Enzyme biosensors whole-cell system

Utilization of whole cells and tissues in biosensor has increasingly been used. Enzyme stability, availability of different enzymes and reaction systems, and characteristics of cell surface are the advantages of using cells and tissues in biosensor designs. Multi-step enzyme reactions in cells also provide mechanisms to amplify the reactions that result in an increase in the detectability of the analytes. The presence of cofactors such as NAD, NADP, and metals in the cells allows the cofactor-dependent reactions to occur in the absence of reagents. (34, 50, 69). However, the diffusion of analytes through cell wall or membrane imposes constraint to this type of biosensors and results in a longer response time compared to the enzyme biosensors. 

A biosensor is a sensing device that is integrated within or intimately associated with a physical transducer. Such a system quantifies electronic signals arising from the interaction between a biosensor and an analyte of interest. Catalytic biosensors use enzymes, microorganisms, or whole cells to catalyze a reaction with the target analyte, while affinity biosensors utilize antibodies, receptors, or nucleic acids to bind with the target analyte. 

Whole cell biosensors may be divided into two groups depending on whether or not it is necessary for the cellular membranes to be intact. If the cells are being used simply as a source of one or more bound enzymes then the integrity of the cellular membranes may be of little import whereas if the enzymes are not bound within the cells then the contiguity of the cellular membranes is of vital importance. The status of the cell membranes is of particular importance when it is necessary that the cells be alive (i.e., potentially or actually capable of cell division, etc.). This requirement imposes additional difficulties on the fabrication of devices. However, biosensors that contain intact whole cells have the potential to act as convenient surrogates for traditional applications of biological cells and systems. At the forefront are those applications... 

In this chapter, we focus on the use of the continuous resonance QCM and EQCM devices to study enzymatic polymerization reactions, biochemical and biomimetic processes and to create thin polymer films electrochemically on the QCM electrode surface. We describe some QCM applications of thin polymer films in enzyme electrode and other biosensors and briefly describe specific cell binding systems to create whole cell biosensors. 

Biosensor A device that uses specific biochemical reactions mediated by isolated enzymes, immune system, tissues, organelles, or whole cells to detect chemical compoimds, usually by electrical, thermal, or optical signals. 

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. 

A different lactate biosensor was proposed by Pfeiffer et al. [152], who used an enzyme sandwich membrane that was commercially available for whole blood lactate analysers. The membrane was inserted into a flow cell connected to a microdialysis probe. This membrane showed a significant day-to-day variation in sensitivity ( 50%), but no trend in sensitivity decrease. The problem of rejecting interference has not been completely solved by this system. However, the continuous monitoring of subcutaneous lactate was feasible at least in small rodents, and results were consistent with liquid chromatographic measurements performed on dialysate samples collected during the in vivo experiment. 

All biosensors exploit a close harmony between a selective biorecognition system and a physicochemical transducer (Figure 12.lA and Figure 12.1B). The biorecognition system is typically an enzyme, sequence of enzymes, lectin, antibody, membrane receptor protein, organelle, bacterial, plant or animal cell, or whole slice of plant or mammalian tissue. This component of the sensor is responsible for the... 

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