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A novel, easily renewable nanocomposite interface based on layer-by-layer (LbL) assembled cationic/anionic layers of carbon nanotubes customized with biopolymers is reported. A simple approach is proposed to fabricate a nanoscale structure composed of alternating layers of oxidized multiwalled carbon nanotubes upon which is immobilized either the cationic enzyme organophosphorus hydrolase (OPH; MWNT-OPH) or the anionic DNA (MWNT-DNA). The presence of carbon nanotubes with large surface area, high aspect ratio and excellent conductivity provides reliable immobilization of enzyme at the interface and promotes better electron transfer rates. The oxidized MWNTs were characterized by thermogravimetric analysis and Raman spectroscopy. Fourier transform infrared spectroscopy showed the surface functionalization of the MWNTs and successful immobilization of OPH on the MWNTs. Scanning electron microscopy images revealed that MWNTs were shortened during sonication and that LbL of the MWNT/biopolymer conjugates resulted in a continuous surface with a layered structure. The catalytic activity of the biopolymer layers was characterized using absorption spectroscopy and electrochemical analysis. Experimental results show that this approach yields an easily fabricated catalytic multilayer with well-defined structures and properties for biosensing applications whose interface can be reactivated via a simple procedure. In addition, this approach results in a biosensor with excellent sensitivity, a reliable calibration profile, and stable electrochemical response.

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of Information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperworlc Reduction Project (0704-01881, Washington, DC 20503. A6iNCY VSt ONLY (Leave blank)2. REPORT DATE 15.Aug.03 REPORT TYPE AND DATES COVERED MAJOR REPORT TITLE AND SUBTITLE"SPECIFIC AND SELECTIVE BIOSENSOR FOR SALMONELLA AND IT'S DETECTION IN THE ENVIRONMENT" FUNDING NUMBERS AUTHOR(S)CAPT OLSEN ERIC V PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)AUBURN UNIVERSITY MAIN CAMPUS , 1998, O'Sullivan and Guilbault, 1999, Cavicacute, et al., 1999, Ivnitski, et al., 1999, 5 Kaspar et al., 2000. Acoustic waves in TSM are excited by the application of a radio frequency 6 alternating voltage to the piezoelectric crystal. Changes in the resonance frequency are usually 7 attributed to the effect of the added mass due to the binding at the solid-liquid interface. Acoustic 6The acoustic devices theory and biological applications were recently reviewed (Kaspar et 7 al., 2000, Cavicacute, et al., 1999, Ivnitski, et al., 1999. 8In our previous work we demonstrated the feasibility of a biosensor based on Langmuir-9 Blodgett monolayers of an antibody for the rapid and sensitive detection of Salmonella 10 typhimurium in liquid samples (Pathirana, et al., 2000). In the present work we investigated 11 specificity and selectivity of the biosensor under environmental conditions and after 12 environmental aging of the biosensors. Additionally, we studied the effects on the biosensor 13 signal of bacterial positioning at the liquid-surface interface.14 2. Materials and methods 19Three types of tests were employed to examine the reactivity of antibodies: 20(1) a dot blot ELISA test using nitrocellulose or nylon filters with antigen fixed and subjected to 21 chromogenic anti-mouse (for monoclonal antibody) or anti-animal-based antibody conjugated 22 with enzyme assay; (2) kit tests for target organisms; and (3) agglutination tests.

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