On-line measurement of potassium in blood by chemical-sensitive field-effect transistors: a preliminary report.

Multisensor for Clinical Analysis with Impact on Public Health Evaluation

“…The diffused source and drain regions have low aspect ratios and the metallization tracks extended as far to the channel as effective encapsulation allows, providing minimal serial parasitic resistance. A common drain connection for all devices minimizes the number of lead-out wires (7).…”

“…In order to provide the clinician with this information, a number of novel microelectronic chemical sensors have been successfully developed for the measurement of pH, pK + , pCa 2+ , pNa + , pO 2 , and which are readily modified for the detection and measurement of other ionic species and chemical substances [6]. Lately it was possible to develop four-channel ChemFET devices, which could be successfully used for the on-line analysis of ions of biological interest in human blood [7]. A multiple function chemical transducer for this application would allow more precise computation of ionic activities because compensation could be made for imperfections in the selectivity of individual sensors by processing data from the transducers array in parallel.…”

Ion-selective field-effect transitors (ISFETs)

“…Ideally, 0.1 mV resolution is necessary, which requires that any offset signal drift (either of electrical or chemical origin) must be better than 0.5 % h-1, or less than 0.13 mV h-1. This is difficult to achieve with ises, and although it is possible to achieve this level of stability with isfets, it is not usually observed during the first 12 h of usage while the electroactive gate is hydrating, nor apparently when anticoagulants are present (Sibbald et al 1982).…”

“…Ionophore-doped polymeric gates were used for the fabrication of the K+, Ca2+ and Na devices, whereas the silicon nitride surface of the composite gate dielectric of the remaining device was used directly as a pH-responsive material (Sibbald 1982;Moss 1976;Vlasov 1981) ; the details are given below.…”

“…The Utah group's ics (Janata & Huber 1981) were mounted on to the tips of glass tubes and were then hand-encapsulated; no true flow-through isfet cells have been reported in the literature other than our early design (Sibbald et al 1982) but some practical difficulties were encountered, in later work, which necessitated the re-evaluation of the cell design.…”