Katayoun Zand

Fundamental Limits on the Mobility of Nanotube‐Based Semiconducting Inks

[∗] N. Rouhi , D. Jain , K. Zand Prof. P. J. Burke Integrated Nanosytems Research Facility Department of Electrical Engineering and Computer Science University of California-Irvine Irvine, CA, USA; pburke@uci.edu 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

Charging the Quantum Capacitance of Graphene with a Single Biological Ion Channel

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.

Nanofluidic platform for single mitochondria analysis using fluorescence microscopy.

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 Ca(2+) 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.

All-semiconducting nanotube devices for RF and microwave applications

Purified, all-semiconducting nanotubes offer great promise for a variety of applications in RF and microwave electronics. In this work, we present device performance of thin-film transistors fabricated using a spin-coating method that is economical and lends itself to mass manufacturing of nanotube electronics.

Resistive flow sensing of vital mitochondria with nanoelectrodes

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.

Fluorescence Analysis of Single Mitochondria with Nanofluidic Channels

Single mitochondrial assays are uncovering a new level of biological heterogeneity, holding promises for a better understanding of molecular respiration and mitochondria-related diseases. Here, we present a nanoscale approach to trapping single mitochondria in fluidic channels for fluorescence microscopy. We fabricate the nanofluidic channels in polydimethylsiloxane and bond them onto a glass slide, creating a highly reproducible device that can be connected to external pumps and mounted to a microscope. Having a unique nanoscale cross section, our channels can trap single mitochondria from a purified mitochondrial preparation flown across. Compared with the traditional fluorescence method to monitor single mitochondrial membrane potential with glass slides and open fluidic chambers, our nanofluidic channels reduce background fluorescence, enhance focus, and allow ease in experimental buffer exchanges. Hence, our channels offer researchers a new effective platform to test their hypotheses on single mitochondria.

Semiconducting-enriched printed carbon nanotube mat used for fabrication of thin film transistors

Semiconducting nanotubes, theoretically, offer great promise for a variety of applications in RF and microwave electronics. In this work, we present device performance of thin-film transistors fabricated using a spin-coating purified all-semiconducting nanotubes that is economical and lends itself to mass manufacturing of nanotube electronics.