ISFET sensors

M.L. Pourciel-Gouzy, W. Sant, I. Humenyuk, L. Malaquin, X. Dollat, and P. Temple-Boyer, Development of pH-ISFET sensors for the detection of bacterial activity. Sens. Actuators B. 103, 247-251 (2004). 

Examples of the use of FIA with ISE detection involve the determination of nitrate and total nitrogen in environmental samples [48, 49, 125, 166], potassium, sodium [125], calcium [51] and urea [124] in serum or major nutrients in fertilizers [73]. An interesting combination of an ISFET sensor with the FIA principle [52] is shown in fig. 5.17. This is a simultaneous determination of potassium, calcium and pH in serum during dialysis on an artificial kidney. 

Fig. 6.26 Individual and differential response of the NaCI ion-sensitive field-effect transistor (ISFET) sensor (a) response of Na-ISFET and (b) Cl ISFET both measured against regular reference electrode (c) differential current measurement of concentration of NaClin 0.01MMgSO4 solution (adapted from Bezegh et al., 1987)...

FIG. 1 Schematic cross sections of selected microelectrode configurations, (a) Nomenclature for parts of microelectrode, (b) Na+-sensitive microelectrode (22), (c) recessed-tip Na+-sensitive microelectrode (27), (d) liquid ion-exchanger micropipette electrode (38), (e) coated wire electrode (16), (f) flow-through ISE (e.g., NOVA 6, Boehringer ISE 2020), (g) micro-capillary glass electrode of tubular shape (e.g., Radelkis OP-266), (h) planar sensor fabricated by microelectronic technology (93), (i) ISFET sensor (94). 

G. J. Moody, J. M. Slater, and J. D. R. Thomas, Some Parameters of Ion-Sensitive Field Effect Transistor (ISFET) Sensors. Anal. Proc., 23 (1986) 287. 

M.J. Schoning, Playing aroimd with field-effect sensors on the basis of EIS structures, LAPS and ISFETs. Sensors 5,126-138 (2005). 

As a supplement for widely used glass electrodes, ISFET sensors provide some unique features. One of them is the capability of dry storage, which helps to avoid the problem of shelf-life and the hydration requirement time for glass electrodes. Fast response is another feature of an ISFET pH sensor. In a comparison study of commercial pH sensors reported by Smit et al. [84], the ISFET sensor showed about a ten times faster response than that of glass electrodes, and a response similar to that of an iridium oxide-based electrode [100, 104], This fast response time of ISFET sensors was attributed to its sensing mechanism, which is based on the electrostatic interaction of H+ ions with surface charge at the gate surface [66]. 

As a membrane matrix, PVC is most frequently used [16]. This type of selective membrane is also suitable for preparing a coated-wire i.s.e. and ion-selective MISFET (ISFET) sensors (see next subparts of this chapter). 

P Bergveld Future applications of ISFETs Sensors and Actuators 125-133... 

There are several potential disadvantages of ISE/ISFET sensors, as compared to standard analytical methods. One is chemical interference by other ions, because ion-selective electrodes are not truly specific but respond more or less to a variety of interfering ions. To overcome interference issues, various data processing methods have been used. For example, multivariate calibration models have been proposed to allow cross responses arising from primary and interfering ions to be decoupled, thus allowing accurate determination of individual ion concentrations within mixtures.In some cases, another compound can be added to suppress the interference effect. For example, Ag2S04 can be used to suppress the chloride interference 10 ... 

The advantage of the ISFET sensors includes reduced drift and noise due to stray currents as a result of the lower impedance compared to an ISE. A number of applications have been described for the determination of environmental water parameters, notably long-term unattended pH measurements in the open ocean. Precise seawater-pH data (better than 0.002 pH units) with good spatial and temporal coverage are particularly critical to appreciate ocean-acidification phenomena and their consequences on the marine carbonate system. 

As with SAMs, nonredox enzymes can also be utilized for BLM sensors. For instance, highly sensitive electrochemical and ISFET sensors for urea, nicUlin, acetylcholine, thyroxine, and triazine herbicides have been produced from phospholipid BLMs with urease, penicillinase, acetylcholinesterase, and antibodies attached electrostatically, covalently, or via avidin-biotin conjugation [130-132]. 

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