Enzyme transistor

P. N. Bartlett and Y. Astier, Microelectrochemical enzyme transistors , Chemical Communications, 105 (2000). 

Bartlett, P.N., and P.R. Birkin. 1994. A microelectrochemical enzyme transistor responsive to glucose. Anal Chem 66 (9) 1552. 

One of the most interesting applications is the development of an enzyme transistor [79], The idea is based on the DET between HRP and a poly(aniline) film, which loses electrical conductivity due to its oxidation by H2O2 catalyzed by the enzyme. As mentioned by the authors, the enzyme transistor can form the basis for a new generation of devices distinctly different from usual amperomet-ric electrodes however, a number of limitations still need to be overcome, such as fast reproducible switching of the transistor and inactivation of peroxidase. The last limitation might not be a problem in the format of a disposable sensor. 

P. N. Bartlett and P. R. Birkin, A microelectrochemi-cal enzyme transistor responsive to glucose. Anal. Chem. 66 1552(1994). 

New natural polymers based on synthesis from renewable resources, improved recyclability based on retrosynthesis to reusable precursors, and molecular suicide switches to initiate biodegradation on demand are the exciting areas in polymer science. In the area of biomolecular materials, new materials for implants with improved durability and biocompatibility, light-harvesting materials based on biomimicry of photosynthetic systems, and biosensors for analysis and artificial enzymes for bioremediation will present the breakthrough opportunities. Finally, in the field of electronics and photonics, the new challenges are molecular switches, transistors, and other electronic components molecular photoad-dressable memory devices and ferroelectrics and ferromagnets based on nonmetals. 

Enzyme-immobilized FETs (ENFETs), 22 269. See also Enzyme ion-selective field-effect transistor (ENFET) Field effect transistors (FETs)... 

ENZYME ION-SELECTIVE FIELD-EFFECT TRANSISTOR (ENFET)... 

Benilova, I. V., Arkhypova, V. M., Dzyadevych, S. V, Jaffrezic-Renault, N., Martelet, C., Soldatkin, A. P. (2006). Kinetic properties of butyrylcholinesterases immobilised on pH-sensitive field-effect transistor surface and inhibitory action of steroidal glycoalkaloids on these enzymes. Ukr. Biokhim. 7h., 78,131-141. 

These electrodes must be distinguished from biosensors with enzymes at their surface. Electrodes constructed from field effect transistors (see 19.7) lead to voltametric detection. 

A particular type of biosensor can be developed by putting a membrane in contact with the semi-conducting layer of a field effect transistor. If the membrane incorporates an enzyme adapted to transform a particular analyte (Fig. 19.8), reaction of that enzyme will modify the polarity at the surface of the insulating layer. This will in turn modify the conduction between the source and the collector of the field effect transistor. The current flowing through these two electrodes (source and collector) serves as the signal. 

Figure 19.8—A selective electrode designed from a MOSFET (metal oxide semiconductor field effect transistor). A specific reaction can be monitored by putting an enzyme in contact with the electrodes. This schematic shows the three electrodes used for amperometric measurement.

S.V. Dzyadevych, A.P. Soldatkin, Y.I. Korpan, V.N. Arkhypova, A.V. El skaya, J.-M. Chovelon, C. Martelet and N. Jaffrezic-Renault, Biosensors based on enzyme field-effect transistors for determination of some substrates and inhibitors, Anal. Bioanal. Chem., 377 (2003) 496-506. 

Local changes in the ion concentration as a result of substrate conversion by the immobilized enzymes have been measured using pH [41] or fluoride sensitive field effect transistors (pF-ISFET) [42] or ammonia-sensitive FETs [43]. 

Recently, hopes have been raised for the use of CNTs as superior biosensor materials. Successful fabrication of various analytical nanotube devices, especially those modified with biomolecules, has made this a possibility. These prototype devices, sometimes prepared as ordered arrays or single-nanotube transistors, have shown efficient electrical communications and promising sensitivities required for such applications as antigen recognition,38 enzyme-catalyzed reactions39 and DNA hybridizations.40 Publications considering a quantum dot bahaviour of CNTs show their promise for biorecognition devices with optical indication.41... 

CNTs and other nano-sized carbon structures are promising materials for bioapplications, which was predicted even previous to their discovery. These nanoparticles have been applied in bioimaging and drag delivery, as implant materials and scaffolds for tissue growth, to modulate neuronal development and for lipid bilayer membranes. Considerable research has been done in the field of biosensors. Novel optical properties of CNTs have made them potential quantum dot sensors, as well as light emitters. Electrical conductance of CNTs has been exploited for field transistor based biosensors. CNTs and other nano-sized carbon structures are considered third generation amperometric biosensors, where direct electron transfer between the enzyme active center and the transducer takes place. Nanoparticle functionalization is required to achieve their full potential in many fields, including bio-applications. 

A new development in the field of potentiometric enzyme sensors came in the 1980s from the work of Caras and Janata (72). They describe a penicillin-responsive device which consists of a pH-sensitive, ion-selective field effect transistor (ISFET) and an enzyme-immobilized ISFET (ENFET). Determining urea with ISFETs covered with immobilized urease is also possible (73). Current research is focused on the construction and characterization of ENFETs (27,73). Although ISFETs have several interesting features, the need to compensate for variations in the pH and buffering capacity of the sample is a serious hurdle for the rapid development of ENFETs. For detailed information on the principles and applications of ENFETs, the reader is referred to several recent reviews (27, 74) and Chapter 8. 

ENFET Enzyme-immobilized field effect transistor... 

Widespread interest has arisen in the potential of LB films as biosensors because many believe that the incorporation of biological molecules such as enzymes will lead to novel devices. Some are exploring the deposition of biologically active molecules onto the gate electrodes or oxides of field-effect transistors, but optical sensors, probably based on fiber optics, are the most favored technique. In all cases, the aim is to couple the specificity of inter-... 

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