Yujing Guo

A high performance nonenzymatic electrochemical glucose sensor based on polyvinylpyrrolidone-graphene nanosheets-nickel nanoparticles-chitosan nanocomposite.

In this report, a new nanocomposite was successfully synthesized by chemical deposition of nickel nanoparticles (NiNPs) on polyvinylpyrrolidone (PVP) stabilized graphene nanosheets (GNs) with chitosan (CS) as the protective coating. The as obtained nanocomposite (PVP-GNs-NiNPs-CS) was characterized by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Benefiting from the synergistic effect of GNs (large surface area and high conductivity), NiNPs (high electrocatalytic activity towards the glucose oxidation) and CS (good film-forming and antifouling ability), a nonenzymatic electrochemical glucose sensor was established. The nanocomposite displays greatly enhanced electrocatalytic activity towards the glucose oxidation in NaOH solution. The PVP-GNs-NiNPs-CS based electrochemical glucose sensor demonstrates good sensitivity, wide linear range (0.1 μM-0.5 mM), outstanding detection limit (30 nM), attractive selectivity, good reproducibility, high stability as well as prominent feasibility for the real sample analysis. The proposed experiment might open up a new possibility for widespread use of non-enzymatic sensors for monitoring blood glucose owing to its advantages of low cost, simple preparation and excellent properties for glucose detection.

Porphyrin functionalized graphene nanosheets-based electrochemical aptasensor for label-free ATP detection

A facile strategy for the preparation of meso-terakis(4-methoxyl-3-sulfonatophenyl) porphyrin (T(4-Mop)PS4)-graphene hybrid nanosheets (TGHNs) was demonstrated for the first time, which combines the features of both graphene (high conductivity and large specific surface area) and porphyrins (photochemical electron-transfer ability and excellent electrochemical activity). The as-obtained TGHNs were characterized by UV-vis spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy, transmission electron microscopy and cyclic voltammetry, which confirmed that the porphyrin had been effectively functionalized on the surface of graphene. Combined with the high affinity and specificity of an aptamer, a simple, rapid, sensitive and label-free electrochemical aptasensor was successfully fabricated for adenosine triphosphate (ATP) detection. The proposed TGHN-based aptasensor achieved the direct electron transfer of porphyrin and showed good affinity and specificity towards ATP, which avoided interference such as the introduction of labeled-substances and the [Fe(CN)6]3−/4− probe. The preferable linear range for ATP was from 2.2 nM to 1.3 μM (R = 0.9982) with a detection limit of 0.7 nM.

Electrochemical sensor for ultrasensitive determination of isoquercitrin and baicalin based on DM-β-cyclodextrin functionalized graphene nanosheets

In this study, 2,6-dimethyl-β-cyclodextrin (DM-β-CD) functionalized graphene nanosheets (DM-β-CD-GNs) were successfully synthesized by a simple wet-chemical strategy. The as obtained DM-β-CD-GNs were characterized by UV-vis spectroscopy, Fourier transform Infrared (FT-IR) spectroscopy, atomic force microscopy (AFM) and transmission electron microscopy (TEM). The new nanocomposite possesses the unique properties of graphene (large surface area and high conductivity) and DM-β-CD (high supramolecular recognition and enrichment capability). Based on the above properties, a highly sensitive electrochemical sensor was developed to detect two flavonoid drugs (isoquercitrin and baicalin). At the DM-β-CD-GNs modified glassy carbon electrode (DM-β-CD-GNs/GCE), the peak currents of the two drugs increased dramatically compared with that on the bare GCE and GNs/GCE which due to the synergetic effects of GNs and DM-β-CD molecules. The linear response ranges for isoquercitrin and baicalin are 10nM-3.0μM and 0.04μM -3.0μM, with the detection limits of 4nM and 10nM, respectively. The method might open up a new possibility for the widespread use of electrochemical sensors for monitoring of ultra-trace flavonoid drugs owing to its advantages of simple preparation, low cost, high sensitivity, good stability and reproducibility.

Rational synthesis of graphene–metal coordination polymer composite nanosheet as enhanced materials for electrochemical biosensing

The designed synthesis of graphene-based nanocomposites for enhancing their different potential application is of great interest recently. In this paper, we demonstrated a new class of high-quality graphene-based nanocomposites: metal coordination polymer–graphene nanosheets (MCPGNs). The as-obtained nanocomposite, combining the unique properties of graphene (excellent conductivity and high specific surface area) and MCPs (tunable pore size, large internal surface areas and versatility of functionality), can act as an efficient matrix to immobilize glucose oxidase (GOD). Furthermore, the as-prepared MCPGNs exhibit better conductivity and electrocatalytic activity for H2O2 reduction than graphene. Based on these excellent properties, a sensitive electrochemical biosensing platform for glucose was fabricated. This novel biosensor displays a linear response range between 50 nM and 1 mM with a detection limit of 5 nM. Our work not only provides a facile, effective and general route for the synthesis of a variety of MCP–graphene nanohybrids, but also sets an example for fabricating an electrochemical biosensor with this new kind of nanohybrid as an enhanced material and can be easily extended to other biosensors. These interesting results suggested the great potential of MCP–graphene nanocomposites in the field of electroanalytical chemistry.

Synthesis of neutral red covalently functionalized graphene nanocomposite and the electrocatalytic properties toward uric acid

The preparation of neutral red covalently-functionalized graphene nanosheets (NR-FGN) is presented via replacement of the carboxyl acid groups at the edges of graphene nanosheets using NR. The obtained NR-FGN was characterized by UV-vis, Fourier transform infrared (FT-IR), Raman spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that the introduction of NR at the edges of graphene nanosheets (GN) improved the solubility and stability of the graphene. The electrochemical impedance result further confirmed that NR-FGN could effectively accelerate the electron transfer. Due to the synergic effect between GN and NR, the nanocomposite exhibited excellent electrocatalytic activity toward the oxidation of uric acid.

Sensitive electrochemical detection of rutin and isoquercitrin based on SH-β-cyclodextrin functionalized graphene-palladium nanoparticles.

In this study, a sensitive electrochemical method based on thio-β-cyclodextrin functionalized graphene/palladium nanoparticles (SH-β-CD-Gr/PdNPs) was developed to detect rutin and isoquercitrin, respectively. The obtained SH-β-CD-Gr/PdNPs were characterized by UV-vis spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The results confirm that SH-β-CD and PdNPs were successfully deposited on the surface of graphene nanosheets (GNs). The peak currents of rutin and isoquercitrin on the SH-β-CD-Gr/PdNPs modified glassy carbon electrode (GCE) are dramatically increased compared with that on the bare GCE and SH-β-CD-Gr/GCE. It indicated that the nanocomposite integrated the excellent electric conductivity and electrocatalytic activity of graphene and PdNPs, as well as the host-guest recognition and enrichment ability of SH-β-CD. Under optimum conditions, differential pulse voltammetry (DPV) was used to measure the peak currents of the two drugs. The linear response ranges for rutin and isoquercitrin are 1.0×10-9-3.0×10-5molL-1 and 5.0×10-12-5.0×10-6molL-1, with low detection limits of 3.0×10-10molL-1 and 1.6×10-12molL-1, respectively. The proposed method might offer a new possibility for electrochemical analysis of rutin and isoquercitrin in pharmaceuticals or human serum owing to its low cost, simplicity, high sensitivity and good stability.

TiO2–graphene hybrid nanostructures by atomic layer deposition with enhanced electrochemical performance for Pb(II) and Cd(II) detection

In this work, atomic layer deposition is applied to coat graphene nanosheets with TiO2. The produced TiO2–graphene (TiO2–Gr) composites are characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. It is revealed that TiO2 is effectively deposited on the surface of graphene. The coatings have a highly controlled thickness. The electrochemical properties of the obtained TiO2–Gr composites are investigated for detection of lead (Pb2+) and cadmium (Cd2+) ions by differential pulse anodic stripping voltammetry (DPASV). It is found that the TiO2–Gr composite exhibits improved sensitivity for detection of these metal ions. The linear dynamic ranges are from 1.0 × 10−8 M to 3.2 × 10−5 M for Pb2+ and 6.0 × 10−7 M to 3.2 × 10−5 M for Cd2+, respectively. The detection limits (S/N = 3) are estimated to be 1.0 × 10−10 M for Pb2+ and 2.0 × 10−9 M for Cd2+, respectively.

Synthesis of a Palladium-Graphene Material and Its Application for Formaldehyde Determination

A novel electrochemical sensor for formaldehyde determination was fabricated by using the Pd-graphene nanohybrides. Pd-graphene nanohybrids were prepared via a concise chemical reduction method. Raman spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM) were used for the characterization of structure and morphology of the nanohybrids. The result showed that Pd nanoparticles were uniformly dispersed and were well-separated on the graphene sheets. The Pd-graphene nanohybrids were dissolved in Nafion and modified on the glassy carbon electrode to fabricate the electrochemical sensor. This proposed electrochemical sensor performed excellent electrocatalytic activity toward formaldehyde oxidation in alkaline medium. The peak current was linearly related to the formaldehyde concentration in the range of 7.75 µM to 62.0 µM with the detection limit of 3.15 µM. The highly sensitive and robust graphene based Pd nanohybrids sensor offers a promising and practical tool for formaldehyde sensing and chemical analysis.

Gold nanoparticles/Orange II functionalized graphene nanohybrid based electrochemical aptasensor for label-free determination of insulin

Nanocomposites, gold nanoparticles on Orange II functionalized graphene (AuNPs/O-GNs), were developed to modify the electrode surface for anchoring an insulin binding aptamer. The nanocomposites integrate the high electrical conductivity of graphene, and the easily functionalized surface chemistry of AuNPs along with excellent biocompatibility. The characterization using UV-vis absorption spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) revealed the successful synthesis of AuNPs/O-GNs. The determination of insulin by electrochemistry indicated the electrochemical aptamer sensor has good selectivity and high sensitivity at physiological conditions. The linear range was from 1.0 × 10−14 to 5.0 × 10−10 mol L−1 with a low detection limit of 6.0 × 10−15 mol L−1 (S/N = 3). The recovery of insulin in human blood serum samples was from 102.3% to 104.7%. The aptamer sensor provided a promising strategy for insulin detection in clinical diagnostics.

Assemblies of brilliant cresyl violet to DNA in the presence of γ-cyclodextrin

The interactions of brilliant cresyl violet (BCV) with herring sperm DNA in gamma-cyclodextrin (gamma-CD) supramolecular system were studied by UV-vis absorption spectroscopy and cyclic voltammetry (CV). Both UV-vis absorption and CV data show that the interaction of BCV with DNA depends on the concentration ratio of BCV to DNA (R), the initial concentration of BCV and gamma-CD. The binding constants of BCV monomer, (BCV)(2) dimer and (BCV)(2)-gamma-CD inclusion complex with DNA are 1.64x10(5), 2.56x10(4) and 2.32x10(3) M(-1), respectively. It was observed that gamma-CD can affect the interactive mode of BCV with DNA. If R is larger than 0.5, the (BCV)(2)-gamma-CD inclusion complex will retain intact and bind to DNA via the electrostatic attraction forces. By contrast, when R is smaller than 0.5, the inclusion complex will be partially dissociated and the free BCV monomer is intercalated into the double-helix structure of DNA attributing to the more favorable microenvironment of DNA for the BCV monomer. Our work postulates the importance of the initial concentration of dye and host molecule on the interaction of dye with DNA in living bodies.