Biosensors & Bioelectronics Vol. 9 No. 6 (7 994)

Biosensors & Bioelectronics Abstracts Valerie Owen

In this international update on new publications in biosensors and related activities, we report on glucose biosensors from Denmark and France and urea sensor controlled artificial kidney from Germany. We begin, however, with an abstract from Switzerland on oxime formation.

Switzerland - Oxime formation used for synthesis

In J. Am. Chem. Sot. (116/l (30-33) 1994), K. Rose of University Medical Center, Geneva, Switzerland, reports on “Facile synthesis of homogeneous artificial proteins”.

The author describes a new approach, involving oxime formation, for the synthesis of stable macromolecules of defined structure and exemplified with polypeptides. Purified polypeptide fragments, carrying either aldehyde or aminooxy groups but devoid of protecting groups, are prepared. Next these fragments spontaneously self-assemble on an appropriate synthetic template under very mild conditions through formation of oxime bonds.

It is claimed that the resulting oximes are stable in water at room temperature at pH 2-7. One of the compounds made, the covalent structure of which is defined by electrospray mass spectrometry [observed MW 19 916.61 +/- 3.05 D; calculated MW 19 916.10 (average isotopic composition)], would seem to be the largest artificial protein ever made, in pure form in good yield, by controlled total synthesis. Possible applications of this method of synthesis of homogeneous macromolecules include vaccines, biosensors, and enhanced peptide libraries.

Contact: Department of Medical Biochemistry, University Medical Center, CH-1211, Geneva 4, Switzerland.

Germany - Uric acid & drug interference

In Klin. Labor, (40/l-2 (7-ll), 1994) K. Oehler, A. Warnecke, G. Rost G, K. Siegler and B. Weber of Hospital Lichtenberg, Germany report on “Comparison of the drug interference with different enzymatic methods for the determination of uric acid: Application of enzyme sensors”.

The authors describe the interaction of some drugs (ascorbic acid, mannitol, analgine, aminophenazone (aminopyrine), isopropyl- phenazone, carbidopa, levodopa) on enzymatic uric acid determination by uricase-PAP-method and the uric acid oxidase electrode.

Mannitol, aminophenazone and isopropylphenazone were found to have no influence in the interesting concentration range. The enzymatic sensor gave distinctly better results than the uricase-PAP-method with regard to ascorbic acid, carbidopa and levodopa, although both methods use the same enzyme.

Contact: Krankenhaus Lichtenberg, ortlicher Ber. O.-Ziethen Krankenhaus, Zentrallabor, Fanningerstr. 32, D-10365 Berlin, Germany.

Germany - Urea sensor controls artificial kidney

In Eur. J. Clin. Chem. Clin. Biochem. (32/3 (145-152) 1994), J.G. Schindler, M.M. Schindler, K. Hema, E. Reisinger, B. Burk, U. Kuhlmann, J.

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Biosensors & Bioelectronics Vol. 9 No. 6 (1994)

Knaack, B. Schmidt and H. Lange of Institut ftir Normale und Pathologische Physiologie, Maryburg, Germany report on “Urea-sensor for the continuous ammonium-selective-enzymatic process control of the artificial kidney”

The authors report on a flow-through method for continuous ammonium-selective enzymatic monitoring of the artificial kidney by means of a bioelectrochemical urea electrode. The urea is converted in an enzyme membrane by covalently bound urease and the ammonium ions are detected by a Nonactin-PVC-membrane. In addition to detailed data from the oxygen-independent solid-state contact sensor, curves are obtained on-line from the patient during the haemodialysis session. The advantages of the method are described in detail. Furthermore, the urea sensor can be used for measurements in heparinized blood.

Contact: Inst Nor-male und Path01 Physiologie, Projekt Biomedizinische Technik, Philipps-Universitat, Karl-von-Frisch-Strasse, D-35033 MarburglLahn, Germany.

Denmark - New glucose biosensor

In Anal. Chim. Acta, (288/3 (193- 196) 1994), J. Kulys, H.E. Hansen, T. Buch-Rasmussen, J. Wang and M. Ozsoz of Novo Nordisk A/S, Denmark report on “Glucose biosensor based on the incorporation of Meldola Blue and glucose oxidase within carbon paste”.

The authors state that the phenoxazine compound Meldola Blue (MB) is shown to efficiently mediate the electron transfer from reduced glucose oxidase to a conventional carbon paste electrode. The mediation process was exploited for developing an amperometric biosensor for glucose, which yielded a linear response to O-25 mM glucose at an operating potential of 50 mV (vs. SCE), where interfering reactions do not occur. Experimental variables such as enzyme loading or operating potential were explored, and a stable response was observed over several months.

Contact: Novo Nordisk AIS, Roskildevej 56, DK-3400 Hillerod, Denmark.

France - Better glucose biosensor response

In ANAL. CHIM. ACTA (288/3 (197-203) 1994), A.P. Soldatkin, A.V. El’skaya, A.A. Shul’ga, A.S. Jdanova, S.V. Dzyadevich, N. Jaffrezic-Renault, C. Martelet and P. Clechet of LPCI, France report on “Glucose sensitive conductometric biosensor with additional Nafion membrane: Reduction of influence of buffer capacity on the sensor response and extension of its dynamic range”

The authors reveal that glucose-sensitive enzyme conductometric biosensors based on interdigitated gold electrodes were prepared by cross-linking glucose oxidase with bovine serum albumin in a saturated glutaraldehyde vapour on the sensor chips.

Nafion membranes were deposited on top of the glucose sensor by a spin-coating procedure. The effects of buffer concentration and ionic strength were examined for the glucose sensors with and without Nafion membranes. Additional Nafion membranes resulted in a substantial reduction of the effect of buffer concentration on the sensor response and in an extension of the dynamic range of the sensor up to a glucose concentration of more than 10 mM. Moreover, the comparison of the properties of the developed conductometric glucose biosensors (operational and storage stability, reproducibility of measurements) demonstrates better performance of the sensor with an additional Nafion membrane.

Contact: LPCI, URA CNRS 404, ,?&ole Centrale de Lyon, BP 163, F-691 31 Ecully Cedex, France.

Canada - ssDNA grown onto optical fibres

In Anal. Chim. Acta (288/3 (205-214) 1994), P.A.E Piunno, U.J. Krull, R.H.E. Hudson, M.J. Damha, H. Cohen of the Department of Chemistry, University of Toronto, Canada report on “Fibre optic biosensor for fluorimetric detection of DNA hybridization”.

The authors state that they have grown single

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stranded deoxyribonucleic acid (ssDNA) thymidylic acid icosanucleotides (dTinf 2inf 0) onto optical fibres. The fibres were first derivatized with gamma- aminopropyl- triethoxysilane (APTES) onto which a spacer arm of 1 ,lO decanediol bis-succinate terminated with 5’-O-dimethoxytrityl- 2’-deoxythymidine was covalently attached.

The synthetic route used to grow the ssDNA was the well established solid-phase phosphoramidite methodology. The covalently immobilized oligomers were able to hybridize with available complementary ssDNA (cDNA) which was introduced into the local environment to form double stranded DNA (dsDNA). This event was detected by the use of the fluorescent DNA stain ethidium bromide (EB).

The sampling configuration utilized total internal reflection of optical radiation within the fibre, resulting in an intrinsic mode optical sensor. The non-optimized procedure used standard hybridization assay techniques to provide a detection limit of 86 ng ml“ cDNA, a sensitivity of 8l3% fluorescence intensity increase per 100 ng ml of cDNA initially present, with a hybridization analysis time of 46 min. The sensor has been observed to sustain activity after prolonged storage times (3 months) and harsh washing conditions (sonication).

Contact: Chemical Sensors Group, Department of Chemistry, University of Toronto, 3359 Mississauga Road North, Mississauga, Ont. L5L 1 C6. Canada.

Switzerland - Plasticizers investigated

In Anal. Chim. Acta (28911 (1-13) 1994) R. Eugster, T. Rosatzin, B. Rusterholz, B. Aebersold, U. Pedrazza, D. Ruegg, A. Schmid, U.E. Spichiger, and W. Simon of the Swiss Federal Inst. Technology in Zurich, Switzerland report on “Plasticizers for liquid membranes of ion-selective chemical.”

The authors investigated a variety of 55 different plasticizers based on various structural elements in respect to their applicability in liquid polymeric membranes of chemical sensors. The plasticizers and the overall performance of the

membrane were judged in respect to the properties of lipophilicity, solubility, exudation and selectivity, respectively.

A strategy for the design of plasticizers is derived from theoretical considerations and verified by experiments. The selectivity data were obtained by measurements with a standard Mg2+ selective electrode optimized for clinical applications. A plasticizer needs several large alkyl and/or aryl residues to exhibit sufficient lipophilicity. In order to avoid crystallization or exudation, the use of branched alkyl chains as well as the link or the substitution of the structural elements by an adequate number of polar or polarizable groups is encouraged. However, to ensure high selectivities, plasticizers should not contain functional groups which may act as coordination sites and therefore compete with the carrier.

In contrast to earlier publications it was observed that other properties than the dielectric constant of the plasticizer are more important for the selectivity of the membrane. A correlation between selectivity coefficient and the dielectric constant of the plasticizer could not be found.

Contact: Department of Organic Chemistry, Swiss Federal Inst. Technology (ETH), Universittitstrasse 16, CH-8092 Zurich, Switzerland.

Japan - Sweaty work by biosensors

In Anal. Chim. Acta (28911 (27-34) 1994) K. Mitsubayashi, M. Suzuki, E. Tamiya and I. Karube of the Japanese Advanced Institute of Science & Technology report on “Analysis of metabolites in sweat as a measure of physical condition”.

The authors collected sweat samples - induced by heating, exhaustive exercise and endurance exercise - from several healthy subjects. Analysis of the metabolites in sweat was performed using either amperometric biosensors, constructed from a dissolved oxygen sensor and immobilized enzyme membranes, or commercial ion-selective electrodes. The average concentrations of lactate and ammonium ion measured in sweat induced by exhaustive exercise

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were 115.8 and 90.5 mM respectively, 5.2 and 10.6 times higher than the results obtained from heat induced sweat. This contrasted with only a 2.0 and 3.0 fold increase following endurance exercise. The lactate concentration in sweat was found to be linearly related to the concentration of ammonium ion, with a slope of 1.07 ([ammonium ion]/[lactate], r = 0.996, lactate range of 16.1 to 110.3 n&l). In view of these results, lactate and ammonium ion in sweat were shown to be related to an increase in anaerobic metabolism, involving the glycolysis pathway and purine nucleotide cycle (PNC). It was demonstrated that the analysis of both lactate and ammonium ion in sweat is an effective, non-invasive and convenient method for estimation of physical condition.

Contact: Japanese Advanced Institute of Science & Technology, Hokurika (JAIST), 15 Asahidai, Tatsuguchi-cho, Nomi-gun, Ishikawa 923-12, Japan.

Germany - Precise modeling and control A monthly newshttar from of fermentations Elsevkr Advanced Tachnology

In Curr. Opin. Biotechnol. (5/2 (187-191) 1994) T.-H. Scheper, F. Lammers of Westfalische Wilhelms-Univ Munster, Germany report on “Fermentation monitoring and process control”

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During the past year, several papers describing the potential of new sensor devices for application in real bioprocesses have been published. Biosensors, optical sensors, and immunosensors are all gaining in importance. At present, the development of correct/adequate interfacing of biosensors to bioprocesses is the major limitation on progress. On the basis of new analytical data, a more precise modeling and control of fermentations can now be performed. Recent research efforts attest to the increasing importance of this area in biotechnology.

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