What are the advantages of biosensors
Biosensors are measuring sensors that are equipped with biological components. These are used in biotechnological measurement technology. Biosensors are based on the direct spatial coupling of an immobilized biologically active system with a signal converter (transducer) and an electronic amplifier. To identify the substances to be determined, biosensors use biological systems at different levels of integration. Such biological systems can e.g. B. antibodies, enzymes, organelles or microorganisms. The immobilized biological system of the biosensor interacts with the analyte. This leads to physicochemical changes, such as B. Changes in the layer thickness, the refractive index, the light absorption or the electrical charge. These changes can by means of the transductor, such as. B. optoelectric sensors, amperometric and potentiometric electrodes or field effect transistors can be determined. After the measurement process, the system must be restored to its original state. The measurement of an analyte by means of a biosensor therefore takes place in three steps. First of all, the analyte is specifically recognized by the biological system of the biosensor. The physicochemical changes that result from the interactions between the analyte and the receptor are then converted into an electrical signal. This signal is then processed and amplified. A biosensor derives its selectivity and sensitivity from the biological system used.
Types of biosensors
Piezoelectric sensors: The oscillation of a quartz is inversely proportional to its mass. A quartz crystal coated with enzymes or antibodies can thus be used as a microbalance. One disadvantage is that each coated sensor can only be used once. However, the cost of such a crystal is low.
Optical sensors: In practice, these sensors are primarily used to track the oxygen content in liquids. The measurement principle here is the fluorescence quenching. An optical waveguide with an indicator attached to its end serves as the measuring device. The luminescence or absorption properties of this indicator are dependent on chemical parameters such as the oxygen concentration.
Electrochemical detection: e.g. by amperometry or potentiometry. In amperometry, the current flow is measured on 2 electrodes in a measuring chamber while the voltage is kept constant. It is suitable for metabolic products that can easily be oxidized or reduced. Potentiometry is used for ionic reaction products. The quantitative determination of these ions is carried out on the basis of their electrical potential on a measuring electrode
The first measuring system, which can be called a biosensor according to the definition given above, was developed by Clark and Lyons in 1962. A measuring system was described that enables the determination of glucose in the blood during and after operations. This biosensor consisted of either a Clark oxygen electrode or a pH electrode as a transducer, in front of which the enzyme glucose oxidase was applied between two membranes. The glucose concentration could be determined as a change in the pH value or as a change in the oxygen concentration as a result of the oxidation of glucose under the catalytic action of the enzyme glucose oxidase.
In this construction, the biological material is enclosed between two membranes, or the biological system is applied to a membrane and is connected directly to the surface of the transducer. The areas of application for biosensors in the analysis of water and wastewater can be divided into biosensors for determining individual components, biosensors for determining toxicity and mutagenicity, and biosensors for determining the biochemical oxygen demand (BOD).
The bacterial content of bathing water or sewage can be determined by means of a biosensor. Antibodies against certain types of bacteria are attached to a vibrating membrane. If the corresponding bacteria swim past the sensor, they attach themselves to the antibodies and thereby slow down the vibrations of the membrane. If the vibrations fall below a certain value, an alarm is triggered.
The penicillin concentration in a bioreactor in which fungal strains are cultivated can be determined with a biosensor. The biological component of the sensor used here is the enzyme acylase. This penicillin-splitting enzyme is applied to a membrane that rests on a pH electrode. If the penicillin concentration in the medium increases, the enzyme splits off ever larger amounts of an acid, phenylacetic acid. This changes the pH value on the electrode. So one can now deduce the concentration of penicillin from the pH value.
- ↑ Clark, L.C. and Lyons, C. (1962): Electrode systems for continuous monitoring in cardiovascular surgery. In: Ann. N.Y. Acad. Sci. Vol. 31, No. 102, pp. 29-45. PMID 14021529
- Eggins, Brian R. (2002): Chemical Sensors and Biosensors. Analytical Techniques in the Sciences. 2nd edition, Wiley, ISBN: 0-471-89914-3
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