Bioreceptor enzyme

Perhaps the most unique component of a biosensor is the biological system that is utilized to identify specific molecules of interest in solutions of complex mixtures. The biological element of course is primarily responsible for the selectivity of biosensors. There are many different types of biological recognition systems that have been explored for sensors, ranging from the molecular scale— e.g., bioreceptors, enzymes, and antibodies— to cellular structures like mitochondria, and even immobilized whole cells and tissues. However, to date for practical reasons most commercially feasible biosensors have primarily utilized enzymes, and to a lesser extent antibodies. 

C and T E Klein 1986. Molecular Graphics and QSAR in the Study of Enzyme-Ligand ractions. On the Definition of Bioreceptors. A ccounts of Chemical Research 19 392-400,... 

Hansch, C. and Klein, T.E. (1986) Molecular graphics and QSAR in the study of enzyme-ligand interactions. On the definition of bioreceptors. Accounts of Chemical Research, 19, 392-400. 

Biological Biosensors with thermally stable enzyme bioreceptors Quaternary structure modeling of known tertiary structures of related proteins 50... 

The inhibitor activity of compounds with respect to different enzymes is important in the design and screening of many pharmaceuticals. Many inhibitors have similar structural groups, yet have different activities, indicating the importance of electronic factors. The electron-topological description, as shown below, is much more specific with respect to the interaction of the molecules with the bioreceptor. 

Response time of bioreceptor-based sensors. As in enzyme-based sensors the two main factors that determine the responsiveness of bioreceptor-based sensors are diffusive and kinetic phenomena. 

A bioreceptor must be able to react specifically with an analyte of interest. For example, a bioreceptor for cholesterol should react only with cholesterol and not with any other compound in the sample. Biological recognition systems such as enzymes or antibodies offer this high specificity and, in addition, ensure high sensitivity and fast response. Usually, the bioreceptor molecules are immobilised at, or close to, the surface of the transducer. Immobilisation can be achieved by physical adsorption or entrapment by an inert membrane. The bioreceptor can also be covalently bound to functional groups on the surface of the transducer. 

Enzymatic bioreceptors have an advantage insofar as the enzyme regenerates itself after reaction. The enzyme is then available for further reaction with the sample. Thus, the response output is directly related to concentration changes in the sample. Antibodies on the other hand can only be used for a one-time measurement. They have to be disposed after reaction or the antigens have to be washed off with suitable reagents. 

The bioreceptor does not have to be an enzyme or antibody, virtually any compound that exhibits molecular recognition for an analyte is suitable. This could be a piece of DNA, a cell, a microorganism, an organelle or a plant or even mammalian tissue. Enzymes and antibodies are used most often, as they are relatively simple to incorporate into a device. This is more difficult with tissue slices and biological cells as they must be supplied with nutrients and have waste fluids removed in order to keep them alive. 

The functioning of a biosensor can thus be summarised as shown in Fig. 5.18. The analyte is recognised by the bioreceptor, which is usually a protein such as an enzyme or antibody. The protein is in close proximity to the detector. This transduces the recognition event into a signal, which can be amplified and displayed. 

GOx has proven to be an almost ideal bioreceptor. It can be produced cheaply by soil fungi and it withstands greater extremes of pH, ionic strength and temperature than many other enzymes. Also it reacts readily over the concentration range of glucose encountered in human blood samples. Furthermore, the oxidation current is directly proportional to the amount of glucose in the sample. 

When the immobilized sensing reagent also contains a bioreceptor, such as an enzyme or an antibody, the device is regarded as a biosensor (23). Such sensors hold great promise as they exploit the inherent ability of the bio molecule to selectively and sensitively recognize a particular chemical spedesln a complex matrix. Enzyme-based sensors produce a signal due to a selective enzyme-catalyzed chemical reaction of an analyte and form a product that is detected by a transduction element in the sensor. The... 

Biocomposites can also be easily prepared by adding the bioreceptor (an enzyme [18] and antibody [23], or an affinity receptor such as Protein A [73] or avidin [74,75]). 

In the field of chemical analysis, biosensors have undergone rapid development over the last few years. This is due to the combination of new bioreceptors with the ever-growing number of transducers [1]. The characteristics of these biosensors have been improved, and their increased reliability has yielded new applications. Recently, a new technique of enzyme immobilization has been developed to obtain biosensors for the determination of enzyme substrates [2]. It is based on the enzyme adsorption followed by a crosslinking procedure. Therefore, a penicillin biosensor can be obtained and associated with a flow injection analysis (FIA) system for the on-line monitoring of penicillin during its production by fermentation [3-4]. This real-time monitoring of bioprocess would lead to optimization of the procedure, the yield of which could then be increased and the material cost decreased. 

Utilize a biochemical mechanism for recognition. They are responsible for binding the analyte of interest to the sensor surface for the measurement. Bioreceptors can generally be classified into five major categories enzyme, antibody/antigen, nucleic acid/DNA, cellular structure/ceU, and biomimetic. The sampling component of a biosensor contains a biosensitive layer that can contain bioreceptors or be made of bioreceptors cova-lendy attached to the transducer. The most common forms of bioreceptors used in biosensing are based on ... 

The enzymes and antibodies are the main classes of bioreceptors that are widely used in biosensor applications. 

Enzymes have been the most widely used bioreceptor molecules in biosensor appHca-tions. Enzymes are often used as bioreceptors because of their specific binding capabilities as well as their catalytic activity. In biocatalytic recognition mechanisms, the detection is amplified by a catalytic reaction. 

Setford, S.J., Newmann, J.D., 2005. Enzyme bioreceptors microbial enzymes and biotransformatiotis. Methods Biotechnol. 17. 

Enzymatic biosensors can be defined as an analytical device having an enzyme as a bioreceptor integrated or intimately associated with the physical transducer to produce a discrete or continuous digital electronic/optical signal that is proportional to the concentration of analyte present in the sample. This chapter describes the enzyme-based electrochemical biosensors for the measurement of clinically important biomatkers, beginning with a history of biosensors. 

The combination of any bioreceptor with any transducer leads to a large number of biosensors. In reality, the two components have to be compatible to give rise to an electrical signal. It is impossible, for example, to use a thermometric transducer if the substrate transformation reaction does not give rise to a variation in enthalpy. Electrochemical transducers couple relatively easily with enzymes, and so such biosensors are already on the market. Other bioreceptor-... 

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