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Development of 2-Dimensional Photonic Crystal Sensors and Pure Protein Organogel Sensing and Biocatalytic Materials

Smith, Natasha (2020) Development of 2-Dimensional Photonic Crystal Sensors and Pure Protein Organogel Sensing and Biocatalytic Materials. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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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 bind 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(hydroxyethylmethacrylate)-based polymers in the ionic liquid ethylguanidinium perchlorate (EGP). Ionogels are suitable gas 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.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Smith, Natashanls49@pitt.edunls490000-0001-9308-5178
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairAsher,
Committee MemberGarrett-Roe,
Committee MemberHorne,
Committee MemberVelankar,
Date: 16 January 2020
Date Type: Publication
Defense Date: 12 August 2019
Approval Date: 16 January 2020
Submission Date: 8 September 2019
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 259
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Chemistry
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Biocatalysts, Biopolymers, Ionic Liquids, Responsive Materials, Sensors, Volume Phase Transitions
Date Deposited: 16 Jan 2020 19:42
Last Modified: 16 Jan 2020 19:42


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