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BIOSENSORS BASED ON RECEPTORS : ELECTRICAL TRANSDUCER PRINCIPLES
No full textBiosensor systems based on receptors are of increasing interest for a variety of potential
fields of application. Typical species to be detected are sugars or antigens (38). Electrical transducer
principles to detect these species are investigated in the present study. These principles
are based on capacitance-voltage measurements with their characteristic changes in flat-band
voltage AV, and capacitance AC, and on measurements with ion-sensitive field effect transistors
(ISFETs)
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)
EASY PRODUCIBLE AMPEROMETRIC AND VOLTAMETRIC GLASS MICROSENSORS WITH TIP-DIAMETERS BETWEEN 0.3 AND 3 micro-m
No full textAMPEROMETRIC GLASS MICROSENSORS FOR PO2-AND H202-MEASUREMENT
Well controlled electro-deposition of gold onto an etched
platinum wire inside a small glass capillary, tip diam. 2-3 pm
Preliminary Investigations on Immunosensorsfor the Gasphase
No full textThe Dragerwerk AGis selling chemical tests for gas phase measurements which are quick
and easy to handle. Today government laws and the market demand more specific and more
sensitive tests. Using enzymes Drager enteredthe field of biosensors by developing a highly sensitive
and highly specific formaldehyde biosensor (1). This sensor allows analysis through simple color
comparison. But lots of substances cannot be measured by using either enzymes or chemicals.
Amongthem areinsecticides like pyrethroids and bacteria like Escherichia coli K-12. Therefore we
started to develop tests based on immunological reactions
FIBER OPTIC BIOSENSING BASED ON RECEPTOR RECOGNITION
No full textEnzymes,ion carriers, and optically active receptors are shownto be useful for specific
recognition and sensing of biologically important species including enzymesubstrates,
metabolites, and drugs. In enzyme-based sensors, optical assays for substrates (such as
glucose, lactate or cholesterol)have bee designed andare fairly established. The specificity
of such sensorsis usually very high. However, quite a numberof assays cannot be performed
with enzymes, and use has to be made ofion carriers and other recognition elements. A
quite different situation is found in such cases. In contrast to enzymes which "digest" their
substrates, receptors do not metabolize their substrates. They therefore offer an promising
alternative for enzymatic recognition of substrates. However, most existing receptors lack
the tremendousspecificity of enzymes. Neutral on carriers which may be considered as a
kind of ion receptors, are a notable exception. If the receptoris enantio-selective(i.e.
preferably binds one speciesoutofa pairof optical isomers)a fairly specific recognition of
enantiomers of biogenic amines (such as some drugs and biogenic amines) becomes
possible. In contrast to enzyme-based sensing where steady-state response is a result of
kinetic equilibration, this type of substrate binding results in thermodynamicequilibration.
Specific examples are given for new types sensors and sensors based on recognition by
enzymes, neutralion carriers, charge-transfer interaction, and hydrogen bonding. Their
respective merits and limitations are discussed
GAS-SENSING DETECTOR WITH INTERNAL NONACTIN BASED ISE FOR FLOW-INJECTION POTENTIOMETRIC DETECTION OF SUBSTRATES PRODUCING AMMONIA IN ENZYMATIC REACTION
No full textIon-selective electrode with polymer membrane containing
nonactin is employed for the potentiometric detection of
ammonia produced in biocatalytic reactions. Elimination of
interferences occuring in the presence of alkali metal ions
can be achieved by covering a nonactin membrane with outer
hydrophobic gas permeable membrane with a layer of internal
solution between the membranes and a miniature reference
electrode.
Optimization of design of such a sensor for the enzymatic
detection of substrates in flow-injection measurements
with a large-volume wall-jet detector was carried out. Among
experimental variables optimized were composition of a nonactin
containing membrane, kind of gas permeable membrane,
geometry of the sensor and composition of the internal solution
Ahnlichkeitsanalyse biologisch aktiver Molekiile mit durch Autokorrelationsvektoren trainierten selbstorganisierenden Karten
No full textTopological autocorrelation vectors can be used to estimate similarities of molecular structures.
In the following paper we examinedifferent data sets of increasing size and complexity
with this measure of similarity. All data sets contain substances with known biologicalactivity
on the dopaminergic and benzodiazepine receptors. These two different classes of biological
active substances can be separated by self-organizing maps, a kind of neural network well
suited for clustering and visualization of similarity. The method is implemented on a massively
parallel SIMD computer (MasPar MP-1) which is able to perform this analysis for databases
of several thousand substances
Carbohydrate Analysis of Glycoproteins on Blots Using the Immunological System: Digoxigenin/Anti-Digoxigenin Antibody
No full textBy introducing the steroid hapten digoxigenin specifically into sugars, a sensitive detection system for
glycoproteins on blots has been developed. Digoxigenin is bound to sugars either as
digoxigenin-hydrazide after oxidation to aldehydes, or as lectin conjugates. Digoxigenin is then detected
with a high-affinity anti-digoxigenin antibody, conjugated with alkaline phosphatase or peroxidase.
Besides of the general labeling of the carbohydrates, the reaction with digoxigenin-hydrazide can further
be made specific for the detection ofsialic acids or terminal galactose. By using digoxigenin labeled
lectins with defined and narrow binding specificity for probing of the glycoproteins, it is possible to
obtain substantial informations on the glycan structures. The high resolution power of electrophoretical
separation systems is widely used for analyzing complex protein mixtures. The combination of these
techniques with the sensitive digoxigenin based labeling and detection system allows the rapid analysis
of small amounts of glycoproteins, which can be further refined by including exo- and endoglycosidase
digestions as specific tools
ENZYMATIC GLYCOSYLATION OF N-LINKED GLYCOPROTEIN GLYCANS
No full textN-linked glycoprotein glycans were modified by combined use of glycosidases and glycosyltransferases.
Human milk 81,4 galactosyltransferase andrat liver 02,6 sialyltransferase
were immobilized by covalent or affinity binding methods. These immobilized glycosyltransferases
were used in a slurry reactor for continuous glycosylation of endoglycosidase H-treated
invertase or r-tPA. Theresulting sialylated glycan chains mimicking the structureof outer
complex N-glycansconferred extended plasma half-life time compared to galactosylated
glycoprotein
THE RELEVANCE OF GLYCOSYLATION TO THE PRODUCTION OF RECOMBINANT GLYCOPROTEINS
No full textIt is being increasingly recognised that many polypeptides of therapeutic interest, which in
their native form are glycoproteins, need to be glycosylated in order to be of benefit in vivo..A
consideration of polypeptide glycosylation therefore becomes relevant throughoutthe
development and production of recombinant glycoproteins, principally for the following reasons.
First, cell lines differ in their glycosylation characteristics, and the same polypeptide expressed in
two different cell lines will generally be glycosylated differently. As a consequence, a recombinant
glycoprotein is usually glycosylated differently to the native form, and such 'non-physiological'
glycosylation can have profoundeffects on functional activity, physicochemical properties, and
pharmacokinetic behaviour in vivo . A limited set of oligosaccharide determinants has been
identified, the members of which influence the pharmacokinetic and immunogenic properties of
a glycoprotein. It can therefore prove valuable to screen anycell line chosen for the production of
a recombinant polypeptide, for expression of such determinants. Second, to ensurethat any
changes in culture method (for example, during scale-up) are not associated with alterations in
glycosylation, and that batch-to-batch uniformity is maintained during production,it is necessary
to follow the glycosylation pattern of the secreted protein. Third, individual glycoformsof a
polypeptide can differ with respect to functional properties. Identification of an improved
product may, in some cases, involve nothing morethan isolation of a particular glycosylation
variant. These and other aspects of the glycosylation of recombinant glycoproteins are discussed ir
this paper