Developing Hybrid Material Interfaces for Microcontact Printing and Molecular Recognition

Monomolecular hybrid organic-inorganic interfaces provide opportunities for applications in fields ranging from sensors to electronics. In this thesis, we report our efforts towards (1) developing a universal method for the modification and soft-lithographic patterning of inorganic materials with stable and functional organic systems; and (2) apply our surface fabrication techniques to advance our understanding of molecular recognition force microscopy.

We report the development of a novel bi-layered molecular system that, in conjunction with an inkless catalytic microcontact printing technique, can be used to accurately replicate micro- and nano-scale patterns of chemically distinctive reactive functionalities on virtually any surface, including inorganic semiconductors. Catalytic printing alleviates problems associated with ink diffusion and enables high resolution replication of patterns through specific chemical or biochemical reaction between a functional surface and a stamp-immobilized catalyst. The methodology provides precise control over shape and size of pattern features and provides access to chemically discriminated patterns that can be further functionalized with organic and biological molecules. We demonstrate catalytic printing on both oxide-free silicon and germanium, substrates that do not react readily with organic molecules and have not heretofore been patterned through traditional approaches. Our approach we relies on a stable highly ordered bilayered molecular system that both affords complete protection of all surface-exposed inorganic atoms with stable covalent bonds and supports covalent immobilization of a reactive overlayer, yielding stability and functionality to the surface. A catalytic acidic stamp was used to achieve pattern-specific hydrolysis of N-hydroxysuccinimide-activated acids immobilized on Si and Ge. Further modification of the chemically discriminated patterns enables chemoselective anchoring of organic molecules and protein.

We demonstrated the utility of the strategy towards a variety of inorganic oxides, including ITO. Utilizing the functionalized bi-layered system on ITO, a single molecular system in combination with different printing approaches can be used to immobilize multiple organic functionalities with exquisite spatial control. The system was used to investigate structure - function relationships of the ordered and functional molecular system on ITO to vertically and laterally control charge injection in organic light emitting diodes (OLEDs).

Finally, we report fabrication of functional hybrid organic-inorganic interfaces for the study of immobilized binding partners, lactose-g3 and complementary ssDNA, in molecular recognition force microscopy (MRFM). We use our system to evaluate the effect of contact force on specific interactions and the effect of dwell time and tether length on the probability of ligand-receptor binding. The methodologies developed enable a reliable evaluation of thermodynamic parameters using MRFM.