No abstract

Microarrays containing up to three different proteins were fabricated by microcontact printing (µCP) techniques and tested as a detection system for specific antibodies. After fabrication, immunoassays were successfully performed using the patterned protein microarrays. The developed immunoassays were characterized by fluorescence microscopy and scanning probe microscopy. The characterization revealed the quality of the protein deposition and indicated a high degree of selectivity for the targeted antigenantibody interactions. The results of this study suggest that µCP is an inexpensive and effective way to fabricate biologically active substrates that can be of use for multiple reagentless immunosensor applications.

Oxidation of exfoliated gallium selenide (GaSe) is investigated through Raman, photoluminescence, Auger, and X-ray photoelectron spectroscopies. Photoluminescence and Raman intensity reductions associated with spectral features of GaSe are shown to coincide with the emergence of signatures emanating from the by-products of the oxidation reaction, namely, Ga2Se3 and amorphous Se. Photoinduced oxidation is initiated over a portion of a flake highlighting the potential for laser based patterning of two-dimensional heterostructures via selective oxidation.

The electrostatic potential produced by a variety of self-assembled monolayers on Au(111) is measured using scanning probe techniques. The molecules chosen for this study contain thiol-terminated end groups and π-conjugated orbitals, making them suitable for molecular electronics applications. We have measured the surface potential of molecules having a symmetric structure and compared these results to those obtained from similar nonsymmetric molecules. The measured potential for nonsymmetric molecules scales with the dipole moment of the molecule comprising the monolayer. For symmetric molecules, the measured surface potential is essentially the same as the substrate. This result suggests that the dipole moment formed by the Au-S bond makes a small contribution to the measured surface potential. The dipole moment of a strong electron accepting molecule was intentionally modified by reaction with a strong electron acceptor. In this case, the surface potential produced by the self-assembled monolayer was found to change polarity after the formation of the charge-transfer complex.

The nonlinear dynamics of an atomic force microcantilever (AFM) with an attached multi-walled carbon nanotube (MWCNT) tip is investigated experimentally and theoretically. We present the experimental nonlinear frequency response of a MWCNT tipped microcantilever in the tapping mode. Several unusual features in the response distinguish it from those traditionally observed for conventional tips. The MWCNT tipped AFM probe is apparently immune to conventional imaging instabilities related to the coexistence of attractive and repulsive tapping regimes. A theoretical interaction model for the system using an Euler elastica MWCNT model is developed and found to predict several unusual features of the measured nonlinear response.

No abstract

Optical lithography based on microfabrication techniques was employed to fabricate one-dimensional nanogaps with micrometre edge lengths in silicon. These one-dimensional nanogaps served as a platform on which organic/nanoparticle films were assembled. Characterization of the gaps was performed with high-resolution TEM, SEM, and electrical measurements. Novel self-assembling attachment chemistry, based on the interaction of silicon with a diazonium salt, was used to iteratively build a multi-layer nanoparticle film across a 7 nm gap. By using nanoparticles capped with an easily displaced ligand, a variable conductive path was created across the 1D nanogap. Electrical measurements of the gap showed a dramatic change in the I(V) characteristics after assembly of the nanoparticle film.

Patterned microarrays of antibodies were fabricated and tested for their ability to bind targeted bacteria. These arrays were used in a series of bacterial immunoassays to detect E. coli 0157:H7 and Renibacterium salmoninarum (RS). Microarrays were fabricated using microcontact printing (µCP) and characterized using scanning probe microscopy (SPM). The high-resolution SPM imaging showed that targeted bacteria had a higher binding selectivity to complementary antibody patterns than to unfunctionalized regions of the substrate. Additional studies indicated a significant reduction in binding of bacteria when the microarrays were exposed to nonspecific bacteria. These studies demonstrate how protein microarrays could be developed into useful platforms for sensing microorganisms.