Rose-like CuO nanostructures for highly sensitive glucose chemical sensor application

This paper reports the synthesis, characterization and glucose chemical sensing applications of well-crystalline rose-like CuO nanostructures. The rose-like CuO nanostructures were synthesized by facile hydrothermal process at low-temperature and characterized in detail in terms of their morphological, compositional, structural, optical and sensing properties. The detailed characterizations revealed that the synthesized rose-like CuO nanostructures are nanocrystalline and possessing monoclinic structure. Further, the synthesized nanostructures were used as efficient electron mediator to fabricate non-enzymatic glucose sensor. The fabricated glucose chemical sensor shows a very high sensitivity of ~4.640 μA mM⁻¹ cm⁻² and an experimental detection limit of ~0.39 mM with correlation coefficient (R) of 0.9498. The observed linear dynamic range for the fabricated chemical sensor was from 0.78 mM to 100 mM. The presented work demonstrates that simply prepared CuO nanomaterials can efficiently be used to fabricate reliable and reproducible glucose chemical sensors.     

In situ growth of copper nanoparticles on multiwalled carbon nanotubes and their application as non-enzymatic glucose sensor materials

Cu-nanoparticles were coated on the sidewall of multiwalled carbon nanotubes (MWCNTs) by a facile and effective in situ approach via the template of a polyelectrolyte (polyethylenimine or poly(sodium 4-styrene sulfonate)) noncovalently functionalized on MWCNTs. Extensive characterizations of the fabricated nanocomposites have been studied using X-ray diffraction, transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, thermal gravimetric analysis and inductively coupled plasma. The results demonstrate that Cu-nanoparticles were well distributed on the surface of MWCNTs. The nanocomposites can be easily modified on the glassy carbon electrodes due to the presence of polyelectrolyte. The electrocatalytic activity of the modified electrodes towards glucose oxidation was investigated by cyclic voltammetry and chronoamperometry. The nanocomposites showed good non-enzymatic electrocatalytic responses to glucose in alkaline media, and can be used for the development of enzyme-free glucose sensors.     

Fabrication of CuO nanoplatelets for highly sensitive enzyme-free determination of glucose

CuO nanoplatelets were grown on Cu foils by a one step, template free process. The structure and morphology of the CuO nanoplatelets were characterized by X-ray diffraction, scanning and transmission electron microscopy. The CuO nanoplatelets grown on Cu foil were integrated to be an electrode for glucose sensing. The electrocatalytic activity of the CuO nanoplatelets electrode for glucose in alkaline media was investigated by cyclic voltammetry and chronoamperometry. The electrode exhibits a sensitivity of 3490.7 μA mM⁻¹ cm⁻² to glucose which is much higher than that of most reported enzyme-free glucose sensors and the linear range was obtained over a concentration up to 0.80 mM with a detection limit of 0.50 μM (signal/noise = 3). Exhilaratingly, the electrode based on the CuO nanoplatelets is resistant against poisoning by chloride ion, and the interference from the oxidation of common interfering species, such as uric acid, ascorbic acid, dopamine and carbonhydrate compounds, can also be effectively avoided. Finally, the electrode was applied to analyze glucose concentration in human serum samples.     

Electrochemical behavior of CuO/rGO nanopellets for flexible supercapacitor,non-enzymatic glucose,and H2O2 sensing application

In the present article, graphene oxide (GO) sheets and monoclinic copper oxide (CuO) nanocrystals are connected with each other and result in the formation of CuO/rGO nanopellets, and these nanopellets synthesized using coprecipitation method. The nanopellet structured CuO/rGO composite on carbon cloth, which act as current collector exhibits specific capacitance of 188 F g^?1 at a current density of 0.2 A g^?1 and up to 96.3% capacity retention after 2000 charge-discharge cycles. It shows a maximum energy density of 7.32 Wh kg^?1 and power density of 53 W kg^?1. The glucose sensing characteristics of CuO/rGO nanopellet is investigated on carbon cloth and ITO substrate. It shows glucose sensitivity of 0.805 mA mM^?1 cm^?2 and 0.2982 mA mM^?1 cm^?2 for a bundle like structured CuO/rGO composite on carbon cloth and ITO substrate, respectively. Further H₂O₂ sensing is studied on ITO substrate, which manifests H₂O₂ sensitivity of 84.39 μA mM^?1 cm^?2. The results indicate that nanopellet structured CuO/rGO composite could be a promising electrode material for supercapacitor, glucose, and H₂O₂ sensor.     

Copper-decorated carbon nanotubes based composite electrodes for non-enzymatic detection of glucose

ABSTRACT: The aim of this study was to prepare three types of multi-wall carbon nanotube (CNT)-based composite electrodes and to modify their surface by copper electrodeposition for non-enzymatic oxidation and determination of glucose from aqueous solution. Copper decorated multi-wall carbon nanotube composite electrode (Cu/CNT-Epoxy) exhibited the highest sensitivity to glucose determination. The reliability of the Cu/CNT-Epoxy electrode was verified by application of this composite electrode for the determination of glucose in real blood serum samples.     

Facile fabrication of chitosan-calcium carbonate nanowall arrays and their use as a sensitive non-enzymatic organophosphate pesticide sensor

Novel nanowall arrays of CaCO(3)-chitosan (CaCO(3)-chi) were deposited onto a cathodic substrate by a facile one-step electrodeposition approach. Results demonstrate that chitosan plays an important role in the formation of nanowall arrays. Freestanding well-aligned CaCO(3)-chi nanowall arrays were observed to be uniformly distributed over the whole substrate with a lateral dimension in the micrometre size and an average pore size of ～400 nm. The as-formed CaCO(3)-chi nanowall arrays featuring interlaced porous network architecture, large surface area, and open boundaries, are highly efficient in the capture of organophosphate pesticides (OPs). Combined with stripping voltammetry, a highly sensitive non-enzymatic OPs sensor was fabricated using the prepared CaCO(3)-chi nanowall arrays for solid phase extraction (SPE). The detection limit for methyl parathion (MP) in aqueous solutions was determined to be 0.8 ng mL(-1) (S/N = 3). The resulting sensor made of novel CaCO(3)-chi nanowall arrays exhibits good reproducibility and acceptable stability. This work not only provides a facile and effective route for the preparation of CaCO(3)-chi nanowall arrays, but also offers a new promising protocol for OPs analysis.     

Design and development of a simple and highly sensitive anthocyanin-based sensing device for colorimetric urea determination

We introduce a rapid anthocyanin-based paper sensor with very high sensitivity and optical visibility for colorimetric detection of urea. The working principle is based on a colour change from purple to blue upon sensor exposure to ammonia generated from urea hydrolysis in the presence of urease as a catalyst. To improve sensor sensitivity and optical visibility, anthocyanin storage, urease solvent, urea hydrolysis time, and temperature were investigated. The results indicated that the anthocyanin extracted from red cabbage and stored in dark and low-temperature conditions, urease extracted into water₅₅ + glycerol₄₅ (Aq₅₅ + G₄₅), and urea hydrolysis time of 40 min and temperature of 45°C offer the best detection condition. The fabricated sensor showed exceptional sensitivity of 0.018 pixel/mg urea-N/L with a very low limit of detection (2.01 mg urea-N/L) and a limit of quantification (6.71 mg urea-N/L). Moreover, the sensor reaction zone is optically visible for urea concentration as low as 5 mg urea-N/L, making it a promising tool for urea screening in diverse applications. The unique analytical features and accuracy of the sensor compared to the spectrophotometry method also suggest that it can be used as a replacement for environmentally unfriendly spectrophotometry methods for on-site urea determination.     

A highly selective and sensitive fluorescence chemosensor based on optically active polybinaphthyls for Hg

The chiral polymer was synthesized by the polymerization of 4,7-diethynylbenzo[2,1,3]-thiadiazole (M-1) with (R)-6,6′-dibutyl-3,3′-diiodo-2,2′-bis(diethylaminoethoxy)-1,1′-binaphthyl (R-M-1) via Pd-catalyzed Sonogashira reaction. The chiral polymer has orange fluorescence due to the extended π-electronic structure between binaphthyl unit and benzo[2,1,3]thiadiazole (BT) group via ethynyl bridge. The responsive optical properties of the polymer on various metal ions were investigated by fluorescence spectra. The fluorescence of the chiral polymer can produce the pronounced enhancement as high as 1.8-fold upon addition of 1:2 molar ratio of Hg²⁺. Compared with other cations, such as K⁺, Mg²⁺, Pb²⁺, Co²⁺, Ni²⁺, Ag⁺, Cd²⁺, Cu²⁺, Zn²⁺, Mn²⁺ and Fe³⁺, Hg²⁺ can produce the pronounced fluorescence response of the polymer. The result indicates this kind of chiral polybinaphthyls incorporating diethylamino and benzo[2,1,3]thiadiazole (BT) moieties as receptors exhibits highly sensitive and selective behavior for Hg²⁺ detection.     

Dual-emission carbon dots-copper nanoclusters ratiometric photoluminescent nano-composites for highly sensitive and selective detection of Hg2+

A novel dual-emission photoluminescent (PL) nano-materials of carbon dots-copper nanoclusters (CDs-CuNCs) nano-composites is prepared for excellent sensitivity and selectivity toward Hg²⁺. The nano-composites are composed of blue photoluminescent CDs and red photoluminescent CuNCs with similar excitation wavelengths through the electrostatic assembly. The red photoluminescence of CuNCs was inhibited by the nano-composites exposed to Hg²⁺, while the blue photoluminescence of CDs remained stable. The color of the nano-composites slowly changed from pink to blue with the added of Hg²⁺ concentration. The limit of detection (LOD) of the nano-composites is 0.31 nmol/L (nM) toward Hg²⁺ in aqueous solution, when the signal to noise ratio is 3. In addition, a visual PL test paper is prepared. When the Hg²⁺ solution is added, the color of test paper transforms from pink to blue immediately. Therefore, the nano-composites are very important for efficient and sensitive detection of Hg²⁺, which show broad application prospects in environmental analysis, food safety detection, biological detection and medical diagnosis in daily life.     

One-pot synthesis of zinc oxide - polyaniline nanocomposite for fabrication of efficient room temperature ammonia gas sensor

Development of efficient room temperature ammonia (NH₃) gas sensor from one pot synthesized zinc oxide (ZnO) – polyaniline (PANI) nanocomposite is reported in the present article. Prior to gas sensing study, the material is characterized to understand the structural, morphological, compositional, optical and thermal properties. Structural and morphological studies indicate good incorporation of ZnO particles in PANI matrix. The gas sensing efficiency of ZnO-PANI nanocomposite is examined at room temperature for ethanol (C₂H₅OH), methanol (CH₃OH) and NH₃ gas. The results confirm that ZnO-PANI nanocomposite to be highly selective for NH₃ with fast response time and better stability. The response and recovery times are observed to be significantly dependent on NH₃ concentration and the lowest detectivity limit of the sensor for NH₃ is found 10 ppm. ZnO-PANI nanocomposite shows better gas sensing efficiency as compared to the sensors developed from single phase PANI film.     

Development of structure-specific electrochemical sensor and its application for polyamines determination

A novel structure-specific electrochemical sensing scheme to monitor analyte, independent of its oxidation potential, is described. Molecules with multidentate chelating sites that can form stable five- or six-membered ring complexes with cupric ions are appropriate for this approach. In the copper-based electrode, potential-accelerating complex formation behavior is observed, and an apparent oxidation current is induced to regenerate the oxide layer until reaching its maximum steady state. In this unique electroanalytical method, a suitable potential is utilized to increase the coordination number of the metal electrode surface rather than direct oxidation of the analyte. The experimental results show that the signal sensitivity depends primarily on the pK_a of the chelating sites and the solution pH. Several aliphatic amines were studied with this simple approach, and the detection limits for spermidine (SPD; 0.19 μM) and spermine (SPM; 0.14 μM) at a low oxidation potential (0.25 V vs. Ag/AgCl) were obtained. A higher operating potential was used to improve the sensitivity for putrescine (PUT) and cadaverine (CAD). The detection limit was improved to 0.05, 0.06, 0.11 and 0.27 μM for SPD, SPM, PUT and CAD, respectively, without surface fouling (less than 3% with RSD). The feasibility of its clinical application is demonstrated by integrating this sensor with high-performance liquid chromatography (HPLC).     

Immobilization of glucose oxidase and platinum on mesoporous silica nanoparticles for the fabrication of glucose biosensor

In this study, amino group modified mesoporous silica nanoparticles (MSN) were prepared and used to immobilize both platinum nanoparticles (PtNP) and glucose oxidase (GOx). The prepared MSN–PtNP demonstrated high stability and reactivity for catalyzing H₂O₂ electro-reduction, mainly due to the large amount of PtNP immobilized, the high surface area of these catalysts and the unique nanostructures formed through the synthetic route. Working at −0.2 V, the linear range in response to H₂O₂ by the prepared MSN–PtNP can be 5 × 10⁻⁷ to 6 × 10⁻² mol L⁻¹. After immobilizing GOx onto MSN–PtNP, the resulting MSN–PtNP–GOx was capable of interference-free determination of glucose with the linear range as wide as 1 × 10⁻⁶ to 2.6 × 10⁻² mol L⁻¹. Furthermore, the fabricated glucose biosensor can offer significant advantages compared with its conventional counterparts, typically like the high sensitivity, good reproducibility and stability, and rapid response ability as well. The fabricated glucose biosensor demonstrated its potential in clinical applications, so as to enable the determination of glucose in real serum samples.     

Dicyclohexano-18-crown-6 as active material in PVC matrix membrane for the fabrication of cadmium selective potentiometric sensor

PVC based membrane containing dicyclohexano-18-crown-6 (I) as active material along with sodium tetraphenyl borate (NaTPB) as an anion excluder and dibutyl phthalate as solvent mediator in the ratio 20:4:150:150 (w/w) (I-NaTPB-DBP-PVC) exhibits good properties with a Nernstian response of 29.0±1.0 mV per decade of activity and a working concentration range of 2.1×10⁻⁵-1.0×10⁻¹ M. The working pH range of the sensor is 1.9-7.0. It exhibits a fast response time as fast as 17 s and has a lifetime of about 6 months. The proposed sensor has good selectivity for cadmium over alkali, alkaline earth, some transition and heavy metal ions. The sensor works satisfactorily in mixtures having 10% (v/v) non-aqueous content without showing any considerable change in working concentration range or slope. It has been successfully used as an indicator electrode for the potentiometric titration of Cd²⁺ against EDTA as well as for its determination in wastewaters.     

Synthesis of porous and nanostructured particles of CuO via a copper oxalate route

CuO have potential applications in various fields, such as gas sensors, solar energy and catalysis. With the aim of trying to obtain CuO with a high specific surface area, an oxalate precipitation route followed by thermal decomposition was studied. Four different copper salts (nitrate, sulfate, chloride, and acetate) were precipitated with sodium oxalate to form copper oxalate, before being decomposed at 275 °C into copper oxide. The different reagent salts all gave very high specific surface areas (> 70 m²/g) with slight differences in the copper oxide morphology. The effect of the initial reagent concentration had a more significant effect on morphology and surface area; cushions were obtained at low concentrations (0.02 M), and spheres at high concentrations (0.10 M with surface areas < 20 m²/g). Also the use of hydroxypropylmethylcellulose (HPMC) gave the expected cubic morphology previously shown due to specific adsorption of the polymer onto the growing crystal. The low specific surface area measured for samples synthesized at high concentration of reagent was related to a significant amount of a secondary phase Cu₂O obtained after thermal decomposition, attributed to local inhomogeneities in the precipitated oxalate due to increased precipitation kinetics at the higher concentrations. Finally a very small amount of copper carbonate could be identified by FTIR which did not affect the main powder characteristic (S_BET), but helped validate the precipitation mechanism predicted by a previous thermodynamic study.     

Microwave assisted synthesis of rGO/ZnO composites for non-enzymatic glucose sensing and supercapacitor applications

Zinc oxide (ZnO) and Graphene Oxide (GO) are known to show good electrochemical properties. In this paper, rGO/ZnO nanocomposites have been synthesised using a simple microwave assisted method. The nanocomposites are characterized using XRD, Raman, SEM and TEM. XRD reveals the wurtzite structure of ZnO and TEM shows the heterogeneous nucleation of ZnO nanocrystals anchored onto graphene sheets. The electrochemical properties of the rGO/ZnO nanocomposite enhanced significantly for applications in glucose sensors and supercapacitors. The non-enzymatic glucose sensor of this nanocomposite tested using cyclic voltammetry (CV) and chronoamperometry, exhibits high sensitivity (39.78 mA cm⁻² mM⁻¹) and a lower detection limit of 0.2 nM. The supercapacitor electrode of rGO/ZnO nanocomposite exhibits a significant increase in specific capacitance.     

A highly selective fluorescent sensor for Hg based on the water-soluble poly(p-phenyleneethynylene)

The conjugated polymer P-1 could be synthesized by the polymerization of 4,7-diethynyl-benzo[2,1,3]thiadiazole (M-1) and 1,4-bis[3′-(N,N-diethylamino)-1′-oxapropyl]-2,5-diiodobenzene (M-2) via Pd-catalyzed Sonogashira reaction. The water-soluble conjugated polyelectrolyte P-2 could be obtained by the reaction of P-1 with ethyl bromide. Both P-1 and P-2 can emit orange fluorescence. The responsive optical properties of P-1 and P-2 on Hg²⁺ were investigated by fluorescence spectra. Hg²⁺ can lead to nearly complete fluorescence quenching of P-1. On the contrary, Hg²⁺ can show the most pronounced fluorescence enhancement response of P-2 in aqueous solution without interference from those coexistent ions, such as K⁺, Mg²⁺, Pb²⁺, Co²⁺, Ni²⁺, Ag⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Zn²⁺. The results also exhibit that this kind of water-soluble conjugated polyelectrolyte can be used as a highly sensitive and selective fluorescence sensor for Hg²⁺ detection in water.     

A facile synthesis of CuI-graphene nanocomposite by glucose as a green capping agent and reductant

For the first time, CuI-graphene nanocomposite has been successfully prepared via combination of co-precipitation and hydrothermal methods. Copper nitrate and lithium iodide were applied as starting reagents to fabricate CuI-graphene nanocomposite. For preparing nanoparticles (NPs)-graphene composite we chose post-graphenization method. In synthesis of NPs-graphene with post-graphenization method, graphite oxide acts as starting reagent, so graphite oxide was synthesized via Hummer method. The effect of glucose on the particle size of nanoparticles and their distribution on the graphene sheets were investigated. The as-produced nanocomposites were characterized with the aid of XRD, SEM, TEM, EDS and FT-IR.     

Oxidation and photo-induced oxidation of glucose at a polyaniline film modified by copper particles

The oxidation and photo-induced oxidation of glucose at a copper-dispersed polyaniline film was studied in an alkaline hydroxide solution. It was found that the copper-dispersed polyaniline electrode was capable of oxidizing glucose at potentials between 0.2 and 0.75 V/(Ag|AgCl), with the rate of oxidation being higher than that observed at a bulk copper electrode. On irradiation of the composite with polychromatic UV light, a further increase in the rate of the glucose oxidation reaction was observed. Formate was identified as the main product of the glucose oxidation reaction under both light and dark conditions using NMR spectrometry. This suggests that illumination does not alter significantly the reaction pathway.     

Tetracarboxylic acid cobalt phthalocyanine SAM on gold: Potential applications as amperometric sensor for H2O2 and fabrication of glucose biosensor

This report describes the applications of cobalt tetracarboxylic acid phthalocyanine (CoTCAPc) self-assembled monolayer (SAM) immobilized onto a preformed 2-mercaptoethanol (Au-ME) SAM on gold surface (Au-ME-CoTCAPc SAM) as a potential amperometric sensor for the detection of hydrogen peroxide (H₂O₂) at neutral pH conditions. The Au-ME-CoTCAPc SAM sensor showed a very fast amperometric response time of approximately 1 s, good linearity at the studied concentration range of up to 5 μM with a coefficient R² = 0.993 and a detection limit of 0.4 μM oxidatively. Also reductively, the sensor exhibited a very fast amperometric response time (∼1 s), linearity up to 5 μM with a coefficient R² = 0.986 and a detection limit of 0.2 μM. The cobalt tetracarboxylic acid phthalocyanine self-assembled monolayer was then evaluated as a mediator for glucose oxidase (GOx)-based biosensor. The GOx (enzyme) was immobilized covalently onto Au-ME-CoTCAPc SAM using coupling agents: N-ethyl-N(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxy succinimide (NHS), and the results demonstrated a good catalytic behavior. Kinetic parameters associated with the enzymatic and mediator reactions were estimated using electrochemical versions of Lineweaver-Burk and Hanes equation, and the stability of the sensor was tested. The biosensor (Au-ME-CoTCAPc-GOx SAM) electrode showed good sensitivity (7.5 nA/mM) with a good detection limit of 8.4 μM at 3σ, smaller Michaelis-Menten constant (4.8 mM from Hanes plot) and very fast response time of approximately 5 s.