Kristine Obusek

 

Education

• BS, Virginia Tech

REU Project

My mentor was Molly Miller and my advisor was Dr. Anne Lazarides. My project aimed to investigate the aggregation characteristics of peptide functionalized gold nanoparticles in the presence of protein and salt in various concentrations. Through examining the optical properties of self-assembled nanostructures, I determined critical conditions to be applied to further in situ studies of aggregate structure. I evaluated the affinity of the peptides for functionalized particles or other particles using SPR studies, UV-Vis Spectrophotometry, and dynamic light scattering. I enjoyed my summer at Duke and learned a lot. The experiences I had further solidified my desire to pursue graduate studies.

Final Abstract

The purpose of this project was to determine the aggregation characteristics of peptide functionalized nanoparticles in the presence of protein and salt in various concentrations. By examining the optical properties of self-assembled nanostructures, critical conditions could be determined for further in situ studies of aggregate structure. Three peptides were used: a 17-amino acid cys-terminated peptide, a neutral hydrophilic pentapeptide (CTTNN) and a hydrophobic pentapeptide (CALNN). The 17-amino acid peptide was adsorbed to a thin gold film in preparation for surface plasmon resonance studies. The pentapeptides were used to functionalize gold nanoparticles prior to solution phase stability studies.

Three optical methods were used to characterize the affinity of the peptides for functionalized particles or other particles. First, SPR studies were used to evaluate the affinity of the 17-amino acid peptide for polystyrene spheres. Next, a UV-Vis Spectrophotometer was employed to monitor the state of assembly by tracking the intensity and wavelength of the gold nanoparticle plasmon band. Finally, dynamic light scattering was used to determine the hydrodynamic radius of certain systems.

In the SPR studies, the polystyrene spheres had a surprising effect by reducing the effective dielectric constant of the layer of material at the surface of the thin, gold, SPR substrate. It is likely that the peptide layer collapses onto the gold surface and upon binding of the polystyrene spheres, the peptide extends, reducing the average refractive index of the system. Through extinction measurements, the stability point, the salt and protein concentrations at which aggregation occurs, were determined for various systems. At 60-mM NaCl, the salt in solution screened the citrate stabilized gold nanoparticles; causing them to form aggregates and precipitate from solution. With the addition of as little as 1-mg/L alginate, the particles do not precipitate. Therefore, alginate is assumed to protect the nanoparticles in certain conditions. In line with the literature, the peptide functionalized particles were stable up to at least 300-mM NaCl without any alginate. When alginate was added to the solution, the CTTNN functionalized particles produced a broad and polydispersed spectra while the CALNN functionalized particles produced a bimodal spectra.

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