Modulating Surface Density of Proteins via Caged Surfaces and Controlled Light Exposure

We demonstrate the possibility of tuning the degree of functionalization of a surface using photoactivatable chemistries and controlled light exposure. A photosensitive organosilane with a protected amine,terminal group and a tetraethyleneglycol spacer was synthesized. A o-nitrobenzyl cage was used as the photoremovable group to cage the amine functionality. Surfaces with phototunable amine densities were generated by controlled irradiation of silica substrates modified with the photosensitive anchor. Protein layers with different densities could be obtained by successive coupling and assembly steps. Protein surface concentrations were quantified by reflectance interference. Our results demonstrate that the protein density correlates with the photogenerated ligand density. The density control was proved over four coupling steps (biotin, SAv, (BT)tris-NTA, MBP, or GFP), indicating that the interactions between underlying layer and soluble targets are highly specific and the immobilized targets at the four levels maintain their full functionality. Protein micropattems with a gradient of protein density were also obtained.