Acetylcholine receptors have been incorporated into planar lipid bilayers and coupled to the surface of a silicon wafer. The binding of ligands to these receptors have been quantified by measuring the concomitant changes of certain electrical properties of the membrane such as impedance and capacitance. The results show that there is principle feasibility to use membrane protein receptors as biosensors.

This report descibes a system for real time biospecific interaction analysis, using biosensor technology based on the optical phenomenon surface plasmon resonance. The biospecific interface is a sensor chip consisting of a thin gold film deposited on a glass support and covered with a dextran polymer. One component of the interaction being studied is attached covalently to the dextran, and other interactants are passed over the sensor chip assisted by a flow injection liquid handling system. Sequential interactions can be followed in real time in terms of changes in the mass concentration of molecules at the sensor interface. Surface concentrations down to 10 pg/mm2 can be measured. Repeated analysis can be performed on the same sensor chip by regeneration of the specific interaction. With this system, the same general procedure can be used for a wide range analytical methodology including: 1) identification and classification, for example antigen specificity and antibody subclass classification 2) concentration and activity determination in crude samples 3) affinity ranking 4) determination of relative association and dissociation rate constants 5) label free detection of multiple sequential interactions, for example epitope mapping of antibody binding sites on an antigen.

The principles of a new, non-flow, injection technique, termed batch injection analysis (BIA), for high speed biosensing are described. BIA is based on the reproducible injection of small samples toward a nearby detector, which is immersedin a large-volume stirred bulk solution. Passage of the sample zone over the detector surface results in sharp peak readouts, similar to those of flow injection analysis (FIA). Sample throughputs and size, the sensitivity, detection limits and reproducibility, are also similar to those of FIA. In addition, the need for pumps and connecting tubingsis eliminated. Becauseof the limited solution handling capability, BIA relies on the use of specific or reactive sensing surfaces. In particular, the inherent specificity of biosensors makes them extremely attractive for the BIA operation. Such characteristics and advantagesareillustrated for the use of enzymes or tissues, coupled to amperometric, potentiometric or thermal BIA detectors. The high-speed and simple BlA/biosensing operation holds a great promisefor clinical screening and bioprocess monitoring.

The continuous measurement of metabolic changesis an important part of the developmentof electrochemical sensors. Stability and sensitivity are essential requests, but compatibility towards biological materials and interferences with other substances need consideration, too. Dueto the high demands on the materials usable for implantation, the application to men is considerably restricted to analysis in vitro or ex vivo.

The signal generation, size and transmission of pre-steady-state and steady-state signals in fluorescence based fiber optic biosensors for on-line use and their applicability in several flow sensor configurations are investigated. In contrast to the theory, the signal for dynamic column biosensorswith larger particles was foundto be onlyslightly higher than for a column sensorwith smaller particles. This is due to interparticle interactions, which reduce the areathat is accessible for mass transfer, on particles with a diameter below 100 pm. Additionally this system has shown that dynamic biosensors with hydrolases can not be used for the determination of the end-pointof hydrolytic processes, when the equilibrium of the substrate conversion remains below 100%. The flow of optical power in fluorescent fiber optic sensors is analyzed, multiplicative noise is identified as the dominantlimitation of sensor performance. Evanescent coupling is a promising concept for fast biosensors. The observed nonlinear relation between absorbance and concentration is explained as an optical effect, caused by multimode operation. The use of special fibers with increased surface area gives higher sensitivity, reduced nonlinearity.

A large number of papers on biosensors have been published in the last few years. However, few of these sophisticated analysis systems have been used to monitor real bioprocesses. In this paper, a newly developed four-channel enzyme thermistor system and its application for biotechnological process monitoring is presented and discussed. Different sugars were detected simultaneously and online during the cultivation of Spodoptera frugiperda and Bacillus licheniformis in technical media. Immobilized enzymes and entrapped microorganisms were used as biological compoundin this biosensor. In addition, enantioselective analysis was performed by two enzyme reactions. For example, the detection of D,L-racemates of aminoacid esters was presented in an aqueous system. Futhermore the possibility of using this detection system in organic solvents was shown.

Single and multisensor Field Effect Transistors FET with a pH-sensitive Si/SiO2/SizN4/TazOs-gate and reference electrode (for single semsor) were developed and used for manufacturing the following BIO-FETs: for glucose analysis: Glucose Oxidase-FETs (GOD-FET), for penicillin G and V analysis: Penicillin G Amidase- and Penicillinase-FETs, for urea analysis: Urease-FET, and for cephalosporin C analysis: Cephalosporinase-FET. The GOD-FETswereintegrated into the FIA-system of Eppendorf (EVA) and used for monitoring the glucose concentration in microbial cultivation and production processes with recombinant_Escherichia coli K12 MF, recombinant Escherichia coli JM103, Saccharomyces cerevisiae H620, and Candida boidinii. Urease-FET-FIA was used to monitor the urea concentration in a simulatedcultivation of Cephalosporium acremonium and UREASE-FET-FIA and GOD-FET-FIA for the monitoring of urea and glucose concentrations in simulated Saccharomyces cerevisiae cultivations.

Electroanalysis of neurotransmitters using carbon fibre electrodes (CFE) is very important for the development of new drugs, for modern brain research and understanding of the molecular processes in the central nervous system. Essential fundamental works have been carried out by Adams [1], Gonon [2], Pons and Fleischmann [3] concerning pretreatment of the electrodes and techniques of measurement. However, there are still some questions, for instance the reproducibility of electrochemical and chemical pretreatment, influence of the kind of the fibre, of the application of polymer layers and of other modifications. Today commercial microelectrodes are still not avalaible. Users of electrodes usually have developed a method to be well applicable for themselves.

The application of new methods and biological components to the determination of pesticides in water is described. Triazines were monitored by competitive immunochemical assays applied to flow-through systems. With a FILA, which was based onthe principle of an ELISA, determination of pesticides within the limits of the European drinking water act was possible without preconcentration of the sample. Alternatively, a fluorescence-labelled antibody was used andthe level of binding measured using the method of the evanescent wave technique. With this system a regeneration was possible up to 300 times without anyloss ofactvity. The determination of particular pesticides was supplemented by the development of biosensors for a class of pesticides. This was achieved by microbial sensors for chlorinated compounds and by a test based on the inhibition of cholinesterase by carbamates and organophosphates. The microbial cells of Alcaligenes eutrophus JMP 134 were immobilized on an oxygen electrode, an increase of oxygen uptake being observed in the presence of 2, 4-dichlorophenoxyacetic acid and its derivatives. The inhibition of cholinesterase was monitored either automatically by a flow injection system or by a disposable sensor madebythick film technology.

During the last decade a new generation of sensors, the biosensors, has been developed for the quantitative measurement of biological substances. Application and specifity of a biosensor are determined by the recognizing biological/biochemical layer and the type of transducer. The specific interactions between enzymes and their substrates, antibodies and antigens or between receptors and hormones are responsible for the selective binding of biological components in solution. In serological diagnosis the rapid and sensitive detection of a viral antigen or the induced immunological response is ofvital interest. Other fields, such as the utilization in production and control processes, extend the spectrum of possible applications for such sensor systems. The HIV-system has been chosen as a model system. A peptide antigen from the p24 core protein and mu- rine monoclonalantibodies were used forinitial experiments. Experiments under morerealistic conditions were performed with a consensus peptide from the hypervariable V3-loop of the HIV-virus and the reactive rabbit immunosera. Ionsensitive fieldeffect transistors and piezoelectric erystals were tested with respect to their suitability for the detection of antibodies. These immunosensors have to be evaluated and optimized with regard to their turn-over periods, sensitivity and cross-selectivity underexactly defined conditions, Theuse of a sensor system based on a biosensor generally possesses - in comparison to conventional analytical systems - advantageslike reduced influence of environmentalinterferences, short response times, and the possibility to develop “intelligent sensors" with the help of integrated signal processing.