Broad spectral domain fluorescence wavelength modulation of visible and near-infrared emissive polymersomes

Incorporation of an extended family of multi[(porphinato)zinc(II)] (PZn)-based supermolecular fluorophores into the lamellar membranes of polymersomes (50 nm to 50 mum diameter polymer vesicles) gives rise to electrooptically diverse nano-to-micron (meso) scale soft materials. Studies that examine homogeneous suspensions of 100 nm diameter emissive polymersomes demonstrate fluorescence energy modulation over a broad spectral domain of the visible and near-infrared (600-900 nm). These polymersomal structures highlight that the nature of intermembranous polymer-to-fluorophore contacts depends on the position and identity of the porphyrins' phenyl ring substituents. Emissive polymersomes are shown to possess reduced spectral heterogeneity with respect to the established optical signatures of these PZn-based supermolecular fluorophores in solution; additionally, selection of fluorophore ancillary substituents predictably controls the nature of polymer-emitter noncovalent interactions to provide an important additional mechanism to further modulate the fluorescence band maxima of these meso-scale emissive vesicles.     

Mixed colloidal suspensions of reduced graphene oxide and layered metal oxide nanosheets: useful precursors for the porous nanocomposites and hybrid films of graphene/metal oxide

Homogeneously mixed colloidal suspensions of reduced graphene oxide, or RGO, and layered manganate nanosheets have been synthesized by a simple addition of the exfoliated colloid of RGO into that of layered MnO(2). The obtained mixed colloidal suspensions with the RGO/MnO(2) ratio of ≤0.3 show good colloidal stability without any phase separation and a negatively charged state with a zeta (ζ) potential of -30 to -40?mV. The flocculation of these mixed colloidal suspensions with lithium cations yields porous nanocomposites of Li/RGO-layered MnO(2) with high electrochemical activity and a markedly expanded surface area of around 70-100?m(2) g(-1). Relative to the Li/RGO and Li/layered MnO(2) nanocomposites (≈116 and ≈167?F?g(-1)), the obtained Li/RGO-layered MnO(2) nanocomposites deliver a larger capacitance of approximately 210?F?g(-1) with good cyclability of around 95-97?% up to the 1000th cycle, thus indicating the positive effect of hybridization on the electrode performances of RGO and lithium manganate. Also, an electrophoretic deposition of the mixed colloidal suspensions makes it possible to easily fabricate uniform hybrid films composed of graphene and manganese oxide. The obtained films show a distinct electrochemical activity and a homogeneous distribution of RGO and MnO(2). The present experimental findings clearly demonstrate that the utilization of the mixed colloidal suspensions as precursors provides a facile and universal methodology to synthesize various types of graphene/metal oxide hybrid materials.     

Influence of graphene oxide nanosheets on the stability and thermal conductivity of nanofluids

Journal of Thermal Analysis and Calorimetry - Many theoretical and experimental studies on heat transfer and flow behavior of nanofluids have been conducted, and the results show that nanofluids...     

Ionic strength and pH as control parameters for spontaneous surface oscillations

A system far from equilibrium, where the surfactant transfer from a small drop located in the aqueous bulk to the air-water interface results in spontaneous nonlinear oscillations of surface tension, is theoretically and experimentally considered. The oscillations in this system are the result of periodically arising and terminating Marangoni instability. The surfactant under consideration is octanoic acid, the dissociated form of which is much less surface-active than the protonated form. Numerical simulations show how the system behavior can be controlled by changes in pH and ionic strength of the aqueous phase. The results of numerical simulations are in good agreement with experimental data.     

Charge storage characteristics of layer-by-layer assembled nickel hydroxide and graphene oxide nanosheets

Journal of Solid State Electrochemistry - In this study, layer-by-layer assembled thin films composed of nickel hydroxide and graphene oxide nanosheets were produced via simple dip coating process....     

Application of graphene oxide nanosheets as probe oligonucleotide immobilization platform for DNA sensing

In this work, a simple and novel electrochemical biosensor based on a glassy carbon electrode (GCE) modified with graphene oxide nanosheets (GO) was developed for detection of DNA sequences. The morphology of prepared nanoplatform was investigated by scanning electron microscopy, infrared (FTIR) and UV/Vis absorption spectra. The fabrication processes of electrochemical biosensor were characterized with cyclic voltammetry and electrochemical impedance spectroscopy (EIS) in an aqueous solution. The optimization of experimental conditions such as immobilization of the probe BRCA1 and its hybridization with the complementary DNA was performed. Due to unique properties of graphene oxide nanosheets such as large surface area and high conductivity, a wide liner range of 1.0 × 10^?17–1.0 × 10^?9 M and detection limit of 3.3 × 10^?18 M were obtained for detection of BRCA1 5382 mutation by EIS technique. Under the optimum conditions, the proposed biosensor (ssDNA/GO/GCE) revealed suitable selectivity for discriminating the complementary sequences from non-complementary sequences, so it can be applicable for detection of breast cancer.     

Titanium dioxide anchored graphene oxide nanosheets for highly selective voltammetric sensing of dopamine

The authors report on an efficient method for the voltammetric sensing of dopamine (DA) by using an electrode modified with alternating monolayers of graphene oxide (GO) and Titanium dioxide (TiO₂) nanoparticles anchored GO nanosheets (NSs)). The as-prepared nanostructures were characterized by photoluminescence spectroscopy, powder X-ray diffraction, Raman spectroscopy, FT-IR spectroscopy, transmission electron microscopy, scanning electron microscopy, atomic force microscopy and Energy Dispersive X-ray Analysis (EDAX) techniques. The GO/TiO₂ nanocomposite (NC) was deposited on a glassy carbon electrode (GCE), where it displayed an excellent electrocatalytic activity toward the oxidation of DA, owing to its excellent conductivity, high specific surface area, enhanced interfacial contact and more negative zeta potential. Figures of merit include (a) a fast response (5 s), (b) a wide linear range (between 0.2 and 10 μM of DA) (c) a particularly low detection limit (27 nM), (d) a working potential as low as 0.25 V (vs. Ag/AgCl) and (e) a sensitivity of 1.549 μA·μM^?1·cm^?2. The GO/TiO₂/GCE exhibited excellent selectivity over the other interferences as revealed by the differential pulse voltammetric and amperometric studies. The analysis of spiked urine samples resulted in recoveries in the range of 96 to 106%, with RSDs between 3.8 and 5.2%.

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Graphical abstract A GO/TiO₂ (graphene oxide/titanium dioxide) nanocomposite (NC) was prepared and exploited as electrochemical probes in DA detection. It displays a low detection limit, wide linear range and excellent selectivity.

     

Preparation and properties of graphene oxide nanosheets/cyanate ester resin composites

Graphene oxide nanosheets (GONSs)/cyanate ester (CE) resin composites were prepared via a solution intercalation method. The structures of the GONSs and the composites were studied using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The mechanical and tribological properties of the composites were investigated. In addition, the thermal behavior of the composites was characterized by thermogravimetric analysis (TGA). Results show that the GONSs/CE resin composites were successfully prepared. The addition of GONSs is beneficial to improve the mechanical and tribological properties of the composites. Moreover, the composites exhibit better thermal stability in comparison with the CE resin matrix.     

Surface assembly of graphene oxide nanosheets on SiO2 particles for the selective isolation of hemoglobin

Graphene oxide (GO) nanosheets have been immobilized onto SiO(2) particles through electrostatic interactions by surface assembly. The surface-assembled composite material was characterized by means of SEM and FTIR and UV/Vis spectroscopy to reveal an assembling ratio of 2.3% (w/w, GO/SiO(2)). The GO/SiO(2) composites were subsequently used, for the first time, as adsorbents for the adsorption/isolation of proteins. Selective isolation of proteins of interest, namely, hemoglobin (Hb) in this case, from complex sample matrices, for example, human whole blood, could be obtained by carefully manipulating the adsorption/desorption process. At pH 7, an adsorption of 85% was achieved for Hb (70 mg L(-1)) in sample solution (1.0 mL) by the GO/SiO(2) composites (3.0 mg). The adsorption behavior was consistent with the Langmuir adsorption model, corresponding to a theoretical adsorption capacity of 50.5 mg g(-1) for Hb. The retained Hb could be readily recovered by using a Tris-HCl buffer at pH 8.9 to give a recovery of 80%. Circular dichroism and specific activity investigations indicated that the GO/SiO(2) composites exhibited favorable biocompatibility, characterized by virtually no effect on the conformation and activity of Hb after adsorption/desorption. The composites were used for the selective isolation of Hb from human whole blood and achieved satisfactory results by assaying with sodium dodecyl sulfate polyacrylamide gel electrophoresis.     

An aptasensor for tetracycline using a glassy carbon modified with nanosheets of graphene oxide

Microchimica Acta - The authors describe an aptasensor for tetracycline (TET) based on the use of a glassy carbon electrode (GCE) modified with graphene oxide nanosheets. The latter were placed on...     

Fluorescence sensor for monitoring ionic strength and physiological pH values

A sensor combination has been developed that measures both pH and ionic strength via two pH determinations. One of the two sensors has an immobilized pH indicator embedded in a micro-environment that makes its dissociation constant highly sensitive towards changes in the ionic strength of the solution. In the second sensor, the indicator is surrounded by charge ammonium groups, which renders the environment of the dye highly charged. Additional changes in ionic strength have practically no adverse effect. The difference in the pH values as displayed by the two sensors can be used to determine ionic strength together with pH in the near-neutral pH range.     

Simultaneous removal of uranium and humic acid by cyclodextrin modified graphene oxide nanosheets

Cyclodextrin-modified graphene oxide nanosheets (denoted as CD/GO) were synthesized by an in-situ polymerization method and characterized by as well as Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and potentiometric acid-base titration. The characterization results indicated that CD was successfully grafted onto GO surfaces by forming a chemical bond. Mutual effects on the simultaneous removal of hexavalent uranium and humic acid by CD/GO from aqueous solution were investigated. The results indicated that U(VI) and humic acid (HA) sorption on CD/GO were greatly affected by pH and ionic strength. The presence of HA enhanced U(VI) sorption at low pH and reduced U(VI) sorption at high pH, whereas the presence of U(VI) enhanced HA sorption. The surface adsorbed HA acted as a “bridge” between U(VI) and CD/GO, and formed strong inner-sphere surface complexes with U(VI). Sorption isotherms of U(VI) or HA on CD/GO could be well fitted by the Langmuir model. This work highlights that CD/GO can be used as a promising material in the enrichment of U(VI) and HA from wastewater in U(VI) and humic substances obtained by environmental pollution cleanup.     

A reversible fluorescence nanoswitch based on bifunctional reduced graphene oxide: use for detection of Hg2+ and molecular logic gate operation

Herein, we demonstrate the first use of a reduced graphene oxide (rGO)-organic dye nanoswitch for the label-free, sensitive and selective detection of Hg(2+) using bifunctional rGO as an effective nanoquencher and highly selective nanosorbent. Moreover, a reversible on-off INHIBIT rGO logic gate based on a cysteine-Hg(2+) system has also been designed.     

Layered assembly of graphene oxide and Co-Al layered double hydroxide nanosheets as electrode materials for supercapacitors

An innovative strategy of fabricating electrode material by layered assembling two kinds of one-atom-thick sheets, carboxylated graphene oxide (GO) and Co-Al layered double hydroxide nanosheet (Co-Al LDH-NS) for the application as a pseudocapacitor is reported. The Co-Al LDH-NS/GO composite exhibits good energy storage properties.     

Ionic polyacrylamide hydrogel improved by graphene oxide for efficient adsorption of methylene blue

Research on Chemical Intermediates - The ionic polyacrylamide/graphene oxide (PAM/GO) hydrogel as an excellent methylene blue (MB) adsorbent was prepared by an improved one-step radical...     

Introduction of CdO nanoparticles into graphene and graphene oxide nanosheets for increasing adsorption capacity of Cr from wastewater collected from petroleum refinery

Graphene and graphene oxide nanocomposites are promising and fascinating types of nanocomposites because of their fast kinetics, unique affinity for heavy metals, and greater specific area. Initially, in this study, a green, cost-effective and facile method was utilized to prepare G, GO, CdO, G-CdO, and CdO-GO nanocomposites by Azadirachta indica and then analyzed using UV–vis spectroscopy, Fourier-transform spectroscopy, Raman, X-ray diffraction and scanning electron microscope. The synthesized nanocomposites were explored for chromium elimination from wastewater collected from a petroleum refinery. CdO-GO, G-CdO nanocomposites showed remarkable adsorption capability of 699 and 430 mg g^?1 which was higher than G (80 mg g^?1), GO (65 mg g^?1), and CdO (400 mg g^?1). Based on the R² (correlation coefficient) values, the kinetic statistics of Cr (VI) onto the G, GO, CdO, G-CdO, and CdO-GO were effectively obeyed by pseudo-second-order than by all other models. The R² values for the five nano-bioadsorbents were extraordinarily high (R² greater than 0.990) which ensured the chemisorption. This study ensured that the adsorptive removal rate of Cr (VI) is still greater than 85 % after repeated five cycles, suggesting that the produced nanomaterials are adsorbents with strong recyclability.     

Cetyltrimethylammonium bromide assisted self-assembly of phosphotungstic acid on graphene oxide nanosheets for selective determination of tryptophan

A one-step method was developed to prepare cetyltrimethylammonium bromide (CTAB) and phosphotungstic acid (PTA)-modified graphene oxide (GO) (PTA/CTAB/GO). In a system containing CTAB, GO, and PTA, negatively charged GO forms stable complex with positively charged CTAB, which assembled on the GO nanosheet surface. And then, with CTAB molecules as the molecular linker, PTA was loaded on CTAB/GO hybrid by electrostatic interaction. The PTA/CTAB/GO was characterized with Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) and subsequently used in the construction of tryptophan (Trp) sensor. Compared with the CTAB/GO, PTA/CTAB/GO exhibits better electrocatalytic activity towards the oxidation of Trp, which is attributed to the synergistic effect of PTA and GO. The differential pulse voltammetry (DPV) curve of Trp at PTA/CTAB/GO/glassy carbon electrode (GCE) exhibited two linear dynamic ranges with a detection limit of 0.02 μM (S/N = 3). In addition, the proposed sensor is successfully employed to detect Trp in the real samples with satisfactory results.     

Electrochemical sensor for monitoring the photodegradation of catechol based on DNA-modified graphene oxide

We have immobilized DNA on a glassy carbon electrode (GCE) modified with graphene oxide (GO) to develop an electrochemical biosensor for catechol. Compared to carbon nanotubes, the use of GO dramatically improved the electrooxidative current of the guanine and adenine moieties in DNA but retained the low background current of unmodified GCEs. Factors such as DNA adsorption time, DNA concentration and pH of solution were investigated to optimize experimental conditions. In the presence of catechol, the voltammetric response to DNA was inhibited due to the interaction between DNA and catechol. The response to adenine is linearly proportional to the concentration of catechol in the range from 1.0?×?10^?6 to 1.0?×?10^?4 mol·L^?1. If catechol is degraded by the combined action of UV light and hydrogen peroxide, the response to DNA is restored. Thus, the modified electrode can act as an efficient biosensor for monitoring the degradation of catechol.