Development of a biosensor specific for cysteine sulfoxides

S-Alk(en)yl cysteine sulfoxides have been observed in several plants, mainly belonging to the onion family (Alliaceae), which are of high commercial interest (e.g. garlic, Allium sativum). The quality of most garlic containing herbal remedies produced from garlic powder is determined by their content of the cysteine sulfoxide alliin. Therefore, a comprehensive method for the documentation of alliin amounts present in the fresh plant material through to the final remedy is desirable. The newly developed biosensoric method described in this paper was designed in order to fulfil these demands. In contrast to conventional HPLC-methods, neither a pre-column derivatization nor a chromatographic separation are required allowing a high throughput of samples. This technique is based on immobilized alliinase (EC 4.4.1.4), which was combined with an ammonia-gas electrode. The enzyme was either placed in a small cartridge or was immobilized in direct contact of the electrode surface giving detection limits of 3.7 x 10(-7) and 5.9 x 10(-6) M. Founded on these experiments, a pH-sensitive electrolyte/insulator/semiconductor (EIS) layer structure made of Al/p-Si/SiO2/Si3N4 was also combined with immobilized alliinase. Measurements could be performed in a range between I X 10(-5) and I X 10(-3) M alliin. All sensors were operated in the flow-through modus. A high specificity for alliin could be demonstrated for the electrode and a number of garlic samples were analyzed. Results gained with the new method showed a good correlation with those obtained with conventional HPLC-methods. In addition, onion and a variety of wild Allium species were analyzed in order to determine the amount of isoalliin or total cysteine sulfoxides present, respectively. (C) 2003 Elsevier Science B.V. All rights reserved

Biosensoric detection of the cystein sulfoxide alliin

Garlic (Allium sativum L.) and related species of the Alliaceae family are known for their cancer-protecting and anti atherosclerotic potential. The bioactivity of these plants is related to organo-sulphur compounds, mainly alliin. In the present investigation, an alliin-specific biosensor exploiting immobilised alliinase (EC 4.4.1.4) has been developed. Enzymatically formed ammonia was detected by a potentiometric sensor based on an ammonia electrode or a pH-sensitive electrolyte/insulator/semiconductor (EIS) layer structure made of Al/p-Si/SiO2/Si3N4. It could be demonstrated with both methods that this biosensoric approach yielded results comparable to sensitivities obtained by HPLC. Alliin concentrations down to 6 x 10(-6) M could be quantified. The EIS biosensor showed also sensitivity to further cysteine sulphoxides, like methiin, ethiin and propiin, which are common for wild Allium species. Besides the analysis of garlic and garlic-containing preparations, like herbal remedies, this biosensor can be additionally used for breeding research and screening purposes of potential medicinal plants. (C) 2003 Published by Elsevier Science B.V

Direct determination of cyanides by potentiometric biosensors

Cyanide (CN-) and its derivatives are widely used in the metal mining and metal plating industry. But also many medicinal and food plants are toxic for man because of their content of cyanogenic glycosides. In the present investigation, a cyanide-specific biosensor exploiting immobilized cyanidase (EC 3.5.5.1) has been developed. Enzymatically formed ammonia was either detected by a potentiometric sensor based on an ammonia electrode or by a pH-sensitive electrolyte/insulator/semiconductor (EIS) layer structure made of Al/p-Si/SiO2/Si3N4. It could be demonstrated with both methods that sensitivity of these biosensors is sufficient to detect cyanide in sub-toxic concentrations. The detection limit was determined to be in the micromolar concentration range. (C) 2004 Elsevier B.V. All rights reserved