Solid-State ISFET Electrodes

Solid-state ISFET electrode. (Courtesy of IQ Scientific Instruments, Inc.) 

What is the liquid-junction potential Residual liquid-junction potential How can these be minimized  

Discuss the mechanism of the glass membrane electrode response for pH measurements. 

What is the alkaline error and the acid error of a glass membrane pH electrode  

Describe the different types of ion-selective electrodes. Include in your discussion the construction of the electrodes, differences in membranes, and their usefulness. 

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Accelerated and microwave extraction and digestion Solid-state ISFET electrodes... 

It contains parameters related to the solid-state (i.e., Ex) as well as to the chemical part(i.e., namL, jcq) of the sensor. Because the reference electrode is physically separate from the ISFET, its potential is not included in the threshold voltage. However, that choice is rather arbitrary. Whether the actual output follows (6.65) or (6.66) depends on the externally applied gate voltage Eg, which has nothing to do with the... 

The integration of chemically sensitive membranes with solid-state electronics has led to the evolution of miniaturized, mass-produced potentiometric probes known as ion-selective field effect transistors (ISFETs). The development of ISFETs is considered as a logical extension of coated-wire electrodes (described in Section 5.2.4). The construction of ISFETs is based on the tech-... 

In these sensors the technology developed for ISFET construction is used in conventional electrodes. Links between the membrane and internal reference are metallic (ohmic contact), by deposition of the metal on the membrane (solid state membranes), or by deposition of an ion-selective membrane on a metal. This latter is an integrated sensor. 

Most ISEs are based on purely physicochemical and non-catalytic recognition elements solid membranes with fixed ionic sites (e.g. the glass pH electrode), ion-exchange polymer membranes or plasticised hydrogel membranes incorporating ionophores [9], Silicon oxide or metal oxides act as the recognition element in pH-ISFETs, gas-sensitive FETs, solid-state electrolyte, solid-state semiconductor and many conductometric gas sensors. 

Ion-Selective Field Effect Transistors. Ion-selective field effect transistors (ISFETs) are semiconductor devices related to the solid-state detectors used in spectroscopy (discussed in Chapter 5). In this case, the surface of the transistor is covered with silicon nitride, which adsorbs H ions from the sample solution. The degree of adsorption is a function of the pH of the sample solution and the adsorption of H" " ions results in a change in the conductivity of the ISEET channel. The cell requires an external reference electrode. ISEET pH sensors can be made extremely small (about 2 mm ) and are extremely rugged, unlike the fragile glass bulb pH electrode. They have rapid response times and can operate in corrosive samples, slurries, and even wet solids such as food products. The sensor can be scrubbed clean with a toothbrush, stored in a dry condition, and does not require hydrating... 

The experimental set-up used in connection with FTIR-ATR-spectrometry enabled us to follow the dilfusion of the components of interest through the membrane under realistic conditions for ISFETs. One side of the membrane is in contact with a solid state electrode the other side with the aqueous solution containing the ion to be determined. This means that the membrane being analysed remains in contact with the solution throughout the whole measurement rather than being separated and dried. This set-up allows an investigation of the diffusion process in model membranes and a direct comparison of the results with the electrochemically measured time dependent parameters of the corresponding electrodes. 

There are two basic types of solid-state chemical sensor (i) potentiometric devices, and (ii) field effect devices, e.g. ion-selective field effect transistors (ISFETs or CHEMFETs). Electrodes of the potentiometric type usually have a metal as the back contact and they also have a high output impedance. Field-effect devices are a variant of the metal oxide field-effect transistor (MOSFET) familiar in electronics, and they have a low output impedance. Hybrid devices attempt to combine the advantages of both. 

The increased interest in using ISEs has led to the development of new sensor materials that show high selectivity for a variety of anions and cations and new approaches for electrode constraction. Several attempts have been made to eliminate the internal reference electrode resulting in a solid-state sensor design. Examples of these types of sensors include coated wire electrodes, graphite rods, graphite-based electrodes, and ion-selective field-effect transistors (ISFETs). 

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