Real-Time Salmonella Detection Using Lead Zirconate Titanate-Titanium Microcantilevers
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Real-Time Salmonella Detection Using Lead Zirconate Titanate-Titanium Microcantilevers John-Paul McGovern, Wan Y. Shih and Wei-Heng Shih Department of Materials Science and Engineering, Drexel University, Philadelphia, PA 19104 Mauro Sergi and Irwin Chaiken Department of Biochemistry and Molecular Biology, Drexel University, Philadelphia, PA 19102 ABSTRACT Current methods for analysis of unknown powders in suspicious packages involve sending samples to laboratory facilities where a variety of time-consuming tests are performed. We have developed and investigated the use of a lead zirconate titanate - titanium (PZT-Ti) microcantilever for in situ detection of the common food- and water-born pathogen, Salmonella typhimurium. Using a bifunctional linking molecule to immobilize antibody on the titanium surface of the microcantilever, we can directly detect salmonella cells in suspensions of differing concentration. This novel surface functionalization technique along with the sub-nanogram sensitivity of the cantilever has allowed for direct quantification of S. typhimurium cells in suspension. INTRODUCTION Salmonella is a water-born/food-born pathogen that causes more than five hundred deaths each year [1]. It is also a category B bioterrorism agent that can seriously contaminate water resources. There is no device at present that can actually monitor a space and perform an analysis of the air or water within that space in real-time. However, the presence of such a device would dramatically decrease the “lag time between release of an agent and its detection,” and thus enable more prompt treatment of those individuals possibly exposed to a particular bioterrorism agent in addition to reducing the total number of individuals affected [2]. The current methods employed for analyzing bacterial pathogens include filtration and subsequent cell colony growth and identification, polymerase chain reaction (PCR) [3], and Enzyme-Linked Immunosorbent Assay (ELISA) [4]. The method of filtration and cell culture (which involves the collection of biological agents by passing the sample through a filter medium and growth of colonies in the filter medium for 12 hours to 2 days) is the current definite method for determining the presence of a bacterial pathogen [3]. With PCR, cells must be lysed to release the DNA which is amplified for detection. The ELISA method requires fluorescent labeling for optical detection. These methods are tedious, time consuming and neither in situ nor quantitative. In addition to the above methods, surface plasmon resonance (SPR) and the quartz crystal microbalance (QCM) are also used for probing biological interactions and the presence of biological agents. SPR detects molecular binding on a surface by measuring the refractive index change due to such binding [5]. QCM detects mass changes by measuring the thickness-mode resonance frequency shift of the quartz crystal [6]. Both SPR and QCM are capable of in situ analysis as well as quantification, but they do not readily lend themselves to the devel
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