Pellets with an immobilized enzyme (acetyl- or butyrylcholinesterase) are the up-to-date type of carriers used for the detection of nerve agents (soman, sarin, tabun, VX, Novichok) and other cholinesterase inhibitors such as organophosphate and carbamate insecticides (parathion, malathion). They are used in the glass detection tubes as a layer containing the enzyme together with the second layer, which contains a colorimetric reagent and substrate. The detection method is based on the visually or spectrophotometrically observable Ellman's reaction, which develops a yellow color in the absence of the cholinesterase inhibitor; otherwise, the detector preserves its original color (preferably white). This reaction occurs very fast and has a high sensitivity to nerve agents but it suffers from an indistinctive color transition from white to yellow. In the presented study, a new approach with the use of the synergic effect of magnesium aluminometasilicate with a high surface area marketed as Neusilin®US2 and a protective semipermeable Eudragit® RL layer was utilized. The prepared pellets have been evaluated for their properties such as the activity of the enzyme, intensity of the developed yellow color, sensitivity to cholinesterase inhibitor physostigmine, which acts as a nerve agent simulant, and physical parameters such as hardness, pycnometric density and sphericity. After the initial evaluation, all samples underwent a stability test under three different storage conditions for 24 months during which they were evaluated at given time points (0, 3, 6, 12 and 24 months). It was found that the prepared samples achieved a much higher intensity of developed yellow color than in the published studies while maintaining similar or better sensitivity, speed of detection and suitable physico-chemical properties.

Department of Pharmaceutics Faculty of Pharmacy University of Veterinary and Pharmaceutical Sciences Palackého 1946 1 Brno Czech Republic

Faculty of Biomedical Engineering Czech Technical University Prague Sítná 3105 Kladno Czech Republic

Oritest Ltd Nábřežní 90 4 Prague Czech Republic

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