Carbon-nanotube-based semiconducting inks offer great promise for a variety of applications including fl exible, transparent, and printed electronics and optics. A critical drawback of such inks has been the presence of metallic nanotubes, which causes high-mobility inks to suffer from poor on/off ratios, preventing their applications in a wide variety of commercial settings. Here, we report a comprehensive study of the relationship between mobility, density, and on/off ratios of solution-based, deposited semiconducting nanotube ink used as the channel in fi eld effect transistors. A comprehensive spectrum of the density starting from less than 10 tubes μ m − 2 to the high end of more than 100 tubes μ m − 2 have been investigated. These studies indicate a quantitative trend of decreasing on/off ratio with increasing density and mobility, starting with mobilities over 90 cm 2 V − 1 s − 1 (approaching that of p-type Si MOSFETs) but with on/off ratios ∼ 10, and ending with on/off ratios > 10 5 (appropriate for modern digital integrated circuits), but with mobilities ∼ 1 cm 2 V − 1 s − 1 . These studies provide the fi rst important roadmap for the tradeoffs between mobility and on-off ratio in nanotube based semiconducting inks.Single-walled carbon nanotube (SWNT) based semiconducting inks may have a wide variety of applications in printed electronics (such as inkjet printing, [ 1 ] role to role gravure, [ 2 ] and pad/screen printings [ 3 ] ) as well as offering the possibility of heterogeneous integration of different semiconductor technologies such as Si CMOS, III-V, and optical display technologies. Recent progress in purifi cation techniques [ 4 ] has lead to the prospect of all-semiconducting SWNT inks for unsurpassed performance in printed circuits.In general, it is known that the mobility of individual, pristine semiconducting nanotubes can be up to 10 000 cm 2 V − 1 s − 1 . [ 5 ] However, mobilities for random networks of carbon nanotubes has hovered until recently around the 1 cm 2 V − 1 s − 1 limit. [ 6 ] What sets the mobility of a random network of semiconducting nanotubes in relationship to individual nanotubes? Can the mobility be increased by increasing the density? How does this affect the on/off ratio and what are the physical processes that set limits on this scaling?The most obvious reason that networks have lower mobilties than individual nantoubes is that tube-tube crossings limit the current fl ow from source to drain if the channel length is longer than the nanotube length. Increasing the network density can increase the current (and hence potentially the mobility).However, the complexity of such a system, coupled with the presence of metallic nanotubes that can short-circuit the device if the density exceeds the percolation threshold, means that there is no general theory that explains quantitatively the relationship between mobility, density, and on/off ratio, so that phenomenological experimental approaches are necessary for progress in the fi eld.Although solution-based processing technique...

The interaction of cell and organelle membranes (lipid bilayers) with nanoelectronics can enable new technologies to sense and measure electrophysiology in qualitatively new ways. To date, a variety of sensing devices have been demonstrated to measure membrane currents through macroscopic numbers of ion channels. However, nanoelectronic based sensing of single ion channel currents has been a challenge. Here, we report graphene-based field-effect transistors combined with supported lipid bilayers as a platform for measuring, for the first time, individual ion channel activity. We show that the supported lipid bilayers uniformly coat the single layer graphene surface, acting as a biomimetic barrier that insulates (both electrically and chemically) the graphene from the electrolyte environment. Upon introduction of pore-forming membrane proteins such as alamethicin and gramicidin A, current pulses are observed through the lipid bilayers from the graphene to the electrolyte, which charge the quantum capacitance of the graphene. This approach combines nanotechnology with electrophysiology to demonstrate qualitatively new ways of measuring ion channel currents.

The magnitude of the optical sheet conductance of single-layer graphene is universal, and equal to e 2 /4ħ (where 2πħ = h (the Planck constant)). As the optical frequency decreases, the conductivity decreases. However, at some frequency in the THz range, the conductivity increases again, eventually reaching the DC value, where the magnitude of the DC sheet conductance generally displays a sample-and doping-dependent value between ~e 2 /h and 100 e 2 /h. Thus, the THz range is predicted to be a non-trivial region of the spectrum for electron transport in graphene, and may have interesting technological applications. In this paper, we present the first frequency domain measurements of the absolute value of multilayer graphene (MLG) and single-layer graphene (SLG) sheet conductivity and transparency from DC to 1 THz, and establish a firm foundation for future THz applications of graphene.

Using nanofluidic channels in PDMS of cross section 500 nm × 2 μm, we demonstrate the trapping and interrogation of individual, isolated mitochondria. Fluorescence labeling demonstrates the immobilization of mitochondria at discrete locations along the channel. Interrogation of mitochondrial membrane potential with different potential sensitive dyes (JC-1 and TMRM) indicates the trapped mitochondria are vital in the respiration buffer. Fluctuations of the membrane potential can be observed at the single mitochondrial level. A variety of chemical challenges can be delivered to each individual mitochondrion in the nanofluidic system. As sample demonstrations, increases in the membrane potential are seen upon introduction of OXPHOS substrates into the nanofluidic channel. Introduction of Ca2+ into the nanochannels induces mitochondrial membrane permeabilization (MMP), leading to depolarization, observed at the single mitochondrial level. A variety of applications in cancer biology, stem cell biology, apoptosis studies, and high throughput functional metabolomics studies can be envisioned using this technology.

We report label-free detection of single mitochondria with high sensitivity using nanoelectrodes. Measurements of the conductance of carbon nanotube transistors show discrete changes of conductance as individual mitochondria flow over the nanoelectrodes in a microfluidic channel. Altering the bioenergetic state of the mitochondria by adding metabolites to the flow buffer induces changes in the mitochondrial membrane potential detected by the nanoelectrodes. During the time when mitochondria are transiently passing over the nanoelectrodes, this (nano) technology is sensitive to fluctuations of the mitochondrial membrane potential with a resolution of 10mV with temporal resolution of order milliseconds. Fluorescence based assays (in ideal, photon shot noise limited setups) are shown to be an order of magnitude less sensitive than this nano-electronic measurement technology. This opens a new window into the dynamics of an organelle critical to cellular function and fate.