The efficient and bioorthogonal chemical ligation reaction between potassium acyltrifluoroborates (KATs) and hydroxylamines (HAs) was used for the surface functionalization
of a self-assembled monolayer (SAM) with biomolecules. An alkane thioether molecule with one terminal KAT group (S-KAT) was synthesized and adsorbed onto a gold surface, placing a KAT
group on the top of the monolayer (KAT-SAM). As an initial test case, an aqueous solution of a hydroxylamine (HA) derivative of PEG (HA-PEG) was added to this KAT-SAM at room temperature to perform the surface KAT ligation. Quartz crystal microbalance with dissipation (QCM-D) monitoring confirmed the rapid attachment of the PEG moiety onto the SAM.
The covalent conjugation of PEG by amide-bond formation was established by complementary surface characterization methods including contact angle, ellipsometry, and X-ray photoelectron
spectroscopy (XPS). To test the applicability of this surface KAT ligation for the attachment of biomolecules to the surfaces, this KAT-SAM was subjected to the reaction with HA derivative of
protein. A HA-derivatized green fluorescent protein (HA-GFP) was added in dilute concentrations to the KAT-SAM under aqueous conditions and rapid protein attachment was observed in real-time by QCM. Despite the fact that such biomolecules have a variety of unprotected functional groups within their structures, the surface KAT reaction proceeded efficiently in a selective manner. Our results clearly demonstrate the versatile applicability of the KAT ligation for the covalent attachment of a variety of biomolecules onto surfaces under dilute and biocompatible
conditions to form stable, natural amide bonds.