We are developing photonic crystal glucose sensing materials to continuously monitor relatively high glucose concentrations, such as found in blood. We modified our synthetic fabrication methodologies in order to increase the glucose concentration range and to increase the reproducibility of our PCCA fabrication. We have also advanced our understanding of the sensing response by developing a mechanical method to independently determine the hydrogel cross-link density. Our investigation of the sensing mechanism indicates that glucose binding depends mainly on the boronic acid concentrations and affinities. We determined the binding constant of 2-fluoro-5-aminophenyl boronic acid for glucose under physiological conditions. We have examined the dependence of glucose sensing upon interferences by other species that ligand to boronic acids, such as lactate and human serum albumin. We examined the stability of our sensors over a period of weeks at room temperature and demonstrated that we could further stabilize our sensing materials by reversibly dehydrating them for storage.

We developed a new photonic crystal hydrogel material based on the biocompatible polymer poly (vinyl alcohol) (PVA), which can be reversibly dehydrated and rehydrated, without the use of additional fillers, while retaining the diffraction and swelling properties of polymerized crystalline colloidal arrays (PCCA). This chemically modified PVA hydrogel photonic crystal efficiently diffracts light from the embedded crystalline colloidal array. This diffraction optically reports on volume changes occurring in the hydrogel by shifts in the wavelength of the diffracted light. We fabricated a pH sensor, which demonstrates a 350 nm wavelength shift between pH values of 3.3 and 8.5. We have also fabricated a Pb(+2) sensor, in which pendant crown ether groups bind lead ions. Immobilization of the ions within the hydrogel increases the osmotic pressure due to the formation of a Donnan potential, swelling the hydrogel and shifting the observed diffraction in proportion to the concentration of bound ions. The sensing responses of rehydrated PVA pH and Pb(+2) sensors were similar to that before drying. This reversibility of rehydration enables storage of these hydrogel photonic crystal sensors in the dry state, which makes them much more useful for commercial applications.

We developed a photonic crystal sensing method for diol containing species such as carbohydrates based on a poly(vinyl alcohol) (PVA) hydrogel containing an embedded crystalline colloidal array (CCA). The polymerized CCA (PCCA) diffracts visible light. We show that in the presence of borax the diffraction wavelength shifts as the concentration of glucose changes. The diffraction shifts result from the competitive binding of glucose to borate, which reduces the concentration of borate bound to the PVA diols.

The properties of hydrogel materials depend on their network structure, which is determined predominantly by the hydrogel polymer volume fraction and the degree of hydrogel crosslinking. [1][2][3] In an effort to optimize the utility of our photonic crystal hydrogel materials, and to improve our understanding of these nanocomposite systems, we investigated how the mechanical properties of these photonic crystal hydrogels depend upon the diameter of the nonbonded embedded nanoparticles.Our photonic crystal hydrogel materials contain mesoscopically periodic arrays of colloidal particles that self-assemble into highly-ordered crystalline colloidal arrays (CCA), with lattice spacings that Bragg diffract visible light ( Figure 1A).4 -10 The CCA are polymerized within hydrogels forming a polymerized CCA (PCCA). 11 These PCCA optically report on volume changes experienced by the hydrogels, since the observed diffraction wavelength directly depends upon the spacing between lattice planes. These PCCA have been used for chemical sensing by functionalizing them such that changes in the concentration of the analyte of interest actuate changes in the PCCA volume and, thereby, the diffraction wavelength.12 -14 Intelligent PCCA have been developed for the detection of multiple analytes, including glucose,15 -17 cations, 18-20 ammonia, 21 pH, 22 organophosphates, 23 and creatinine. 24 The viscoelastic properties of a hydrogel are predominantly determined by the hydrogel network structure. 1,3 In the work here we develop new insight into this network structure by oscillatory shear rheometry measurements, which characterize the PCCA shear storage modulus. This modulus monitors the effective crosslink density of the PCCA hydrogels. 1,3 The effective crosslink density is derived from normal hydrogel crosslinks, as well as from interactions of the hydrogel network with the embedded nanoparticles.In spite of the numerous studies that examined the impact of nanoparticle inclusions on elastomer mechanical properties, there still remains significant quantitative disagreement on the dependence of these properties on nanoparticle size. 1,3,[25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] We present here the first definitive study of how the mechanical properties of a swollen hydrogel depend upon the diameter of nonbonded embedded nanoparticles.*asher@pitt.edu Department of Chemistry, University of Pittsburgh, 219 Parkman Avenue, Pittsburgh, PA 15260, 412-624-8570 (phone), 412-624-0588 (fax). Supporting Information Available. Text giving the experimental details; materials; synthesis of nanoparticles; fabrication of hydrogel materials; characterization of nanoparticles and PCCA hydrogel materials; mechanical analysis of hydrogel materials; graph of modulus versus particle size. This material is available free of charge via the Internet at http://pubs.acs.org. NIH Public Access Author ManuscriptMacromolecules. Author manuscript; available in PMC 2010 July 14. Published in final edited form as:Macromolecules. Mon...