Controlling the morphology of Photosystem I assembly on thiol-activated Au substrates

Morphological variations of Photosystem I (PS I) assembly on hydroxyl-terminated alkanethiolate self-assembled monolayer (SAM)/Au substrates with various deposition techniques is presented. Our studies indicate that deposition conditions such as PS I concentration and driving force play a central role in determining organization of immobilized PS I on thiol-activated Au surfaces. Specifically, atomic force microscopy (AFM) and ellipsometry analyses indicate that gravity-driven deposition from concentrated PS I solutions results in a large number of columnar PS I aggregates, which assemble perpendicular to the Au surface. PS I deposition yields much more uniform layers when deposited at lower concentrations, suggesting preassembly of the aggregate formation in the solution phase. Moreover, in electric field assisted deposition at high field strengths, columnar self-assembly is largely prevented, thereby allowing a uniform, monolayer-like deposition even at very high PS I concentrations. In situ dynamic light scattering (DLS) studies of solution-phase aggregation dynamics of PS I suspensions in both the presence and absence of an applied electric field support these observations and clearly demonstrate that the externally imposed electric field effectively fragments large PS I aggregates in the solution phase, thereby permitting a uniform deposition of PS I trimers on SAM/Au substrates.