Sharon Marx

Molecular Imprinting of Sol Gel Polymers for the Detection of Paraoxon in Water

The molecular imprinting technique of the toxic organophosphate compound paraoxon was applied in thin films of organically modified silica (ORMOSIL) matrix. Paraoxon was imprinted in the ORMOSIL through π-π interaction and hydrogen or polar bonds originating from functional alkoxysilane monomers. The binding of paraoxon to the imprinted sol gel matrix was evaluated by inhibition of butyryl cholinesterase (BuChE) using the Ellman colorimetric assay. Two ORMOSILs that differ in the structure of the backbone monomer and functional monomers were investigated, and found to have similar specific binding properties. The kinetic profile of paraoxon binding to the polymer matrix was studied, and saturation was found to occur after ca. 2 h. The binding of paraoxon to the synthetic receptor was evaluated by application of the two site Langmuir analysis. Two classes of receptor sites were detected, with binding affinities of 0.04 and 7 nM, and site population of 57 and 25 nM, respectively.

Induction and detection of chirality in doped sol–gel materials: NMR and circular dichroism studies

We have studied diastereomeric chiral interactions within sols, gels and xerogels of silicas and derivatized silicas (20% phenylated and 10% octadecylated silicas) doped with the chiral surfactant (−)-N-dodecyl-N-methylephedrinium bromide (DMB). Two spectral methods – new in the context of chiral sol–gel materials – have been used for that purpose. In the first method, we were able to detect the diastereomeric interactions between DMB and each of the pure enantiomers of co-doped 1,1′-binaphthyl-2,2′-diyl hydrogenphosphate using 31P-NMR spectroscopy. In the second method, we were able to obtain an induced circular dichroism (ICD) signal from the achiral dye Congo Red co-doped with DMB. NMR and ICD are complementary in understanding the way in which the chiral surfactant creates chiral environments inside the sol–gel materials. In particular, we provide ICD evidence that the silica network itself becomes chiral due to the entrapment of the chiral surfactant.

Kinetic study of the thermal inactivation of cholinesterase enzymes immobilized in solid matrices.

The thermal inactivation of immobilized cholinesterase enzymes (ChE) in solid matrices where the protein unfolding is blocked was studied, thus enabling investigation of the kinetics of the inactivation process directly from the native structure to the inactivated state. The thermal inactivation of butyrylcholinesterase (BChE), recombinant human acetylcholinesterase (rHuAChE), and eel acetylcholinesterase (AChE) enzymes was studied in dry films composed of poly(vinyl pyrollidone) (PVP), bovine serum albumin (BSA) and trehalose at 60 degrees -120 degrees C. The kinetics follows a bi-exponential decay equation representing a combination of fast and slow processes. The activation enthalpy DeltaH(#) and the activation entropy DeltaS(#) for each of the three enzymes have been evaluated. The values of DeltaH(#) for the fast process and for the slow process of BChE are 33+/-3, and 28+/-2 kcal/mol, respectively, and the values of DeltaS(#) are 0.84+/-0.04, and -18.2+/-0.5 cal/deg, respectively. The appropriate value of DeltaH(#) for rHuAChE is 26+/-2 Kcal/mol, for both processes and the values of DeltaS(#) are -17.6+/-0.9, and -23.0+/-0.9 cal/deg, respectively. Similarly, the values of DeltaH(#) for eelAChE are 30+/-3, 31+/-1 kcal/mol, and the values of DeltaS(#) are -6.7+/-0.5, -9.1+/-0.2 cal/deg respectively.

Porous graphene oxide chemi-capacitor vapor sensor array

A new type of cross-selective gas sensor has been developed, based on a vapor-induced capacitance modulation of chemically-functionalized porous graphene oxide (pGO). The dielectric pGO matrix was assembled in situ upon an electrode surface via a combined room-temperature annealing/freeze-drying process. Extraordinary vapor sensing properties are demonstrated, specifically extremely high sensitivity, wide dynamic range, rapid response and recovery times, fidelity, and detection of a broad range of molecular targets. The excellent sensing capabilities correspond to the open porous framework of pGO and high surface area within the pores, as well as molecular interactions between the vapor molecules and functional units displayed on the pGO framework. Array-based identification of different vapors is demonstrated via functionalization of the pGO scaffolds with distinct chemical residues.

Transfer hydrogenation of diarylacetylenes by polymethylhydrosiloxane in the presence of the RhCl3-Aliquat 336 catalyst

Abstract The ion pair [(C 8 H 17 ) 3 NCH 3 ] + [RhCl 4 (H 2 O) 2 ] − , formed from aqueous rhodium chloride and Aliquat® 336, has been shown to catalyze transfer hydrogenation of diarylacetylenes by polymethylhydrosiloxane (PMHS) to give Z - and E -stilbenes as the major and the minor products, respectively. The reduction of diphenylacetylene was found to follow first-order kinetics in the substrate between 0.025 and 2.0 M. Both the steric and the electronic nature of the substrate proved to affect the rate. The electronic effect could be expressed in terms of two separate Hammett plots, one with ϱ = 0.64 for electron-withdrawing substituents and one with ϱ = −1.10 for the alkynes with electron-releasing groups. Application of either a deuterium-labelled organic phase or D 2 O led to mono and dideuterated products. The observed activation energy E a = 11.47 kcal mol −1 suggests that the process is both chemically and diffusion controlled.

Acoustic and optical transduction of BuChE binding to procainamide modified surfaces

A novel polymer, poly(procainamide), PPA, containing numerous binding sites for cholinesterases was synthesized as a recognition layer for butyryl cholinesterase (BuChE) interaction with the ligand procainamide, utilizing TSM and SPR sensors. The polymer was synthesized by the reaction of methacryloyl chloride and procainamide followed by radical polymerization. Sensor surfaces (Au or SiO(2)) were spin-coated by the polymer solution to form thin layers. Binding of BuChE was found to be sensitive to the drying procedure of the polymer layer. The binding of BuChE to the polymer coated sensors was monitored on-line by following the response of thickness shear mode (TSM) and surface plasmon resonance (SPR) sensors. Binding of BuChE to PPA-coated TSM sensors were shown to follow a Langmuir isotherm giving association constant 3.4x10(6) M(-1).

Highly Stable Lyophilized Homogeneous Bead-Based Immunoassays for On-Site Detection of Bio Warfare Agents from Complex Matrices

This study shows the development of dry, highly stable immunoassays for the detection of bio warfare agents in complex matrices. Thermal stability was achieved by the lyophilization of the complete, homogeneous, bead-based immunoassay in a special stabilizing buffer, resulting in a ready-to-use, simple assay, which exhibited long shelf and high-temperature endurance (up to 1 week at 100 °C). The developed methodology was successfully implemented for the preservation of time-resolved fluorescence, Alexa-fluorophores, and horse radish peroxidase-based bead assays, enabling multiplexed detection. The multiplexed assay was successfully implemented for the detection of Bacillus anthracis, botulinum B, and tularemia in complex matrices.

Gold Fibers as a Platform for Biosensing

A new form of high surface bioelectrode based on electrospun gold microfiber with -immobilized glucose oxidase was developed. The gold fibers were prepared by electroless deposition of gold nanoparticles on a poly(acrylonitrile)-HAuCl(4) electrospun fiber. The material was characterized using electron microscopy, XRD and BET, as well as cyclic voltammetry and biochemical assay of the immobilized enzyme. The surface area of the gold microfibers was 2.5 m(2)/g. Glucose oxidase was covalently crosslinked to the gold surface using cystamine monolayer and glutardialdehyde, and portrayed characteristic catalytic currents for oxidizing glucose using a ferrocene methanol mediator. Limit of detection of glucose is 0.1 mM. The K(m) of the immobilized enzyme is 10 mM, in accordance with other reports of immobilized glucose oxidase. The microfiber electrode was reproducible and showed correlation between fiber weight, cathodic current and enzymatic loading.

High Frequency Acoustic STW Biosensor

A Surface Transverse Wave (STW) acoustic biosensor for monitoring chemical interactions in aqueous solution has been developed. The STW acoustic biosensor was utilized to monitor antigen-antibody and ligand-receptor interactions, and to follow sorption kinetics of organic chemicals dissolved in aqueous solution. The STW delay-line sensor has been designed to control the oscillation frequency of an rf oscillator at ~ 80 MHz. SiO2 and poly[methylmethacrylate] (PMMA) served as wave guiding layers for the STW devices. The acoustic devices were placed in a thermostatic (25 °C) stainless steel flow-cell, and frequency has been followed with time. The applicability of the STW device in three model systems will be presented and discussed: The immunosensor model was based on the interaction between rabbit IgG and goat anti rabbit IgG peroxidase conjugate. The receptor-ligand interaction model was studied by use of a matrix bound procainamide and a soluble butyrilcholinesterase (BuChE). A special methacrylic-procainamide polymer (PPA) was designed and synthesized as an anchor for the BuChE molecule. Chemical sorption of organic solvents in aqueous phase was studied by poly[nbutylmethacrylate] (PBMA) coated STW sensors with SiO2 as a wave guiding layer. Sorption kinetics were analyzed by a simulation method to derive the chemical diffusion and partition coefficients.