Label-free optical detection of small-molecule compound microarrays immobilized on solid support using macromolecular scaffolds and subsequent protein binding reactions

Small-molecule microarrays composed of tens of thousands of distinct synthetic molecules, natural products, and their combinations/modifications provide a high-throughput platform for studying protein-ligand interactions. Immobilization of small molecule compounds on solid supports remains a challenge as widely varied small molecules generally lack unique chemical groups that readily react with singly or even multiply functionalized solid support. We explored two strategies for immobilizing small molecule compounds on epoxy-functionalized glass surface using primary-aminecontaining macromolecular scaffolds: bovine serum albumin (BSA) and amine-modified poly-vinyl alcohol (PVA). Small molecules with N-hydroxysuccinimide (NHS) groups were conjugated to BSA or amine-modified PVA. Smallmolecule-BSA conjugates and small-molecule-PVA conjugates were subsequently immobilized on epoxy-functionalized glass slides through amine-epoxy reactions. Using an oblique-incidence reflectivity difference (OI-RD) scanning microscope as a label-free detector, we performed a comparative study of the effectiveness of BSA and PVA as macromolecular scaffolds for anchoring small molecule compounds in terms of conjugation efficiency, surface immobilization efficiency, effect of the scaffold on end-point and kinetics of subsequent binding reactions with protein probes.