Controlled Formation of Thiol and Disulfide Interfaces

The work reported herein describes the controlled creation of uniform thiol-functionalized siloxane-anchored self-assembled monolayers (SAMs) and their selective transformation into intramonolayer (bridging) disulfides. These disulfides provide for the efficient immobilization of (bio)­molecules bearing pendant thiols or disulfides, with no need for added oxidant. The unambiguous development of this surface chemistry required analytical methods that distinguish thiol and disulfide moieties on a surface. Physical properties such as wetting and monolayer thickness do not suffice nor do routine spectroscopic techniques (e.g., XPS, IR). Therefore, a method for distinguishing and quantifying thiol and disulfide surface functionality on a monolayer array based on the reaction with 2,4-dinitrofluorobenzene (DNFB, Sanger’s reagent) is reported. DNFB readily reacts with thiol-SAMs (but not with disulfides) to form stable derivatives with distinctive IR, UV, and XPS signatures. Finally, the thiol–disulfide chemistry is applied to thiol-functionalized hybrid silica nanoparticles. These high-surface-area nanoparticles provide solid supports heavily loaded with thiol groups whose chemistry is also reported herein