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CARRIER BASED SENSORS
No full textThe applicability of membranes with selective substrate permeability
in chemical sensors is reviewed. lIonophore membranes in
potentiometric ion sensors exhibit a highly specific permeability
for given ionic substrates, but no net transport of these ions
results at zero current. Novel sensors make use of a carriermediated
transport of ionic or neutral substrates through artificial
membranes, and their response can be characterized in analogy to
enzyme-based biosensors
ENZYME IMMUNOASSAY WITH ELECTROCHEMICAL DETECTION IN FLOW SYSTEMS
No full textThe selectivity of an antigen/antibody reaction combined with the chemical am plif ication
feature of an enzyme label enables high specificity and low detection levels to be achieved by
enzyme immunoassays. Electrochemical enzyme immunoassay is based on antigen labeled with
an enzyme that catalyzes the production of an electroactive product. Hydrodynamic electrochemical
techniques such as liquid chromatography and flow injection analysis with electrochemical
detection have proved to be very effective for the rapid determination of the
enzyme-generated product in enzyme immunoassays.
Heterogeneous enzyme imm unoassays in which antibody is adsorbed on the walls of polystyrene
cuvettes have been developed. Alkaline phosphatase, which catalyzes the conversion of
electroinactive phenylphosphate to phenol, is the enzyme label. The rate of phenol production
is measured by either liquid chromatography/electrochemistry or flow injection
analysis/electrochemistry with a thin-layer carbon paste electrode at +0.87V vs. the Ag/AgCl
reference electrode. An example is an assay for digoxin, a cardiac glycoside used to treat
chronic heart disease. The assay has a detection limit of 50 pg/mL and exhibits good correlation
with radioimmunoassay on patient serum samples over the therapeutic range of 0.8-2.0
ng/mL. Assays have also been developed for orosomucoid and rabbit imm unoglobulin G.
Homogeneous enzyme immunoassays are based on a reduction in catalytic activity of
enzyme-labeled drug when bound to antibody. The enzyme label glucose-6-phosphate dehydrogenase,
which catalyzes the conversion of NAD+ to NADH, has been used. The drug is quantitated
by measuring the rate of NADH production by liquid chromatography/electrochemistry.
Good results have been obtained for clinical samples of serum from patients on drug maintenance
for both phenytoin, an antiepileptic drug, and digoxin over their therapeutic ranges.
The heterogeneous enzyme immunoassay with electrochemical detection has several
advantages. The detection limit, as demonstrated for digoxin and IgG, is typically in the low
picogram-per-milliliter range and is a function of the antigen-antibody binding constant rather
than the ability to detect phenol. Consequently, even lower limits should be attainable.
Because the sample is rinsed out of the reagent tubes before adding substrate, problems with
interferences from electroactive constituents in the sample and possible fouling of the
electrode by the adsorption of protein films are eliminated. The main advantage of a homogeneous
immunoassay is the absence of a step for separating the antibody-bound antigen from
the free antigen. This usually translates into a simpler, faster assay procedure. However,
homogeneous assays are usually restricted to higher detection levels than are heterogeneous
assays and are more susceptible to interferences from other sample constituents that would
otherwise be removed in a separation step
NON-SPREADING CYTOPHAGAS IN ACTIVATED SLUDGE
No full textSpreading and non-spreading colonies of yellow pigmented, flexirubin-
positive bacteria were observed regularly on agar plates inoculated
with samples from different activated sludge and trickling
filter sources. One part of the non-spreading colonies formed spreading
colonies after transfer to more suitable growth media. The other
part was never observed to form spreading colonies on various growth
media tested. However, when examined microscopically in wet mount
preparations most of the non-spreading isolates showed the same type
of gliding motility as the spreading isolates. In order to test the
taxonomic homogeneity as well as possible relationships to "classical"
cytophagas, 25 non-spreading isolates were examined for 41 morphological
and physiological characteristics. Of the strains tested,
19 had more than 80 % of the characteristics in common. Besides their
deviating colony growth, the isolates differed from "classical" cytophagas
by their more complex growth requirements and by a less wide
spectrum of degradation capacities. It is concluded that the nonspreading
isolates represent a distinct cluster within a Cytophaga
group comprising all strains with gliding motility, flexirubin pigmentation
and a G + C base ratio in the range of 32 - 36 %
A NEW APPROACH TO THE SYNTHESIS OF GLYCOCONJUGATES
No full text1-0-Unsubstituted aldoses afford with trichloroacetonitrile under base catalysis
0-(glycosyl)trichloroacetimidates in high yields. Depending on the reaction conditions
either 0-(a-glycosyl) or 0-(ßB-glycosyl)trichloroacetimidates may be obtained
highly selectively or even exclusively. The extraordinary diastereoselectivity control
is mainly due to stereoelectronic effects.
The 0-(a- or B-glycosyl)trichloroacetimidates are stable compounds, which can be
isolated easily, quite often as erystalline material. They may be stored for a long
period of time. However, upon mild acid catalysis they become strong glycosylating
agents. They have proven as versatile intermediates in complex glycosidation reactions
with different nucleophiles (0-, S-, N-, and C-nucleophiles).
The application of this methodology to the synthesis of glycosphingolipids, glycophospholipid
type compounds, and to the synthesis of the tetrasaccharide of the core
region of 0-glycoproteins is presented. In addition, the 0-(glycosyl)trichloroacetimidate
based synthesis of the repeating unit of Neisseria meningitidis (Serogroup
L) will be outlined. Halogenoses and heavy metal salt catalysis are not required in
these procedures
ANWENDUNGEN VON MEMBRANEN BEI CHEMISCHEN UND BIOCHEMISCHEN SENSOREN
No full textZur Verbesserung der Kontrolle biotechnologischer Prozesse benötigt man mehr und bessere
Informationen über die Zelle und ihre physikalisch-chemische Umwelt. Die Entwicklung
von chemischen und biochemischen Sensoren ermöglicht die on-line Analyse der
chemischen Umwelt der Zellen. Im folgenden soll die Rolle der Membran, die ein wesentlicher
Bestandteil der Sensoren ist, bei verschiedenen Sensoren untersucht werden
MEASUREMENT OF SUBCUTANEOUS GLUCOSE CONCENTRATION IN SHEEP WITH AN AMPEROMETRIC ENZYME ELECTRODE
No full textAn amperometric enzyme electrode was developped for measurement of
glucose in subcutaneous tissue. In vitro, this sensor exhibited an
linear range extending to 500 mg/dl and was stable for at least 7
days. The measurement was relatively independent from ambient oxygen
concentrations and was not significantly influenced by stirring. In
short term in vivo experiments this sensor was successfully used for
glucose measurement in subcutaneous tissue of sheep
A CHEMFET MICROCELL SYSTEM FOR MEDICAL AND BIOTECHNOLOGICAL ONLINE ELECTROLYTE MONITORING
No full textA ChemFET microcell system for online electrolyte monitoring is described. The sampling
sensor element only consists of a two lumen catheter and a sandwich flow through cell with
spatially separated ISFETs, temperature sensor and heater. The required sample volume is
about 10 ul
MULTI-FUNCTIONAL SENSING DEVICE TO BE PLACED IN THE CENTER OF THE HEART
No full textThe first generation of electrical pacemakers stimulate the heart
at a fixed rate, usually 70 beats per minute. It was evident that
this did not completely correct the the effects of the underlying
pathological disorder. Therefore several methods were tried to adapt
the frequency to the physiological needs
BIOSENSORS BASED ON THE PYROELECTRIC BEHAVIOUR OF BIOLOGICAL SYSTEMS
No full textLiving organisms contain pyroelectric structures which function extremely
well as pyroelectric detectors and transducers. Organisms
are thus able to detect and discriminate between different stimuli
in the environment, such as rapid changes of temperature, of illumination,
of uniaxial and hydrostatic pressure. The different stimuli
represent different forms of energy and are transduced into the
nearly uniform type of electrical signals, whose voltage/time-course
frequently depends on dX/dt (X, stimulus; t, time). The voltage/timecourses
of the pyroelectric responses of biological systems (like
nerve tissue) on the one hand, and of nonbiological pyroelectric
crystals (like tourmaline) or nonbiological pyroelectric polymers
(like polyvinylidene fluoride) on the other hand, to external
stimuli are analogous
STARTERKULTUREN IN DER MILCHVERARBEITENDEN INDUSTRIE - NEUE ERKENNTNISSE UND IHRE UBERFUHRUNG IN DIE ANWENDUNGSTECHNOLOGIE
No full textStarter cultures are used today in the controlled fermentation of a wide variety of
foodstuffs. Since the beginning of this century, lactic acid bacteria and - depending
upon the end product - propionic acid bacteria, yeasts and/or moulds have been employed
as starter cultures in the fermentation of milk and maturing of milk products.
Without exact knowledge of the biochemical potential and genetic characteristics of
lactic acid bacteria in conjunction with a fundamental change in the types of cultures
offered by the starter culture industry, the technological transformation of the
traditional small artisan plant into the present-day industrial-scale - and often
automated - production processes would hardly have been possible.
The most comprehensive scientific knowledge available is on lactic acid bacteria —
primarily lactic acid streptococci. It is known that the important technological
features are linked to plasmids, for instance in the case of lactose conversion, proteolysis,
the formation of flavours in phage resistance and others. Particularly in
combating bacteriophages, diverse concepts have been developed and progress achieved.
Nowadays attempts are being made to create phage-resistant cells through genetic
manipulation. A more thorough knowledge of proteolysis and the formation of flavours
could lead to increased influence on the maturing and aromatization of milk products