ISSN 1070-3632, Russian Journal of General Chemistry, 2008, Vol. 78, No. 12, pp. 2413–2417. © Pleiades Publishing, Ltd., 2008. Original Russian Text © O.M. Petrukhin, O.O. Maksimenko, 2008, published in Rossiiskii Khimicheskii Zhurnal, 2008, Vol. 52, No. 2, pp. 3–6.
Sensors in Analytical Chemistry O. M. Petrukhina and O. O. Maksimenkob a
Mendeleev Russian University of Chemical Technology, Moscow, Russia Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, B-334, Moscow, 119991 Russia b
NANOSISTEMA Research and Production Complex, Moscow, Russia Received February 20, 2008
Abstract―Chemical sensorics is an independent domain of modern analytical chemistry. In Germany and Japan, multivolume encyclopedias dedicated to sensors were published. The publication of the nine-volume encyclopedia [1] in Germany was immediately followed by the appearance of the annual publication [2] incorporating additional data available from US. The preparations to publication of the next encyclopedia of sensors are under way now. It san be said with a good reason that chemical sensorics is a well-established sphere which is still under active development. This is specifically a testing ground for novel ideas and novel materials. This issue of Rossiiskii Khimicheskii Zhurnal (Zhurnal Rossiiskogo Khimicheskogo O–va im. D. I. Mendeleeva) is dedicated to chemical and biochemical sensors. It makes readers acquainted with the current state of the art in this sphere and covers various types of sensors. Here, we attempt to outline the general situation in this domain of analytical chemistry.
DOI: 10.1134/S1070363208120232 Chemical sensors are portable devices intended for selective and typically continuous (reversible) realtime determination of the concentration of a substance in a single stage, most often without undertaking preliminary sample preparation efforts. The analytical technique is once and forever “hardwired” into such devices which can be produced on a fairly large scale [3]. Every sensor is comprised of a sensing element “recognizing” the analyte and an analytical signal converter, which transforms a characteristic parameter of a chemical or biochemical reaction to a physical parameter. Integration of the sensing element and the converter within a single analytical device, sensor, represents a novel approach to analytical practice, rather than a formal procedure. One of the major advantages offered by sensors is their suitability for outdoor, field, applications without the use of complex equipment. We briefly discuss below the chemical and biochemical sensors that are the focus of individual articles in this issue.
Optical Sensors The operation of the earliest mass-produced sensing elements was underlain by optical methods of analysis. They were used in test-methods [4–6] intended for visual solid-phase molecular absorption analysis. In such elements, a photometric reagent is preliminary applied to a paper strip or another solid substrate. One of the first, if not the very first, among the chemical firms that undertook provision of this line was Merk. In this issue, optical chemical sensors are the focus of review by Savvin et al. from Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, and Mendeleev Russian University of Chemical Technology. The molecular-absorption analysis principles also underlay the development of clinical analytical chemistry. Originally, various medically important compounds were determined using analytical reactions in solutions [7]. More recently, clinical analytical chemistry took a route along which the implementation of solid-phase analysis methods was paralleled by designing compact devices for analysis of biologically active compounds and diagnostic applications.
2413
2414
PETRUKHIN, MAKSIMENKO
Of crucial importance for reliable operation of optical sensors is selectivity of analytical reactions. With antibodies and DNAs as analytical reagents, a deeper insight into selectivity of chemical reactions can be gained.
elements is comprised of ion-sensitive electrochemical membranes, i.e., solutions of ionophores or ion exchangers in a hydrophobic solvent or in a polymer whose glass transition point lies above the room temperature.
Mass-Sensitive Sensors
Extensive electroanalytical application has been found by organic electroconducting materials which embody one of the advances in organic chemistry of the second half of the XX century. The converters for these sensors are manufactured from diversified solid current-conducting materials like carbon, graphite, glassy carbon, pastes, and other modified currentconducting materials.
In mass-sensitive, or gravimetric, sensors the transducers are represented by piezoelectric quartz crystals [8]. A change in the mass of a piezocrystal, caused by selective sorption of the target substance on a polymer film deposited onto the crystal surface or on a surface-grafted layer of the receptor molecules induces variation of the oscillation frequency of the piezoelectric crystal. The underlying principle of such analysis, piezoelectric-crystal microweighing, was proposed in the 1960s. A fairly wide application is received by gas sensors, in which the target substances are sorbed from the gas medium onto sensitive polymer films applied onto the piezoelectric-crystal surface. Piezoelectric crystals with a surface receptor coating are used for analysis of aqueous solutions. Examples of application of piezoelectric-crystal microweighing in analytical chemistry can be found in the collection of works presented at an international symposium dedicated to multisensor systems [9]. High performance capabilities are exhibited by piezocrystal immune sensors with piezocrystal surfaceimmobilized biochemical reagents, antibodies or antigens. Immune sensors are suitable for determination of pesticides, medicines, drugs, and viruses. In this issue, piezoelectric-crystal biosensors are discussed in the article by Ermolaeva et al. from Lipetsk State Technical University. Electrochemical Sensors Glass рН-sensitive electrode, whose designing is often qualified as an event signifying the “birth” of chemical sensors, belongs to the most widespread electrochemical ion-selective electrodes and ionselective field-effect transistors. Sensing elements most widely employed in these sensors include solid electrolytes and semiconductors, e.g., lanthanum fluoride and silver iodide, as well as zirconium dioxide, a high-temperature solid electrolyte. Motherglass is also classed with this type of sensing elements. Another group in this class is formed by solid electrodes with covalently-grafted complexing and ion-exchangeable groups. A large group of sensing
Ion-selective electrodes and ion-selective fieldeffect transistors are still the most demanded sensors. In this issue, chemical sensors of this type are discussed in three articles. The state of the art in ionometry in its classical version is analyzed in reviews by K.N. Mikhel’son from St. Petersburg State University and V.V. Egorov from Belarus State University, Minsk. The potential measured in an ion-selective electrode is formed at the electrode membrane– solution interface, in which respect ionometry has much in common with extraction. The review by Shipulo et al. from Mendeleev Russian University of Chemical Technology analyzes how extraction affects the development of ionometry. Specifically, it is demonstrated how the extraction parameters, stability, and hydrophobicity of electroactive compounds are related to the analytical characteristics of ion-selective electrodes. Intensive development is experienced now by electrochemical sensors intended for analysis of bioactive compounds. This concerns, in particular, biosensors whose operation is underlain by enzymatic reactions yielding compounds to which an ionselective electrode is sensitive. For example, a biosensor for determination of carbamide was designed, whose operation is underlain by its enzymatic decomposition, accompanied by elimination of ammonia. Electrochemical biosensors based on horseradish peroxidase are the subject of review by Presnova et al. from Lomonosov Moscow State University. They discussed both direct (mediator-free) biosensors characterized by direct electron transfer between the electrode surface and the reactive center of the enzyme in electrocatalytic processes and biosensors in which
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 12 2008
SENSORS IN ANALYTICAL CHEMISTRY
the electron transfer between the electrode and enzyme is effected by specially introduced diffusing mediators. As known, DNAs are able of complexing with metal cations and organic compounds and, in a certain respect, can be regarded as complex organic analytical reagents. This property of DNAs is employed in cancer chemotherapy. At the present time, complexing by native and single-chain DNAs represents one of the approaches taken in designing sensing elements of biosensors. The development of electrochemical DNA-sensors intended for determination of biologically active lowmolecular-weight compounds is discussed by Evtyugin et al. from Kazan State University. These biosensors employed composite membranes based on currentconducting polymers. Interestingly, this study demonstrates the suitability of such sensors for determination of autoantibodies, i.e., antibodies secreted by the human immune system and directed against the individual’s proteins. For example, a biosensor for Lupus Erythematosus (Le) identification was designed at the Kazan State University. A large developmental effort is dedicated now to electrochemical sensors intended for determination of plant bioactive compounds, in particular, various antioxidants. In human body, there exists a multitude of buffer redox systems playing diversified roles, of which the major one consists in the body protection against the oxidative stress. In this respect, the severest hazard is posed by reactive oxygen species (О2, Н2О2, HO·, etc.). Oxygen-containing radicals in a human body are neutralized by antioxidants, among which the best known compounds are ascorbic acid soluble in aqueous solutions, including blood plasma, and fatsoluble vitamin Е. The assessment of the antioxidant activity of substances with the use of electrochemical DNA-sensors is also discussed by G.A. Evtyugin et al. Sensors Employing Physical and Physicochemical Converters There exist gas sensors whose operation is underlain by interaction of the analyzed gas mixtures with semiconductor materials. In such sensors, the semiconductor surface serves as a sorption-sensitive element which can function as converter owing to the semiconductor properties of the material. In this issue, sensor gas analysis is the focus of articles by Rumyantseva et al. from Lomonosov Moscow State University and by L.A. Obvintseva from Karpov Institute of Physical Chemistry.
2415
Novel Materials and Technologies for Chemical Sensor Designing In researchers’ opinion, further development of chemical sensorics will attract new materials and technologies to sensor designing. The article by Shvedene et al. from Lomonosov Moscow State University is dedicated to the specific features and advantages offered by ionic liquids used in electrochemical sensors. Ionic liquids are peculiar in being suitable not only as solvents with fairly attractive electrochemical properties [10] but also as chemical reagents. Ionic liquids comprising various functional analytical groups open new prospects in sensor operation. Relevant studies are in the very early stage now, and it can be safely predicted that many surprises are awaiting the researchers along this route. Much promise in the field of sensorics is offered by nanomaterials and nanotechnologies [11–13], which are the focus of the review by S.N. Shtykov and T.Yu. Rusanova from Saratov State University. Originally, sensors were used for individual measurements and analysis of liquids, in particular, solutions of electrolytes. This domain of analytical chemistry still represents the major application field for sensors. This is paralleled by extensive sensor network designing and application activities. In this context, pertinent is the opinion of the natural, biological, sensors, expressed by K.U.M. Smith [14], who regards the world the humans live in as a sensor world (in a certain respect), created, above all, by their sight, hearing, smell, taste, and tactile sensors. The question about the extent to which this world is adequate to the real world is qualified by Smith as that of a philosophic nature. There is no simple answer to it, at least because each individual has its own idea of the outworld, which seldom coincides with the ideas of others. In turn, the article “Sensor Systems” in the Big Encyclopedic Dictionary (Biology) [15] states in conclusion that some principles and mechanisms of information processing in sensor networks were identified to a significant extent, but is still remains to be elucidated by what mechanisms an integer sensor image is formed. The lack of a clear idea of how the image of a real object is formed is specifically responsible for the need in preliminary learning of the sensor network, on the one hand, and for the capability of a sensor network to identify, in some cases, an analyte that is not represented by an individual sensor in the network, on the other [14]. In any way, the development and
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 12 2008
2416
PETRUKHIN, MAKSIMENKO
application of sensor systems represent the most promising line in sensing. It should be noted that, in this case, sensor networks serve as test-methods of analysis for the classification purposes with respect to the analyzed objects, i.e., operate by yes/no principle and are most suited to revealing counterfeit products. Designing biosensor systems is the focus of the article by Vlasov et al. from the St. Petersburg State University. Macroanalytical Chemistry Methods in Sensor Aanalysis The sensor application practice is closely adjoined by the use of macroanalytical chemistry methods in sensor analysis. This approach is best illustrated by chromato-massspectrometric methods of analysis, which employ databases containing mass spectra of thousands of compounds. The computer of a spectrometer automatically compares the spectrum of the compound analyzed with that from the database, thereby identifying the compound of interest and estimating its concentration in the sample from the analytical signal intensity. Another example can be found in high-performance ion chromatography with electrochemical detection, used to determine organic compounds comprising electrochemically active groups [16]. In this issue, the application of the macroanalytical chemistry method in sensor analysis is discussed in the article by A.Ya. Yashin. CONCLUSIONS A milestone in chemical sensorics was achieved in 1972, when Bergfeld combined the electrochemical ion-sensitive membrane with a field-effect transistor into an integer whole, an ion-sensitive field-effect transistor. The theoretically possible arrangement of micron-sized ion-sensitive membrane(s) on the surface of a field-effect transistor gate, coupled with the potentially possible use of planar technology caused an outburst of analysts’ imagination. This is manifested in definition of sensors or, in a more correct way, of the analytical community’s expectations associated with sensors. For example, in opinion of Zimina and Luchinin [17], “after a period of several years, a horde of nanorobots will be engaged in medical treatment of humans and monitor the environmental condition. Plentiful microscopic robots will be released into the
ocean, each capable to assess the cleanliness of water in which it occurs and to communicate this information to its neighbors, using appropriate radio equipment” [17]. Nanorobots generate great medicinal expectations. Transdermal medicine delivery systems find ever increasing application as plasters or bandages that afford penetration of medicines deep inside the skin layers and into the blood flow system in a way that avoids the fluctuations of the medicine content in blood, observed with different ways of delivery. The designing prospects for such systems were analyzed by James Gimzewski, one of the founders of the California Nanosystems Institute [18], who anticipates the designing, within the next couple of years, of biodetectors that will identify viruses and various hazardous materials. In Gimzewski’s opinion, already at the present time there exist all the opportunities for reaching this goal, but they need to be combined with one another. Gimzewski notes an inspiring possibility available, e.g., for many research teams in the US. It consists in application of nanotechnology in the work with individual cells, which represent an ideal sensor to monitor various chemical and biochemical processes. J. Gimzewski believes that specifically nanobiotechnology will be of crucial importance for medicine delivery systems. It is difficult to judge to what extent, now and in the future, the designing of a chemical nanoanalyzer is a real opportunity, but this domain of analytical chemistry is undoubtedly in line with the general trend for miniaturization of technical facilities. These and other, similar speculations can be regarded differently, in particular, as a myth invented by numerous participants of various conferences and workshops dedicated to chemical sensors and chemical sensorics. One cannot expect that chemical sensorics will allow these expectations to fulfill. However, it clearly played a preparatory role with respect to the next stage in development of analytical chemistry, designing integrated microanalytical systems or hybrid integrated systems for total chemical analysis, microanalytical systems [μ-Total Analytical System (μ-TAS), Lab-on-a-Chip] [19]. REFERENCES 1. Sensors Update 1, Grandke, T., and Ko, W.H., Eds., Wiley: 1996, vol. 1. 2. Micro Total Analysis Systems, van den Berg, A. and Bergfeld, P., Eds., Netherlands: Kluwer, 1995, p. 250.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 12 2008
SENSORS IN ANALYTICAL CHEMISTRY 3. Zolotov, Yu.A., Zh. Anal. Khim., 2005, no. 10, p. 1011. 4. Feigl, F. and Anger, V., Spot Tests in Inorganic Chemistry, New York, 1972. 5. Feigl, F. and Anger, V., Spot Tests in Organic Analysis, New York: Elsevier, 1966. 6. Zolotov, Yu.A., Ivanov, V.M., and Amelin, V.G., Khimicheskie test-metody analiza (Chemical TestsMethods of Analysis), Moscow: Editoral URSS, 2002. 7. Pustovalova, L.M., Praktikum po biokhimii (Practical Course of Biochemistry), Rostov-on-Don; Feniks, 1999. 8. Kuchmenko, T.A., Primenenie metoda p’ezokvartsevogo mikrovzveshivaniya v analiticheskoi kihimii (Application of Piezoelectric Crystal Microweighing Method in Analytical Chemistry), Voronezh: Vorohezh. Gos. Tekh. Akad., 2001. 9. Int. Symp. on Olfaction and Electronic Noses, St. Petersburg (Russia), May 3–5, 2007. 10. Aslanov, L.A., Zakharov, M.A., and Abramysheva, N.L., Ionnye zhidkosti v ryadu rastvoritelei (Ionic Liquids in the Solvent Series), Moscow: Mosk. Gos. Univ., 2005. 11. Rakov, E.G., Nanotrubki i fullereny: Uchebnoe posobie
12.
13. 14. 15.
16. 17.
18. 19.
2417
(Nanotubes and Fullerenes: Manual), Moscow: Universitetskaya Kniga, Logos, 2006. Nanotechnology Research Directions. Vision for Nanotechnology in the Next Decade, IWGN Workshop Report, Roco, M.C., Williams, R.S., and Alivasatos, P., Eds., 1999. Prasada Rao, T., Kala, R., and Danirl, S., Anal. Chim. Acta, 2006, vol. 578, p. 105. Smith, K.U.M., Biology of Sensory Systems, New York: Wiley, 2000. Bol’shoi entsiklopedicheskii slovar’: Biologiya (Big Encyclopedic Dictionary: Biology), Moscow: Bol’shoi Rossiiskoi Entsikliklopedii, 1998, p. 568. Sensors Ser., Gopel, W., Hesse, J., and Zemel, J.N., Eds., Weinheim: Wiley-VCH, 1989–1996, vols. 1–9. Zimina T.M. and Luchinin, V.V., Ot sensorov k mikroanaliticheskim sistemam (From Sensors to Micro-Analytical Systems), Moscow: Tekhnosfera, 2005, p. 302. http//www.offline.computerra.ru./print/offline/2004/ 553/35459/. Drug Discovery Today, 2001, vol. 6 (19), p. 967.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 12 2008
