Elissa H. Williams

Helical cationic antimicrobial peptide length and its impact on membrane disruption

Cationic antimicrobial peptides (CAMPs) are important elements of innate immunity in higher organisms, representing an ancient defense mechanism against pathogenic bacteria. These peptides exhibit broad-spectrum antimicrobial activities, utilizing mechanisms that involve targeting bacterial membranes. Recently, a 34-residue CAMP (NA-CATH) was identified in cDNA from the venom gland of the Chinese cobra (Naja atra). A semi-conserved 11-residue pattern observed in the NA-CATH sequence provided the basis for generating an 11-residue truncated peptide, ATRA-1A, and its corresponding D-peptide isomer. While the antimicrobial and biophysical properties of the ATRA-1A stereoisomers have been investigated, their modes of action remain unclear. More broadly, mechanistic differences that can arise when investigating minimal antimicrobial units within larger naturally occurring CAMPs have not been rigorously explored. Therefore, the studies reported here are focused on this question and the interactions of full-length NA-CATH and the truncated ATRA-1A isomers with bacterial membranes. The results of these studies indicate that in engineering the ATRA-1A isomers, the associated change in peptide length and charge dramatically impacts not only their antimicrobial effectiveness, but also the mechanism of action they employ relative to that of the full-length parent peptide NA-CATH. These insights are relevant to future efforts to develop shorter versions of larger naturally occurring CAMPs for potential therapeutic applications.

Analytical Electron Microscopy of Semiconductor Nanowire Functional Materials and Devices for Energy Applications

Functionalized individual semiconductor nanowires (SNWs) and 3D SNW arrays attract a continuously growing interest for applications in optoelectronics, sensing, and energy storage. High-resolution field-emission analytical (scanning) transmission electron microscopy ((S)TEM) enables critical insights into the morphology, crystalline and electronic structures and chemical composition of single-crystalline high-aspect-ratio SNWs as prospective building blocks suitable for both a large scale-up synthesis and fabrication. Furthermore, SNW-based lab-on-a-chip devices may allow direct correlation between functional properties tailored for specific performance and the heterostructure morphology and atomic arrangement of the nanoscale structure being analyzed in various (S)TEM modes.

Biofunctionalization of Si nanowires using a solution based technique

Here we present a solution based functionalization technique for streptavidin (SA) protein conjugation to silicon nanowires (Si NWs). Si NWs, with a diameter of 110 nm to 130 nm and a length of 5 μm to 10 μm, were functionalized with 3-aminopropyltriethoxysilane (APTES) followed by biotin for the selective attachment of SA. High-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM) showed that the Si NWs were conformally coated with 20 nm to 30 nm thick APTES, biotin, and SA layers upon functionalization. Successful attachment of each bio/organic layer was confirmed by X-ray photoelectron spectroscopy (XPS) and fluorescence microscopy. Fluorescence microscopy also demonstrated that there was an undesirable non-specific binding of the SA protein as well as a control protein, bovine serum albumin (BSA), to the APTES-coated Si NWs. However, inhibition of BSA binding and enhancement of SA binding were achieved following the biotinylation step. The biofunctionalized Si NWs show potential as label-free biosensing platforms for the specific and selective detection of biomolecules.

Immobilization of proteins on semiconductor nanowires for biosensor development

Silicon (Si), silicon carbide (SiC), gallium nitride (GaN), zinc oxide (ZnO) and other semiconductor nanowires (NWs) show great promise as sensing elements for the electrical detection of biomolecules [1–3]. In order to enable chemiresistor-type NW devices that utilize direct electronic sensing of biomolecules, one must first develop an analyte-specific functionalization of the nanowire surface and deduce mechanisms by which the functional and analyte molecules bind to the surface. Here we present a solution based bioconjugation technique for the attachment of protein molecules to the NW surfaces. Example of selective immobilization of streptavidin on biotinylated Si, SiC, and GaN NWs was studied and verified by a suite of surface characterization techniques.