Glucose sensors with increased sensitivity based on composite gels containing immobilized boronic acid

Copolymerization of N-acryloyl-m-aminophenylboronic acid (NAAPBA) with acrylamide (AAm) on the surface of glass plates resulted in the formation of a hydrogel film with porous structure and capable of optical response to the changes in concentration of glucose in the contacting solution. The boronate specific dye, Alizarin Red S (ARS) was incorporated into hydrogel film to increase the sensitivity towards glucose and poly(N-vinylpyrrolidone) (PVP) was incorporated to prevent the dye leakage. The obtained boronate-containing polymer film responded to submicromolar concentration Of glucose with optical density changes being a linear function of glucose concentration in the range from 0.1 to 1 mM. The PVP-ARS-containing gel exhibited a 10-fold higher glucose sensitivity compared with the colorless NAAPBA-AAm gel. The equilibrium dissociation constants of soluble ARS-PVP and ARS-NAAPBA-containing copolymer complexes at pH 7.3 were found to be 1.4 and 0.44 mu M, respectively. The low dissociation constants enabled the preparation of the sensor with increased operational stability of at least two months allowing more than 20 assays of with no loss in the sensitivity or dye leakage. (C) 2008 Elsevier Ltd. All rights reserved

Optical responses, permeability and diol-specific reactivity of thin polyacrylamide gels containing immobilized phenylboronic acid

Thin semitransparent gels were prepared by radical copolymerization of N-acryloyl-m-aminophenylboronic acid (NAAPBA) and acrylamide (AAm) taken in molar ratios from 8:92 to 16:84, respectively, in water. The gels were characterized by the content of immobilized NAAPBA and monomer conversion. Scanning electron microscopy revealed the micrometer size pores in the dried gels. The wet gels displayed a linear optical response to sugars with sensitivity decreasing in the series: D-fructose, D-galactose, D-glucose, D-mannose, N-acetyl-D-glucosamine in the sugar concentration range from 1 to 40-60 mM at pH 7.3. Cross-linking of the gels with N,N-methylene-bis-acrylamide decreased the strength of optical response. Specific binding capacity of a diol-containing dye Alizarin Red S in the gels at pH 7.0 coincided with the content of immobilized NAAPBA indicating the 1: 1 stoichiometry of the reaction and, therefore, good accessibility of the boronic acid ligands for water-soluble diols. Permeability of the gels was studied with a non-interacting dye Ethyl Orange exhibiting the pore diffusion coefficient of 1.4 x 10(-7) cm(2)/s. The rate of optical response of the gels to glucose was found to be determined by diffusion of sugar into the relatively thick gels (1 = 0.35-1 mm) with effective diffusion coefficients of 2 x 10(-7) cm(2)/S. In the thinner gels (l = 0.1 mm) the input of other kinetic processes, such as affinity binding or structural rearrangements of the gel, was noticeable. (c) 2008 Elsevier Ltd. All rights reserved

Thin semitransparent gels containing phenylboronic acid: porosity, optical response and permeability for sugars.

Radical copolymerization of acrylamide (Am) (90 mol%) with N-acryloyl-m-aminophenylboronic acid (NAAPBA) (10 mol%) carried out on the surface of glass slides in aqueous solution and in the absence of chemical cross-linkers, resulted in the formation of thin semitransparent gels. The phenylboronic acid (PBA) ligand density was ca. 160 micromol/ml gel. The gels exhibited a macroporous structure and displayed optical response to sucrose, lactose, glucose and fructose in 50 mM sodium phosphate buffer, in the pH range from 6.5 to 7.5. The response was fairly reversible and linearly depended on glucose concentration in the wide concentration range from 1 to 60 mM at pH 7.3. The character of response was explained by the balance of two competing equilibrium processes: binding of glucose to phenylboronate anions and binary hydrophobic interactions of neutral PBA groups. The apparent diffusion coefficient of glucose in the gels was ca. 2.5 x 10(-7) cm(2)/s. A freshly prepared gel can be used daily for at least 1 month without changes in sensitivity. Autoclaving (121 degrees C, 1.2 bar, 10 min) allows for the gels sterilization, which is important for their use as glucose sensors in fermentation processes. Copyright (c) 2008 John Wiley & Sons, Ltd

Evaluation of boronate-containing polymer brushes and gels as substrates for carbohydrate-mediated adhesion and cultivation of animal cells.

Boronate-containing thin polyacrylamide gels (B-Gel), polymer brushes (B-Brush) and chemisorbed organosilane layers (B-COSL) were prepared on the surface of glass slides and studied as substrates for carbohydrate-mediated cell adhesion. B-COSL- and B-Brush-modified glass samples exhibited multiple submicron structures densely and irregularly distributed on the glass surface, as found by scanning electron microscopy and atomic force microscopy. B-Gel was ca. 0.1mm thick and contained pores with effective size of 1-2mum in the middle and of 5-20mum on the edges of the gel sample as found by confocal laser scanning microscopy. Evidence for the presence of phenylboronic acid in the samples was given by time-of-flight secondary ion mass-spectrometry (ToF SIMS), contact angle measurements performed in the presence of fructose, and staining with Alizarin Red S dye capable of formation specific, fluorescent complexes with boronic acids. A comparative study of adhesion and cultivation of animal cells on the above substrates was carried out using murine hybridoma M2139 cell line as a model. M2139 cells adhered to the substrates in the culture medium without glucose or sodium pyruvate at pH 8.0, and then were cultivated in the same medium at pH 7.2 for 4 days. It was found that the substrates of B-Brush type were superior both regarding cell adhesion and viability of the adhered cells, among the substrates studied. MTT assay confirmed proliferation of M2139 cells on B-Brush substrates. Some cell adhesion was also registered in the macropores of B-Gel substrate. The effects of surface microstructure of the boronate-containing polymers on cell adhesion are discussed. Transparent glass substrates grafted with boronate-containing copolymers offer good prospects for cell adhesion studies and development of cell-based assays