are in situ deposited on three-dimensional graphene foam (3DGF) by a facile hydrothermal procedure. The structure and morphology of the hierarchical NiCo2O4/3DGF are characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. With the self-standing NiCo2O4/3DGF as electrochemical electrode, it can realize the high-sensitivity detections for glucose and calcium ion. The limit of detection can reach 0.38 and 4.45 μM, respectively. In addition, the electrochemical electrode presents excellent selectivity for glucose and calcium ion. This study demonstrates that NiCo2O4/3DGF is a unique and promising material for practical application in both glucose and calcium ion sensing.

Electrodeposited spinel NiCo2O4 nanosheet arrays for glucose sensing application

Non-enzymatic glucose sensing properties of NiCo₂O₄ nanosheets show linear response with respect to the change in glucose concentration varying from 5 to 65 μM and exhibit the sensitivity value of 6.69 μA μM⁻¹ cm⁻² with a LOD value of 0.38 μM.