Polymer-Oligopeptide Composite Coating for Selective Detection of Explosives in Water Marta Cerruti,* ,†,‡ Justyn Jaworski, §,| Digvijay Raorane, ‡,⊥ Chris Zueger, ‡ John Varadarajan, ‡ Carlo Carraro, † Seung-Wuk Lee, | Roya Maboudian, † and Arun Majumdar ‡ Department of Chemical Engineering, Department of Mechanical Engineering, and Department of Bioengineering, University of California at Berkeley, Berkeley, California 94720, and Joint Graduate Group in Bioengineering, University of California, Berkeley and University of California San Francisco, California 94720 The selective detection of a specific target molecule in a complex environment containing potential contaminants presents a significant challenge in chemical sensor de- velopment. Utilizing phage display techniques against trinitrotoluene (TNT) and dinitrotoluene (DNT) targets, peptide receptors have previously been identified with selective binding capabilities for these molecules. For practical applications, these receptors must be immobi- lized onto the surface of sensor platforms at high density while maintaining their ability to bind target molecules. In this paper, a polymeric matrix composed of poly(eth- ylene-co-glycidyl methacrylate) (PEGM) has been pre- pared. A high density of receptors was covalently linked through reaction of amino groups present in the receptor with epoxy groups present in the co-polymer. Using X-ray photoelectron spectroscopy (XPS) and gas-chromatogra- phy/mass spectroscopy (GC/MS), this attachment strat- egy is demonstrated to lead to stably bound receptors, which maintain their selective binding ability for TNT. The TNT receptor/PEGM conjugates retained 10-fold higher TNT binding ability in liquid compared to the lone PEGM surface and 3-fold higher TNT binding compared to non- specific receptor conjugates. In contrast, non-target DNT exposure yielded undetectable levels of binding. These results indicate that this polymeric construct is an effec- tive means of facilitating selective target interaction both in an aqueous environment. Finally, real-time detection experiments were performed using a quartz crystal mi- crobalance (QCM) as the sensing platform. Selective detection of TNT vs DNT was demonstrated using QCM crystals coated with PEGM/TNT receptor, highlighting that this receptor coating can be incorporated as a sensing element in a standard detection device for practical applications. The detection of explosives has been the focus of many studies, both in the gas phase, to detect the presence of buried or conceived explosives from the sublimating vapors, 21,30,34,38 and in the liquid phase, to detect contamination in soil and ground- water in proximity of ammunition depots. 1,8,13,24,34,37 The latter is particularly important because explosives such as TNT and its derivatives are known to be toxic. 16 While most sensors presented in the literature are highly sensitive, often their selectivity is insufficient for performance in the field. In practical applications selectivity is critical to successful detection, where the molecule of interest exists in a complex environment together with many other species that can create false positive signals. This is primarily attributed to the lack of diversity available for sensor coatings specific for these targets, 10 as most current coating technologies rely on weak or non-specific molecular interaction. 3,7,9,11,12,14,17,18,21,27,30 In the case of explosive detection, highly selective coatings capable of discriminating between TNT, DNT, and other explosive molecules have been achieved through the use of molecule specific antibodies. 1,8 Antibodies, while often possessing high affinities for their target molecules, are limited to aqueous environments within a limited pH range, temperature range, and ionic activity to retain their active binding configuration. Further- * To whom correspondence should be addressed. E-mail: marta.cerruti@ gmail.com. † Department of Chemical Engineering. ‡ Department of Mechanical Engineering. § Joint Graduate Group in Bioengineering. | Department of Bioengineering. ⊥ Current affiliation: Applied Materials Inc., 3050 Bowers Avenue, Santa Clara, CA 95054, U.S.A. (1) Anderson, G. P.; Moreira, S. C.; Charles, P. T.; Medintz, I. L.; Goldman, E. R.; Zeinali, M.; Taitt, C. R. Anal. Chem. 2006, 78, 2279–2285. (2) Arya, S. K.; Solanki, P. R.; Singh, R. P.; Pandey, M. K.; Datta, M.; Malhotra, B. D. Talanta 2006, 69, 918–926. (3) Casalini, R.; Kilitziraki, M.; Wood, D.; Petty, M. C. Sens. Actuators, B 1999, 56, 37–44. (4) Cerruti, M. Fissolo, S. Carraro, C. Majumdar, A., and Maboudian, R. Langmuir 2008, ASAP. (5) Clark, D. T.; Thomas, H. R. J. Polym. Sci. Pol. Chem. 1978, 16, 791–820. (6) Clochard, M.-C.; Betz, N.; Goncalves, M.; Bittencourt, C.; Pireaux, J.-J.; Gionnet, K.; Deleris, G.; Le Moel, A. Nucl. Instrum. Methods Phys. Res., Sect. B 2005, 236, 208–215. 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Mater. 2003, 2, 19–24. Anal. Chem. 2009, 81, 4192–4199 10.1021/ac8019174 CCC: $40.75  2009 American Chemical Society 4192 Analytical Chemistry, Vol. 81, No. 11, June 1, 2009 Published on Web 04/30/2009