Fuzzy Graphene Research Articles

Covalent Functionalization of Silicon with Plasma-Grown "Fuzzy" Graphene: Robust Aqueous Photoelectrodes for CO2 Reduction by Molecular Catalysts.

Carbon electrodes are ideal for electrochemistry with molecular catalysts, exhibiting facile charge transfer and good stability. Yet for solar-driven catalysis with semiconductor light absorbers, stable semiconductor/carbon interfaces can be difficult to achieve, and carbon's high optical extinction means it can only be used in ultrathin layers. Here, we demonstrate a plasma-enhanced chemical vapor deposition process that achieves well-controlled deposition of out-of-plane "fuzzy" graphene (FG) on thermally oxidized Si substrates. The resulting Si|FG interfaces possess a silicon oxycarbide (SiOC) interfacial layer, implying covalent bonding between Si and the FG film that is consistent with the mechanical robustness observed from the films. The FG layer is uniform and tunable in thickness and optical transparency by deposition time. Using p-type Si|FG substrates, noncovalent immobilization of cobalt phthalocyanine (CoPc) molecular catalysts was employed for the photoelectrochemical reduction of CO2 in aqueous solution. The Si|FG|CoPc photocathodes exhibited good catalytic activity, yielding a current density of ∼1 mA/cm2, Faradaic efficiency for CO of ∼70% (balance H2), and stable photocurrent for at least 30 h at -1.5 V vs Ag/AgCl under 1-sun illumination. The results suggest that plasma-deposited FG is a robust carbon electrode for molecular catalysts and suitable for further development of aqueous-stable Si photocathodes for CO2 reduction.

Modulation of Early Stage Neuronal Outgrowth through Out-of-Plane Graphene.

The correct wiring of a neural network requires neuron to integrate an incredible repertoire of cues found in their extracellular environment. The astonishing efficiency of this process plays a pivotal role in the correct wiring of the brain during development and axon regeneration. Biologically inspired micro- and nanostructured substrates have been shown to regulate axonal outgrowth. In parallel, several studies investigated graphene's potential as a conductive neural interface, able to enhance cell adhesion, neurite sprouting and outgrowth. Here, we engineered a 3D single- to few-layer fuzzy graphene morphology (3DFG), 3DFG on a collapsed Si nanowire (SiNW) mesh template (NT-3DFGc), and 3DFG on a noncollapsed SiNW mesh template (NT-3DFGnc) as neural-instructive materials. The micrometric protruding features of the NWs templates dictated neuronal growth cone establishment, as well as influencing axon elongation and branching. Furthermore, neurons-to-graphene coupling was investigated with comprehensive view of integrin-mediated contact adhesion points and plasma membrane curvature processes.

3D fuzzy graphene microelectrode array for dopamine sensing at sub-cellular spatial resolution

The development of a high sensitivity real-time sensor for multi-site detection of dopamine (DA) with high spatial and temporal resolution is of fundamental importance to study the complex spatial and temporal pattern of DA dynamics in the brain, thus improving the understanding and treatments of neurological and neuropsychiatric disorders. In response to this need, here we present high surface area out-of-plane grown three-dimensional (3D) fuzzy graphene (3DFG) microelectrode arrays (MEAs) for highly selective, sensitive, and stable DA electrochemical sensing. 3DFG microelectrodes present a remarkable sensitivity to DA (2.12 ± 0.05 nA/nM, with LOD of 364.44 ± 8.65 pM), the highest reported for nanocarbon MEAs using Fast Scan Cyclic Voltammetry (FSCV). The high surface area of 3DFG allows for miniaturization of electrode down to 2 × 2 μm2, without compromising the electrochemical performance. Moreover, 3DFG MEAs are electrochemically stable under 7.2 million scans of continuous FSCV cycling, present exceptional selectivity over the most common interferents in vitro with minimum fouling by electrochemical byproducts and can discriminate DA and serotonin (5-HT) in response to the injection of their 50:50 mixture. These results highlight the potential of 3DFG MEAs as a promising platform for FSCV based multi-site detection of DA with high sensitivity, selectivity, and spatial resolution.

Multi-Dimensional Fuzzy Graphene Bioelectronic Actuators

The ability to manipulate the electrophysiology of electrically active cells and tissues has enabled a deeper understanding of healthy and diseased states. This has primarily been achieved via bioelectronic actuators that interface engineered materials with biological entities. Graphene has gained recent interest as a building-block for bioelectronic actuators due to its advantageous electrochemical properties and biocompatibility. However, functional graphene bioelectronics exhibit a two-dimensional (2D) topology. This leads to inherent performance limitations due to the limited exposed surface-area and poor interactions with interfaced cells and tissues. Ideal geometry of graphene-based actuators needs to leverage the material’s high surface-area-to-volume ratio to facilitate maximum interaction with the electrode.Here we report a breakthrough three-dimensional (3D) topology of graphene: nanowire templated 3D fuzzy graphene (NT-3DFG), for actuation of electrically active cells and tissues. Using a bottom-up approach, we synthesize an interconnected network of free-standing graphene flakes on Si nanowires (SiNWs). The 3D topology leads to enhanced surface-area compared to planar surfaces allowing NT-3DFG microelectrodes to exhibit lower electrode impedance. The increased surface area also leads to an increase of up to 5-fold and 10-fold in the cathodic charge storage capacity (CSCC) and the charge injection capacity (CIC), respectively, for 20 µm NT-3DFG compared to 20 µm conventional Pt electrodes. To enhance the electrical actuation capabilities of NT-3DFG, we electrodeposit poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) on the 3D electrodes. This results in further enhancement in the exhibited CSCC and CIC thus enabling further miniaturization of graphene-based microelectrodes to ultra-microelectrodes for functional bioelectronics. Our results demonstrate the importance of extending the topology of nanomaterials to 3D to push the physical and functional limits of conventional bioelectronics.

Three-Dimensional Graphene Microelectrode Arrays for Detection of Wound Healing Biomarkers

Volumetric muscle loss (VML) injuries, such as those from high-energy trauma or tumor ablation, often result in scar tissue formation and permanent loss of skeletomuscular function. Directly after VML injury formation, neutrophils and macrophages arrive at the wound site, releasing cytokines and growth factors to allow proliferation and innervation. Monitoring the wound healing process by spatially mapping key regulatory wound biomarkers, such as nitric oxide (NO), can elucidate the state of the wound and thus inform critical clinical interventions. While single-point NO probes with sufficient performance for short-term measurements have been produced previously, improvements in device sensitivity, stability, and the number of sensing nodes are needed for in vivo applications. Here we leverage novel nanomaterials and their exceptional electrochemical properties to construct three-dimensional fuzzy graphene (3DFG) microelectrode arrays (MEAs) for the multiplexed electrochemical sensing of NO. We report in vitro results for 3DFG MEAs capable of selectively detecting NO (versus known interferents such as nitrite, ascorbic acid, and uric acid) at physiological concentrations in the nanomolar regime (limit of detection < 10 nM). Future work will entail in vivo NO detection to aid in monitoring wound states in animal models.

(Invited) Bioelectronics with Nanocarbons

We focus on developing a new class of nanoscale materials for the investigation of biological entities at multiple length scales, from the molecular level to complex cellular networks. Our highly flexible bottom-up nanomaterials synthesis capabilities allow us to form unique hybrid-nanomaterials. Recently, we have demonstrated highly controlled synthesis of 3D out-of-plane single- to few-layer fuzzy graphene (3DFG) on a Si nanowire (SiNW) mesh template. By varying graphene growth conditions, we control the size, density, and electrical properties of the NW templated 3DFG (NT-3DFG). This flexible synthesis inspires formation of complex hybrid-nanomaterials with tailored optical and electrical properties to be used in biosensing, and energy-related research. The exceptional synthetic control and flexible assembly of nanomaterials provide powerful tools for fundamental studies and applications in life science and open up the potential to seamlessly merge either nanomaterials-based platforms or unique nanosensor geometries and topologies with cells, fusing nonliving and living systems together.

Intracellular action potential recordings from cardiomyocytes by ultrafast pulsed laser irradiation of fuzzy graphene microelectrodes.

Graphene with its unique electrical properties is a promising candidate for carbon-based biosensors such as microelectrodes and field effect transistors. Recently, graphene biosensors were successfully used for extracellular recording of action potentials in electrogenic cells; however, intracellular recordings remain beyond their current capabilities because of the lack of an efficient cell poration method. Here, we present a microelectrode platform consisting of out-of-plane grown three-dimensional fuzzy graphene (3DFG) that enables recording of intracellular cardiac action potentials with high signal-to-noise ratio. We exploit the generation of hot carriers by ultrafast pulsed laser for porating the cell membrane and creating an intimate contact between the 3DFG electrodes and the intracellular domain. This approach enables us to detect the effects of drugs on the action potential shape of human-derived cardiomyocytes. The 3DFG electrodes combined with laser poration may be used for all-carbon intracellular microelectrode arrays to allow monitoring of the cellular electrophysiological state.

Multidimensional graphene nanostructures – synthesis and applications

Abstract Conventional graphene electronics fail to leverage the exceptional surface-area-to-volume ratio of graphene due to the challenges imposed by arranging two-dimensional (2D) nanomaterials in three-dimensional (3D) spaces. Recently, a new topology of graphene, nanowire template 3D fuzzy graphene (NT-3DFG), has been developed to overcome this limitation. We provide an overview of the unique physical and chemical properties of NT-3DFG that are a direct consequence of the material structure and describe NT-3DFG’s promising applications in bioelectronics and energy-related research.

Characterization of the Coupling between Out‐of‐Plane Graphene and Electrogenic Cells

AbstractThe cell‐chip coupling is in general regulated by the interplay between cells and the material surface at the interface. Electroactive planar materials have shown limited crosstalk with cells, whereas pseudo 3D patterned materials promote a more intimate contact with the biological system. Here, unprecedented physical properties of a carbon‐based material, i.e., graphene, to engineer out‐of‐plane morphologies are exploited: 1) 3D single‐ to few‐layer fuzzy graphene morphology (3DFG), 2) 3DFG on a collapsed Si nanowire mesh template, and 3) 3DFG on a noncollapsed Si nanowire mesh template. These materials are synthesized and interfaced with cardiomyocyte‐like cells focusing on the characterization of the cytoskeletal arrangement as well as membrane wrapping processes yet regulated by endocytic proteins. Finally, some major conditions to promote tight coupling to the device and eventually spontaneous intracellular penetration are found.

Fuzzy graphene for neuron control

An article in PNAS demonstrates optical control of neuronal activity using graphene flakes grown on silicon nanowires.

Remote nongenetic optical modulation of neuronal activity using fuzzy graphene

The ability to modulate cellular electrophysiology is fundamental to the investigation of development, function, and disease. Currently, there is a need for remote, nongenetic, light-induced control of cellular activity in two-dimensional (2D) and three-dimensional (3D) platforms. Here, we report a breakthrough hybrid nanomaterial for remote, nongenetic, photothermal stimulation of 2D and 3D neural cellular systems. We combine one-dimensional (1D) nanowires (NWs) and 2D graphene flakes grown out-of-plane for highly controlled photothermal stimulation at subcellular precision without the need for genetic modification, with laser energies lower than a hundred nanojoules, one to two orders of magnitude lower than Au-, C-, and Si-based nanomaterials. Photothermal stimulation using NW-templated 3D fuzzy graphene (NT-3DFG) is flexible due to its broadband absorption and does not generate cellular stress. Therefore, it serves as a powerful toolset for studies of cell signaling within and between tissues and can enable therapeutic interventions.

(Invited) Modulating Neuronal Activity with out-of-Plane Grown Three Dimensional (3D) Fuzzy Graphene

The ability to modulate cellular electrophysiology is a fundamental aspect for investigation of tissue development, maturation and function. Currently, there is a need for remote, non-genetic, light-induced control of cellular activity in native-like state, three-dimensional (3D) tissues such as spheroids and organoids. Here, we report a breakthrough hybrid-nanomaterial for remote, non-genetic photostimulation of both two-dimensional (2D) and 3D neural cellular systems. We combine one-dimensional (1D) nanowires (NWs) and 2D graphene flakes grown out-of-plane for highly controlled photostimulation at subcellular precision with laser energies lower than hundred nanojoules, 1-2 orders of magnitude lower than Au-, C- and Si-based photostimulation. Photostimulation using NW-templated 3D fuzzy graphene (NT-3DFG) is flexible due to its broadband absorption and does not generate cellular stress. Therefore, it serves a novel powerful toolset for studies of cell signaling within and between tissues and can enable new therapeutic interventions.

Three-dimensional fuzzy graphene ultra-microelectrodes for subcellular electrical recordings

Microelectrode arrays (MEAs) have enabled investigation of cellular networks at sub-millisecond temporal resolution. However, current MEAs are limited by the large electrode footprint since reducing the electrode's geometric area to sub-cellular dimensions leads to a significant increase in impedance thus affecting its recording capabilities. We report a breakthrough ultra-microelectrodes platform by leveraging the outstanding surface-to-volume ratio of nanowire-templated out-of-plane synthesized three-dimensional fuzzy graphene (NT-3DFG). The enormous surface area of NT-3DFG leads to 140-fold reduction in electrode impedance compared to bare Au microelectrodes, thus enabling scaling down the geometric size by 625-fold to ca. 2 μm × 2 μm. The out-of-plane morphology of NT-3DFG leads to a tight seal with the cell membrane thus enabling recording of electrical signals with high signal-to-noise ratio (SNR) of > 6. This work highlights the possibility to push the limits of the conventional MEA technology to enable electrophysiological investigation at sub-cellular level without the need of any surface coatings. This presented approach would greatly impact our basic understanding of signal transduction within a single cell as well as complex cellular assemblies.

Engineering Three-Dimensional (3D) Out-of-Plane Graphene Edge Sites for Highly Selective Two-Electron Oxygen Reduction Electrocatalysis

Selective two-electron oxygen reduction reaction (ORR) offers a promising route for hydrogen peroxide synthesis, and defective sp2 carbon-based materials are attractive, low-cost electrocatalysts for this process. However, due to a wide range of possible defect structures formed during material synthesis, identification and fabrication of precise active sites remain a challenge. Here, we report a graphene edgebased electrocatalyst for two-electron ORR - nanowire-templated three-dimensional fuzzy graphene (NT3DFG). NT-3DFG exhibits excellent efficiency (onset potential of 0.79 $\pm$ 0.01 V versus RHE), selectivity (93 $\pm$ 3 % H2O2), and tunable ORR activity as a function of graphene edge site density. Using spectroscopic surface characterization and density functional theory calculations, we find that NT-3DFG edge sites are readily functionalized by carbonyl (C=O) and hydroxyl (C-OH) groups under alkaline ORR conditions. Our calculations indicate that multiple site configurations at both armchair and zigzag edges may achieve a local coordination environment that allows selective, two-electron ORR. We derive a general geometric descriptor based on the local coordination environment that provides activity predictions of graphene surface sites within ~0.1 V of computed values. Herein we combine synthesis, spectroscopy, and simulations to improve active site characterization and accelerate carbon-based electrocatalyst discovery.

(Invited) Novel Three-Dimensional Fuzzy Graphene (3DFG)-Based Platform for Interrogation of Excitable Cells

Investigating and modulating electrical activity of cardiomyocytes and neurons is essential to understanding their physiology, regeneration of excitable cells/tissues, and treatment of various disorders. Recently, microelectrode arrays (MEAs) have gained tremendous popularity since they enable multi-site recordings at sub-msec temporal resolution, provide two-way interaction with cells i.e. recording and stimulation, and have well-established microfabrication methods. However, currently used planar MEAs are not able to record and stimulate at sub-cellular resolution due to significant increase in electrode impedance which reduces the signal-to-noise ratio (SNR) of recorded signal. Currently there is a need to (i) enable high density electrode arrays, (ii) provide high spatial resolution, and (iii) prevent averaging of signals from multiple cells. To address these needs, we have developed three-dimensional out-of-plane grown fuzzy graphene (3DFG)-based MEA. Out-of-plane growth of single-to-few layers of graphene flakes leverages graphene's outstanding surface-to-volume ratio. The high surface area leads to significant reduction in impedance, thus enabling electrical recordings with high SNR and development of ultra-microelectrode arrays to perform sub-cellular measurements. Furthermore, the high flake density of graphene in 3DFG lead to high photo-absorbance in UV-NIR range. This opens up avenues to enable photo-thermal stimulation of cells with high precision and sub-cellular resolution. Our presented approach would greatly impact our basic understanding of signal transduction in complex cellular assemblies. Furthermore, it would provide a platform for developing and screening of therapeutics, and treatment of various cardiac and neurological diseases.

Nanowire-Templated Three-Dimensional Out-of-Plane Fuzzy Graphene as an Oxygen Reduction Reaction Catalyst

Rate-limiting oxygen reduction reactions (ORR) and high-cost platinum at fuel cell cathodes are substantial barriers to commercial fuel cell viability. Carbon-based, metal-free ORR catalysts have high catalytic stability and can potentially dramatically reduce cost and increase efficiency of fuel cells. For increased ORR efficiency, nitrogen doping of graphene sp2-hybridized carbon lattice is utilized, to induce a net positive charge on adjacent C atoms to alter the O2 chemisorption mode and attract electrons from the ­electrode. We have recently reported synthesis of a novel graphene-based hybrid-nanomaterial composed of three-dimensional (3D) out-of-plane fuzzy graphene (3DFG) on 3D Si nanowire mesh template (NT-3DFG). Leveraging graphene’s outstanding surface-to-volume ratio and electrical conductivity, we attained exceptional electrochemically active surface area of ca. 1017 m2 g-1 (with high density of exposed, active graphene edges) and electrical conductivity of ca. 2400 S m-1. Here we report fine control over 3DFG flake size and edge density by varying the partial pressure of CH4 precursor as well as the plasma enhanced chemical vapor deposition (PECVD) process time and temperature (Figure 1.A-B). XPS analysis of C1s confirms the presence of graphite via the sp2 hybridized C bonds in 3DFG structures (Figure 1.C.I and III). We also show both in-situ and post synthesis N-doping of NT-3DFG through either incorporation of N2 during the PECVD process or post-synthesis N2-plasma treatment. XPS analysis of N1s confirms the presence of pyridinic-, pyrrolic-, and graphitic-N doping in the NT-3DFG structure (Figure 1.C.II and IV). In-situ N-doping of NT-3DFG resulted in ca. 87% pyridinic-N doping compared to ca. 52% through post-synthesis N2-plasma treatment. This pyridinic-N stabilizes the active site responsible for the chemical disproportionation of peroxide ions during ORR. Through cyclic voltammetry under acidic conditions, we demonstrate the functionality and properties of N-doped NT-3DFG as an ORR catalyst. With pyridinic-N doping and a high density of graphene edges, N-doped NT-3DFG demonstrates greater ORR efficiency than existing graphene-based hybrid nanomaterials. Figure 1. Characterization of N-doped NT3DFG. (A) SEM image of NT-3DFG synthesized with increasing partial pressure of CH4 and increasing PECVD process time. (B) Effect of increasing PECVD process temperature on NT-3DFG synthesized under 25 mTorr partial pressure of CH4 for 10 min. (C) X-ray photoelectron (XPS) spectra of (I) C1s and (II) N1s of in-situ N-doped NT-3DFG synthesized under 25 mTorr partial pressure of CH4 and 400 mTorr partial pressure of N2 for 30 min at 800˚C; and (III) C1s and (IV) N1s of NT-3DFG synthesized under 25 mTorr partial pressure of CH4 for 30 min at 800˚C doped with N post-synthesis under 300 mTorr partial pressure of N2 for 5 min at 300˚C. Cyan, purple, pink, red, green and blue represent C sp2, C sp3, C=O, Pyridinic N, Pyrrolic N and Graphitic N XPS spectra, respectively. Figure 1

Nanowire-Templated Three-Dimensional out-of-Plane Fuzzy Graphene As Thin Film Supercapacitor

Supercapacitors have gained popularity as future energy storage solutions due to their simple architecture, long cycling life, pulse power supply, and high dynamic charge propagation.1 They are generally categorized as Electrical Double Layer Capacitors (EDLCs) or pseudo-capacitors.2 EDLCs store energy as electrostatic charge on the electrodes’ surfaces; their efficiency is thus limited by the electrochemically active surface area available to the electrolyte.3 Whereas, pseudo-capacitors utilize fast and reversible faradaic processes due to electro-active species localized on the electrode surface to enhance current density.1, 4 Concentration of electro-active charged species and electro-chemical efficiency governs the efficiency of these supercapacitors. Recently, carbon-based materials (such as CNTs, graphene foams, graphene aerogels) have received research interest as promising candidates for supercapacitors due to their high electrochemical surface area, high electrical conductivity and accessible surface active sites for modification with electro-active species.5 Graphene has emerged as an ideal EDLC electrode material due to its superior electrical properties and high theoretical surface area.6 Current graphene electrodes are either pinned to a two-dimensional (2D) surface (such as graphene foams) or are tethered to a 2D substrate (such as carbon nanowalls). Graphene based hybrid-nanomaterials that leverage graphene’s outstanding surface-to-volume ratio coupled with pseudo-capacitive species for high efficiency supercapacitors have not been demonstrated to date. Here we demonstrate that direct synthesis of three-dimensional (3D) out-of-plane fuzzy graphene (3DFG) on Si nanowire (SiNW) mesh template (NT-3DFG) provides an ideal surface for functionalization with electro-active species to develop EDLC and pseudo-capacitive supercapacitors. We report fine control over 3DFG flake size and edge density by varying the partial pressure of CH4 precursor, plasma enhanced chemical vapor deposition (PECVD) synthesis process time, and PECVD synthesis temperature (Figure 1.A and B).7 Through electron microscopy (SEM and TEM) and Raman spectroscopy a distinct increase in single-to-few layer out-of-plane graphene edges is observed. High density of graphene edges presents high concentration of active sites for surface functionalization through surface doping, such as that through treatment with HNO3. Post treatment, the electrical conductivity of NT-3DFG is observed to be as high as 2400 S m-1. Leveraging on graphene’s outstanding surface-to-volume ratio, we have developed a material capable of attaining electrochemically active surface area of ca. 1017 m2 g-1. The introduction of electro-active species on this high surface area material renders specific capacitance as high as 87 ± 8 F g-1 (Figure 1.C). This value is further enhanced by decorating the template with metal oxide nanoparticles. The reported novel graphene based hybrid-nanomaterial shows great potential to be utilized in next-generation energy storage solutions. Figure 1. Characterization of NT-3DFG. (A) SEM image of NT-3DFG synthesized with increasing partial pressure of CH4 and increasing PECVD process time. (B) Effect of increasing PECVD process temperature on NT-3DFG synthesized under 25 mTorr partial pressure of CH4 for 10 min. (C) Cyclic voltammetry characterization of NT-3DFG before and after HNO3 treatment. (I) Representative cyclic voltammograms presenting double layer capacitance of NT-3DFG. Blue, yellow and red denote Au working electrode, NT-3DFG synthesized under 25 mTorr partial pressure of CH4 for 30 min and NT-3DFG synthesized under 25 mTorr partial pressure of CH4 for 90 min, respectively. Dashed lines represent respective samples after 2-hour HNO3 treatment. (II) Current density as a function of scan rate. Blue, yellow and red denote Au working electrode, NT-3DFG synthesized under 25 mTorr partial pressure of CH4 for 30 min and NT-3DFG synthesized under 25 mTorr partial pressure of CH4 for 90 min, respectively. Closed and open square represent samples before and after 2-hour HNO3 treatment, respectively.

(Invited) Multiscale Topological Design of Biological Interfaces to Novel Nanocarbons

We focus on developing a new class of nanoscale materials and novel strategies for the investigation of biological entities at multiple length scales, from the molecular level to complex cellular networks. Our highly flexible bottom-up nanomaterials synthesis capabilities allow us to form unique hybrid-nanomaterials. Recently, we have demonstrated highly controlled synthesis of 3D out-of-plane single- to few-layer fuzzy graphene (3DFG) on a Si nanowire (SiNW) mesh template. By varying graphene growth conditions, we control the size, density, and electrical properties of the NW templated 3DFG (NT-3DFG). This flexible synthesis inspires formation of complex hybrid-nanomaterials with tailored optical and electrical properties to be used in future applications such as biosensing, and bioelectronics. Currently, we target the limits of cell-nanodevices interfaces using nanosensor based array assembled in 3D with subcellular spatial resolution (<5μm) and μsec temporal resolution. Our approach enables simultaneous multiplexed electrical measurements to directly monitor the development of electrical activities of microscale tissues (μtissues, ca. 100-400μm) which are engineered from induced pluripotent stem cell or embryonic stem cell derived cardiomyocytes. Last, we have developed a unique transparent graphene-based electrical platform that enables concurrent electrical and optical investigation of ES-derived cardiomyocytes’ intracellular processes and intercellular communication. In summary, the exceptional synthetic control and flexible assembly of nanomaterials provide powerful tools for fundamental studies and applications in life science, and open up the potential to seamlessly merge either nanomaterials-based platforms or unique nanosensor geometries and topologies with cells, fusing nonliving and living systems together.

Nanowire-Mesh-Templated Growth of Out-of-Plane Three-Dimensional Fuzzy Graphene.

Graphene, a honeycomb sp2 hybridized carbon lattice, is a promising building block for hybrid-nanomaterials due to its electrical, mechanical, and optical properties. Graphene can be readily obtained through mechanical exfoliation, solution-based deposition of reduced graphene oxide (rGO), and chemical vapor deposition (CVD). The resulting graphene films' topology is two-dimensional (2D) surface. Recently, synthesis of three-dimensional (3D) graphitic networks supported or templated by nanoparticles, foams, and hydrogels was reported. However, the resulting graphene films lay flat on the surface, exposing 2D surface topology. Out-of-plane grown carbon nanostructures, such as vertically aligned graphene sheets (VAGS) and vertical carbon nanowalls (CNWs), are still tethered to 2D surface. 3D morphology of out-of-plane growth of graphene hybrid-nanomaterials which leverages graphene's outstanding surface-to-volume ratio has not been achieved to date. Here we demonstrate highly controlled synthesis of 3D out-of-plane single- to few-layer fuzzy graphene (3DFG) on a Si nanowire (SiNW) mesh template. By varying graphene growth conditions (CH4 partial pressure and process time), we control the size, density, and electrical properties of the NW templated 3DFG (NT-3DFG). 3DFG growth can be described by a diffusion-limited-aggregation (DLA) model. The porous NT-3DFG meshes exhibited high electrical conductivity of ca. 2350 S m-1. NT-3DFG demonstrated exceptional electrochemical functionality, with calculated specific electrochemical surface area as high as ca. 1017 m2 g-1 for a ca. 7 μm thick mesh. This flexible synthesis will inspire formation of complex hybrid-nanomaterials with tailored optical and electrical properties to be used in future applications such as sensing, and energy conversion and storage.

Nanowire Templated Growth of Three-Dimensional Fuzzy Graphene

Graphene, a two-dimensional (2D) hexagonal arrangement of sp2 carbon, is gaining popularity as a material for electrochemical sensors. Graphene outstanding electrical properties has led researchers to develop three-dimensional (3D) atomic layer graphene materials with increased surface area as more efficient electrodes. Although 3D graphene materials such as foams and multilayered carbon nanowalls have already been synthesized, synthesis of 3D vertical atomic layer graphene still remains a challenge. Here we demonstrate a novel synthesis of high density single to few layer vertical graphene on semiconductor nanowire mesh templates. The presence of graphene on the nanowires was confirmed by Raman spectroscopy. The progression of the templated growth of the 3D graphene flakes was verified by using scanning electron microscopy. Moreover, the growth of single to few layer crystalline graphene flakes that are vertically orientated with respect to the nanowire axis was validated by transmission electron microscopy. The sheet resistance of the new hybrid nanomaterial decreased with an increase in graphene flake size and density. Lastly, high electrochemically active surface area of the material was ascertained by cyclic voltammetry. These results pave way for the use of 3D vertical atomic layer graphene on nanowire mesh templates as electrodes for electrochemical sensing of biomolecules, quantification of fast-electron transfer reactions, and energy harvesting in fuel cells.