Nihar Mohanty

Biocompatible, robust free-standing paper composed of a TWEEN/graphene composite.

Nonspecific binding (NSB), a random adsorption of biocomponents such as proteins and bacteria on noncomplementary materials,isoneofthebiggestproblemsinbiological applications including biosensors, protein chips, surgical instruments, drug delivery, and biomedicine. Polyoxyethylene sorbitan laurate (TWEEN), a commercially available chemical with aliphatic ester chains, has shown promise as a medical material and in overcomingproblems associated withNSB. [1‐4] However,stability during solution-based processing and uniformity of the materials that have TWEEN coating on flat substrates or nanomaterials using the selfassembled-monolayer (SAM) method has been an important issue. Further, biocompatible materials with high strength are important for several medical applications including stents, nail implants, and strong invasive instruments. Here, we present the production of a free-standing ‘‘paperlike’’ material composed of TWEEN and reduced graphene oxide (RGO) platelets and obtained by simple filtration of a homogeneous aqueous colloidal suspension of TWEEN/RGO hybrid. The ‘‘TWEEN paper’’ was highly stable in water without leakage of TWEEN and is compliant and sufficiently robust to be handled by hand without breaking. Furthermore, the TWEEN paper was noncytotoxic to three mammalian cell lines and biocompatible, inhibiting nonspecific binding of Gram-positive bacteria. [5] In contrast, RGO paper without TWEEN showed nonspecific bacterial binding. TWEEN is composed ofthree chemical parts (Fig. 1a): aliphatic esterchains that can prevent NSB ofbiomolecules, three-terminal hydroxyl groups that are hydrophilic and can be chemically modified for further applications, and an aliphatic chain that can easily be adsorbed on a hydrophobic surface by noncovalent interaction. Protein microarrays on flat substrates with SAM of TWEEN [4] and highly sensitive biosensors, [1‐3] built using field-effect transistor (FET) behavior of individual carbon nanotube (CNT) strands coated with TWEEN, have demonstrated that TWEEN can be effectively used to overcome NSB.

Impermeable Graphenic Encasement of Bacteria

Transmission electron microscopy (TEM) of hygroscopic, permeable, and electron-absorbing biological cells has been an important challenge due to the volumetric shrinkage, electrostatic charging, and structural degradation of cells under high vacuum and fixed electron beam.(1-3) Here we show that bacterial cells can be encased within a graphenic chamber to preserve their dimensional and topological characteristics under high vacuum (10(-5) Torr) and beam current (150 A/cm(2)). The strongly repelling π clouds in the interstitial sites of graphenes lattice(4) reduces the graphene-encased-cells permeability(5) from 7.6-20 nm/s to 0 nm/s. The C-C bond flexibility(5,6) enables conformal encasement of cells. Additionally, graphenes high Youngs modulus(6,7) retains cells structural integrity under TEM conditions, while its high electrical(8) and thermal conductivity(9) significantly abates electrostatic charging. We envision that the graphenic encasement approach will facilitate real-time TEM imaging of fluidic samples and potentially biochemical activity.

Nanotomy-based production of transferable and dispersible graphene nanostructures of controlled shape and size

Because of the edge states and quantum confinement, the shape and size of graphene nanostructures dictate their electrical, optical, magnetic and chemical properties. The current synthesis methods for graphene nanostructures do not produce large quantities of graphene nanostructures that are easily transferable to different substrates/solvents, do not produce graphene nanostructures of different and controlled shapes, or do not allow control of GN dimensions over a wide range (up to 100 nm). Here we report the production of graphene nanostructures with predetermined shapes (square, rectangle, triangle and ribbon) and controlled dimensions. This is achieved by diamond-edge-induced nanotomy (nanoscale-cutting) of graphite into graphite nanoblocks, which are then exfoliated. Our results show that the edges of the produced graphene nanostructures are straight and relatively smooth with an I(D)/I(G) of 0.22-0.28 and roughness <1 nm. Further, thin films of GN-ribbons exhibit a bandgap evolution with width reduction (0, 10 and ~35 meV for 50, 25 and 15 nm, respectively).

High‐Throughput, Ultrafast Synthesis of Solution‐ Dispersed Graphene via a Facile Hydride Chemistry

Graphene is a single-atom-thick two-dimensional macromolecule with sp-bound carbon atoms arranged in a honeycomb lattice. Recently, graphene has emerged as an attractive candidate for several applications, including ultrafast nanoelectronic devices, tunable spintronics, ultracapacitors, transparent conducting electrodes, single-molecule chemical sensors, ultrasensitive biodevices, and nanomechanical devices. These applications have evolved from its atypical properties, such as weakly scattered ballistic transport of charge carriers behaving as massless fermions at room temperature, magneto-sensitive transport, tunable bandgap, quantum Hall effect at room temperature, tunable optical transitions, exceptional mechanical strength, megahertz characteristic frequency, carrier collimation, and ultrahigh stiffness. Graphene can be 1) synthesized on-substrate, 2) deposited on-substrate via mechanical processes, or 3) deposited onsubstrate from solution. On-substrate synthesis includes hightemperature (>1000 8C) epitaxial growth on SiC, ruthenium or chemical vapor deposition on nickel and copper, while mechanical deposition includes adhesive-tape exfoliation of highly oriented pyrolytic graphite (HOPG) and the ensuing transfer. The third process, which is based on onsubstrate deposition from a graphene suspension, has several advantages including the large-scale production of reduced graphene oxide (RGO) and easy-to-apply chemical and physical manipulations for functionalization and directed deposition. Graphene suspension synthesis methods include 1) p–p intercalation or graphite intercalation compound (GIC)-based exfoliation of graphite flakes into graphene sheets, and 2) in-solution reduction of graphite oxide prepared by Hummers method with hydrazine. The p–p intercalation and GIC-based methods produce highquality graphene; however, the yield is low with relatively low stability of the graphene solution, in which the graphene sheets have a tendency to settle down. The graphene suspension

Synthesis and Characterization of Amphiphilic Reduced Graphene Oxide with Epoxidized Methyl Oleate

Amphiphilic reduced graphene oxide is obtained by oleo-functionalization with epoxidized methyl oleate (renewable feedstock) using a green process. The excellent diverse solvent-dispersivity of the oleo-reduced amphiphilic graphene and its reduction chemistry are confirmed in this study. Oleo-reduction of amphiphilic graphene is amenable to industrially viable processes to produce future graphene-based polymer composites and systems.