Anal. Chem. 2004, 76, 7023-7027
Boosting Sensitivity of Organic Vapor Detection with Silicone Block Polyimide Polymers Radislav A. Potyrailo* and Timothy M. Sivavec
General Electric Company, Global Research Center, Niskayuna, New York 12309
We demonstrate that silicone block polyimide polymers have an unusually high sensitivity to nonpolar organic vapors, including chlorinated organic solvent vapors. When 0.18-5.34-µm-thick films of silicone block polyimide polymers were deposited onto 10-MHz thickness shear mode (TSM) oscillators, these films were implemented to detect parts-per-billion concentrations of trichloroethylene (TCE) with a detection sensitivity of 0.5-23.5 Hz per 500 ppb of vapor. With a film thickness of 3.4 µm (91.5-kHz frequency shift upon film deposition), optimized for the minimal sensor noise of 0.04 Hz, the calculated detection limit of sensor response (S/N ) 3) was 3 ppb of TCE. Detection limits for other chlorinated organic solvent vapors, such as perchloroethylene (PCE), cis-1,2-dichloroethylene (DCE), trans-1,2-DCE, 1,1DCE, and vinyl chloride (VC) were 0.6, 6, 6, 11, and 13 ppb, respectively. Assuming only the mass-loading response when deposited onto the TSM devices, silicone block polyimide polymers have partition coefficients of over 200 000 to parts-per-billion concentrations of TCE that make them at least 100 times more sensitive than other known polymers for TCE detection. We observed that unlike conventional polyimides, water sensitivity of the new hybrid polyimides is suppressed because of the silicone soft block. Water sensitivity is comparable with the sensor response to nonpolar organic vapors. The high sensitivity and long-term stability of these sensor materials make them attractive for ultrasensitive practical sensors. An increasing demand for ultrasensitive chemical detection for medical, biotechnological, industrial, environmental, and homeland security purposes is stimulating development of new sensor materials with improved sensitivity and selectivity. Despite recent valuable contributions to the sensor materials,1-12 reliable, selec* Corresponding author. E-mail:
[email protected]. (1) Ehlen, A.; Wimmer, C.; Weber, E.; Bargon, J. Angew. Chem., Int. Ed. Engl. 1993, 32, 110-112. (2) Finklea, H. O.; Phillippi, M. A.; Lompert, E.; Grate, J. W. Anal. Chem. 1998, 70, 1268-1276. (3) Crooks, R. M.; Ricco, A. J. Acc. Chem. Res. 1998, 31, 219-227. (4) Rakow, N. A.; Suslick, K. S. Nature 2000, 406, 710-713. (5) Schlupp, M.; Weil, T.; Berresheim, A. J.; Wiesler, U. M.; Bargon, J.; Mu ¨ llen, K. Angew. Chem., Int. Ed. 2001, 40, 4011-4015. (6) Buss, C. E.; Mann, K. R. J. Am. Chem. Soc. 2002, 124, 1031-1039. (7) Mello, J. V.; Finney, N. S. Angew. Chem., Int. Ed. 2001, 40, 1536-1538. (8) Fabbrizzi, L.; Leone, A.; Taglietti, A. Angew. Chem., Int. Ed. 2001, 40, 30663068. (9) Janata, J.; Josowicz, M. Nat. Mat. 2002, 2, 19-24. 10.1021/ac049481l CCC: $27.50 Published on Web 10/23/2004
© 2004 American Chemical Society
tive, and rapid determinations of organic vapors at parts-per-billion and parts-per-trillion levels over extended periods of time still remain an unsolved challenge because of the lack of highly sensitive materials that can be used in the field over extended periods of time. We have been developing and field-testing sensors for determination of toxic industrial organic contaminants at trace levels13-17 in groundwater. Chlorinated organic solvents, such as trichloroethylene (TCE), perchloroethylene (PCE), and their daughter products are at the top of the priority list for environmental determinations at trace levels because they represent the most prevalent organic groundwater contaminants.18 In our efforts toward sensor materials with high sensitivity toward chlorinated organic vapors, we have found that one class of hybrid polymers containing both hard and soft blocks serves as an extremely sensitive sensor material. From a variety of such hybrid polymers that included silicone block bisphenol A polycarbonate, polyoxyalkylene diimide diacid block polyalkylene terephthalate, polyether block polyamide, silicone block polyimide polymers, and some others, silicone block polyimide polymers have this highly desired property.19 These polymers demonstrated more than 100-fold improvement in sensitivity toward organic solvent vapors when compared to conventional currently used sensor materials, such as phenylmethylpolysiloxanes, poly(epichlorohydrin), poly(isobutylene), poly(ethylene maleate), poly(ethylenimine), and many others.20-25 To evaluate new sensor materials, we used acoustic(10) Chopra, S.; McGuire, K.; Gothard, N.; Rao, A. M. Appl. Phys. Lett. 2003, 83, 2280-2282. (11) Novak, J. P.; Snow, E. S.; Houser, E. J.; Park, D.; Stepnowski, J. L.; McGill, R. A. Appl. Phys. Lett. 2003, 83, 4026-4028. (12) Convertino, A.; Capobianchi, A.; Valentini, A.; Cirillo, E. N. M. Adv. Mater. 2003, 15, 1103-1105. (13) Potyrailo, R. A.; May, R. J.; Sivavec, T. M. Proc. SPIE 1999, 3856, 80-87. (14) Potyrailo, R. A.; Sivavec, T. M.; Bracco, A. A. Proc. SPIE. 1999, 3856, 140147. (15) Potyrailo, R. A.; Morris, W. G.; Wroczynski, R. J. In High Throughput Analysis: A Tool for Combinatorial Materials Science; Potyrailo, R. A., Amis, E. J., Eds.; Kluwer Academic/Plenum Publishers: New York, 2003, Chapter 11. (16) Potyrailo, R. A.; May, R. J.; Sivavec, T. M. Sens. Lett. 2004, 2, 31-36. (17) Potyrailo, R. A.; Morris, W. G.; Wroczynski, R. J. Rev. Sci. Instrum. 2004, 75, 2177-2186. (18) Westerick, J. J.; Mello, J. M.; Thomas, R. F. J. Am. Water Works Assoc. 1984, 76, 52-59. (19) Sivavec, T. M.; Potyrailo, R. A. Polymer coatings for chemical sensors; U.S. Patent 6,357,278, 2002. (20) Grate, J. W.; Abraham, H.; McGill, R. A. In Handbook of Biosensors and Electronic Noses. Medicine, Food, and the Environment; Kress-Rogers, E., Ed.; CRC Press: Boca Raton, FL, 1997. (21) Rosler, S.; Lucklum, R.; Borngraber, R.; Hartmann, J.; Hauptmann, P. Sens. Actuators, B 1998, 48, 415-424.
Analytical Chemistry, Vol. 76, No. 23, December 1, 2004 7023
Scheme 1. Synthesis Steps of New High Partition Coefficient Sensor Materials
wave devices. These transducers coated with sensor materials are used in demanding practical applications.26-28 EXPERIMENTAL SECTION Polymer Synthesis. Our silicone polyimides were synthesized using the process developed in our company.29-31 The reaction and resulting repeat units are shown in Scheme 1. For enhanced reproducibility, polymers were synthesized in bulk quantity and extruded as pellets. The molecular weight of the resulting polymer was determined using gel permeation chromatography (polystyrene standards, chloroform solvent) as Mw ) 39 350, Mn ) 18 880, Mw/Mn ) 2, Mpeak ) 38 750. Reaction yield was 81%.30 Polymer Evaluation. For materials evaluation, the AT-cut quartz crystals with gold electrodes (ICM Corp, Oklahoma City, OK) were used as acoustic-wave sensor substrates. These crystals oscillated in the thickness-shear mode (TSM) with a fundamental frequency of 10 MHz. Before use, the crystals were cleaned by sonication in chloroform.32 The crystals were arranged in a lowdead-volume flow-through gas cell. Each crystal in the sensor array was dip-coated with a polymer film. The polymers were dissolved in chloroform and deposited on both sides of the crystal using a dip-coating method as ∼0.5- to 10-µm-thick films with thickness reproducibility of
