d-Serine is an endogenous ligand for N-methyl-d-aspartate (NMDA) receptors, and alterations in its concentration have been related to several brain disorders, especially schizophrenia. It is therefore an important target neuromodulator for the pharmaceutical industry. To monitor d-serine levels in vivo, we have developed a microbiosensor based on cylindrical platinum microelectrodes, covered with a membrane of poly-m-phenylenediamine (PPD) and a layer of immobilized d-amino acid oxidase from the yeast Rhodotorula gracilis (RgDAAO). By detecting the hydrogen peroxide produced by enzymatic degradation of d-serine, this microbiosensor shows a detection limit of 16 nM and a mean response time of 2 s. Interferences by ascorbic acid, uric acid, l-cysteine, and by biogenic amines and their metabolites are rejected at more than 97% by the PPD layer. Although several d-amino acids are potential substrates for RgDAAO, d-serine was the only endogenous substrate present in sufficient concentration to be detected by our microbiosensor in the central nervous system. When implanted in the cortex of anesthetized rats, this microbiosensor detected the increase in concentration of d-serine resulting from its diffusion across the blood-brain barrier after an intraperitoneal injection. This new device will make it possible to investigate in vivo the variations in d-serine concentrations occurring under normal and pathological conditions and to assess the pharmacological potency of new drugs designed to impact d-serine metabolism.

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MADICA 2006 Conference, Fifth Maghreb-Europe Meeting on Materials and their Applicatons for Devices and Physical, Chemical and Biological Sensors, MADICA 2006 Conference, Fifth Maghreb-Europe Meeting on Materials and their Applicatons for Devices and Physical, Chemical and Biological SensorsInternational audienceA lactate oxidase-based amperometric biosensor is designed for lactate determination. Two methods of lactate oxidase immobilization on the surface of commercial SensLab platinum printing electrodes are compared. The sensor with lactate oxidase immobilized by physical adsorption in Resydrol polymer is shown to have both narrower dynamic range (0.004–0.5 mМ lactate) and higher sensitivity (320 nA/mM) as compared with that immobilized in poly(3,4-ethylenedioxythiophene) by electrochemical polymerization (0.05–1.6 mM and 60 nA/mM respectively). The operational stability of the biosensors developed is studied; the immobilization method is shown to be of no influence. The lactate content in wine and in wine material during fermentation is analyzed. The data obtained by amperometric lactate biosensor correlated with those of standard chromatography. The biosensor developed can be used in food industry for control and optimization of process of wine fermentation as well as for control of wine quality

ABSTUCTDisposable conductometric microbiosensors based on immobilization of acetyl and butyrylcholinesterases (BuChEs) on interdigitated electrodes were fabricated. Enzymes were immobilized by crosslinking with bovine serum albumin and the differential output between the pair of electrodes covered with the enzyme membrane and the pair covered with albumin only was recorded. On the basis of these biosensors, a biochemical assay for pesticides in liquids was developed. Respective detection limits were 5 X lo-" M for diisopropyl fluorophosphate (DFP), lo-' M for trichlorfon, and M for paraoxon-methyl and paraoxon-ethyl for the assavs based on the enzymes tested. The presence of pesticides in the sample in concentration exceeding the detection limits can be detected after only 10 minutes of incubation, whereas, in order to extend the range of the determined pesticide concentration and to improve the accuracy of the assay, it is better to use incubation times longer than 30 minutes. Use of pyridin-2-aldoximide methiodide as reactivating agent allowed one to achieve the complete recovery of the sensor response when it was incubated in lowconcentrated pesticide solutions, e.g., less than M for paraoxon-methyl and during a short time, e.g., 10 to 20 minutes, for M paraoxon-methyl solution.

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