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Focus On Materials
Materials Day 2006 - Posters
Chemical- and Bio-Sensors
- B01 - Fabrication of Reproducible, High-Sensitivity SERS Substrates for Trace Chemical Detection
D. W. Dwight, M. C. Dixon, D. L. Allara, E. J. Basgall, D. B. Lysak, D. C. Swanson, S. Stewart, J. Demuth
Abstract: Surface Enhanced Raman Spectroscopy has the potential to be a very sensitive and selective technique to identify organic compounds. Thus, we have been developing methods to manufacture environmentally stable, sensitive and reproducible SERS substrates. Here we report results on five different methods to prepare gold SERS substrates: (1)De-alloying, (2) Electro-chemical roughening,(3)Sequential application of (1) and (2),(4)Nanofabrication, and (5)Glancing-Angle Deposition (GLAD). Spectral intensities of para-nitrobenzene thiol self-assembled monolayers (SAMs) deposited on the substrates were used to judge relative enhancement factors (EF). A provisional patent has been issued on the two-step process (#3), which produces EF = 107. In that system, conjectures about structure-property relationships are supported by the juxtaposition of the SERS response with surface analyses. Using Nanofabrication, arrays of 100-nm diameter gold posts at different spacings show an inverse power-law.
- B02 - Conformational Analyses of Engineered Green Fluorescent Protein
M. C. Demirel, M. Cetinkaya, A. Zeytun
Abstract: Green fluorescent protein (GFP) is an excellent candidate as a scaffold to develop an affinity binder. However, attempts to insert linkers or random peptides within GFP loop region have been unsuccessful and most insertions were either non- or weakly fluorescent. A computer-based modeling and bench-top experiments were combined to understand the fluorescence behavior of engineered GFP. Random peptides were inserted into individual loops of GFP. Amino acid sequences and fluorescence levels of clones (10-90% of parent GFP) from each loop were determined. Molecular simulations showed that some insertions cause large fluctuations in the loop region. Large vibrational motion at the loop region results water molecule to penetrate into the chromophore region and subsequently, fluorescence of GFP may be lost due to the collisional quenching. Our simulation strategy can be used to choose stable loop insertions for design purposes of GFP.
URL: http://www.esm.psu.edu/~mcd18
- B03 - Chemical Sensors based on Semiconducting Nanowires and Nanotubes
A. Gupta, Q. Xiong, P. C. Eklund
Abstract: Micron long semiconducting nanowires and single-walled carbon nanotubes are receiving considerable attention worldwide for fundamental science investigation and new nanotechnology. We synthesize and study many of these semiconductor nanowire systems and with diameters in the range 4-40 nm (e.g.,Si,Ge,GaAs,GaP,GaN,ZnS,etc.); we are involved in the synthesis and study of single-walled carbon nanotubes as well. These nanowires and nanotubes are quite crystalline and found to exhibit narrow line Raman spectra indicative of nearly perfect structures; they exhibit clear lattice fringes in HRTEM. Recently, we have learned how to "wire up" these nanowires using photo- and e-beam lithographic techniques and the Penn State Nanofab to make what we call "ChemFETs", or field effect transistors that can be used as chemical sensors. A change in the transconductance of the FET signals the chemical attachment of the analyte. Reversing the gate voltage has been reported to detach the analyte. Because of its extremely small size, the ChemFET is expected to be a very fast, and sensitive. The sensor selectivity is obtained through chemical functionalization of the tube wall. We present some preliminary results from our efforts in this area, and also on nanotube chemical sensors yielding a thermoelectric response.
- B05 - Nanoscale Protein Patterning using Self-Assembled Diblock Copolymers
N. Kumar, J. Hahm
Abstract: Novel methods for immobilizing proteins on surfaces have the potential to impact basic biological research as well as various biochip applications. Here, we demonstrate a unique method to pattern proteins with a nanometer periodicity on silicon oxide substrates using microphase-separated diblock copolymer thin films. We developed a straightforward and effective protein immobilization technique using the microphase-separated domains of polystyrene-block-polymethylmethacrylate to localize various model protein molecules such as bovine immunoglobulin G, fluorescein isothiocyanate conjugated anti-bovine immunoglobulin G, and protein G. This diblock copolymer-based, self-assembly approach represents a step forward for facile, nanometer-spaced protein immobilization with high areal density, and could provide a pathway to high-throughput proteomic arrays and biosensors.
