Label-Free Screening Small-Molecule Compound Libraries for Protein-Ligands Using a High-Throughput Optical Scanning Microscope

We describe a new oblique-incidence reflectivity difference (OI-RD) scanning microscope for high-throughput screening, in microarray format on functionalized glass slides, small-molecule compound libraries for protein ligands. The microscope employs a combination of scan mirror for y-scan and single-axis translation stage for x-scan. For a printed microarray with over 10,000 features, each of 100 μm in diameter and distinct small molecule targets, we can acquire an end-point image of the microarray in 90 minutes with pixel resolution of 20 μm ×20 μm. The microscope is also capable of measuring binding kinetics of over 10,000 protein-ligand reactions simultaneously. We also describe a number of strategies for immobilizing small molecule compounds on functionalized glass slides: (1) conjugating the compounds (through a chemically inert linker) with a lysine residue so that the primary amine on the lysine serves as the anchor to epoxy-functionalized glass surface; (2) conjugating the compounds (through a linker) with a biotin residue so that the biotin serves as the anchor to streptavidin-functionalized glass surface; (3) immobilizing small molecule compounds without modification on isocyanate-functionalized glass surface through non-specific reaction of nucleophilic molecular motifs on most bioactive compounds with isocyanate groups. We present preliminary measurements of protein-small molecule binding reactions using the new microscope and the surface immobilization strategies.