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POTENTIAL RELAXATION AS A MEASUREMENT PROCEDURE FOR BIOSENSORS
No full textWe present a discontinuously working procedure for long-term measurement of the
concentration of an analyte in a solution with an enzyme electrode.
As compared with this method the well-known amperometric procedure works
continuously: The working electrode is permanently forced to a certain voltage, and
a current results, the magnitude of which is a measure of the concentration of the
analyte. The disadvantage may arise that the function of the working electrode can
be affected by products of interfering reactions and succeeding reactions (e.g.
polymerization). In in-vivo- application the permanently applied voltage at such
electrodes can also cause electrochemical conversion of physiological substances
into toxic ones and stimulate immune reactions leading to encapsulating of the
sensor.
The presented relaxation procedure uses the same biosensor arrangement as the
amperometric one. The respective voltages, however, are applied only for a short
time (about one second) and the interruptions are long (in the range of minutes)
Noninvasive Recording of Neuronal Activity by Fieldeffect Transistors and Fluorescent Dyes
No full textMultisite recording of electrical activity of neurons is a prerequisite to
investigate signal processing in arborized neurons and in neural nets.
Such a method must be noninvasive and should detect changes of the
intracellular voltage at a high spatio-temporal resolution. Two approaches
are considered: (i) Influence-Technique [1]; A probe capacitor - silicon
oxide on silicon - is attached to the neuron membrane. Part of the
membrane potential drops across the probe capacitor. That voltage
modulates the charge distribution in silicon which is observed by the
source-drain current in field-effect transistor configuration. (ii) Field-
Technique A charged probe molecule - amphiphilic dye - is bound
to the neuron membrane. The electrical field at the site of the probe
affects the location of the dye at the membrane/water-interface.
Resolvation modulates the spectroscopic and photochemical properties of
the probe as observed by fluorescence. The methods are tested with
identified neurons of the leech which are cultivated with designed
geometry of their arborizations [4,5]
Microbiosensors Prepared by Micromachining
No full textThis paper introduces the application of micromachining techniques to biochemical
sensing. The micromachined biosensors have small size, low production cost, and good
reproducibility. Therefore,it is suitable for in vivo measurement, microanalysis and disposable
use. We developed two types of micromachined amperometric biosensor, one is based on a
micro oxygenelectrode, and another is an integrated micro electrochemical cell whichconsists
of micro electrodes and small sample chamber. We made a CO, sensor, L-lysine sensor and
hypoxanthine sensor using the micro oxygen electrode, and a glucose sensor using the
integrated micro electrochemical cell
3D-Segmentierungstechniken und vektorwertige Bewertungsfunktionen für symbolisches Protein-Protein-Docking
No full textThe growing number of known 3D protein structures asks for computing systems predicting
whether and where two molecules interact with each other. This requires search for
possible docking sites of proteins. Based on results of preprocessing techniques like computation
of molecular surfaces and segmentation, a knowledge based control algorithm
implemented with the semantic network ERNEST searches for geometrical and chemical
complementarity on molecular surfaces, computes coarse docking positions considering
steric clash and simple geometric judgement functions. Additionally, ERNEST guides a
more detailed analysis of finer calcultations including correlation of geometry and hydrophobicity.
The proposed hierarchical system allows to predict completely automatically
and in reasonable short computing times possible docking sites for two given proteins. A
set of 18 representative examples is discussed
Algebraic Methods for the Analysis of Redundancy and Identifiability in Metabolic 13C-Labelling Systems
No full textStationary !?C tracer experiments supply a large amount of information related to metabolic
fluxes in microorganisms. The unknownintracellular fluxes can be determined from some
directly measured metabolic fluxes and the fractional labelling of intracellular carbon atom
pools. Metabolic ?C-Labelling Systems are modelled by large algebraic equation systems with
respect to fluxes and fractional labels. Identifiability of the unknownintracellular fluxes and
redundancy of measured quantities are of great importance for the design and evaluation of
experiments. This contribution presents algebraic methods to treat these problemsa priori and a
posteriori. The Gröbnerbasis algorithm from polynomialideal theory is shownto be capable of
solving all relevant problems. Ideas from algebraic geometry prove to be helpful in designing
corresponding computer algebraic solution strategies. As an application example some global
results on the identifiability of bidirectional reaction steps are derived
MALATE DETERMINATION BY FLOW INJECTION ANALYSIS ( FIA ) USING A COUPLED DEHYDROGENASE/TRANSFERASE SYSTEM
No full textThe determination of L-malate was based on its oxidation by NADt catalyzed
by immobilized malate dehydrogenase (MDH, EC 1.1.1.37) in a flow
injection system. The NADH produced in an enzyme reactor was detected
fluorimetrically. Malate dehydrogenases from different sources were
immobilized on aminoderivatized controlled pore glass by glutardialdehyde.
Hence the equilibrium of the MDH catalyzed reaction is far in
favour of L-malate only little response could be obtained by malate
injection. To achieve higher substrate conversion, aspartate aminotransferase
(AST, EC 2.6.1.1) was coimmobilized to transform the
reaction product oxaloacetate. Enzyme reactors with and without AST
were compared and optimized. With the bienzyme reactor, malate concentrations
between 5 and 500 uM could be monitored
MEASUREMENT OF THE ACCUMULATION OF BIOMOLECULES IN A SOLUTION BY MEANS OF PIEZOELECTRIC CRYSTALS
No full textThe principle of micro weighingis used to detect minute amounts of biological and
chemical substances in liquids. By this micro weighing mass accumulation onto a
sensitive layer can be measured,e. g. the accumulation of antigens onto a layer of
antibodies.
This paper deals with micro weighing based on the principle of measuring the
change of the resonant frequency of a piezoelectric resonator in consequence of
the above-mentioned mass accumulation
CALIBRATION TECHNIQUES OF GAS SENSORS AND SENSORSPECIFIC SIGNAL PROCESSING
No full textThe calibration techniques of gas sensors are powerful and irreplacible
tools for measuring multidimensional characteristique fields and
are guarantying more reliability in practical application. It is
wellknown, that gas sensors normally are as well influenced by parameters
as temperature, pressure, massflow and moisture as there often
exist non linear cross-sensitivities to other related gases. All these
properties effect that in the past the suitability of gas sensors
for analytical measurement was not sufficient enough. In spite of all
these disadvantages there is a real chance for utilization in analytical
instrumentation, when only the sensors are working reproducible
under equal conditions. By means of high-performance microprocessortechnology
combined with high standard gascalibration techniques it
is possible to create low cost and wellworking smart sensor systens.
The act of part is, to prepare very carefully the multicomponent
testgases, which have to be controlled by corresponding analytical
methods. Considering that the sensors are even formed to all the relevant
parameters, as temperature, pressure, massflow and moisture,
the microprocessor controlled signal recording can be done.
Last but not least it is unimportet which gas sensor signals has to
be recorded. For all detectable signals like current, voltage, capacity
or any impedance relationship there exist high sensitive and
corresponding measuring-programs. Therefore it is possible to measure
not only "chemical sensors" like chem-FETs or semiconductor divices
but also sensors which are based on biological or enzymatical materials
A NOVEL ENZYMATIC ASSAY METHOD FOR HYPOXANTHINE
No full textWe developed a highly sensitive and rapid enzymatic assay for hypoxanthine with a
Clark oxygen electrode as sensor. In the presence of sodium sulfite, oxidation of
hypoxanthine by milk xanthine oxidase caused very rapid and increased oxygen consumption
in excess of the stoichiometric requirement for hypoxanthine oxidation. Hypoxanthine
from 0.5 to 10 uM can be assayed within a few minutes by addition of 25 mM
sodium sulfite to the reaction mixture. This assay proved to be more than 10 times
more sensitive and much more rapid than control method without sulfite
Title, Foreword, In Memoriam Takashi Murachi, Contents, List of Authors, Photo of the participants
No full textFlowinjection analysis (FIA), at the age of 16 (1), has come ofage and as a lively adolescent promises to
contribute many new methods to automated analysis. Novel FIA concepts are far from being exhausted, as
outlined in a brillant lecture during this workshop (2).
FIA has madeits impact in manyfields, e.g. chemical process control (3). In recent years, the life sciences
in particular have profited from and contributed to the development of FIA (4). As a result, it seemed
appropriate to devote a special workshopto the application of FIA in this area of research and technology.
The GBF, with its emphasis in biotechnology-related R&D and some pioneering activities in this area,
seemed an appropriate location to host this meeting.
As a result, about 70 FIA enthusiasts gathered in Braunschweig from May 13 - 15. 1990. On the eve of
German unification, it was not too astonishing that the good links of the GBF with the Academy of
Sciences, and to other research groups in the German Democratic Republic,led to a significant participation
of scientists from GDR. Table 1 indicates the statistics of the participants.
As documented in this monograph, the meeting provided a useful platform to assess the applicability of FIA
based on enzymes and antibodies in medicine, bioprocess control, food and environmental analysis. For the
GBF groupin particular, whose emphasis has been focused in this area for the past 3 years (Fig. 1), this
forum provided an excellent Opportunity to discuss present achievements and future plans with the leaders
in this field.
Alas, one of the pioneers of FIA in clinical analysis was missing. Prof. Takashi Murachi, eminent scientist,
teacher and peer, had passed away on theeve ofthe workshop.Prof. Murachi, Director of the Department
of Clinical Science and Laboratory Medicine of Kyoto University and former President of the Japanese
Biochemical Society, had presented a most memorable lecture at the GBF International Workshop on
Biosensors in 1987 (5). He was a leading authority in thefield of clinical biochemistry, and far beyond. In
FIA, he and his coworkers have made outstanding contributions. Their concept of a "one-shot FIA system"
(which has been commercialized by Shimadzu Co., Kyoto) is especially noteworthy.
At the GBF we wantto express the feelings of the attendants of this workshop as we dedicate this FIA
monograph to the memory of Prof. Takashi Murachi. Our deep sympathy is with his wife, his family and
his laboratory, which was most professionally represented at the workshop by Dr. Masayoshi Tabata.
Many coworkers have helped to turn this workshop into a successful event. Special thanks are due to my
secretaries, Heidi Rabe and Sylvia Schmidt, whoassisted in early preparations; Birgit Balster, a B. Sc. student
in biology, who proved to be a competent and charming assistant workshopsecretary; Dr. Joh.-Heinr.
Walsdorff, the copy editor of this monograph, who took great professional care in organizing the
proceedings; the GBF biosensor group, under the guidance of Dr. Ursula Bilitewski, who helped in all
aspects of the workshop organization. Finally, the moral and financial support from the managementof the
GBF,Prof. J. Klein and Dr. H. Zeitträger, and from the Project Management Group of Biology, Ecology
and Energy, of the Federal Ministry of Research and Technology, is gratefully acknowledged