Anal. Chem. 1988. 60. 62R-74R (G18) Zhuravleva, E. Y. Radlats.-Stimul. Yavlenlya Tverd. Telakh 1984,6 , 52-4 [CA 705(12): 107501~]. (G19) Melonl, S.; Genova, N.; Oddone, M. Sci. TofalEnviron. 1987,64(1-2), 13-20, (G24 lyengar, G. V. J. Redbanal. Nucl. Chem. 1987, 770(2), 503-17. (G21) Coetzee, P. P.; Pleterse, H. S. Afr. J . Chem. 1988, 39(2), 85-8 [CA 705(3): 21291x1. (G22) Potts. P. J.; Rogers, N. W. Geostand. News/. 1986, 10(2), 121-5. (G23) Ebihara, M.; Minai, Y.; Kubo, M. K.; Torninaga, T.; Aota, N.; Nlkko, T.; Sakarnoto, K.; Ando. A. Anal. Sci. 1985, 7(3), 209-13. (G24) Sun, J.; Jervls, R. E. Proc. Int. Conf. Nucl. Methods Environ. Energy Res., 5th, CONF-840408; Vogt, J. R., Ed.; NTIS: Springfield, VA, 1984; pp 394-405 [CA 704(8): 61185bl. (G25) Song, L.; MacMahon, T. D.; Ward, N. I. J . Radioanal. Nuci. Chem. 1987, 713(1), 285-98. (G26) Zhang, Y.; LI, X.; Song, L.; Yuan, L.; Chen, B.; Chen, B.; Wang, Y.; Sun, J. Geostand. Newsl. 1988, 70(1), 61-71. (G27) Chen, B.; Wang, Y.; Sun, J.; Zhang, Y. Wutan Yu Huatan 1985,9(3). 227-30. (G28) Korotev. R. L. J . Radioanal. Nuci. Chem. 1987, 770(1), 159-77. (G29) Kresten, P.; Brunfelt, A. 0. Geol. Foeren. Sfockhoim Foerh. 1985, 707(2), 107-8. (G30) Grosman, L.; Khakar, D. P. Smithson. Contrib. Earth Sci. 1987,(27), 22-3. (G31) Ehrnann, W. D.; Glllurn, D. E.; Sya, C. L.; Garg, A. N. Smithson. Contrib. Esrth Sci. 1987,(27), 18-19. (G32) Becker, R.; Koller, P.; Morschl, P.: Kiesl, W.; Hermann, F. Smithson. Contrib. Earth Sci. 1987,(27), 16-17. (G33) bedecker, P. A.; Chou, C. L.; Wasson, J. T. Smithson. Contrib. Earth Sci. 1987,(27). 15. (G34) Allen, R. O., Jr. Smithson. Contrib. Earth Sci. 1987,(27), 13. (G35) Showalter, D. L.; Wakita, H.; Smith, R. H.; Schrnltt. R . A. Smithson. Contrib. Earth Scl. 1987,(27), 40-2. (G36) Madaro, M.; Moauro, A. J . Radioanal. Nucl. Chem. 1987, 774(2), 337-43. (037) Morrison, G. H.; Potter, N. M.; Rothenberg, A. M.; Gangadharem. E. V.; Wong, S. F. Smithson. Contrlb. Earth Sci. (27), 32-3. (G38) Masumoto, K.; Yagi, M. Kakuriken Kenk u Kokoku (Tohoku Daigaku) 1987,20(1), 71-8 [CA 707(17): 153385gf (G39) Bower, N. W.; Kim. D. K.; Gladney, E. S. Geastand. Newsl. 1987, 77(1), 37-40. (G40) Kerr, S. A.; Oliver, R. A.; Vittoz, P.; Vivier, G.; Hoyler, F.; MacMahon, T. D.; Ward, N. I.J . Radioanal. Nucl. Chem. 1987, 773(1), 249-58 (041) Podracky, P.; Bouda. T. Acta Mont. 1984. 68, 245-51 [CA 704(4) 27989gl. (G42) Rogers, P. S. 2.; Dum, C. J.; Benjamin, T. M. Microbeam Anal. 1988, 27st, 157-63. INSTRUMENTATION (Hl) Knoll, G. F. Nuci. Instrum. Methods Phys. Res., Sect. 8 1987,82425, 1021-27. (H2) . . Andersen. H. H. Nucl. Instrum. Methods Phys. Res., Sect. 8 1986, 875(1-6), 722-8. (H3) Niese, S.; Helbig, W. J . Radioanal. Nucl. Chem. 1988, 700(1), 155-63. (H4) Helbig, W.; Niese, S. Nuci. Instrum. Methods Phys. Res., Sect. 8 1988,817(5-6), 431-4, (H5) Das, H. A.; Zonderhuis, J. J. Radioanal. Nucl. Chern. 1987, 774(2), 207-13. (H6) Morioka, T. Jpn. Kokai Tokkyo Koho JP 611157540 A2 [86/157540]; 17 Jul 1986, Appl. 84/279396, 28 Dec 1984, 5 pp [CA 706(14): 109767~1,
(H7) Reference deleted in proof. (HE) Yagi, M.; Masumoto, K.; Muto, M. J . Redbanal. Nucl. Chem. 1988, 98(1), 31-38. (H9) Larnbrecht, R. M.; Koehier, C. J. Radloenal. Nucl. Chem. 1985, 92(1), 177-82. DATA ANALYSIS AND COMPUTATIONALMETHODS (11) Stolyarova, E. L.; Novlkov, A. I.; Srapenyants, R. A. Priki. Yad. SpektrOSk. 1984, 73, 239-43 [CA 104(22): 195033jl. (12) Zagpal, P.; SOlymOsl, J.; Nagy, L. G. Perlod. Polytech., Chem. Eng. 1984,28(3-4), 217-24. (13) Lin, X.; Zhang, W.; Tang, N. Hejishu 1985, (3), 20-3 [CA 705(2): 13896hl. (14) Benes. J.; Frana, J.; Hnatowicz, V.; Mastalka, A. Jad. Energ. 1988, 32(1), 34-8 [CA 705(12): 107408cJ. (15) Srnakhtin, L. A. J . Radloenal. Nucl. Chem. 1988,99(1), 171-80. (16) Das, H. A. J . Radioanal. Nucl. Chem. 1986, 99(1). 61-73. (17) Nicolaou, G. E.; Khrbish, Y. S.; Spyrou, N. M. Appl. Radlat. Isot. 1986, 37(12), 1219-24. (18) Dirnchav, T. God. Vissh. Mlnno-Geoi. Inst., Sofiya 1984,30(4), 75-83 [CA 703(26): 226436dl. (IS) Currie, L. A. Opt. Eng. 1985, 24(6), 1004-8. (110) Pak, Y. N.; Vdovkin, A. V. Izv. Vyssh. Uchebn. Zaved., e r n . Zh. 1988, (5), 1-3 [CA 705(14): 126241jI. TRACER STUDIES (Jl) Cassidy, R. M.; Miller, F. C.; Knight, C. H.; Roddick, J. C.; Suiilvan, R. W. Anal. Chem. 1988,58(7). 1389-94. (J2) De Bruin, M.; Wolterbeek, H. T. Proc. Int. Conf. Nuci. Methods Envlron. Energy Res., 5th, CONF-640408; Vogt, J. R., Ed.; NTIS: Spring field, VA, 1984; pp 768-74 [CA 104(1): 3495~1. (J3) Link, R.; Nuding, W.; Sauerwein, K. Atomkernenerg./Kerntech. 1988, 48(2), 65-7 [CA 705(10): 86733nl. ISOTOPIC DATING METHODS (Kl) Burleigh, R.; Leese, M.; Tlte, M. Radlocarbon 1988, 28(2A), 571-7. (K2) Kubik, P. W.; Elmore, D.; Conrad, N. J.; Nishilzuml, K.; Arnold, J. R. Nature (London) 1988,379(6054), 568-70. (K3) Fehn, U.; Teng, R.; Elmore, D.; Kublk, P. W. Nature (London) 1986, 323(6090), 707-10. (K4) Kubik, P. W.; Elmore, D.: Fehn, U.; Phllllps, F. M. Nucl. Instrum. Methods Phys. Res., Sect. 8 1987,624-25(Pt. 2), 678-81. (K5) Thomsen, M. S.; Heinemeier, J.; Hornshoej, P.; Rud. N. Nuci. Instrum. Methods Phys. Res ., Sect, 8 W87,628(3), 433-7. (K6) McKeown, R. D. Philos. Tran. R . SOC. London, A 1987,323(1569), 145-54. (K7) Elmore, D.; Kublk. P. W.; Hernmick, T.; Teng, R.; Kagan, H.; Haas, P.; Boyd, R. N.; Turner, R.; N b , D. et al. Nucl. Instrum. Methods Phys. Res., Sect. 8 1985,870-17(2), 738-42. (K8) Pachlaudl, C.; Marechai, J.; Van Strydmck, M.; Dupas, M.; DauchotDehon, M. Radlocarbon 1988, 28(2A), 691-7. (K9) Froehllch, K.; Geilermann, R. Chem. Geol. 19B7,65(1), 67-77. (K10) Bonhomme, M. G. Chem. Geol. 1987,65(3-4), 209-22. RELATED TOPICS (Ll) Bethe, H. A. Phys. Rev. Lett. 1986,56, 1305-8. (L2) Mlkheyev, S. P.; Smknov, A. Y. Yad. Flz. 1985,42, 1441-48. (L3) Elliott, S. R.; Hahn, A. A.; Moe, M. K. Phys. Rev. Lett. 1987, 59, 2020-23.
Chemical Sensors Jiii Janata* and Andras Bezegh' Center for Sensor Technology, University of Utah, Salt Lake City, Utah 84112
1. INTRODUCTION When the search of the Chemical Abstracts data base was done for the purpose of this review, it netted over 1500 references under the general entry of "chemical sensors" for the Period between January '985 and December 1987;chemical sensor is undoubtedly a popular object. But, what is it? It seems that so far nobody has been able to give an unambig-
* Author t o whom correspondence should be addressed. 'Present address: Institute for General and Analytical Chemistry, Technical University, 1502 Budapest, Hungary. 62 R
uous and universally accepted definition. We have not attempted to do this either, but because the review had to be within the context of some we had to up with o~ own definition for we no beyond these pages. According to u8 a chemical SellSOris a transducer which provides direct information about the chemical cornposition of its environment. consists of a physical transducer ada chemically selectiue layer. The four fundamental transduction modes by which this review is divided are thermal, mass, electrochemical, and optical. For Purely Pragmatic reasons we had to leave out sensor systems which, again by our definition, are analytical
0003-2700/88/0360-62R$06.50/00 1988 Amerlcan Chemical Society
CHEMICALSENSORS
Table 1. Sensor Papers in the Data Base
reviews
thermal mass Utah. He receivedi;lo M.Sc. (1961) and Ph.0. (1965) degrees in anabilcal chemistry from lhe Charles university h Raha. Czech osksvakie. His ctment ~esearchInterests h dud0 sOl&state chemical S B ~ S M Sand elecbochemlrtry. a
insrrumenra in which ORQ or more operations have to be made before a darn poinr is obtained. Thus, for example, all flow injection analysis procedures are left out even though they may provide information faster and more accurately than many directly operating sensors. Likewise, we have avoided the criterion of -continuity- becawe the response of some sensors is so slow in that they can be used only in very specialized applications when the chemical comporition changes very slowly. The size is not a very useful criterion either: an on-line gas chromatograph is not a sensor but a spertrophotometer uperating a iiher-optic probe is. Another cempting definition of a chemical sensor could be made acrording to the uniqueness of its operation. Thus, it could be a disrrete probe which allows the determinations which could nor be done by some equivalent bavh analytical pnredure. This definition would pass all electrorhemical and mass sensors because neither o i these two types of measurements can be dune withwt electrodes or a microbalance, respectively. However. it would reject most optical and thermal sensors because there are equivalent spectrophotometrir and calorimetric batch analytical determinations available. We shall not pursue this line of reasoning further for the fear of being tied up with a multimode optical fiher and Jpeared hy an enzymatic thermistor at the next biosensor conference. Clearly, any definition immediately creates its own exceptions and many 30-called -chemical sensors" have now become a part of the scientific folklore tn the extent thnt they had to be inrluded in this review. 'There are two other reviews published in this issue which are closely related to the topic of rhemical sensors: 'IonSelective Electrodes' (R. Solaky) and 'Dynamic Electrochemistry" (D. Johnson, M. Ryan, and G. Wilson]. Ion-selective electrodes are the largest. oldest. and best understood group of chemical sensors. They are not included in our review, but the number of papers is listed in Table I for comoariuon. Therefore oocentiometric ion sensors in this review i h u d e only integraied ion sensors, i.e. hyhrid senson and CHEMFETs. The overlap with -Dynamic Electrochemistry" is murh smaller. The amperometric elertrodes are discussed only when they are used as chemical sensors and not for electrochemical studies. Even with these limits we had to restrict the number of references to approximately one-third of the original entries. We apologize to our colleagues whose papers have not been mentioned. It is because of the space limitation and not because of our judgement of the importance of their work. This review deals almost entirely with articles published in English. The number of entries in the original data base (Table I) attests to the vitality of this field. It is interesting
1985
1986
1987
total
76 9 15
101 8
87
264
2 17 59 79 94 74
19 58 110 248 280 196
208
1007
412
1175
optical
20
26 31
potentiometric amperometric
conductometric ion-sel. electr.
80 80 68
89 106 54
404
year total'
348
395 415
Without ISE.
to note that the single largest group were the reviews of chemical sensors: 1review per 3.4 original papers. I t means that whenever three original papers appeared somebody reviewed them. This proliferation of "review", "position", or "concept" papers can be partly explained by the general availability of word processors and by the tendency to publish "proceedings" of any sensor-related gathering regardless whether the presented work is original or not. The distribution of the number of papers among different types of sensors speaks for itself. The combined electrochemical sensors (without ISEs) represent 80% of the total sensor publications for the last three years. Optical sensors are 12% and rising, masa sensors are steady 690,and thermal sensors are 2%. Our review is not written in these proportions. There have been numerous proceedings of sensor meetings published (1-3) either in the form of a book or as a special issue of specialized journals. Several original reviews dealing with the general subject of principles and classification of 7j have been written. Two mulchemical sensors (4,5,6a, tiauthored books, one dealing with four rather narrow topics of hydrogen MOSFET, CHEMFET, piezo-, and pyroelectric sensors and sensor fabrication (66) and one covering the whole general area of biosensors (81, have been published. Perhaps the most basic issue of any chemical sensor is the selectivity. It has been reviewed for the three types of biologically derived selectivity which constitutes the area of biosensors: enzymatic sensors ( 9 1 2 ) ,immunochemical sensors (131,and receptor-based sensors (14-16). The use of immobilized enzymes for sensing of inhibitors falls also into this category (17). The chemical selectivity produced by membranes (18), ceramics (19), and conducting polymers (20) applies more or less to all types of chemical sensors. Several reviews deal with the subject of fabrication techniques (66, 21-23) particularly of solid-state microsensors. Relativelv few DaDerS have been devoted to the imoortsnt subject of chemometrics as it applies IO chemical sensors in general (24.2Fi). Equally important is the h u e of the biocompatibility of chemical sensurs (26. 27) used in medical applications. There me extensive reviews dealing with specific application areas. General clinical chemistry (28-30) and sensors for management of diabetes (31) have been covered. Various types of sensors for detection and monitoring of individual gases such as O2and CO and groups of gases (19,32-36) and environmental pollutants (3) have been published. Sensor applications in process control, namely in food and fermentation industries (37-39) have been extensively reviewed. ~
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2. THERMAL SENSORS Heat is a general property of any chemical reaction. As such it should be a n ideal physical parameter to use for sensing. Unfortunately its flow is difficult to control. The partial solution for the heat management in any integrated chemical sensor has been suggested (40). Enzymatic reactions act as chemically selective heat generators. For this reason almost all thermal sensors rely on enzymes for their selectivity. Because the search has produced only a small number of entries, we shall relax somewhat our rule not to include the sensor systems. The term "enzymatic transistor" coined by Daniekon and Mosbach (41,421 is slightly misleading because it applies to flow calorimetry in which the enzymatic reaction occurs in a column reactor and the heat output is monitored a t the reactor outlet. In a flow-through arrangement using ANALYTICAL CHEMISTRY, VOL. 60. NO. 12, JUNE 15, 1988
63R
CHEMICAL SENSORS
cycled pair of substrates (lactate/pyruvate), it is possible to achieve the detection limit of 10 nM pyruvate (43). Enzyme-linked immunoassay with thermometric detection has been also developed (44).The thermistor appears to be the most popular temperature-sensing probe because of its cost, availability, stability, and sensitivity. However, thermoelectric power devices have been also used and the application of the Seebeck effect for sensing has been reviewed (45). The first integrated thermal sensor for glucose using the temperature dependence of the output of the Darlington amplifier has been constructed (46). The dynamic range of this sensor is 5-100 mM, which is comparable with electrochemicalglucose sensors.A thermal sensor for humidity is based on the changes of heat conductivity of TaN thin film (47). Because of their very high sensitivity, pyroelectric devices have been proposed for chemical sensing (6b). It has been shown that they are capable of measuring the heat of absorption corresponding to a monolayer of gas. A multisensor chip utilizing pyroelectric ZnO has been constructed (48).
3. MASS SENSORS The measurement of the change of mass as the means of chemical sensing is almost as universal as is the measurement of reaction heat. In principle it is applicable to any reactions in which there is a net change of mass which, by definition, leaves out most of the selective catalytic reactions including the enzymatic ones. There are two types of mass chemical sensors: those based on piezoelectric bulk oscillators, and those based on surface acoustic wave (SAW) devices. In principle any mechanical oscillator can be used, such as vibrating beam, as has been shown by Muller et al. (49). Although quartz is the most common material used for the bulk oscillators, i.e. quartz crystal microbalances (QCM), other materials, such as poly(vinyl fluoridone) (PVF)(50)and ZnO can be also used. The latter has been used to construct an integrated multisensor array (51). The domain of applicability of mass sensors has been sensing in gas phase. There are many new applications of both SAW and QCM sensors described in the literature and only a few will be given here. There are several older reviews and books dealing with the application of QCM and one new review of the SAW applications (52)which deals mainly with the issue of selective coatings. Because they are relatively inexpensive, QCM have been used with all possible and impossible coatings. The general rule here seems to be that anything that can be dissolved should be tried as the chemical coating for a piezoelectric crystal. It is not surprising that the attention of chemometricians has turned to mass sensors in the attempt to rationalize the selectivity issue by the use of pattern recognition (53-57). However, two stories have dominated the development of mass sensors in last three years: the ossibility of their use for general chemical sensing in liqui phase, and immunochemically produced selectivity in gas phase. 3.1. Gas Phase Applications. An elegant design of a humidity/temperature sensor utilizing dual-delay line SAW and polyimide film has been published (58,59). The response to hydrogen of Pd-coated QCM (60) is slow at room temperature and relatively insensitive compared to Pd MOSFET. A small and very sensitive (
