Distinguishing Self-Assembled Pyrene Structures from Exfoliated Graphene

Modified exfoliated graphene functionalized with carboxylic acid-group and thionine on a screen-printed carbon electrode as a platform for an electrochemical enzyme immunosensor

An enzyme immunoassay was developed based on the coulometric measurement of immunoglobulin M (IgM) against Hantaan viruses (HTNV) by using virus-like particles (VLPs) as recognition molecules. The surface functionalization of screen-printed carbon electrodes (SPCEs) was achieved through paste-exfoliated graphene that was modified with a COOH group and a thionine mediator through supramolecular-covalent scaffolds, on SPCEs by using the binder contained in the ink. After the covalent immobilization of the antibody, the sensor was used for the sandwich enzyme immunoassay of IgM against HTNV. By using HTNV VLPs as the second recognization molecules, the resulting sensor efficiently monitored the reaction of IgM against HTNV and anti-IgM antibody with high specificity. By attaching HTNV nucleocapsid protein antibody conjugate with horseradish peroxidase (HRP) onto VLPs, the signal response of the assay was derived from the coulometric measurement of H2O2 reduction mediated by thionine on the electrode surface after the application of a potential (- 0.2 V vs. Ag/AgCl). The ratio of charges measured before or after H2O2 addition was used to quantify IgM because these charges could be used as background charges or total charges, respectively. The ratio exhibited good agreement with IgM concentration within a range 0.1 to 1000 pg mL-1, and a detection limit of 0.06 pg mL-1 was obtained. The assay demonstrated high sensitivity and specificity toward HTNV-specific IgM in serum.

Simultaneous exfoliation and colloidal formation of few-layer semiconducting MoS2 sheets in water

A simple method allowing for simultaneous liquid-phase exfoliation of MoS₂ crystals into few-layer sheets and colloidal formation of the exfoliated sheets is reported.

Initial Studies Directed toward the Rational Design of Aqueous Graphene Dispersants

This study presents preliminary experimental data suggesting that sodium 4-(pyrene-1-yl)butane-1-sulfonate (PBSA), 5, an analogue of sodium pyrene-1-sulfonate (PSA), 1, enhances the stability of aqueous reduced graphene oxide (RGO) graphene dispersions. We find that RGO and exfoliated graphene dispersions prepared in the presence of 5 are approximately double the concentration of those made with commercially available PSA, 1. Quantum mechanical and molecular dynamics simulations provide key insights into the behavior of these molecules on the graphene surface. The seemingly obvious introduction of a polar sulfonate head group linked via an appropriate alkyl spacer to the aromatic core results in both more efficient binding of 5 to the graphene surface and more efficient solvation of the polar head group by bulk solvent (water). Overall, this improves the stabilization of the graphene flakes by disfavoring dissociation of the stabilizer from the graphene surface and inhibiting reaggregation by electrostatic and steric repulsion. These insights are currently the subject of further investigations in an attempt to develop a rational approach to the design of more effective dispersing agents for rGO and graphene in aqueous solution.

3-Arm star pyrene-functional PMMAs for efficient exfoliation of graphite in chloroform: fabrication of graphene-reinforced fibrous veils

3-Arm PMMAs end-functionalized by pyrene were designed as dispersing/stabilizing agents for the liquid-phase exfoliation of graphite in low-boiling point solvents like chloroform. The synthetic procedure comprised ARGET ATRP controlled polymerization, click chemistry and the quaternization reaction of triazole, ensuring tailor-made, well-defined pyrene-functional star PMMAs. Among a series of different pyrene-functional macromolecular topologies, the (PMMA-py2)3 proved the most efficient exfoliation agent giving relatively high graphene concentration (0.36 mg ml-1) at exceptionally low polymer/graphite mass ratio (mP/mGF = 0.003) and short sonication time (3 h). A 5-cycle iterative procedure relying on the redispersion of the sediment was developed yielding CG = 1.29 mg ml-1 with 14.8% exfoliation yield, under the favorable conditions of 10.5 h total shear mixing/tip sonication time and overall mP/mGF ratio as low as 0.15. In parallel, all-atom molecular dynamics simulations were conducted which helped understand the mechanism by which pyrene-functional macromolecular topologies act as efficient dispersing agents of graphene. Finally the G@(PMMA-Py)3 hybrids were well dispersed into the PMMA matrix by electrospinning to fabricate graphene-based nanocomposite fibrous veils. These graphene/polymer nanocomposites exhibited enhanced stiffness and strength by a factor of 4.4 with 1.5 wt% graphene hybrids as nanofillers.

Water Dispersible Few-Layer Graphene Stabilized by a Novel Pyrene Derivative at Micromolar Concentration

The search for graphene or few-layer graphene production methods that are simple, allow mass production, and yield good quality material continues to provoke intense investigation. The present work contributes to this investigation through the study of the aqueous exfoliation of four types of graphene sources, which are namely graphite and graphite nanoflakes with different morphologies and geographical origins. The exfoliation was achieved in an aqueous solution of a soluble pyrene derivative that was synthesized to achieve maximum interaction with the graphene surface at low concentration (5 × 10⁻⁵ M). The yield of bilayer and few-layer graphene obtained was quantified by Raman spectroscopic analysis, and the adsorption of the pyrene derivative on the graphene surface was studied by thermogravimetric analysis and X-ray diffraction. The whole procedure was rationalized with the help of molecular modeling.

Fabrication of Graphene-Polyimide Nanocomposites with Superior Electrical Conductivity

We report on the fabrication of a novel class of lightweight materials, polyimide-graphene nanocomposites (0.01-5 vol %), with tunable electrical conductivity. The graphene-polyimide nanocomposites exhibit an ultra-low graphene percolation threshold of 0.03 vol % and maximum dc conductivity of 0.94 S/cm, which we attribute to excellent dispersion, extraordinary electron transport in the well-dispersed graphene, high number density of graphene nanosheets, and the π-π interactions between the aromatic moieties of the polyimide and the carbon rings in graphene. The dc conductivity data are shown to follow the power-law dependence on the graphene volume fraction near the percolation threshold. The ac conductivity of the nanocomposites is accurately represented by the extended pair-approximation model. The exponent s of the approximation is estimated to be 0.45-0.61, indicating anomalous diffusion of charge particles and a fractal structure for the conducting phase, lending support to the percolation model. Low-temperature dc conductivity of the nanocomposites is well-approximated by the thermal fluctuation-induced tunneling. Wide-angle X-ray scattering and transmission electron microscopy were utilized to correlate the morphology with the electrical conductivity. The lack of maxima in X-ray indicates the loss of structural registry and short-range ordering.

Capacitive Sensing of Glucose in Electrolytes Using Graphene Quantum Capacitance Varactors

A novel graphene-based variable capacitor (varactor) that senses glucose based on the quantum capacitance effect was successfully developed. The sensor utilizes a metal-oxide-graphene varactor device structure that is inherently compatible with passive wireless sensing, a key advantage for in vivo glucose sensing. The graphene varactors were functionalized with pyrene-1-boronic acid (PBA) by self-assembly driven by π-π interactions. Successful surface functionalization was confirmed by both Raman spectroscopy and capacitance-voltage characterization of the devices. Through glucose binding to the PBA, the glucose concentration in the buffer solutions modulates the level of electrostatic doping of the graphene surface to different degrees, which leads to capacitance changes and Dirac voltage shifts. These responses to the glucose concentration were shown to be reproducible and reversible over multiple measurement cycles, suggesting promise for eventual use in wireless glucose monitoring.

Compartmentalized Assembly of Motor Protein Reconstituted on Protocell Membrane toward Highly Efficient Photophosphorylation

Molecule assembly and functionalization of protocells have achieved a great success. However, the yield efficiency of photophosphorylation in the present cell-like systems is limited. Herein, inspired by natural photobacteria, we construct a protocell membrane reconstituting motor protein for highly efficient light-mediated adenosine triphosphate (ATP) synthesis through a layer-by-layer technique. The assembled membrane, compartmentally integrating photoacid generator, proton conductor, and ATP synthase, possesses excellent transparency, fast proton production, and quick proton transportation. Remarkably, these favorable features permit the formation of a large proton gradient in a confined region to drive ATP synthase to produce ATP with high efficiency (873 ATP s^-1). It is the highest among the existing artificial photophosphorylation systems. Such a biomimetic system provides a bioenergy-supplying scenario for early photosynthetic life and holds promise in remotely controlled ATP-consumed biosensors, biocatalysts, and biodevices.

Light Energy Accumulation from Pyrene Derivative to Tris(bipyridine)ruthenium on Clay Surface

A novel type of energy donor-acceptor system on a clay surface has been prepared. The energy transfer between an energy-donating cationic pyrene derivative (An-Py²⁺) and an energy-accepting tris(bipyridine)ruthenium complex (Ru²⁺) on the clay surface was investigated using absorption, emission, and lifetime measurements. An obvious energy transfer was observed, and one Ru²⁺ molecule quenched the emission from five molecules of An-Py²⁺ with an emission quenching efficiency of 85% on the clay surface. This suggests that the light energies absorbed by five of the An-Py²⁺ molecules were accumulated in the one Ru²⁺ molecule. Near-quantitative emission quenching was observed for stoichiometric amounts of An-Py²⁺ and Ru²⁺. The apparent quenching rate constant is approximately 10¹⁷ L mol^-1 s^-1, and thus the quenching rate constant is 10⁷-10⁸ times higher than the diffusion rate constant in a homogeneous solution.