| AVS 59th Annual International Symposium and Exhibition | |
| Applied Surface Science | Tuesday Sessions |
| Session AS+BI-TuA |
| Session: | Surface Analysis of Materials Using Vibrational Techniques (2:00-3:20 pm)/ Multi-Technique Analysis (4:00-6:00 pm) |
| Presenter: | A. Rafati, University of Washington |
| Authors: | A. Rafati, University of Washington D.G. Castner, University of Washington |
| Correspondent: | Click to Email |
Extensive surface analysis of available gold nanoparticles (AuNPs) is crucial to understand how their production and functionalization affects their final properties. This information is needed to improve the performance of engineered nanoparticles in research and commercial applications. Ethylene glycol functionality is desirable owing to the benefits such as the reduction of protein adhesion which if not properly controlled can lead to activation of an immune response and/or clearance.
In this work AuNPs ~14nm and ~40nm in diameter are synthesized and functionalized with 1-undacanethiol (HS-CH2)11 terminated with either (OEG)4OH or (OEG)4CH3. The AuNPs were characterized with transmission electron microscopy (TEM), time of flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and low energy ion scattering (LEIS). These studies provided both qualitative and quantitative information about the functionalization of the AuNPs with an OEG containing monolayer.
TEM showed the 14nm AuNPs had a narrower size distribution and more spherical shape than the 40nm AuNPs. ToF-SIMS clearly differentiates the two SAMs based on the C3H7O+ peak attributed to the CH3 terminated SAM. Angle-resolved XPS high-resolution C1s spectra from flat gold samples at photoelectron take-off angles of 0˚, 55˚ and 75˚ from the surface normal shows an increase in the ether component and reduction in CH with an increase in take-off angle. The changes in these values are comparable for both SAMs. This illustrates the increased presence of ethylene glycol monomers in the outer surface region and shows little difference between the two types of terminal functional groups. The 40 nm AuNPs show a sightly greater surface OEG concentration than 14 nm AuNPs, possibly indicating a more vertically oriented SAM on the 40 nm AuNPs. FTIR indicates similar crystalline CH2 backbones for all samples, however it appears the structure of OEG head groups are less crystalline on the 14nm AuNPs. This likely results in thicker and/or higher density SAMs on the 40 nm AuNPs compared to the 14nm AuNPs. This is consistent with the nearly identical XPS determined surface elemental compositions determined for OEG SAMs on the two different sized AuNPs. This is contrary to previously XPS results observed for AuNPs functionalized with COOH SAMs [1].
1. Techane, S.D., L.J. Gamble, and D.G. Castner, Multi-technique Characterization of Self-assembled Carboxylic Acid Terminated Alkanethiol Monolayers on Nanoparticle and Flat Gold Surfaces. J Phys Chem C Nanomater Interfaces, 2011. 115(19): p. 9432-9441.