A graphene nanoribbon network and its biosensing application.

Graphene oxide nanoribbons (GONRs) have been prepared by chemically unzipping multiwalled carbon nanotubes (MWCNTs). Thin-film networks of GONRs were fabricated by spray-coating, followed by a chemical or thermal reduction to form reduced graphene oxide nanoribbons (rGONRs). Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) characterizations indicate that the thermal reduction in the presence of ethanol vapor effectively restores the graphitic structure of the GONR as compared to chemical reduction with hydrazine vapor. Electrical measurements under a liquid-gate configuration demonstrates that rGONR network field-effect transistors exhibit much higher on/off ratios than a network of microsized reduced graphene oxides (rGOs) or a continuous film of single-layered pristine or chemical vapor deposited (CVD) graphene. Furthermore, we demonstrated the potential applications of rGONR networks for biosensing, specifically, the real-time and sensitive detection of adenosine triphosphate (ATP) molecules.

Enrichment of (8,4) single-walled carbon nanotubes through coextraction with heparin.

Heparin sodium salt is investigated as a dispersant for dispersing single-walled carbon nanotubes (SWNTs). Photoluminescence excitation (PLE) spectroscopy is used for identification and abundance estimation of the chiral species. It is found that heparin sodium salt preferentially disperses larger-diameter Hipco SWNTs. When used to disperse CoMoCAT nanotube samples, heparin has a strong preference for (8,4) tubes, which have larger diameter than the predominant (6,5) in pristine CoMoCAT samples. PLE intensity due to (8,4) tubes increases from 7% to 60% of the total after threefold extractions. Computer modeling verifies that the complex of (8,4) SWNTs and heparin has the lowest binding energy amongst the four semiconducting species present in CoMoCAT. Network field-effect transistors are successfully made with CoMoCAT/heparin and CoMoCAT/sodium dodecylbenzene sulfonate (SDBS)-heparin (x3), confirming the easy removability of heparin.

Large-scale submicron horizontally aligned single-walled carbon nanotube surface arrays on various substrates produced by a fluidic assembly method.

Single-walled carbon nanotube (CNT) arrays have been assembled on various substrates over mm-scale surface areas by combining fluidic alignment with soft lithography (micropatterning in capillaries) techniques. The feature size of the nanotube patterns reaches down to submicrometre scale. To this end, tailored substrate surface modification and pre-alignment of chopped CNTs in suspension are highly critical.

CF4 plasma treatment of poly(dimethylsiloxane): effect of fillers and its application to high-aspect-ratio UV embossing.

Surface modification of poly(dimethylsiloxane) (PDMS) was carried out via CF4 plasma treatment. The test PDMS used contains significant amounts of quartz and silica fillers, while the control material is the same PDMS with quartz removed by centrifugation. Fluorination accompanied with roughening was produced on both PDMS surfaces. With short plasma times (15 min or less), a macromolecular fluorocarbon layer was formed on the PDMS surfaces because of the dominant fluorination, leading to significant increase in F concentration, decrease of surface energy, and some roughening. With intermediate plasma times (15-30 min), dynamic balance between fluorination and ablation was achieved, leading to a plateau of the surface roughness, fluorine content, and [F-Si]/[F-C] ratio. At our longest investigated plasma time of 45 min, the plasma ablated the fluorinated covering layer on the PDMS surfaces, leading to significant increase in roughness and [F-Si]/[F-C] ratio and decrease of surface F concentration. The effect of additional quartz in the test PDMS on surface F concentration, [F-Si]/[F-C] ratio, and roughness was dramatic only when ablation was significant (i.e., 45 min). The obtained Teflon-like surface displays long-term stability as opposed to hydrophobic recovery of other plasma-treated PDMS surfaces to increase hydrophilicity. On the basis of the optimized plasma treatment time of 15 min, a microstructured PDMS mold was plasma treated and successfully used for multiple high-aspect-ratio (about 8) UV embossing of nonpolar polypropylene glycol diacrylate (PPGDA) resin.