Bioactivity sensor

Another assay of bioactivity sensors exploits microorganisms immobilized oti electrode surfaces and monitors their activity in dependence on the surrounding conditions. ... 

Holtmann D, Schrader J, Sell D (2006) Quantitative Comparison of the Signals of an Electrochemical Bioactivity Sensor During the Cultivation of Different Microorganisms. Biotechnol Lett 28 889-896... 

The design and implementation of a portable fiber-optic cholinesterase biosensor for the detection and determination of pesticides carbaryl and dichlorvos was presented by Andreou81. The sensing bioactive material was a three-layer sandwich. The enzyme cholinesterase was immobilized on the outer layer, consisting of hydrophilic modified polyvinylidenefluoride membrane. The membrane was in contact with an intermediate sol-gel layer that incorporated bromocresol purple, deposited on an inner disk. The sensor operated in a static mode at room temperature and the rate of the inhibited reaction served as an analytical signal. This method was successfully applied to the direct analysis of natural water samples (detection and determination of these pesticides), without sample pretreatment, and since the biosensor setup is fully portable (in a small case), it is suitable for in-field use. 

Immobilization of bioactive material on/in the electrode allows combining bio-reaction selectivity with sensitivity of electrochemical detection. Irrespective of reaction in the biosensor, the electrochemical response is measured, in particular, as current at the given potential (amperometric sensor) or electrode potential (potentiometric sensor). 

Sensors for the detection of enantiomers are of great interest, as so far the on-line monitoring of production processes and medical diagnostics using standard chemical analytical methods is not possible. Quite often only one enantiomer of a chiral compound is actually a bioactive therapeutic. Therefore a proper analysis of the final product is essential. Currently, this involves separation techniques like liquid chromatography, GC and capillary electrophoresis, and determination of enantiomeric purity with circular dichro-ism and specific rotation. These are all off-line procedures and therefore no real-time analysis can be performed. Sensing devices for the distinction of different enantiomers would be a much cheaper, faster and easier-to-use alternative for this task, amenable to automation. 

Near-IR sensors are also a topic of increased interest for the analysis of biological materials, from food quality control to bioactivity measurements. First applications... 

Beyond the complete assembly of biomimetic membranes, interfacial supramolec-ular assemblies which incorporate biocomponents represent an important approach to replicating the biological functions outside of living systems. For example, the ability to link or wire otherwise electro-inactive enzymes to electrodes so that they can efficiently transport electrons allows sensitive and selective sensors to be developed for important bioactive molecules, e.g. glucose, lactate, urea, etc. 

A practical approach for toxicity screening combines bioactivation and DNA damage detection into a single biosensor for toxicity screening. To make these types of sensors, ultrathin films (20—4-0 nm thick) containing myoglobin or cytochrome P450cam and DNA were... 

Glasses and ceramics can bond to living tissues if there is bioactive layer. The development of a bioactive hydroxyapatite layer in vivo at body temperature is therefore an important problem.89 Materials with the highest level of bioactivity develop a silica layer that enhances the formation of such a layer. Such sol-gel processes are used to produce bioactive coatings, powders and substrates which allow molecular control over the incorporation and behavior of proteins and cells with applications as sensors and implants. Sol-gel encapsulation of biomolecules within silica matrices has encompassed... 

Liu L, Massey T (1992) Bioactivation of aflatoxin B by hpoxygenases, prostaglandin H synthase and cytochrome P450 monooxygenase in guinea-pig tissues. Carcinogenesis 13 533-539 Maragos CM (2002) Novel assays and sensor platforms for the detection of aflatoxins. Adv Exp, Med Biol 504 84-93... 

An example of a sensor utilizing these three components is illustrated in figure 1.2, which shows a schematic of a typical enzyme electrode for the detection of glucose (also see chapter 17 of this text). The bioactive surface consists of immobilized glucose oxidase (GOD) sandwiched between a polycarbonate and cellulose acetate membrane. The transducer is a platinum electrode and the electronics are those typically found in any polarograph, i.e. an electronic system to measure low currents (on the order of microamperes) at a fixed voltage bias on the platinum electrode. The action of glucose... 

Biomaterials are stractural or functional materials in the constinction of medical devices for implantation or application to living tissues or organs. Tliey need to be biocompatible, i.e. to perform their function without negative side effects such as interference with the circulation or coagulation, impairment of the immune system, facilitation of infections or scar-formation. Bioactive materials such as enzymes, antibodies or living cells can be integrated as functional parts of sensors, acmators or total systems. 

The technique of the immobilization of the biological elements has changed according with the different events, catalytic or affinity. The simplest way to retain enzymes on the tip of a transducer is to trap them behind a perm-selective membrane. This method has been mainly used in addition to embedding procedures in polyacrylamide gels. Then, mainly in the 80th, the trend shifted to use disposable membranes with bound bioactive material. Several companies put on the market preactivated membranes suitable for the immediate preparation of any bioactive membrane and this appeared as a real improvement at least for the easy use of enzyme sensors. 

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