GLUCOSE MINISENSOR BASED ON SELF-ASSEMBLED BIOTINYLATED PHOSPHOLIPID MEMBRANE ON A SOLID SUPPORT AND ITS PHYSICAL-PROPERTIES

We have developed a glucose minisensor based on a biotinylated, suppor ted phospholipid membrane (s-BLM). We immobilized glucose oxidase (GOX ) by coupling an avidin-GOX complex to a phospholipid bilayer formed f rom biotinylated crude ox brain extract (COB). The bilayer was support ed on the free metal tip of a Teflon-coated stainless steel wire (diam eter, 0.33 mm). The determination of glucose was based on detection of enzymatically generated hydrogen peroxide at a potential of +670 mV. We found an almost linear increase of membrane current with increasing glucose concentration up to IO mM and a saturation effect above 30 mM glucose. A lower voltage for detection of glucose was made possible b y modification of the membrane by the electron carrier TCNQ. Several m ethods have been used to study the physical properties of native and m odified s-BLM and conventional BLM. With the electrostriction method w e showed that addition of avidin-GOX complex to the electrolyte in whi ch the biotinylated s-BLM was formed resulted in a decrease of membran e capacitance and a decrease of membrane compressibility perpendicular to the bilayer surface. The capacitance relaxation method was used to determine the changes of dielectric relaxation times (reorientation o f dipole moments of polar groups of individual lipid molecules or lipi d clusters) following addition of avidin-GOX. Native BLM formed from C OB extract (2% solution in n-decane:butanol (8:1 v/v)) exhibited one r elaxation time of (5 +/- 1) mu s. Additional relaxation components (11 5 +/- 27 mu s and 26 +/- 1 mu s) appeared in BLM modified by biotin. A ddition of the avidin-GOX complex to the biotinylated BLM resulted in the appearance of a slow component 505 +/- 16 ys. These results clearl y document the interaction of the strongly immobilized enzyme with the bilayer. (C) 1997 Elsevier Science S.A.