Title Page Development of 2-Dimensional Photonic Crystal Sensors and Pure Protein Organogel Sensing and Biocatalytic Materials by Natasha Lynn Smith B.S. West Virginia University, 2009 Submitted to the Graduate Faculty of the Dietrich School of Arts and Sciences in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Pittsburgh 2019 Committee Membership Page UNIVERSITY OF PITTSBURGH DIETRICH SCHOOL OF ARTS AND SCIENCES This dissertation was presented by Natasha Lynn Smith It was defended on August 12, 2019 and approved by Dr. Sean Garrett-Roe, Associate Professor, Department of Chemistry, University of Pittsburgh Dr. Seth Horne, Associate Professor, Department of Chemistry, University of Pittsburgh Dr. Sachin Velankar, Associate Professor, Mechanical Engineering and Material Science, University of Pittsburgh Dissertation Director: Dr. Sanford A. Asher, Distinguished Professor of Chemistry, Department of Chemistry, University of Pittsburgh ii Copyright © by Natasha Lynn Smith 2019 Abstract iii Development of 2-Dimensional Photonic Crystal Sensors and Pure Protein Organogel Sensing and Biocatalytic Materials Natasha L. Smith, PhD University of Pittsburgh, 2019 We developed responsive hydrogels, organogels, and ionogels for chemical sensing and catalysis applications. Gels have two components, polymer networks and solvent mobile phases. Hydrogels contain an aqueous mobile phase; organogels an organic solvent; and ionogels an ionic liquid. Different solvent types were required to target different applications, e.g. gas sensing requires solvents that resist evaporation. Colorimetric chemical sensors utilize our 2-Dimensional Photonic Crystals (2DPC) technology. 2DPC are arrays of self-assembled polystyrene nanoparticles that have close-packed, hexagonal crystal structures. 2DPC diffract wavelengths of light into discrete angles according to the 2D Bragg equation. Diffraction depends on 2DPC particle spacing and ordering. 2DPC— embedded into gels that were designed such that analytes actuate polymer volume phase transitions (VPT)—change particle spacing with the VPT, shifting diffraction angles. VPT occur when analytes cause Gibbs free energy changes, ∆G. 2DPC surfactant sensors utilized poly(N-isopropylacrylamide) (PNIPAAm) hydrogels. PNIPAAm hydrogels swell when the hydrophobic tail of ionic surfactants binds to the PNIPAAm isopropyl group. A Donnan potential created by bound charges induces ∆GIonic, causing swelling that red shifts the diffraction. 2DPC gas sensors for humidity and ammonia utilized poly(hydroxyethyl methacrylate)- based polymers in the ionic liquid ethylguanidine perchlorate (EGP). Ionogels are suitable gas iv sensors—ionic liquids have negligible vapor pressures, delivering mobile phases that don’t evaporate. ∆GMixing occurs when EGP absorbs water vapor, causing ionogel shrinking that blue shifts the diffraction. Ammonia sensors incorporated acrylic acid into the polymer. Ammonia absorbed by EGP deprotonated the carboxyl groups, causing swelling that red shifts the diffraction. Responsive pure protein organogels were fabricated from protein hydrogels by exchanging water with ethylene glycol. 2DPC albumin organogels swell when the proteins bind ligands, enabling water insoluble analyte detection that utilizes protein selectivity. Organophosphorus Hydrolase organogels catalyze hydrolysis of organophosphate nerve agents ~160 times faster than their monomers in organic solvent. Organic solvents typically denature proteins. Crosslinked organogel proteins mostly retain their native protein reactivity because the proteins are immobilized—i.e. stabilized— during hydrogel polymerization. Protein polymer phase separation that accompanies the solvent exchange irreversibly changes the polymer morphology, however the proteins retain their secondary structure and solvation shell waters in pure ethylene glycol. v Table of Contents 1.0 Introduction ............................................................................................................................. 1 1.1 Scope of Introduction ..................................................................................................... 1 1.2 Motivations ...................................................................................................................... 1 1.3 Organophosphate Nerve Agent Background ............................................................... 3 1.3.1 Organophosphate Sensing and Decontamination ............................................ 5 1.4 2-Dimensional Photonic Crystal Chemical Sensors .................................................. 10 1.5 2-Dimensional Photonic Crystal Diffraction .............................................................. 13 1.6 Chemically Stimulated Polymer Volume Phase Transitions .................................... 19 1.6.1 Free Energy of Mixing ...................................................................................... 21 1.6.2 Elastic Free Energy ........................................................................................... 22 1.6.3 Ionic Free Energy .............................................................................................. 22 1.7 Overview of Research Program .................................................................................. 23 1.8 References ..................................................................................................................... 26 2.0 Debye Ring Diffraction Elucidation of 2D Photonic Crystal Self-Assembly and Ordering at the Air-Water Interface ........................................................................................ 33 2.1 Introduction .................................................................................................................. 34 2.2 Experimental ................................................................................................................. 36 2.2.1 Materials ............................................................................................................ 36 2.2.2 Polymerization and Characterization of Monodisperse Negatively Charged Polystyrene Nanoparticles ......................................................................................... 36 2.2.3 2DPC Fabrication Using Needle Tip Flow Method ....................................... 37 vi 2.2.4 2DPC Debye Ring Diffraction Measurements ................................................ 40 2.2.5 2DPC Ordering Analysis .................................................................................. 42 2.3 Results and Discussion ................................................................................................. 44 2.3.1 Needle Tip Flow Nanoparticle Self-Assembly at the Air-Water Interface .. 44 2.3.2 Estimating 2DPC Order from Debye Ring Measurements ........................... 46 2.3.3 2DPC Ordering and Particle Spacing at the Air-Water Interface ............... 52 2.3.4 Electrostatic Interactions of Charged Particles at the Air-Water Interface 56 2.3.5 Mechanism of Self-Assembly for Close Packed Particle Arrays at the Air- Water Interface .......................................................................................................... 58 2.4 Conclusions ................................................................................................................... 60 2.5 References ..................................................................................................................... 61 3.0 Two-Dimensional Photonic Crystal Surfactant Detection ................................................ 67 3.1 Introduction .................................................................................................................. 68 3.2 Experimental ................................................................................................................. 69 3.2.1 Materials ............................................................................................................ 69 3.2.2 2D Array Sensor Preparation .......................................................................... 70 3.2.3 Diffraction Measurements ................................................................................ 71 3.3 Results and Discussion ................................................................................................. 72 3.4 Conclusions ................................................................................................................... 79 3.5 References ..................................................................................................................... 80 4.0 Responsive Ionic Liquid-Polymer 2D Photonic Crystal Gas Sensors .............................. 83 4.1 Introduction .................................................................................................................. 84 4.2 Experimental ................................................................................................................. 88 vii 4.2.1 Materials ............................................................................................................ 88 4.2.2 Ionic Liquid, Ethylguanidine Perchlorate (EGP) Synthesis ......................... 88 4.2.3 Fabrication of IL2DPC Humidity Sensors ..................................................... 89 4.2.4 Testing Humidity Sensor Response ................................................................. 90 4.2.4.1 Stagnant Air Response .......................................................................... 90 4.2.4.2