III-V semiconductor surface modification and characterization: Biomolecules on surfaces for sensor platforms

The attachment of biomolecules on III-V semiconductor materials has received attention because of their versatile applications. We described the detailed characterization of alkanethiol and cysteine-terminated peptide layers using two different methods on InP surfaces: (1) immobilization using solution based molecules and (2) patterning which directly transfers molecules using microcontact printing and Dip-Pen Nanolithography (DPN). We evaluated the surfaces using several surface techniques; contact angle measurements, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and ellipsometry were performed. The surface characterization techniques for solution based immobilization showed that the composition of the mixed monolyers (peptide and alkanethiols) can be controlled through the concentration of each adsorbate solution. The surface coverage of the adsorbates on the InP(100) surface was lower than that of similar self-assembled monolayers (SAMs) on gold. To increase packing of peptides on GaAs surface, the mixed monolayers of ODT and peptides were prepared. The chemical composition of each monolayers was characterized by X-ray photoelectron spectroscopy (XPS). The data showed that the make-up of the monolayers and its stability largely depends on the solvent used. In this dissertation examined the sensing devices using biomolecules. GaAs junction field-effect transistors (JFETs) were utilized to achieve label-free detection of the biological interaction between a probe (TAT peptide) and a target (trans-activation-responsive (TAR) RNA). The GaAs JFETs were modified with a mixed monolayer of 1-octadecanethiol (ODT) and TAT peptide. The ODT molecules passivated the GaAs surface from the polar ions present in physiological solutions and the TAT peptide provided selective binding sites for TAR RNA. The devices shows that the successful chemical functionalization of III-V semiconductor surfaces that are part of biosensor platforms