Zvi Liron

Surface-enhanced Raman scattering detection of cholinesterase inhibitors.

A new sensitive surface-enhanced Raman scattering (SERS) assay for detection of cholinesterase inhibitors such as organophosphorous pesticides using silver colloidal nanoparticles was developed and optimized. Acetylcholinesterase (AChE) mediated the hydrolysis of acetylthiocholine to produce thiocholine, which interacted with the silver nanoparticles to give a specific SERS spectrum. Variation in enzyme activity due to inhibition was measured from changes in intensity of a characteristic peak (772 cm(-1)) of the SERS spectrum that was directly correlated with the concentration of produced thiocholine. The method was demonstrated for the detection of paraoxon as reference AChE inhibitor. Limit of detection of paraoxon for 5 min incubation at 25 °C was 1.8×10(-8) M. This assay can be utilized for the detection of trace amounts of any AChE inhibitor.

Temperature effect and chemical response of surface acoustic wave (SAW) single-delay-line chemosensors

Abstract The effects of temperature and chemical vapour absorption on the frequency shift of coated and uncoated SAW single-delay-line oscillators are reported. It is found that the temperature-induced frequency-shift function depends on the nature of the coating of the delay-line surface. It changes from the flat parabolic temperature dependence of an uncoated ST-quartz delay line near room temperature, to a steep, almost linear, curve for polymer-coated delay lines in the same temperature range. The slope of the curves depends on the nature of the polymers. The dual-delay-line concept, where an uncoated SAW delay line is used as a reference element to compensate for the ambient temperature variations, is therefore not universal and should be implemented with great caution. The response of an array of four different SAW delay-line sensors to various chemical vapours is represented by pie charts, visualizing chemical pattern variability that can be used for pattern recognition. The frequency shifts are correlated with calculated theoretical partition-coefficient values, based on thermodynamic parameters and regular solution theory. It is shown that this approach may be used to predict the interaction between the polymer and a specific target chemical vapour. A simple method for a preliminary design of a SAW chemosensor is thus suggested.

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).

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.