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OPTICAL RECOGNITION OF SUBSTRATES IN MEMBRANES
No full textMacrocyclic and non-macrocyclic ion-selective carriers containing
structural elements that heavily change their optical properties in the
uv / VIS region upon ion complexation have been introduced earlier as
chromoionophores and fluoroionophores, respectively. Here we present
membrane morphologies resulting in a successful design of sensor
membranes with an optical transduction of the chemical substrate
recognition process. Novel optodes based on membranes containing a
neutral carrier for a selected ion, a neutral chromoionophore (e.g. for
H30*) as well as lipophilic anionic sites can be made to selectively
respond to at least 20 different ions
POTENTIOMETRIC FLOW-INJECTION DETERMINATION OF UREA IN BLOOD SERUM USING ASYMMETRIC MEMBRANE ION-SELECTIVE ELECTRODE
No full textThe potentiometric response of urea biosensor based on asymmetric cellulose
triacetate membrane with nonactin and immobilized urease is strongly
interfered by the presence of ammonium and potassium ions. The coveting
of biosensor surface with microporous hydrocarbon anion-exchange membrane
does not eliminate the cationic interferences sufficiently. The
complete removal of interferences was obtained when fluorocarbon polymer
anionic membrane was used either in a compact biosensor in wall-jet flow
cell or in a separate dialyzer unit. For the latter case, in the optimized
conditions of the flow-injection measurements, the lower detection
limit of Nernstian response was 2mM urea. In measurements with maximum
sampling rate 70 hr-l total removal of 10 mM potassium and 1 mM ammonium
ion interference was obtained. Results of flow-injection urea determination
in human blood serum samples were correlated with those obtained with
Kodak EktaChem 700 clinical analyzer
AUTOMATED LIPOSOME-BASED FLOW INJECTION IMMUNOASSAY SYSTEM
No full textA liposome-based flow injection immunoassay (FIIA) system for quantitation ofa clinical analyte,
theophylline, and also, with very minor changes in the assay format, of an antibody to theophylline,
has been developed. Automated sequential analyses were performed at room temperaturewith
picomolesensitivity and a day-to-day coefficient of variation of less than 5 %. The system components
include liposomesthat contain fluorophoresin their aqueouscentral cavities and an
immobilized-antibody reactor column. The immunoreactor was regenerated hundreds of times
over three monthsof continuoususe with no measurable loss of antibody activity. The special
advantages ofusing flow injection analysis for immunoassays and ofusing liposomesin FIIA,
compared to most current immunoassay techniques,are described
DEVELOPMENT OF ELECTROCHEMICAL FIA SYSTEM WITH IMMOBILIZED ENZYMES AS SPECIFIC POST-COLUMN DETECTOR OF HPLC
No full textA sensitive and highly selective method for the simultaneous determination
of a variety of species is proposed. An amperometric flowinjection
system with the immobilized enzyme reactors or enzyme sensors
is used as the specific post detection system of HPLC, to convert
compounds separated by a reversed-phase HPLC column to electroactive
species (hydrogen peroxide and uric acid) which can be detected at 0.5
V vs. Ag/AgCl. The proposed system has been applied to the optically
specific detection of L- and D-amino acids, the simultaneous detection
of acetylcholine and choline, specific detection of a group of purine
bases and purine nucleosides, and the high-sensitive detection of Llactate
and pyruvate with substrate amplification. Specificity of the
method is proposed by the HPLC column, the enzymatic reactions, and the
electrochemical detector
BIOLOGICALLY MODIFIED ELECTRODES AS FIA DETECTORS
No full textThis chapter describes new amperometric biosensors and measurement
strategies for electrochemical monitoring of flowing streams. Special attention
will be given to thin-layer devices based on incorporating the biological entity in
polishable and robust graphite-epoxy or soft carbon paste matrices, as well as
into micropores of reticulated vitreous carbon. The elimination of supporting
membranes (diffusional barriers) and the intimate contact between the
biological and transducing sites assure very fast response, as desired in dynamic
flour systems. Similar advantages accrue from the use of a series flow thinlayer
detector with an upstream biological generator and downstream
amperometric "collector." The sensory ability of numerous biological entities,
including plant tissues, enzymes or microorganisms will be described in
connection with these flow detectors. Potential interferences (electroactive and
surface-active) are minimized via enzymatic consumption (digestion) at the
surface. Additional advantages are achieved from the simultantous
immobilization of several enzymes, enzyme/tissue or enzyme/electron acceptor.
The FIA operation allows systematic characterization of electrochemical
biosensors, compared to manual, batch, testing
ASCORBIC ACID DETERMINATION IN FRUIT JUICES BASED ON A FIBRE OPTIC ASCORBIC ACID BIOSENSOR AND FLOW INJECTION ANALYSIS
No full textA new method using a fibre optic ascorbic acid biosensor as the
detection unit in a flow injection analysis (FIA) system is presented.
The biosensor is based on a fibre optic oxygen optrode which measures
the oxygen consumption via dynamic quenching of the fluorescence of a
dye by molecular oxygen. Ascorbic acid oxidase is immobilised onto the
surface of the oxygen optrode as biological component.
To detect ascorbic acid in fruit juices it is necessary to protect
the biosensor from low pH, such as is present in fruit juices (e.g.
lemon juice pH 1.5), using a FIA-system which automatically buffers and
dilutes the juice samples
Biosensor Systems for Process Control in Biotechnolgy
No full textThree different types of biosensor systems will be presented in this paper: a
microbial optrode (measuring the intracellular NAD(P)H-content in
immobilized cells), an optrode with immobilized coenzymes and enzymes
(measuring the fluorescence of molecular weight increased NADH/NADPH),
an enzymethermistor system (measuring the heat evolved during enzymatic
or microbial reactions) and a automized immunoanalysis system. The
application of these sensor systemswill be discussed
FLOW INJECTION IMMUNOANALYSIS (FIIA) FOR THE DETERMINATION OF PESTICIDES IN WATER
No full textThe principle of a heterogeneous competitive enzyme immunoassay was
applied to a flow injection system. This flow injection immunoassay
(FIIA) can be run automatically. Antibodies to the triazine herbicide
atrazin were immobilized on membranes. Antibody containing membranes
were mounted in a cross-flow reactor and changed after each assay. In
the assay atrazin competed with an atrazin-peroxidase conjugate for the
antibody binding sites. The product of the enzyme reaction was measured
fluorimetrically. One assay is completed within 15 minutes. Sensitivities
of the FIIA proved similar to the ELISA and depended mainly
on the properties of the antibodies and conjugation strategies. The
potential and limitations of the FIIA system will be discussed
ADSORPTION OF DYES AND PROTEINS TO MONOLAYERS
No full textThe reflection of light at the air/water interface is modified by formation of a monolayer.
In the presence of dye molecules at the interface the reflection spectrum coincides with
the absorption spectrum of the dye monolayer. Using the reflection technique the adsorption
of ionic dyes from the aqueous subphase to mixed monolayers including head groups of
opposite charge have been investigated. Electrostatic binding of the dye is enhanced at
constant charge density if the charge distribution matches that of the adsorbate. Binding
of cytochrome c to phospholipid monolayers is dominated by electrostatic interactions. The
porphin chromophore of the adsorbed protein is oriented parallel to the monolayer plane
SENSITIVE DETECTION OF PROTEIN ADSORPTION TO SUPPORTEDLIPID BILAYERS BY CAPACITANCE MEASUREMENTS
No full textWereport experiments on the sensitive detection of protein adsorption to lipid bilayers deposited
onto chromium electrodes on glass substrates by capacitance measurements. The sensitivity of
the present type of sensor (better than 3A average protein layer thickness) is at least equivalent
to that of ellipsometry. A high specific resistance of the supported bilayer of (1-5)-10%cm® is
achieved by deposition of a tightly packed (crystalline) cadmium arachidate monolayer in contact
with the substrate, whereas the outer monolayer can be more loosely packed (fluid phase or
state of fluid-solid coexistence) which is essential for the incorporation of receptors. In the
present work, charged lipids are incorporated as nonspecific receptors for polylysine and cytochrome
c. Furthermore, the capacitance measurements provide a very sensitive test for the
tightness and long-time stability of supported bilayers