A CARBON-DIOXIDE BIOSENSOR BASED ON HEMOGLOBIN INCORPORATED IN METAL SUPPORTED BILAYER-LIPID MEMBRANES (BLMS) - INVESTIGATIONS FOR ENHANCEMENT OF RESPONSE CHARACTERISTICS BY USING PLATELET-ACTIVATING-FACTOR

The present article reports the development of a novel electrochemical carbon dioxide minisensor based on hemoglobin which is incorporated i nto self-assembled bilayer lipid membranes (s-BLMs) on a metal support . The presence of carbon dioxide in solution was found to modulate the ion conductivity of BLMs containing hemoglobin, when using a lipid co mposition containing egg phosphatidylcholine (egg PC) and dipalmitoylp hosphatidic acid (DPPA). The use of stabilized metal-supported BLMs ha s allowed the electrochemical investigation of the reversibility of th e response to carbon dioxide and of hemoglobin binding to lipid membra nes. The effects of hemoglobin concentration, composition of BLMs in D PPA and pH on the sensitivity of the response were examined. The senso r provides the advantages of fast response times (on the order of ca. 10 s) to alterations of carbon dioxide concentration, low detection li mits (ca. 0.4 x 10(-6) M) and capability of analysing small sample vol umes. Semisynthetic platelet-activating factor (PAF; -O-alkyl-2-acetyl -sn-glyceryl-3-phosphorylcholine, AGEPC) was found to improve the resp onse characteristics of the carbon dioxide sensor (i.e., decrease of t he detection limit to nM range and increase of the dynamic range of ca rbon dioxide determination). The biosensor was routinely mechanically stable and functional for over 48 h. During this time it showed reprod ucible sensitivity and response to a given concentration of carbon dio xide in solution.