Nicole, Jessica, Tonya, and Dewi in SF Cable Car

National Conference of Undergraduate Research -2007 April 12-14 Dominican University, CA.

Investigation of gold colloidal

nanoparticles embedded in a

silica-based sol-gel

T. Gilbert and K. Yokoyama

Gold colloidal nanoparticles ranging

from 5 nm to 100 nm were embedded

in a silica based sol-gel matrix and

studied spectroscopically. In our

study, the TEOS was mixed with the

gold colloid and sodium tetraborate

buffer (pH 9.18) in a volume ratio of 2:1:2.

Among all tested buffers, pH 6-12, only sodium tetraborate buffer preserved gold

colloidal particles in the sol-gel by demonstrating the same spectroscopic

character as that observed by gold colloid n aqueous solutions at neutral pH, with

a SPR (Surface Plasmon Resonance) peak at around 530 nm.

Through immersion in an acidic (0.1M HCl) solution, a

distinct color change, from red to blue was observed. However, only gold colloid

size of 50 nm embedded silica gel did not exhibit a complete color change. While

this observation suggests that the gel is permeable to acid, it exhibits a colloidal

size dependence for permeability of the acid. Since this size dependence does not

take place in the solution, the acid penetration must be restricted by the special

matching between gold colloids and the average cavity sizes.

At the Conference Site

At the SF Bay Area

At SF Downtown Area

K. Yokoyama

Conjugation of the Amyloid Beta protein on the surface of gold colloidal

nanoparticles.

J. MacCormac, N. Briglio, Dewi Sri Hartati and K. Yokoyama

Proteins immobilized at an interface are expected to behave differently from their 
counterparts in bulk solutions, and understanding the interactions of the proteins on 
the interface surface is crucial to designing a bio-composite device. Our particular 
interest is in conformational changes in Amyloid Beta protein solution (A-Beta) on 
the surface of gold colloidal nanoparticles. The conjugation of various sequences 
of the amino acids in A-Beta, A-Beta1-42, A-Beta1-40, A-Beta1-11, A-Beta12-28, and 
ABeta32-35, with gold colloidal suspension of 20 nm size was examined. 
Absorption spectroscopy was utilized to identify changes in the optical
property of the gold colloidal nanoparticles for a pH range of 2 to 10. Color
changes were seen for all tested sequences in this study at a higher pH than
bare gold colloid which shifts at approximately pH 3.09. All tested A-Beta
sequences exhibited color changes around pI of A-Beta1-40, c.a. pH 5.0,
except for A-Beta1-42 which constantly exhibited clear precipitants in all pH
levels lower than pH 7. The bonding between A-Beta and the gold colloidal
surface is speculated to be due to hydrophobic attraction between nonpolar
amino acids and the negatively charged lyophobic sol surface. Interestingly,
only A-Beta1-40-coated gold colloidal nanoparticles exhibited a reversible color
change as the pH was externally altered between pH 4 and 10. This
reversibility is an important implication of the observation of a reversible step
reported for the fibrillogenesis of the protein. It was interpreted that the reversible
process takes place when the hydrophilic A-Beta possesses a three dimensional
network containing both Beta sheets and alpha helices.