Focus sor is obtained if the gate is coated with a thin film of palladium—a de tection limit of less than 1 ppm of H2 is possible. Detection of other gases, such as H 2 S, NH3, and CO, has also been reported. The small size and low output im pedance of the CHEMFET make it ideal for in vivo monitoring and analy sis of small sample volumes. Janata and his co-workers at the University of Utah are developing devices that will detect accumulations of trace heavy metals, such as lead and cadmi um, in the body. According to Janata, the electrochemical approach to ana lyzing trace heavy metals is more sen sitive and accurate than the currently used optical techniques. The simplici ty of the CHEMFET would also allow it to be used in physicians' offices rather than in remote laboratories. Janata and his group are also inves tigating enzymatic coatings for the sensors. ENFETs (enzymatic field ef fect transistors) could be used to mon itor enzymatic reactions. The small size of the CHEMFET is particularly important if expensive enzymes are to be used in the device. "There are some 1500 different en
zymes that could be used," explains Janata. "So it's a matter of putting an enzyme on a transistor that is sensi tive to a particular species for which that enzyme is the catalyst." Many in dustrial processes, especially those in biotechnology, require careful moni toring of reactions, and the probes would be suitable for these. The small size of the CHEMFET enables multiple sensors to be placed on the probe tips, allowing simulta neous monitoring of many different compounds. Such multisensors would be especially useful to biomedical re searchers, but Janata points out that they may also find applications in such diverse fields as agriculture, mineral resource exploitation, and ef fluent monitoring. The main technological problem that has prevented wide-scale use of CHEMFETs is the difficulty of prop erly encapsulating the device (2). Microsensors are routinely exposed to media that are incompatible with the CHEMFET's solid-state electronic circuitry. Instability can result if even a trace of moisture or ionic contami nant penetrates the encapsulation coating of a CHEMFET.
According to Janata, "The bulk of the problems that remain are in the area of materials science, not in solidstate electronics or chemistry." He hopes to find a partner in industry in terested in refining the encapsulation and packaging techniques that protect the sensor and its electronic compo nents from inherently hostile environ ments. The University of Utah lab will build the basic chips, up to and in cluding the solid-state electronics, but researchers who purchase the sensors will have to coat the probe with the desired chemically selective mem brane and encapsulate it themselves. Cost feasibility of the project is based on providing 50,000 chips per year— the cost of the probes will depend somewhat on the number of requests received. For further information, contact Jiri Janata, Dept. of Bioengineering, Uni versity of Utah, Salt Lake City, Utah 84112, 801-581-3837.
Reference (1) Wohltjen, H. Anal. Chem. 1984,56, 87-103 A. M.D.W.
^^^^^^ Now our FS-capillary columns have their own place... make life easier, hut also
nation problems Midi tfi rulofornis. pesticides. I»l JwlwBrXyle*» H». 2,4-Xyfcnol
Macherey-Nagel • P.O.Box 307 • D-5160 Diiren -W. Germany · β02421-61071 -[Β 8 33 893 maria d
MACHEREY-NAGEL- DÜREN CIRCLE 144 ON READER SERVICE CARD
402 A · ANALYTICAL CHEMISTRY, VOL. 57, NO. 3, MARCH 1985
] > l l . .·•>
Comprehensive pro gramme of accessories including test and standard mixtures. A free GC brochure >HW IIMUl'llI LiUlipll.li.
ι ιιΐϋι-ιιΙ L.ipill.irv nihiiim-, ll(.'"ll lLl|lH.st
