By Nitesh Madaan, Aaron Terry, John Harb,
Robert C. Davis, and Matthew R. Linford (et al.)
Abstract: Self-assembly of organic thiols is the most common S H way to introduce functional groups onto gold surfaces. Although the gold-sulfur (Au-S) bond is moderately strong (similar to 45 kcal/mol), it is also prone to oxidation, which substantially weakens the Au-S interaction. In this work, we describe the creation of more robust molecular assemblies on gold. As a first step, a thiolated monolayer is prepared on gold with an a,alpha,omega-dithiol. Experiments are also reported for a mercaptosilane monolayer on silicon dioxide. An oligomer of polybutadiene (PBd) was then tethered to these surfaces using thiol-ene chemistry. Residual groups on the PBd are then reacted with thiols, including octadecanethiol (ODT), 1H,1H,2H,2H-perfluoroalkanethiol, and a thiol-terminated 25-mer of DNA. Little nonspecific adsorption of a non-thiolated DNA oligomer was observed. Surface characterization was performed with X-ray photoelectron spectroscopy (XPS), contact angle goniometry, time-of-flight secondary ion mass spectrometry (ToF-SIMS), and spectroscopic ellipsometry. A thiol-gold monolayer and an analogous assembly of the same thiol tethered to gold through PBd on a dithiol monolayer were both exposed to air and light for 2 weeks and then rinsed with water. The monolayer on gold was removed in this process, while the thiol in the assembly appeared unaffected.