CuNiO nanoparticles assembled on graphene as an effective platform for enzyme-free glucose sensing

We utilized CuNiO nanoparticles modified graphene sheets (CuNiO–graphene) to the application of enzymeless glucose sensing. The hydrothermal synthesized CuNiO nanoparticles were successfully assembled on graphene sheets. Distinct from general method, the high quality pristine graphene was produced by chemical vapor deposition (CVD) and bubbling transferred on the electrode. Incorporating the excellent electronic transport of graphene and high electrocatalytic activity of CuNiO nanoparticles, the CuNiO–graphene nanocomposite modified electrode possessed strong electrocatalytic ability toward glucose in alkaline media. The proposed nonenzymatic glucose sensor exhibited wide linear range up to 16 mM (two parts, from 0.05 to 6.9 mM and 6.9–16 mM) and high sensitivity (225.75 μA mM⁻¹ cm⁻² and 32.44 μA mM⁻¹ cm⁻², respectively). Excellent selectivity and acceptable stability were also achieved. Such an electrode would be attractive to sensor construction for its good properties, simple operation and low expense.     

Preparation of magnetic CoFe2O4-functionalized graphene sheets via a facile hydrothermal method and their adsorption properties

Magnetic CoFe₂O₄-functionalized graphene sheets (CoFe₂O₄-FGS) nanocomposites have been synthesized by hydrothermal treatment of inorganic salts and thermal exfoliated graphene sheets. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations show that cobalt ferrite nanoparticles with sizes of 10-40 nm are well dispersed on graphene sheets. OH⁻ was recognized as a tie to integrate the inorganic salts with the graphene sheets, which made reaction started and developed on the surface of graphene sheets and formed cobalt ferrite nanoparticles on graphene sheets. The adsorption kinetics investigation revealed that the adsorption of methyl orange from aqueous solution over the as-prepared CoFe₂O₄-FGS nanocomposites followed pseudo-second-order kinetic model and the adsorption capacity was examined as high as 71.54 mg g⁻¹. The combination of the superior adsorption of FGS and the magnetic properties of CoFe₂O₄ nanoparticles can be used as a powerful separation tool to deal with water pollution.     

Controllable synthesis of graphene sheets with different numbers of layers and effect of the number of graphene layers on the specific capacity of anode material in lithium-ion batteries

High quality graphene sheets are synthesized through efficient oxidation process followed by rapid thermal expansion and reduction by H₂. The number of graphene layers is controlled by tuning the oxidation degree of GOs. The higher the oxidation degree of GOs is getting, the fewer the numbers of graphene layers can be obtained. The material is characterized by elemental analysis, thermo-gravimetric analysis, scanning electron microscopy, atomic force microscopy, transmission electron microscopy and Fourier transform infrared spectroscopies. The obtained graphene sheets with single, triple and quintuplicate layers as anode materials exhibit a high reversible capacity of 1175, 1007, and 842 mA h g⁻¹, respectively, which show that the graphene sheets with fewer layers have higher reversible capacity.     

A colloidal suspension of nanostructured poly(N-butyl benzimidazole)-graphene sheets with high oxidase yield for analytical glucose and choline detections

A colloidal suspension of nanostructured poly(N-butyl benzimidazole)-graphene sheets (PBBIns-Gs) was used to modify a gold electrode to form a three-dimensional PBBIns-Gs/Au electrode that was sensitive to hydrogen peroxide (H₂O₂) in the presence of acetic acid (AcOH). The positively charged nanostructured poly(N-butyl benzimidazole) (PBBIns) separated the graphene sheets (Gs) and kept them suspended in an aqueous solution. Additionally, graphene sheets (Gs) formed “diaphragms” that intercalated Gs, which separated PBBIns to prevent tight packing and enhanced the surface area. The PBBIns-Gs/Au electrode exhibited superior sensitivity toward H₂O₂ relative to the PBBIns-modified Au (PBBIns/Au) electrode. Furthermore, a high yield of glucose oxidase (GOD) on the PBBIns-Gs of 52.3 mg GOD per 1 mg PBBIns-Gs was obtained from the electrostatic attraction between the positively charged PBBIns-Gs and negatively charged GOD. The non-destructive immobilization of GOD on the surface of the PBBIns-Gs (GOD-PBBIns-Gs) retained 91.5% and 39.2% of bioactivity, respectively, relative to free GOD for the colloidal suspension of the GOD-PBBIns-Gs and its modified Au (GOD-PBBIns-Gs/Au) electrode. Based on advantages including a negative working potential, high sensitivity toward H₂O₂, and non-destructive immobilization, the proposed glucose biosensor based on an GOD-PBBIns-Gs/Au electrode exhibited a fast response time (5.6 s), broad detection range (10 μM to 10 mM), high sensitivity (143.5 μA mM⁻¹ cm⁻²) and selectivity, and excellent stability. Finally, a choline biosensor was developed by dipping a PBBIns-Gs/Au electrode into a choline oxidase (ChOx) solution for enzyme loading. The choline biosensor had a linear range of 0.1 μM to 0.83 mM, sensitivity of 494.9 μA mM⁻¹ cm⁻², and detection limit of 0.02 μM. The results of glucose and choline measurement indicate that the PBBIns-Gs/Au electrode provides a useful platform for the development of oxidase-based biosensors.     

Ultrasensitive and simultaneous detection of heavy metal ions based on three-dimensional graphene-carbon nanotubes hybrid electrode materials

A green and facile method was developed to prepare a novel hybrid nanocomposite that consisted of one-dimensional multi-walled carbon nanotubes (MWCNTs) and two-dimensional graphene oxide (GO) sheets. The as-prepared three-dimensional GO–MWCNTs hybrid nanocomposites exhibit excellent water-solubility owing to the high hydrophilicity of GO components; meanwhile, a certain amount of MWCNTs loaded on the surface of GO sheets through π–π interaction seem to be “dissolved” in water. Moreover, the graphene(G)-MWCNTs nanocomposites with excellent conductivity were obtained conveniently by the direct electrochemical reduction of GO–MWCNTs nanocomposites. Seeing that there is a good synergistic effect between MWCNTs and graphene components in enhancing preconcentration efficiency of metal ions and accelerating electron transfer rate at G-MWCNTs/electrolyte interface, the G-MWCNTs nanocomposites possess fast, simultaneous and sensitive detection performance for trace amounts of heavy metal ions. The electrochemical results demonstrate that the G-MWCNTs nanocomposites can act as a kind of practical sensing material to simultaneously determine Pb²⁺ and Cd²⁺ ions in terms of anodic stripping voltammetry (ASV). The linear calibration plots for Pb²⁺ and Cd²⁺ ranged from 0.5 μg L⁻¹ to 30 μg L⁻¹. The detection limits were determined to be 0.2 μg L⁻¹ (S/N = 3) for Pb²⁺ and 0.1 μg L⁻¹ (S/N = 3) for Cd²⁺ in the case of a deposition time of 180 s. It is worth mentioning that the G-MWCNTs modified electrodes were successfully applied to the simultaneous detection of Cd²⁺ and Pb²⁺ ions in real electroplating effluent samples containing lots of surface active impurities, showing a good application prospect in the determination of trace amounts of heavy metals.     

微波固相剥离法制备功能化石墨烯及其电化学电容性能研究(英文)

通过微波固相剥离氧化石墨制备了功能化石墨烯材料。石墨烯的剥离,是由于微波加热过程中氧化石墨烯片上的官能团分解为CO2和H2O,产生的压力超过了片层间的范德华力。形貌表征显示了石墨烯的有效剥离和纳米孔结构的形成。红外光谱分析结果表明微波剥离的功能化石墨烯仍然有少量的官能团残留。N2等温吸附-脱附测试结果表明样品具有高比表面积(412.9m2·g-1)和大孔容(1.91cm3·g-1)。电化学测试结果表明功能化石墨烯具有良好的电化学电容行为和207.5F·g-1的比电容。     

Superior cycle performance of Sn@C/graphene nanocomposite as an anode material for lithium-ion batteries

A novel anode material for lithium-ion batteries, tin nanoparticles coated with carbon embedded in graphene (Sn@C/graphene), was fabricated by hydrothermal synthesis and subsequent annealing. The structure and morphology of the nanocomposite were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The size of the Sn@C nanoparticles is about 50-200 nm. The reversible specific capacity of the nanocomposite is ∼662 mAh g⁻¹ at a specific current of 100 mA g⁻¹ after 100 cycles, even ∼417 mAh g⁻¹ at the high current of 1000 mA g⁻¹. These results indicate that Sn@C/graphene possesses superior cycle performance and high rate capability. The enhanced electrochemical performances can be ascribed to the characteristic structure of the nanocomposite with both of the graphene and carbon shells, which buffer the volume change of the metallic tin and prevent the detachment and agglomeration of pulverized tin.     

Functionalized graphene oxide for the fabrication of paraoxon biosensors

There is an increasing need to develop biosensors for the detection of harmful pesticide residues in food and water. Here, we report on a versatile strategy to synthesize functionalized graphene oxide nanomaterials with abundant affinity groups that can capture histidine (His)-tagged acetylcholinesterase (AChE) for the fabrication of paraoxon biosensors. Initially, exfoliated graphene oxide (GO) was functionalized by a diazonium reaction to introduce abundant carboxyl groups. Then, N_α,N_α-bis(carboxymethyl)-l-lysine hydrate (NTA-NH₂) and Ni²⁺ were anchored onto the GO based materials step by step. AChE was immobilized on the functionalized graphene oxide (FGO) through the specific binding between Ni-NTA and His-tag. A low anodic oxidation potential was observed due to an enhanced electrocatalytic activity and a large surface area brought about by the use of FGO. Furthermore, a sensitivity of 2.23 μA mM⁻¹ to the acetylthiocholine chloride (ATChCl) substrate was found for our composite covered electrodes. The electrodes also showed a wide linear response range from 10 μM to 1 mM (R² = 0.996), with an estimated detection limit of 3 μM based on an S/N = 3. The stable chelation between Ni-NTA and His-tagged AChE endowed our electrodes with great short-term and long-term stability. In addition, a linear correlation was found between paraoxon concentration and the inhibition response of the electrodes to paraoxon, with a detection limit of 6.5 × 10⁻¹⁰ M. This versatile strategy provides a platform to fabricate graphene oxide based nanomaterials for biosensor applications.     

Graphene enhanced electrochemiluminescence of CdS nanocrystal for H2O2 sensing

Graphene-CdS (G-CdS) nanocomposites were successfully prepared by CdS nanocrystals (CdS NCs) formed in situ on the surface of graphene sheets, using graphene oxide (GO) sheets with rich negatively charged carboxylic acid groups as starting materials. Compared with pure CdS NCs, the presence of the graphene doped in G-CdS nanocomposites could facilitate the electrochemical redox process of CdS NCs; further, the as-prepared G-CdS nanocomposite can react with H₂O₂ to generate strong and stable electrochemiluminescent (ECL) emission, which not only enhances its ECL intensity by about 4.3-fold but also decreases its onset potential for about 320 mV. The as-prepared solid-state ECL H₂O₂ sensor shows acceptable linear response from 5 μM up to 1 mM with a detection limit of 1.7 μM (S/N = 3). The ECL H₂O₂ sensor exhibits excellent reproducibility and long-term stability. Such a property would promote the potential application of the graphene as enhanced materials in fabricating sensors for chemical and biochemical analysis.     

Graphene-based solid-phase extraction combined with flame atomic absorption spectrometry for a sensitive determination of trace amounts of lead in environmental water and vegetable samples

Graphene, a novel class of carbon nanostructures, has great promise for use as sorbent materials because of its ultrahigh specific surface area. A new method using a column packed with graphene as sorbent was developed for the preconcentration of trace amounts of lead (Pb) using dithizone as chelating reagent prior to its determination by flame atomic absorption spectrometry. Some effective parameters on the extraction and complex formation were selected and optimized. Under optimum conditions, the calibration graph was linear in the concentration range of 10.0–600.0 μg L⁻¹ with a detection limit of 0.61 μg L⁻¹. The relative standard deviation for ten replicate measurements of 20.0 and 400.0 μg L⁻¹ of Pb were 3.56 and 3.25%, respectively. Comparative studies showed that graphene is superior to other adsorbents including C18 silica, graphitic carbon, and single- and multi-walled carbon nanotubes for the extraction of Pb. The proposed method was successfully applied in the analysis of environmental water and vegetable samples. Good spiked recoveries over the range of 95.3–100.4% were obtained. This work not only proposes a useful method for sample preconcentration, but also reveals the great potential of graphene as an excellent sorbent material in analytical processes.