Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Zhang, Dongmao

Committee Member

Wipf, David

Committee Member

Foster, Stephen C.

Committee Member

Saebø, Svein

Committee Member

Mlsna, Todd E.

Date of Degree

8-15-2014

Document Type

Dissertation - Open Access

Major

Chemistry

Degree Name

Doctor of Philosophy

College

College of Arts and Sciences

Department

Department of Chemistry

Abstract

Self-assembly of organothiols (OTs) and thiolated biomolecules onto gold nanoparticle (AuNP) surfaces remains one of the most intense areas of nanoscience research and understanding molecular interfacial phenomena is crucial. Investigation of OT adsorption onto AuNPs, including OT structure and orientation on nanoparticle surfaces, is of fundamental importance in understanding the structure and function relationship of functionalized nanoparticles. Despite the great importance of the interfacial interaction of AuNPs, the exact mechanism of OT interactions with AuNPs has remained unclear and quantitative investigation of OT adsorption has been very limited. The research reported here focused on developing a fundamental and quantitative understanding of OT interactions with AuNPs in water. In studies of OT interactions with AuNPs in water, we found that the OTs form an adsorbed monolayer on AuNPs by releasing the sulfur-bound hydrogen as a proton and acidifying the ligand binding solution. The pH measurements suggest that there is a substantial fraction (up to 45%) of the protons derived from the surface adsorbed OTs retained close to the gold surface, presumably as the counter-ion to the negatively- charged, thiolate-covered AuNPs. Charge-transfer between the surfacesorbed thiolate and the AuNPs is demonstrated by the quenching of the OT UV-vis absorption when the OTs are adsorbed onto the AuNPs. Using a combination of surface enhanced Raman spectroscopy (SERS), density function calculations, and normal Raman spectroscopy, the pH dependence of mercaptobenzimadazole (MBI) adsorption onto AuNPs was systematically studied. By using the ratiometric SERS ligand quantification technique, MBI adsorption isotherms were constructed at three different pHs (1.4, 7.9, and 12.5). The Langmuir isotherms indicate that MBI thione has a higher saturation packing density (~­631 pmol/cm2) than MBI thiolate (~­568 pmol/cm2), but its binding constant (2.14 x 106 M-1) is about five times smaller than the latter (10.12 x 106 M-1). The work described in this dissertation provides a series of new insights into AuNP-OT interaction, and structure and properties of OTs on AuNPs.

URI

https://hdl.handle.net/11668/20740

Comments

surface enhanced Raman spectroscopy||Charge-transfer||organothiols||Self-assembly||gold nanoparticles

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