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Title:Functional gel for directed molecular transport and sensor applications
Author(s):Zhang, Shiyan
Director of Research:Braun, Paul V
Doctoral Committee Chair(s):Braun, Paul V
Doctoral Committee Member(s):Alleyne, Andrew G; Leal, Cecilia; Evans, Christopher
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):hydrogel, gel, molecular transport, sensor
Abstract:A facile approach to transport and concentrate molecules to specified regions on a substrate will enhance the potential to detect such molecules and to establish a miniaturized, integrated chemical-analysis system. This dissertation focuses on the establishment of molecular transport systems in chemical gradient-imbedded gels and their integration with nanosensors. After the introduction in chapter 1, chapter 2 focuses on the effect of the chemical gradient miniaturization on the analyte collection capability and the spatial control of such gradient. Electrohydrodynamic printing, an ink-jet printing method that can minimize the ink droplet volume, was introduced to construct a micrometer scale radial chemical gradient in a polyacrylamide hydrogel. Collaborating with Spencer Joseph Kieffer in prof. Alleyne group, we discovered that by downscaling the chemical gradient from a few millimeters to 100s of micrometers, the analyte collection capability was enhanced. A cationic gradient model demonstrate that anionic analytes can be collected in the chemical gradient with a >50-fold concentration enhancement relative to the surrounding area. In addition to the size effect on the analyte collection capability, we can also well control the position of chemical gradient and print an array of micro-scale chemical gradients on the same substrate. Simultaneous transport and concentration to the array was observed. Compared to traditional microfluidic-based species manipulation techniques, this strategy provides a novel molecular manipulation in the micrometer scale, and can effectively improve the detection limit. Chapter 3 focuses on the integration of chemical gradient-imbedded hydrogel system with a nanosensor and explores the possibility to lower the detection limit of organophosphate, a kind of substance that is widely used in pesticides and nerve agents and is usually present in trace amounts. As the organophosphate are usually analyzed with FTIR characterization, the surface-enhanced infrared adsorption nanoantenna chip, which can be designed to selectively enhanced the signature organophosphate vibrational peak, was selected to be coated with the chemical gradient-imbedded hydrogel. The center of a radially distributed cationic center was aligned with the nanoantenna array. Combining the analyte collection capability from the chemical gradient and the infrared absorption enhancement from the nanoantenna array, this integrated chemical analysis platform can provide a combined two orders of magnitude detection limit improvement compared to that provided by the current ATR spectroscopy using a plain substrate. Chapter 4 broadens the selectivity of target molecules not solely based on charge, but also on molecular size, and develops cyclodextrin-based chemical gradients in hydrogels to transport organophosphates. The interaction between the cyclodextrin and analyte is supramolecular interaction, which is significantly influenced by the size match between the host cyclodextrin and the guest analyte. To study the size effect, α-, β-, and γ-cyclodextrins, which are of varied cavity size, are introduced to construct the cyclodextrin-based chemical gradient for comparison. Using an aromatic and a non-aromatic organophosphate as target analyte, we discovered that the transport and molecular concentration behavior are strongly influenced by the specific cyclodextrin forming the gradient. The aromatic organophosphate can be accumulated better in the β-cyclodextrins gradient while the non-aromatic organophosphate is only observed to be accumulated in the α-cyclodextrins. This supramolecular interaction-based strategy was also integrated with the SEIRA sensor. Chapter 5 explores the use of organo-gels instead of hydrogels as the transport matrix and a photo-defined method to control the gradient shape and size. The organo-gel consists of the poly(nitrobenzene methacrylate) as the polymer network and the DMSO as the medium. Through covering the organo-gel with photomasks and exposing the sample to UV irradiation, a hydrogen bond gradient can be established with a photo-cleavage reaction. Using a sample fluorescence dye, this hydrogen bond gradient within the organo-gel demonstrates its capability to direct the transport and concentration of molecules in an organic solvent environment.
Issue Date:2019-11-04
Rights Information:Copyright 2019 Shiyan Zhang
Date Available in IDEALS:2020-03-02
Date Deposited:2019-12

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