James F. Klemic

Label-free immunodetection with CMOS-compatible semiconducting nanowires

Semiconducting nanowires have the potential to function as highly sensitive and selective sensors for the label-free detection of low concentrations of pathogenic microorganisms. Successful solution-phase nanowire sensing has been demonstrated for ions, small molecules, proteins, DNA and viruses; however, ‘bottom-up’ nanowires (or similarly configured carbon nanotubes) used for these demonstrations require hybrid fabrication schemes, which result in severe integration issues that have hindered widespread application. Alternative ‘top-down’ fabrication methods of nanowire-like devices produce disappointing performance because of process-induced material and device degradation. Here we report an approach that uses complementary metal oxide semiconductor (CMOS) field effect transistor compatible technology and hence demonstrate the specific label-free detection of below 100 femtomolar concentrations of antibodies as well as real-time monitoring of the cellular immune response. This approach eliminates the need for hybrid methods and enables system-scale integration of these sensors with signal processing and information systems. Additionally, the ability to monitor antibody binding and sense the cellular immune response in real time with readily available technology should facilitate widespread diagnostic applications.

Analysis of yeast protein kinases using protein chips

We have developed a novel protein chip technology that allows the high-throughput analysis of biochemical activities, and used this approach to analyse nearly all of the protein kinases from Saccharomyces cerevisiae. Protein chips are disposable arrays of microwells in silicone elastomer sheets placed on top of microscope slides. The high density and small size of the wells allows for high-throughput batch processing and simultaneous analysis of many individual samples. Only small amounts of protein are required. Of 122 known and predicted yeast protein kinases, 119 were overexpressed and analysed using 17 different substrates and protein chips. We found many novel activities and that a large number of protein kinases are capable of phosphorylating tyrosine. The tyrosine phosphorylating enzymes often share common amino acid residues that lie near the catalytic region. Thus, our study identified a number of novel features of protein kinases and demonstrates that protein chip technology is useful for high-throughput screening of protein biochemical activity.

An air-molding technique for fabricating PDMS planar patch-clamp electrodes

We present a new technique for fabricating planar patch electrodes in the laboratory. Planar electrodes are micromolded using a micron-sized stream of air to define an aperture in the silicone elastomer, polydimethylsiloxane (PDMS). We have previously demonstrated that planar PDMS electrodes make excellent patch electrodes after surface modification. We demonstrate single-channel measurements of the rSlo channel in Xenopus oocytes and whole-cell measurements in CHO and RBL mammalian cell lines, using planar PDMS electrodes.

Growth and characterization of aligned carbon nanotubes from patterned nickel nanodots and uniform thin films

Microstructures of well-aligned multiwall carbon nanotubes grown on patterned nickel nanodots and uniform thin films by plasma-enhanced chemical vapor deposition have been studied by electron microscopy. It was found that growth of carbon nanotubes on patterned nickel nanodots and uniform thin films is different. During growth of carbon nanotubes, a nickel particle sits at the tip of each nanotube, and its [220] is preferentially oriented along the plasma direction, which can be explained by a channeling effect of ions coming into nickel particles in plasma. The alignment of nanotubes is induced by the electrical field direction relative to substrate surface.

Molecular wires, switches, and memories.

Abstract: Design and measurements of molecular wires, switches, and memories offer an increased device capability with reduced elements. We report: Measurements on through‐bond electronic transport properties of nanoscale metal‐1,4‐phenylene diisocyanide‐metal junctions are reported, where nonohmic thermionic emission is the dominant process, with isocyanide‐Pd showing the lowest thermionic barrier of 0.22 eV; robust and large reversible switching behavior in an electronic device that utilizes molecules containing redox centers as the active component, exhibiting negative differential resistance (NDR) and large on‐off peak‐to‐valley ratio (PVR) are realized; erasable storage of higher conductivity states in these redox‐center‐containing molecular devices are observed; and a two‐terminal electronically programmable and erasable molecular memory cell with long bit retention time is demonstrated.

Methods for fabricating Ohmic contacts to nanowires and nanotubes

A comparison of methods to create Ohmic contacts to semiconductor nanowires (NWs) and carbon nanotubes (CNTs) is presented. A Ni∕Au lift-off metallization was used to contact GaN and In2O3 NWs and CNTs using electron-beam (e-beam) or optical lithography. In order to render the metal-semiconductor contacts Ohmic, e-beam-processed devices are found to require a postfabrication, high-temperature anneal, whereas the use of an oxygen plasma prior to metallization is found to be crucial for devices defined by optical lithography.