Force-Based Biosensors

AFM biosensors Biosensors using scaiming force microscope Cantilever biosensors Force-based biosensors Force biosensors... 

Many of the latter requirements are being met for many chemical sensors and for enzyme-electrode-based biosensors and products based on these sensors are commercially available (see chapter 23). Other, more advanced sensors, such as antibody- and receptor-based biosensors, have been commercialized to only a limited extent, primarily due to fabrication and cost limitations. New, simpler, and more cost-effective immobilization methods now being developed will be the driving force for the commercial emergence of these sensors within the next 5-10 years. 

A high yield of glucose oxidase on the surface can be obtained due to electrostatic forces. The nondestructive immobilization of glucose oxidase on the surface retained most of its bioactivity. A choline biosensor was formed, simply by dipping the electrode into a choline oxidase solution for enzyme loading. In summary, the electrode provides a useful platform for the development of oxidase-based biosensors [25]. 

Biosensors based on cantilever action were briefly mentioned above. Nanosized cantilevers have been first used in AFM. Here, intermolecular forces between the cantilever and a smface are detected by monitoring the motion of the cantilever tip. In the case of biosensor applications, they are... 

High sensitivity, selectivity, and ability to operate in turbid solutions are advantages of electrochemical biosensors. Amperometric detection is based on measuring the oxidation or reduction of an electroactive compound at a working electrode (sensor). A potentiostat is used to apply a constant potential to the working electrode with respect to a second electrode (reference electrode). A potentiostat is a simple electronic circuit that can be constructed using a battery, two operational amplifiers, and several resistors. The applied potential is an electrochemical driving force that causes the oxidation or reduction reaction. 

Figure 4.6 Thrombin biosensor based on a ferrocene-labeled aptamer. In the absence of thrombin, the aptamer (green) displays a random coil strnctnre, allowing contact between the ferrocene label (striped ball) and the electrode. Addition of thrombin forces the aptamer into the thrombin-binding structure, thus removing the redox label from the electrode, allowing no further electrochemical contact. (See insert for color representation.)...

Biosensors using atomic force microscopes (AFMs) are devices which employ an atomic force microscope for biological recognition events. The principle of biosensors using atomic force microscopy is mainly based on the mass-sensitive detection of binding events that change the deflection of a cantilever whose surface is modified with immobilized bioreceptors. 

The FABS, whose working principle was very similar to that of the AFM biosensor, was a cantilever-based immunosensor [7]. However, its configuration was much simpler than that of the AFM. Rather than using a piezoceramic translator to pull on intermolecular bonds, it used magnetic particles, which eliminated the need to manually position a tip and sample next to each other with picometer precision and stability. The cantilever-beam force transducer was the only element of the AFM retained by the FABS. 

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