Development of new sensor platforms: Applications and characterization of self -assembled monolayers on semiconductor materials

Rosangelly Flores-Perez, Purdue University

Abstract

We developed new sensor platforms of molecular self-assembly monolayers (SAMs) on semiconductor materials. We designed and characterized an amine terminated quartz surfaces that can anchor retinal molecules. We mimicked the environment of the opsin protein which accommodates the binding of chromophore molecules in the human eye. Each coupling step was characterized by water contact angle, ellipsometry, atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and transmission infrared spectroscopy (FT-IR). After we confirmed the chromophores’ immobilization via Schiff base, we functionalized silicon-based microcantilevers in order to recognize the binding of retinal molecules to the surfaces. Our results indicated that properly designed and functionalized microcantilevers can be used to construct economical, fast and sensitive sensors for quality control in cosmetics. In our laboratory, we also studied SAMs of alkanethiols and DNA biomolecules on gallium phosphide. By the use of surface sensitive techniques, we quantitatively characterized the nature and organization of alkanethiol adsorbates on GaP (100) substrates. Water contact angle, AFM, FT-IR and XPS data showed evidence of the wettiability, roughness, molecular orientation, characteristic chemical and elemental composition, adlayer thicknesses, tilt angles and molecular coverages for the different adsorbates. Subsequent to the understanding of the alkanethiol surface modification, we used microcontact printing (ìCP) and dip-pen nanolithography (DPN) to create patterns on GaP (100). A complete characterization was done in order to understand the quality of each type of pattern, its chemical structure and the organization of the molecules on the surface. The differences between the two methods were dependent on the chosen molecular “ink.” After a comprehensive study of lithographic methods on gallium phophide using alkanethiols, we described the SAMs of DNA biomolecules on H-doped GaP (100). Various analytical techniques confirmed the molecular well-packed DNA molecules and the DNA’s bioactivity on the inorganic surface. The results of this series of studies demonstrated the high-quality performance of SAMs on semiconductor materials. These modification methodologies can be applied for passivation methods and as possible biosensor platforms.

Degree

Ph.D.

Advisors

Ivanisevic, Purdue University.

Subject Area

Analytical chemistry

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