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.