International audienceA new trace glucose analyzer has been designed using electrochemical sensors. The differential device includes (a) a glucose sensor consisting of a modified gas electrode in which ihe pH detector was replaced by a platinum disk and the porous film by a collagen membrane on which beta-D-glucose oxidase has been covalently bound after an acyl-azide activation process; (b) a compensating electrode mounted with a nonenzymatic collagen membrane. After injection of a glucose containing sample into the reaction vessel, where the probes are immersed, an anodic current is detected at the enzyme working electrode. Current outputs of both electrodes are subtracted and twice differentiated; a steady state is reached and the stationary and dynamic responses are recorded. Both responses are proportional to glucose concentration in the 0.1 µM-2 mM range, and the reproducibility was found to be better than 2% using these conditions. The extreme sensitivity exhibited by our system, i.e., 10 nM, is better than previously reported data by 3 orders of magnitude, and is very favorable for trace glucose assays in food and biological samples

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In view of obtaining homogeneous LB films, monolayers of dipalmitoylphosphatidic acid (DPPA) and of mixed DPPA and dipalmitoylphosphatidylcholine (DPPC) (molar ratio, 2:1) were transferred onto hydrophilic (fluorine, glass, and silicon) or hydrophobic (silanized glass) substrates with conditions derived from the optimized procedure previously proposed in our group for the transfer of a fatty acid monolayer. Whatever the substrate used, the phospholipid multilayers obtained are homogeneous through Nomarski microscopic observations. The silicon substrate appears to be the most efficient to build up Y-type multilayers. A new type referred to as "YZ" was defined to describe the structure of the LB film stacking. We demonstrate that the transition observed between the different Y-, YZ-, and Z-types depends directly on the strength of the interaction between the first layer and the hydrophilic substrate surfaces.