Controlling Surface Chemistry on the Microscopic and Nanoscopic Scale through Photopatterned Self-Assembled Monolayers

ABSTRACT OF DISSERTATION Controlling Surface Chemistry on the Microscopic and Nanoscopic Scale through Photopatterned Self-Assembled Monolayers by Matthew J. Hynes Doctor of Philosophy in Chemistry Washington University in St. Louis, 2013 Professor Joshua A. Maurer, Chair The development of new patterning strategies for self-assembled monolayers: SAMs) using photolithography described here allows for the production of highly functional substrates for biological applications. Photolithography methods have been developed that utilize either high or low irradiation doses of 325 nm ultraviolet light. Utilizing high power led to the development of photo-induced monolayer desorption in which patterns were generated by thermally ablating glycol-terminated thiol monomers from gold substrates. A direct relationship between laser intensity and surface modulus was observed using scanning probe microscopy: SPM), which was expected since higher laser intensities should remove more glycol monomers from the surface exposing a greater percentage of the bare gold substrate. Conversely, an inverse relationship was determined between laser intensity and surface adhesion. Utilizing direct-write photolithography provided a facile means to generate complex protein patterns containing both gradients and punctate regions. Proteins adsorption to patterned substrates was quantified by surface plasmon resonance imaging: SPRi) and fit to a Boltzmann function, which allowed us to correlate laser intensity with protein adsorption. Thus, the concentration of the protein could be precisely controlled by adjusting the gray scale level in the 8-bit image, since this file is used to modulate the laser intensity during patterning. Moreover, adsorbed neutravidin was detected using a commercial biotin labeled anti-avidin antibody, which allowed for significant signal enhancement over background. The ability to produce complex protein patterns will contribute greatly to creating in vitro models that more accurately mimic an in vivo environment. In order to utilize low irradiation doses, two unique photoprotected thiol monomers were designed and synthesized. A nitroveratryl-protected carboxylic acid thiol monomer was synthesized, which when irradiated at 325 nm, resulted in cleavage of the nitroveratryl groups to produce free carboxylic acids on the surface. Direct-write photolithography provided a means to create complex patterns containing functional group gradients, which were observed directly using SPM. In addition, two different amine molecules were sequentially coupled on to a single substrate with spatial control. Coupling was visualized using Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry: MALDI TOF) imaging, which demonstrated the utility of this method for generating complex multi-molecule patterns. A new cyclopropenone monomer was also developed, which was used to site-selectively pattern azide terminated molecules. Exposure of the monomer to UV light under an argon atmosphere generated a strained cyclooctyne, which was used for Cu-free [3+2] cycloadditions with azide terminated molecules. Using direct-write photolithography, neutravidin gradients were produced by coupling an azido-biotin monomer to the patterned surfaces and a linear relationship, with an R2 value of 0.993, between laser intensity and protein coupling was found. These patterned surfaces were also visualized using traditional immunohistochemistry by coupling an azido-cRGD peptide to the surface and probing with a primary anti-RGD antibody followed by a fluorescently labeled secondary antibody. Moreover, patterned surfaces with cRGD could be used to control NIH/3T3 cell growth at various concentrations of functional monomer