| AVS 54th International Symposium | |
| Applied Surface Science | Wednesday Sessions |
| Session AS-WeM |
| Session: | Chemical Imaging at High Spatial Resolution and Nanoscale Materials |
| Presenter: | S.D. Techane, University of Washington |
| Authors: | S.D. Techane, University of Washington L.J. Gamble, University of Washington D.G. Castner, University of Washington |
| Correspondent: | Click to Email |
Gold nanoparticles (AuNPs) are non-toxic and have a high percentage of surface atoms, which gives them special electronic properties and reactivities. Since these properties are dependent on the size, shape and surface chemistries of the AuNPs, one can vary these quantities to achieve desirable applications for AuNPs in biomedicine, microarray and biosensor fields. In this research, AuNPs of different diameters (14nm - 50nm) were synthesized with a citrate reduction method and later functionalized with various chain lengths (3, 6, 8, 11, and 16 carbon chain) of carboxyl terminated alkyl thiol by direct displacement of the citrate ions. To obtain a hydrophobic surface, functionalization with 1-dodecanethiol was tried using a two step functionalization method. The size, shape, and size distribution of the AuNPs were characterized with transmission electron microscopy (TEM) and ImageJ, where the distribution in terms of 3 σ ranged from 2.5 to 20nm, depending on the average diameter of the AuNPs. Surface chemistries of the self assembled monolayer (SAMs) of alkyl thiol were analyzed with X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry. Comparison between SAMs of 16-mercaptohexadecanoic acid (C/O = 8 and C/S = 16) on AuNPs and flat Au surface was done to verify the applicability of XPS data analysis method for curved nanoparticle surfaces. Surface atomic composition ratios: C/S (26 for AuNPs and 42 for flat Au), C/O (5 for AuNPs and 8 for flat Au), C/Au (1.7 for AuNPs and 1.2 for flat Au) exhibited some differences between the two surface types. These differences indicate the need to develop specific XPS data analysis methods to accurately represent the surface chemistries of curved nanoparticles surfaces. XPS results for the two-step functionalization method, which uses thioctic acid as an intermediate, showed 11% oxygen surface composition with 6% carboxyl carbon indicating incomplete displacement of the intermediate carboxyl thiol and a need for a better functionalization method to achieve hydrophobic surface. AuNPs with carboxyl terminated SAMs are being used to investigate adsorption thermodynamics of short chain peptides onto these surfaces. Protein assay, XPS, and NMR are being used to characterize the adsorbed peptides.