Silver nanodendrites were synthesized on Cu rods by a simple and facile displacement reaction without using any surfactants. The morphologies were investigated by scanning electron microscopy (SEM). The phase analysis of the dendritic nanostructure was revealed by X-ray diffraction (XRD). The element analysis was characterized by energy dispersive X-ray spectroscopy (EDS). Then a novel Ag nanodendrites/Cu rod electrode (named Ag NDS/CRE) based non-enzymatic hydrogen peroxide (H2O2) and glucose (GO) sensor was fabricated and evaluated by cyclic voltammetry (CV) and typical amperometric response (I–t) method. Exhilaratingly, the electrode shows significant electrocatalytic activity toward the reduction of H2O2 and oxidation of GO. Its advantage lies in its wide linear range from 0.2 mM to 19.2 mM for the detection of H2O2 with a low detection limit of 0.1 μM (S/N = 3) and also has a good response for GO with a linear range from 0.02 mM to 7.4 mM with the optimized detection limit of 0.1 μM (S/N = 3). The response time of the proposed electrode is less than 3 s. What's more, the proposed sensor displays excellent selectivity, good stability, and satisfying repeatability.

A facile and low-cost approach has been developed to fabricate porous CuO nanobelts directly grown on a Cu substrate. The as-prepared CuO samples can be directly used as integrated electrodes for lithium-ion batteries and pseudo-supercapacitors without the addition of other ancillary materials such as carbon black or a binder to enhance electrode conductivity and cycling stability. The unique nanostructural features endow them with excellent electrochemical performance as demonstrated by high capacities of 640 mA h g−1 after 100 cycles at 0.2 C rate and an excellent specific capacitance of 340 F g−1, which corresponds to the energy density of 45 W h kg−1. The cyclability of the electrode demonstrates only a 10–15% loss in capacitance over 5000 cycles.

The electrocatalytic activities between glucose and three integrated electrodes made up of Cu2S nanoplates on Cu rods with different cross-sectional areas are studied. The results showed that the Cu2.5–Cu2S integrated electrode displayed the highest catalytic activity on glucose oxidation and the highest peak current density, which are due to the Cu2.5–Cu2S integrated electrode having the highest calculated active area.

This article reviews the progress made in the past 5 years in the field of direct and non-enzymatic electrochemical sensing of glucose. Following a brief discussion of the merits and limitations of enzymatic glucose sensors, we discuss the history of unraveling the mechanism of direct oxidation of glucose and theories of non-enzymatic electrocatalysis. We then review non-enzymatic glucose electrodes based on the use of the metals platinum, gold, nickel, copper, of alloys and bimetals, of carbon materials (including graphene and graphene-based composites), and of metal-metal oxides and layered double hydroxides. This review contains more than 200 refs.

Based on the protecting effect of folate receptor (FR) toward folic acid (FA) modified DNA and the signal amplification of supersandwich DNA structure, we designed an interesting electrochemical biosensor for FR. In the present system, with the increase of FR, protecting more FA bound DNA from hydrolysis by exonuclease I (Exo I), FA bound DNA will hybridize to form more supersandwich DNA structure resulting in an increased electrochemical signal. A relationship between the concentration of the target protein, FR, and the obtained electrochemical signal can be established. The signal was obtained by the catalysis on H2O2 in the system containing Fc and hemin/DNAzyme. The detection concentration range of FR was from 1.0to 20.0 ng/mL with an achieved detection limit of 0.3 ng/mL which approached clinically relevant concentrationsof FR.Highlights► An interesting electrochemical biosensor for folate receptor (FR) was designed. ► The protecting effect of FR toward folic acid (FA) modified DNA was used in the system. ► The supersandwich DNA structure was used for the signal amplification. ► The approach showed high sensitivity and low detection limits.

Determination of nucleotide kinase activity is valuable due to its importance in regulating nucleic acid metabolism. Herein, we describe a strategy for simply and accurately determining nucleotide kinase activity by TiO2 nanotubes mediated signal transition and Au nanoparticles amplification. In this method, DNA containing 5′-hydroxyl group is self-assembled onto a gold electrode and used as a substrate for T4 polynucleotide kinase (PNK). By the specific immobilization affinity of TiO2 nanotubes with the phosphorylated DNA, TiO2 nanotubes were linked with phosphorylated substrate DNA on the electrode. And then Au nanoparticles modified 5′-phosphate DNA was conjugated with the TiO2 nanotubes and hybridized with methylene blue labeled signal DNA. Because gold nanoparticles have high loading of signal indicator methylene blue, the electrochemical signal is generated and amplified. It presents an excellent performance with wide linear range and low detection limit. Additionally, inhibition effects of some salts have also been investigated. The developed method is a potentially useful tool in researching the interactions between proteins and nucleic acids and provides a diversified platform for a kinase activity assay.Highlights► TiO2 nanotubes for the immobilization of phosphorylated DNA were synthesized by a novel method. ► T4 polynucleotide kinase (PNK) activity was determined in the sandwich DNA structure. ► Au nanoparticles were used for signal amplification. ► Wide linear range and low detection limit were obtained in the present system.

Cu2S nanoplates (named Cu2S NPs) were synthesized on the Cu substrate by a simple etching method. The morphology and structure of Cu2S NPs were characterized by scanning electron microscopy and X-ray diffraction. Then the Cu–Cu2S composites were directly used as electrode to nonenzymatic detect glucose. The electrochemical study has demonstrated that the Cu–Cu2S electrode shows a perfect catalytic effect on the glucose due to the large surface area of Cu2S nanoplates and high electric conductivity of Cu rod. At an applied potential of − 0.10 V, the sensor produces an ultra high sensitivity of 361.58 μA mM− 1 with a low detection limit of 0.1 μM (S/N = 3). What's more, the proposed sensor displays excellent selectivity, good stability, and satisfying repeatability.Highlights► Cu2S nanoplates were synthesized on the Cu substrate by a simple etching method. ► The composites were directly used as electrode to detect nonenzymatic glucose. ► High sensitivity, high selectivity and low detection limit up to 0.1 μM.

Ni(OH)2 nanoplates grown on Cu substrate were synthesized by a simple hydrothermal method. Au nanoparticles were dropped onto Ni(OH)2 nanoplates according to optimal ratio to get Au NPs–Ni(OH)2–Cu nanocomposites. These were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and X-ray energy dispersive spectrometer (EDS). The electrode (Au NPs–Ni(OH)2–Cu/glassy carbon electrode) constructed by the composites was evaluated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and typical amperometric response (i-t). Its wide linear range covered 2.5 μM to 1229.5 μM for the detection of peroxide hydrogen (H2O2), the optimized detection limit 0.3 μM (S/N = 3) and the response time was less than 3 s. Besides, the proposed electrode showed satisfactory selectivity, and good stability.

Porous Cu–NiO nanocomposites were successfully prepared by calcination of the Cu–Ni(OH)2 precursor at 400 °C for 2 h. During the process of calcination, Ar was used to deaerate O2. The structure and morphology of Cu–NiO were characterized by X-ray diffraction spectrum (XRD), energy dispersive X-ray analyses (EDX), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Using porous Cu–NiO nanocomposites, a simple non-enzymatic amperometric sensor has been fabricated (Cu–NiO/GCE) and evaluated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and typical amperometric method. When applied to detect glucose by the amperometric method, Cu–NiO/GCE produced an ultrahigh sensitivity of 171.8 μA mM−1, with a low detection limit of 0.5 μM (S/N = 3). What's more, interference from common co-existing species, such as UA, AA, and fructose can be avoided at the sensor. Results in this study imply that porous Cu–NiO nanocomposites are promising nanomaterials for the enzyme-free determination of glucose.

In this report we simply prepared a copper(II) doped nanoporous TiO2 composite, which combines the capabilities of an immobilizing enzyme with electrocatalyzing glucose. Transmission electron microscopy and energy dispersive X-ray analysis were used for the characterization of the composite. Comparison experiments of the cyclic voltammetry and electrochemical impedance spectroscopy of Cu(II) doped TiO2 composites with different doping ratio modified electrodes demonstrate that when the ratio of Cu(II) and TiO2 is kept at 1:1, the electrochemical response to glucose is the best. We suggest that in the doping materials too little TiO2 would decrease the immobilization of GOx, which leads to a poorer response to glucose. However, too little Cu(II), would decrease the electron transfer ability. Cu(II) doped TiO2 with the ratio of 1:1 displays a good linear relation between the oxidation peak current and the concentration of glucose with the range from 0.5 μM–3 mM, correlation coefficients of 0.9989 and a fast response time of within 5 s. The experimental limit of detection, based on a signal-to-noise ratio of 3, was 0.1 μM and the sensitivity of the sensor was 0.9040 μA μM−1. The experimental results also showed that the sensor has good reproducibility, long-term stability and is interference free.

In this work, Ni(OH)2 nanoplates grown on the Cu substrate were synthesized and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Then a novel Cu–Ni(OH)2 modified glass carbon electrode (Cu–Ni(OH)2/GCE) was fabricated and evaluated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and typical amperometric response (i–t) method. Exhilaratingly, the Cu–Ni(OH)2/GCE shows significant electrocatalytic activity toward the reduction of H2O2. At an applied potential of −0.1 V, the sensor produces an ultrahigh sensitivity of 408.1 μA mM−1 with a low detection limit of 1.5 μM (S/N = 3). The response time of the proposed electrode was less than 5 s. What's more, the proposed sensor displays excellent selectivity, good stability, and satisfying repeatability.

Enzyme-free determination of glucose on an ordered CuO nanowall-based Cu substrate modified electrode is investigated. The structure and morphology of the CuO nanowalls were characterized by X-ray diffraction and scanning electron microscopy. The growth mechanism of the sample and the influence factor of the preparation process are discussed. The electrochemical study has shown that the CuO nanowalls exhibit a higher catalytic effect on the glucose than the CuO nanosphere without Cu substrate. This may be attributed to the special structure of the nanomaterials and the substrate of the electronic conductive Cu. The amperometric response showed that the CuO nanowall-modified glassy carbon electrode has a good response for glucose with a linear range of 0.05 μM to 10 μM with a sensitivity of 0.5563 μA μM−1 in pH 9.2 phosphate buffered solutions.

Ag2O nanowalls consisting of densely packed nanoplates based on a Cu substrate were synthesized through a facile one-pot hydrothermal method. A new enzymeless glucose sensor of Cu−Ag2O nanowalls was fabricated. The Cu−Ag2O nanowalls showed higher catalysis on glucose oxidation than traditional Ag2O nanoflowers and Cu−Ag2O nanospindles. At an applied potential of 0.4 V, the sensor produced an ultrahigh sensitivity to glucose (GO) of 298.2 μA mM−1. Linear response was obtained over a concentration range from 0.2 mM to 3.2 mM with a detection limit of 0.01 mM (S/N = 3). Satisfyingly, the Cu−Ag2O nanowalls modified electrode was not only successfully employed to eliminate the interferences from uric acid (UA) acid ascorbic (AA) and also fructose (FO) during the catalytic oxidation of glucose. The Cu−Ag2O nanowalls modified electrode allows highly sensitive, excellently selective, stable, and fast amperometric sensing of glucose and thus is promising for the future development of nonenzymatic glucose sensors.Keywords: Ag2O nanowalls; electocatalysis; enzymeless; glucose sensor

Hexagonal β-Ni(OH)2 nanosheets were synthesized by a simple template- and surfactant-free hydrothermal approach. They were characterized by scanning electron microscopy, X-ray powder diffraction, and thermal gravimetric analysis. The nanosheets were incorporated, along with chitosan, into an amperometric sensor which displayed a good performance in terms of detection of hydrogen peroxide. The linear range is from 5.0 µM to 0.145 mM, the sensitivity is 24.76 µA mM−1, the detection limit is 0.5 µM, and the response time is <5 s. The sensor was successfully applied to detect pyrocatechol (PC) and hydroquinone (HQ) via cyclic voltammetry and differential pulse voltammetry and also enabled simultaneous determination of both PC and HQ.

Cu2O/MWCNT (multi-walled carbon nanotubes) nanocomposites were successfully prepared in large quantities with a new fixure-reduction method under low temperature. The morphology and shape of the Cu2O/MWCNTs nanocomposites were characterized by field emission scanning electron microscopes (FESEMs), energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD), respectively. Cyclic voltammetry (CV) was used to evaluate the electrochemical performance of the Cu2O/MWCNTs nanocomposites modified electrode towards glucose. Compared to the bare GCE, the Cu2O nanoparticles and the MWCNTs modified electrode, the Cu2O/MWCNTs modified electrode displays high electrocatalytic activity towards the oxidation of glucose. With a potential of −0.20 V, the Cu2O/MWCNTs modified electrode was used to determine glucose by amperometric, showing significantly lower overvoltage and a linear dependence (R = 0.9958) in the concentration up to 10 μM with a sensitivity of 6.53 μA μmol L−1 and a detection limit of 0.05 μmol L−1 (signal-to-noise ratio of 3). In summary, the preparation process of the nanocomposites is very simple and the nanocomposites could be used for the development of enzyme-free glucose sensor.

CuS nanotubes (NTs) made up of nanoparticles were successfully prepared in large quantities in an O/W microemulsion system under low temperature. Based on the characteristics of synchronous fluorescence spectroscopy (SFS), a new method with high sensitivity and selectivity was developed for rapid determination of silver ion with functional copper sulphide (CuS) nanotubes as a fluorescence probe. Under optimal conditions, functional copper sulphide displayed a calibration response for silver ion over a wide concentration range from 1.0 × 10−10 to 1.0 × 10−8 mol L−1. The limit of detection was 0.5 × 10−10 mol L−1 and the relative standard deviation of eight replicate measurements for the highest concentration (1 × 10−8 mol L−1) was 3%. Compared with several fluorescence methods, the proposed method had a wider linear range and improved the sensitivity. Furthermore, the concentration dependence of the synchronous fluorescence intensity is effectively described by a Langmuir-type binding isotherm.

CuS nanotubes made up of nanoparticles were successfully prepared in large quantities in an O/W microemulsion system under low temperature; the as-prepared CuS nanotube modified electrode was used as an enzyme-free glucose sensor.

Highly uniform copper dendrites were successfully prepared in large quantities using a facile hydrothermal approach, which was prepared from the reaction of cupreous nitrate and sodium hypophosphite with different ratios of diethanolamine (DEA)/water. Well-defined assembly of uniform dendrites with an average size of 20 µm can be obtained after a simple size-selection process. The influences of the ratio of DEA/water, and different reaction times and temperatures have been discussed. In addition, a gold electrode modified with copper dendrites was constructed and characterized by electrochemical impendance spectrum (EIS) and cyclic voltammetry (CV). The resulting copper dendrite modified gold electrode was used to detect l-tyrosine in the solution. The results showed that the copper dendrites may be of great potential in the determination of l-tyrosine.

The preparation and characterization of a large-scale epitaxial array of single-crystalline CuO nanowires (NWs) on the surface of a Cu nanostructure (Cu−CuO nanocomposite) by a simple liquid−solid growth process at room temperature is demonstrated. The field-emission scanning electron microscopy image analysis indicated that the NWs are 50−80 nm wide at the root and 300−400 nm long. The high-resolution transmission electron microscopy study on individual CuO NWs revealed that the NWs are single crystalline with a growth orientation of [110]. X-ray powder diffraction and energy dispersive X-ray analysis of the samples revealed that the CuO NWs only cover the surface of dendritic Cu and that Cu dendrites still exist in the center of the Cu−CuO nanocomposite. Electrochemical impendance spectroscopy and cyclic voltammetry showed that the Cu−CuO nanocomposite has a stronger ability to promote electron transfer than the CuO NWs or CuO nanoparticles individually. The Cu−CuO nanocomposite was successfully used to modify a glassy carbon electrode to detect H2O2 and glucose with chronoamperometry. The result shows that the Cu−CuO nanocomposite may be of great potential as H2O2 and glucose electrochemical sensors.

Three different nanostructures of CuO (wires, platelets, and spindles) have been synthesized by one precursor. First, Cu(OH)2 nanowires have been prepared by a two-step, template-free, wet chemical approach. And then the transformation from the 1D Cu(OH)2 nanostructures to a variety of novel CuO nanostructures has been realized by thermal dehydration of the as-prepared Cu(OH)2 in solution. The electrochemical characters of the three different nanostructures are studied by their investigation of electrochemical impendance spectrum and cyclic voltammetry. A comparison of the three nanostructures showed us an attractive phenomenon, that is, the electron transfer ability of CuO nanospindles was stronger than that of CuO nanowires or nanoplatelets. We suggest the possible reason is the assembly of the nanostructrue. The electrochemical response of the as-prepared samples on H2O2 is also investigated, and good application in electrochemical detecting of glucose is exhibited.

The electrocatalytic activities between glucose and three integrated electrodes made up of Cu2S nanoplates on Cu rods with different cross-sectional areas are studied. The results showed that the Cu2.5–Cu2S integrated electrode displayed the highest catalytic activity on glucose oxidation and the highest peak current density, which are due to the Cu2.5–Cu2S integrated electrode having the highest calculated active area.

Ni(OH)2 nanoplates grown on Cu substrate were synthesized by a simple hydrothermal method. Au nanoparticles were dropped onto Ni(OH)2 nanoplates according to optimal ratio to get Au NPs–Ni(OH)2–Cu nanocomposites. These were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and X-ray energy dispersive spectrometer (EDS). The electrode (Au NPs–Ni(OH)2–Cu/glassy carbon electrode) constructed by the composites was evaluated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and typical amperometric response (i-t). Its wide linear range covered 2.5 μM to 1229.5 μM for the detection of peroxide hydrogen (H2O2), the optimized detection limit 0.3 μM (S/N = 3) and the response time was less than 3 s. Besides, the proposed electrode showed satisfactory selectivity, and good stability.

A facile and low-cost approach has been developed to fabricate porous CuO nanobelts directly grown on a Cu substrate. The as-prepared CuO samples can be directly used as integrated electrodes for lithium-ion batteries and pseudo-supercapacitors without the addition of other ancillary materials such as carbon black or a binder to enhance electrode conductivity and cycling stability. The unique nanostructural features endow them with excellent electrochemical performance as demonstrated by high capacities of 640 mA h g−1 after 100 cycles at 0.2 C rate and an excellent specific capacitance of 340 F g−1, which corresponds to the energy density of 45 W h kg−1. The cyclability of the electrode demonstrates only a 10–15% loss in capacitance over 5000 cycles.

CuS nanotubes made up of nanoparticles were successfully prepared in large quantities in an O/W microemulsion system under low temperature; the as-prepared CuS nanotube modified electrode was used as an enzyme-free glucose sensor.

In this report we simply prepared a copper(II) doped nanoporous TiO2 composite, which combines the capabilities of an immobilizing enzyme with electrocatalyzing glucose. Transmission electron microscopy and energy dispersive X-ray analysis were used for the characterization of the composite. Comparison experiments of the cyclic voltammetry and electrochemical impedance spectroscopy of Cu(II) doped TiO2 composites with different doping ratio modified electrodes demonstrate that when the ratio of Cu(II) and TiO2 is kept at 1:1, the electrochemical response to glucose is the best. We suggest that in the doping materials too little TiO2 would decrease the immobilization of GOx, which leads to a poorer response to glucose. However, too little Cu(II), would decrease the electron transfer ability. Cu(II) doped TiO2 with the ratio of 1:1 displays a good linear relation between the oxidation peak current and the concentration of glucose with the range from 0.5 μM–3 mM, correlation coefficients of 0.9989 and a fast response time of within 5 s. The experimental limit of detection, based on a signal-to-noise ratio of 3, was 0.1 μM and the sensitivity of the sensor was 0.9040 μA μM−1. The experimental results also showed that the sensor has good reproducibility, long-term stability and is interference free.