Detection of organophosphate (OP) compounds has attracted much attention in terms of safeguarding human health, owing to their frequent use as pesticides in agriculture and their potential use as chemical warfare agents. Among a variety of biological methods based on the biocatalytic activity of organophosphorus hydrolase (OPH), amperometric, potentiometric, and optical biosensing devices have been developed for detecting OPs. Electrochemical biosensors in particular have been widely investigated to monitor various pesticides including OP compounds such as paraoxon, parathion, sarin, and soman via an enzyme-catalyzed hydrolysis reaction by OPH due to their fast speed, high efficiency, low cost, and small sample size.

Considering the requirements for the detection of OPs, carbon nanotubes (CNTs) have been considered as potential electrode materials of electrochemical biosensors due to their high accessible surface area, electronic conductivity, stability, and capacity to immobilize enzymes. Bucky gels (BGs) consisting of ionic liquids (ILs) and CNTs have served as advanced electrode materials of electrochemical biosensor devices. They offer good bio-compatibility, ease of preparation, and chemical and environmental stability. There have been very few reports regarding the underlying relationship of the electrochemical properties of CNT/IL-composite electrodes according to the types of ILs for developing biosensors. Furthermore, no work has been reported on the application of CNT/IL electrodes to detect OP compounds.

OPH immobilized on CNT/IL electrodes were prepared by using three different intrinsic kinds of ILs as binders: 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), and 1-buytl-3-methylimidazolium bis(trifluoromethl-sulfonyl)imide ([bmim][TF2N]). CNTs/ ILs lead to dramatic electrochemical enhancements with respect to response time, stability, and sensitivity of composite electrodes. In addition, the electro-chemical and biocatalytic properties of three-composite electrodes were strongly influenced by different types of ILs used, as verified by cyclic voltammetry and chronoamperometry. These results were attributed to the conformational changes of the microenvironment between the OPH and the composite electrodes within three different types of ILs. In particular, the biocatalytic signals of three OPH/CNT/IL-modified electrodes increased linearly to the concentration of paraoxon in a wide range. These findings provide a deep understanding of the role of each IL on the modified electrodes, enabling enhanced electrochemical properties for biosensors.

Modification of MWNTs by ILs resulted in high dispersion of CNT bundles and the formation of a 3D network structure, good compatibility with OPH, and accelerated electron transfer reaction at the interface. Electrochemical properties and sensor performances of composite electrodes depend on the types of ILs. In particular, electron transfer rate of the three modified electrodes increased after the immobilization of OPH on the modified electrode surface in the following order: OPH/MPGE < OPH/MBGE < OPH/MTGE. Among three-composite electrodes, MPGE provided the best sensitivity, 4.37 μA μM-1, and a fast response time of ~10 s for detecting OP. Composite electrodes could be applied to various electro-chemical biosensors, based on their fast, stable, and sensitive properties.

This work was done by Sang Yup Lee of the Korea Advanced Institute of Science and Technology for the Asian Office of Aerospace Research and Development. For more information, download the Technical Support Package (free white paper) at  under the Physical Sciences category. AFRL-0167

This Brief includes a Technical Support Package (TSP).
Development of an Electrochemical Biosensor for Organophosphate Chemicals

(reference AFRL-0167) is currently available for download from the TSP library.

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