Second-generation biosensors

1800s Alessandro Giuseppe Anastasio Volta (1745-1827) introduced modern electrochemistry, and 

1839 The principle of the fuel cell was discovered by Christian Friedrich Schonbein (1799-1868) 

1894 Emil Fischer (1852-1919) introduced the key-lock-principle (specific binding between enzyme 

1913 Leonor Michaelis (1875-1949) and Maud Leonora Menten (1879-1960) developed the basis for 

1916 Immobilization of proteins (adsorption of invertase on activated charcoal) reported for the first 

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Enzyme sensors are based primarily on the immobilization of an enzyme onto an electrode, either a metallic electrode used in amperometry (e.g., detection of the enzyme-catalyzed oxidation of glucose) or an ISE employed in potentiometry (e.g., detection of the enzyme-catalyzed liberation of hydronium or ammonium ions). The first potentiometric enzyme electrode, which appeared in 1969 due to Guilbault and Montalvo [140], was a probe for urea with immobilized urease on a glass electrode. Hill and co-workers [141] described in 1986 the second-generation biosensor using ferrocene as a mediator. This device was later marketed as the glucose pen . The development of enzyme-based sensors for the detection of glucose in blood represents a major area of biosensor research. 

An interesting feature of DET biosensors is a simple and robust electrode architecture (e.g., no leaking of soluble redox mediators). Additionally, many interfering substances affecting the detection in first- and second-generation biosensors do not interfere with biosensors based on DET. The number of possible analytes is of course restricted to the number of available enzymes, but by use of modem protein engineering techniques the spectmm of analytes will be broadened in future. An example is the modification of the substrate specificity of cellobiose... 

FIGURE 3.2 Sequence of events that occur in second-generation (mediator-based) glucose biosensor mediated systems. 

The second-generation 02" biosensors are mainly based on the electron transfer of SOD shuttled by surface-confined or solution-phase mediators, as shown in Scheme 2(b). In 1995, Ohsaka et al. found that methyl viologen could efficiently shuttle the electron transfer between SOD and the glassy carbon electrode and proposed that such a protocol could be useful for developing 02 biosensors [125], Recently, Endo et al. reported an 02, biosensor based on mediated electrochemistry of SOD [148], In that case, ferrocene-carboxaldehyde was used as the mediator for the redox process of SOD. The as-developed 02 biosensor showed a high sensitivity, reproducibility, and durability. A good linearity was obtained in the range of 0 100 pM. In the flow cell system, tissue-derived 02 was measured. 

Second-generation electrodes have biosensor configurations that use an electron acceptor (redox mediator), which is able to shuttle electrons from the redox center of the enzyme to the surface of the working electrode ... 

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