ORIGINAL ARTICLE Colorimetric / fluorescent bacterial sensing by agarose- embedded lipid / polydiacetylene films D. Meir 1 , L. Silbert 1 , R. Volinsky 1 , S. Kolusheva 1 , I. Weiser 2 and R. Jelinek 1 1 Department of Chemistry and Ilse Katz Institute for Nanotechnology, Ben Gurion University, Beer Sheva, Israel 2 Institute for Food Microbiology and Consumer Goods Ltd, Nesher, Israel Introduction The development of simple and rapid bacterial detection techniques is drawing intense scientific and technological interest owing to the recurring incidents of bacterial con- taminations in foods and water, the anthrax scares in the United States, and global bioterrorism threats. Numerous technologies for reporting on bacterial presence have been developed (Hobson et al. 1996; Canhoto and Magan 2003; Gfeller et al. 2005b; Schmidt et al. 2005; Simpson and Lim 2005).There are, however, limitations to the existing bacterial detection techniques as rapid and simple approaches. Specifically, many bio-analytical techniques employed for pathogen detection (such as culture-based methods) provide results after relatively long time spans (generally days) (Ivnitski et al. 1999). Other currently employed technologies often involve complex detection mechanisms that require specialized instrumentation, application by trained personnel and the need for active operation (addition of reagents, initiation of chemical reactions, etc.), which on the whole do not lend their use in settings other than laboratory environments (Canhoto and Magan 2003; Gfeller et al. 2005a). Furthermore, a prerequisite for many detection methods is the detailed Keywords bacterial detection, bacterial sensors, Langmuir–Schaeffer films, membrane active molecules, polydiacetylene. Correspondence Raz Jelinek, Department of Chemistry, Ben Gurion University, Beer Sheva, Israel 84105. E-mail: razj@bgu.ac.il 2007 ⁄ 1081: received 8 July 2007, revised and accepted 29 August 2007 doi:10.1111/j.1365-2672.2007.03614.x Abstract Aim: Development of a new chromatic (colorimetric ⁄ fluorescence) bacterial sensor, for rapid, sensitive and versatile detection of bacterial proliferation. Methods and Results: We constructed agarose-embedded chromatic films which produce dramatic colour changes and fluorescence transformations in response to bacterial growth. The sensing constructs comprise glass-supported Langmuir–Schaeffer phospholipid ⁄ polydiacetylene films that undergo both blue-red transformations and induction of intense fluorescence following inter- actions with bacterially secreted amphiphilic compounds that diffuse through the agarose. The agarose matrix coating the sensor film further contains growth nutrients, facilitating signal amplification through promotion of bacterial cul- ture proliferation. The agarose layer also constitutes an effective barrier for reducing background signals not associated with the bacteria. We demonstrate the applications of the new sensor for the detection of Gram-negative and Gram-positive bacteria, and for screening specimens of physiological fluids (blood and urine) and foods (meat) for bacterial contaminations. Conclusions: The experiments demonstrate that the new agarose-embedded film constructs are capable of bacterial detection through visible colour transi- tions and fluorescence emission recorded in conventional apparatuses. Significance and Impact of the Study: This work demonstrated a new simple chromatic platform for bacterial detection, based on the generation of easily recorded colour and fluorescence changes. The new bacterial detection scheme is highly generic and could be employed for varied practical uses, in which, rapid reporting on bacterial presence is required. Journal of Applied Microbiology ISSN 1364-5072 ª 2007 The Authors Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 104 (2008) 787–795 787