We demonstrate a method by which few-layer graphene samples can be etched along crystallographic axes by thermally activated metallic nanoparticles. The technique results in long (>1 µm) crystallographic edges etched through to the insulating substrate, making the process potentially useful for atomically precise graphene device fabrication. This advance could enable atomically precise construction of integrated circuits from single graphene sheets with a wide range of technological applications.Due to its remarkable electronic properties, few layer graphene is emerging as a promising new material for use in a vast array of postsilicon nanoelectronic devices incorporating quantum size effects.1,2 Of particular interest would be the construction of atomically precise graphene nanoribbons, in which charge carriers are confined in the lateral dimension whereby the electronic properties are controlled by the width and specific crystallographic orientation of the ribbon.3−14 Such structures hold enormous promise as nanoscale devices similar to those recently developed using carbon nanotubes 2,11,15 with the added advantage that graphenes two-dimensionality lends itself to existing device architectures based on planar geometries.However, these structures have so far been impossible to achieve because of the rough noncrystalline edges of the graphene that result from current state-of-the-art nanolithography techniques.2,16,17 These rough edges are thought to be the crucial limiting factor to attaining useful performance and on/off current ratios from nanoscale graphene devices. 13,18,19 As a step toward band gap engineering of this material, we have developed a means by which fewlayer graphene (FLG) samples can be etched along crystallographic axes by thermally activated metallic nanoparticles. 20 The technique results in long (>1 µm) trenches commensurate with the crystal lattice that are etched through to the supporting insulating substrate, making the process potentially useful for atomically precise graphene device fabrication, as well as indicating a possible method by which entire circuits could be carved out from single graphene sheets. Our initial samples (before etching) consisted of pristine few-layer graphene sheets transferred onto highly doped Si substrates with 300 nm thermally grown SiO 2 by mechanical exfoliation under ambient conditions, similar to the technique described in ref 21. Flakes of few-layer graphene are identified using optical microscopy. Height imaging of our samples is done using a Veeco Dimension 3100 atomic force microscope (AFM) operating in intermittent contact mode, with Si 3 N 4 -coated tips (NSC15, Mikromasch) of curvature * E-mail: drstrach@sas.upenn.edu † E-mail: cjohnson@physics.upenn.edu 1 radius ≤ 20 nm. Samples are also characterized using a JEOL JSM6400 scanning electron microscope (with a LaB 6 filament).The FLG on SiO 2 /Si substrates are uniformly spin-coated with ∼15 mL solution of 50 mg/L Fe(NO 3 ) 3 ·9H 2 O in isopropyl alcohol (HPLC grade). The samples are th...

We have designed and implemented a practical nanoelectronic interface to G-protein coupled receptors (GPCRs), a large family of membrane proteins whose roles in the detection of molecules outside eukaryotic cells make them important pharmaceutical targets. Specifically, we have coupled olfactory receptor proteins (ORs) with carbon nanotube transistors. The resulting devices transduce signals associated with odorant binding to ORs in the gas phase under ambient conditions and show responses that are in excellent agreement with results from established assays for OR–ligand binding. The work represents significant progress on a path toward a bioelectronic nose that can be directly compared to biological olfactory systems as well as a general method for the study of GPCR function in multiple domains using electronic readout.

We investigated the biocompatibility, specificity, and activity of a ligand-receptor-protein system covalently bound to oxidized single-walled carbon nanotubes (SWNTs) as a model proof-of-concept for employing such SWNTs as biosensors. SWNTs were functionalized under ambient conditions with either the Knob protein domain from adenovirus serotype 12 (Ad 12 Knob) or its human cellular receptor, the CAR protein, via diimide-activated amidation. We confirmed the biological activity of Knob protein immobilized on the nanotube surfaces by using its labeled conjugate antibody and evaluated the activity and specificity of bound CAR on SWNTs, first, in the presence of fluorescently labeled Knob, which interacts specifically with CAR, and second, with a negative control protein, YieF, which is not recognized by biologically active CAR proteins. In addition, current-gate voltage (I-V(g)) measurements on a dozen nanotube devices explored the effect of protein binding on the intrinsic electronic properties of the SWNTs, and also demonstrated the devices' high sensitivity in detecting protein activity. All data showed that both Knob and CAR immobilized on SWNT surfaces fully retained their biological activities, suggesting that SWNT-CAR complexes can serve as biosensors for detecting environmental adenoviruses.

We have explored the abilities of all-electronic DNA-carbon nanotube (DNA-NT) vapor sensors to discriminate very similar classes of molecules. We screened hundreds of DNA-NT devices against a panel of compounds chosen because of their similarities. We demonstrated that DNA-NT vapor sensors readily discriminate between series of chemical homologues that differ by single methyl groups. DNA-NT devices also discriminate among structural isomers and optical isomers, a trait common in biological olfactory systems, but only recently demonstrated for electronic FET based chemical sensors

We demonstrate a versatile class of nanoscale chemical sensors based on single-stranded DNA (ssDNA) for chemical recognition and single-walled carbon nanotube field effect transistors (SWNT FETs) for electronic read-out. SWNT FETs with a nanoscale coating of ssDNA respond to vapors that cause no detectable conductivity change in bare devices. Sensor responses differ in sign and magnitude for different gases and can be tuned by choice of the ssDNA base sequence. Sensors respond and recover rapidly (seconds), and the sensor surface is self-regenerating. Preliminary results of all-atom molecular dynamics simulations agree with experiment.

We demonstrate a versatile class of nanoscale chemical sensors based on single-stranded DNA (ssDNA) for chemical recognition and single-walled carbon nanotube field effect transistors (SWNT FETs) for electronic read-out. SWNT FETs with a nanoscale coating of ssDNA respond to vapours that cause no detectable conductivity change in bare devices. The gases tested are methanol, trimethylamine, propionic acid, dimethylmethylphosphonate and dinitrotoluene. Sensor responses differ in sign and magnitude for different gases and can be tuned by choice of the ssDNA base sequence. Sensors respond and recover rapidly (seconds), and the sensor surface is self-regenerating. Preliminary results of all-atom molecular dynamics simulations are consistent with experiment.

We have developed a photolithographic process for the fabrication of large arrays of single walled carbon nanotube transistors with high quality electronic properties that rival those of transistors fabricated by electron beam lithography. A buffer layer is used to prevent direct contact between the nanotube and the novolac-based photoresist, and a cleaning bake at 300C effectively removes residues that bind to the nanotube sidewall during processing. In situ electrical measurement of a nanotube transistor during a temperature ramp reveals sharp decreases in the ON-state resistance that we associate with the vaporization of components of the photoresist. Data from nearly 2000 measured nanotube transistors show an average ON-state resistance of 250 ± 100 kΩ. This new process represents significant progress towards the goal of high-yield production of large arrays of nanotube transistors for applications including chemical sensors and transducers, as well as integrated circuit components

A nanoenabled gravimetric chemical sensor prototype based on the large scale integration of single-stranded DNA (ss-DNA) decorated single-walled carbon nanotubes (SWNTs) as nanofunctionalization layer for aluminum nitride contour-mode resonant microelectromechanical (MEM) gravimetric sensors has been demonstrated. The capability of two distinct single strands of DNA bound to SWNTs to enhance differently the adsorption of volatile organic compounds such as dinitroluene (simulant for explosive vapor) and dymethyl-methylphosphonate (simulant for nerve agent sarin) has been verified experimentally. Different levels of sensitivity (17.3 and 28 KHz μm2/fg) due to separate frequencies of operation (287 and 450 MHz) on the same die have also been shown to prove the large dynamic range of sensitivity attainable with the sensor. The adsorption process in the ss-DNA decorated SWNTs does not occur in the bulk of the material, but solely involves the surface, which permits to achieve 50% recovery in less than 29 s.