Affinity‐Based Protein Surface Pattern Formation by Ligand Self‐Selection from Mixed Protein Solutions

Abstract Photolithographically prepared surface patterns of two affinity ligands (biotin and chloroalkane) specific for two proteins (streptavidin and HaloTag, respectively) are used to spontaneously form high‐fidelity surface patterns of the two proteins from their mixed solution. High affinity protein‐surface self‐selection onto patterned ligands on surfaces exhibiting low non‐specific adsorption rapidly yields the patterned protein surfaces. Fluorescence images after protein immobilization show high specificity of the target proteins to their respective surface patterned ligands. Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) imaging further supports the chemical specificity of streptavidin and HaloTag for their surface patterned ligands from mixed protein solutions. However, ToF‐SIMS did detect some non‐specific adsorption of bovine serum albumin, a masking protein present in excess in the adsorbing solutions, on the patterned surfaces. Protein amino acid composition, surface coverage, density, and orientation are important parameters that determine the relative ToF‐SIMS fragmentation pattern yields. ToF‐SIMS amino acid‐derived ion fragment yields summed to produce surface images can reliably determine which patterned surface regions contain bound proteins, but do not readily discriminate between different co‐planar protein regions. Principal component analysis (PCA) of these ToF‐SIMS data, however, improves discrimination of ions specific to each protein, facilitating surface protein pattern identification and image contrast.