We developed a novel photo-polymerized hydrogel material and a new technique for embedding a crystalline colloidal array (CCA) within a thermo-reversible gelation polymer. The CCA lattice is locked into place within a polymeric hydrogel, forming a polymerized crystalline colloidal array (PCCA). The face-centered cubic (fcc) lattice into which the CCA self-assembles, Bragg diffracts light in the visible, near IR and UV regions of the spectrum. We utilized a poly(hydroxyethyl acrylate) hydrogel to detect ammonia in both buffer solutions and human serum. Phenols attached to the hydrogel backbone cross-link upon the addition of hypochlorite in a sample containing ammonia. The cross-linking causes an increase in the elastic constant of the hydrogel which forces the gel to shrink, blue-shifting the wavelength of Bragg diffracted light proportional to the concentration of ammonia present in solution. The sensor functions within the clinically relevant ammonia interval with a 50 μM detection limit in 1:1 serum/buffer solutions.A slight modification of this hydrogel material enabled its use within a bi-modular sensing approach for an organophosphorus (OP) nerve agent. The bi-modular sensing utilized the enzyme organophosphorus hydrolase (OPH) and the pH-sensitive group 3-aminophenol as recognition agents. OPH hydrolyzes OPs at basic pH and produces protons. These protons lower the pH inside the hydrogel changing the phenolates to phenols, lowering the free-energy of mixing and blue-shifting the Bragg diffracted light wavelength proportional to the OP concentration. The sensor is reversible, functions in high-ionic strength media, and has a 0.2 μM OP detection limit in aqueous media.We also developed a new technique for the synthesis of PCCA materials by embedding CCA within a thermo-reversible gelation polymer. Poly(vinyl alcohol) (PVA) in a solution of water and DMSO exhibits cononsolvency resulting in the formation of nanocrystallites, which act as physical cross-links. The hydrogel formed is thermo-reversible. It melts at 70oC and is optically clear when formed at temperatures below −10 oC. This gelation technique enables the facile synthesis of arbitrarily large PCCA materials.
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