Biosensors - Development and Application
As per definition of IUPAC, a biosensor – in contrast to biotic sensors or biotests – is a self-contained, integrated receptor-transducer device, which is capable of providing selective quantitative or semi-quantitative analytical information and which uses a biological recognition element (bio-receptor) and a transducer in direct spacial contact [IUPAC, 1996. A definition of biosensors. Electrochemical biosensors: proposed definitions and classification. Biosens. Bioelectron. 11 (4), i].
Principle of biosensor
At the transducer, the biological recognition reaction of the receptor is converted into an electronic signal. Biosensors can be used for a selective detection of a chemical compound in complex mixtures. Biosensors are relatively novel analytical systems providing simple, fast and cost-effective analyses in medical or environmental analytics, as well as in the food industry, the pharmaceutical and biotechnological industries. Analysis using biosensors is reagent-free, no toxic wastes are produced and therefore it is per se envionmentally friendly. Further advantages are the simple preparation of the sample (normally, mixing with buffer solution is enough), high selectivity and high sensitivity.
The bio-receptors most widely used are enzymes, microorganisms, tissue sections, antibodies, lectins, aptamers, and DNA. In order to attach the biological compound to the transducer, various immobilization procedures can be utilized, e.g., adsorption, entrapment within a polymeric matrix, covalent bonding, or cross-linking. The method of choice has to fulfill several needs: firstly, the biological compound must be attached well enough to prevent diffusion into the measuring solution, then, the bio-component must remain sufficiently active even in immobilized form and finally, it must remain available for the analyte. Enzymes that are used in biosensors often belong to the classes of oxidoreductases and hydrolases. Oxidoreductases are one part of the charge transfer reaction chain shuttling electrons. Thus, they are particularly suitable for their coupling with electrochemical transducers.
A well-known example: the glucose sensor
A well-known example of a enzyme sensor is the sensor for glucose. It normally consists of the enzyme glucose oxidase (GOD) being immobilized at an amperometric transducer. In a catalytic reaction, glucose is transformed by GOD to gluconolactone by use of oxygen and production of hydrogen peroxide:
Due to the stoichiometric conversion, the electrochemical oxidation of the produced hydrogen peroxide, for example, can be employed as the measurement signal.
Enzyme sensors in general are utilized in medical diagnostics and sports medicine, for self-monitoring and in lab based devices (e.g., blood glucose measurement for diabetics, lactate determination for fitness control of athletes). For bioprocess control, on-line analytical systems with biosensors for the detection of glucose, lactate, sucrose, ethanol, methanol, acetate and others are on offer.
Antibodies and Aptamers
Antibodies are proteins that are produced by the immune system and belong to the class of globulines. They are the response of the immune system to contacts with exogenous substances. Antibodies for use in biosensors or other test systems mostly are manufactured by immunization of test animals against the target substance and subsequent isolation of the produced antibodies from their blood. When immobilized antibodies are the receptor components in biosensors, these are referred to as immunosensors. The affinity of the antibodies to their respective antigenes are used for detection. Immunosensors are applied in the fields of medical diagnostics, food and environmental analytics. For instance, medically relevant antigenes in blood can be detected (e.g., heart attack markers), as well as antibiotics in milk, or pesticides and other contaminants in the environment. Immunosensors are also utilized to detect explosives or drugs in security sectors.
Aptamers are novel biomolecular recognition elements, which can be utilized as receptors in biosensors (amongst other applications). Aptamer based biosensors are able to detect analytes which were, up to now (using antibody technology), only very difficult to measure or even not at all, like toxic or non-immunogenic substances.
Antibodies and aptamers likewise show high affinities for their respective target substance. Signal formation originates from the bonding to the target molecule and is detected mainly by optical or microgravimetric transducers. Optical transducers are based on the principles of photometry, where usually changes in color or luminescence are recorded, or they detect changes in the film thickness, e.g. by surface plasmon resonance (SPR) or reflectometric interference spectroscopy (RIfS). The principle of microgravimetry forms the basis of the so-called QCM-sensors (quartz crystal microbalance), which detect changes in mass.
Completed third party funded projects
QUALI-JUICE: Quality Assurance and Development of an Early Warning System for Microbial Spoilage for the European Fruit Juice Industry
UFZ-Teilprojekt: Testung, Applikation und Validierung von Laktat-Biosensor-Systemen, Empfehlungen und Schulungsmaterialien für Anwender
EU Collective Research COLL-CT-2005-012461
16 european partners
Feldtest eines FIA-Monitors zur Phenolbestimmung mittels Biosensoren
UFZ-Teilprojekt: "Anpassung von Dickschichtenzymsensoren zur Phenolbestimmung an Feldtestbedingungen"; DBU AZ: 13753
Partner: IMT Dresden
DBU AZ: 10660
Koordinator: SensLab GmbH Leipzig
Neue Biosensoren zur Bestimmung halogenierter Organika
UFZ-Teilprojekt: Validierung des Testsystems
Deutsch-Israelische Stiftung für Wissenschaftliche Forschung und Entwicklung (GIF)
AZ: I 0442-168.09/95
Koordinator: Prof. Belkin, Hebrew University Israel,
Partner: Prof. Schmid, TU Stuttgart
FIA - Umweltmonitoring mit Biosensoren für die Überwachung von Schadstoffen und Metaboliten
DBU AZ: 03867
Partner: IMT Dresden