Enzyme bioreceptors biosensors

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. 

With the exception of a small group of catalytic ribonucleic acid molecules, all enzymes are proteins. Some enzymes require no chemical groups other than their amino acid residues for activity. Others require an additional component called a cofactor, which may be either one or more inorganic ions, such as Fe, Mg, Mn 

or a more complex organic or organometaUic molecule called a coenzyme. The catalytic activity provided by enzymes allows for much lower limits of detection than would be obtained with common binding techniques. As expected, the catalytic activity of enzymes depends upon the integrity of their native protein conformation. If an enzyme is denatured, dissociated into its subunits, or broken down into its component amino acids, its catalytic activity is destroyed. Enzyme-coupled receptors can also be used to modify the recognition mechanisms. For instance, the activity of an enzyme can be modulated when a ligand binds at the receptor. This enzymatic activity is often gready enhanced by an enzyme cascade, which leads to complex reactions in the cell. 

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

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. 

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... 

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. 

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. 

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. 

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-... 

Considering that molecular recognition generally uses well-defined reaction types and that the deletion method may be extremely varied, it is logical that biosensors should be classified primarily as a function of the bioreceptor used. However, a laboratory that only ever worics with enzymes, for example, could use a classification according to the transducer employed (electrochemical, thermometric, etc). In what follows, we have opted to use the classification by bioreceptor because this component determines the primary action of the biosensor. 

Plants are useful sources of enzymatic material for analytical chemistry. Using the appropriate transducer, very stable biosensors can be produced because the enzymes remain in their natural environment. Similarly, animal tissue can be considered as a useful bioreceptor for the selective detection of L-amino acids without any notable interference from D-amino acids. Sensor selectivity can also be improved by incorporation of an antimicrobial agent to avoid bacterial contamination. For example, it is recommended that 0.02 % sodium azide is used in the glutamine electrode [17]. 

Use of membranes — Biological compounds have limited lifetimes and so removable bioreceptors are useful. Hence the idea of immobilizing an enzyme on a membrane, and attaching the membrane to the transducer. The step also avoids the constraints of direct enzymatic immobilization on the transducer, and allows mass production, which improves the reproducibility of the biosensor signal. 

Future olfactive (olfactive mucus) detection systems will probably be ultrasensitive chemical sensors [16] detecting nucleotides and hormones (e.g., pheromones). Biosensor research may also become orientated towards new bioreceptors [265], and perhaps even new biocatalysts, such as artificial enzymes [266]. 

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