Cell surface analytes, detection

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. 

The distinction between chemical sensors and biosensors is more complex. Many authors attempt to define a sensor based on the nature of the analyte detected. This approach can be misleading since nearly all analytes measured by a chemical or biosensor are chemicals or Wochemicals, the exception being sensors which detect whole cells. Other authors attempt to define a chemical of biosensor by the nature of the reaction which leads to the detection event. Again, this is confusing since all reactions at chemical and biosensor surfaces are chemical (or biochemical) reactions. 

Maurel, D., Kniazeff, J., Mathis, G., Trinquet, E., Pin, J.P., and Ansanay, H. (2004) Cell surface detection of membrane protein interaction with homogeneous time-resolved fluorescence resonance energy transfer technology. Analytical Biochemistry, 329, 253-262. 

The use of nanomaterials [545] such as gold nanoparticles and carbon nanotubes increases the sensor surface and enhances analytical detection. The use of PEGylated arginine functionalized magnetic nanoparticles for early detection of cervical cancer has been reported [553]. This sensor displayed good selectivity and sensitively down to 10 cells mL ... 

Figure 17 illustrates a tensile fracture stage developed in the author s laboratory for use on surface analytical systems. It is computer controlled, accepts specimens in standard-shaped holders and allows both fracture faces to be analyzed following fracture 148). The. specimen is loaded into two standard holders back to back, and this assembly is in turn loaded into the fracture stage. The slack in the system is taken up by the computer which moves the jaws apart until a small load is detected on the load cell. The required extension rate is then specified by the operator and the Jaws are moved apart at this rate while the force on the load cell is recorded. The computer senses when the specimen has fractured and moves the jaws apart to allow each half of the specimen to be removed and presented for analysis. An advantage of this type of system is that fracture is more controllable than in the impact method, and, furthermore, a load/extension curve is produced which gives additional information regarding the mechanical properties of the material. 

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