Biosensors and Bioelectronics 35 (2012) 308–312 Contents lists available at SciVerse ScienceDirect Biosensors and Bioelectronics jou rn al h om epa ge: www.elsevier.com/locate/bios Long period grating based biosensor for the detection of Escherichia coli bacteria Saurabh Mani Tripathi a,∗ , Wojtek J. Bock a , Predrag Mikulic a , Raja Chinnappan b , Andy Ng b , Mona Tolba b , Mohammed Zourob b a Centre de Recherche en Photonique, Département d’informatique et d’ingénierie, Université du Québec en Outaouais, Gatineau, QC, J8Y 3G5, Canada b Institut National de la Recherche Scientifique - Énergie, Matériaux et Télécommunications, Varennes, QC, J3X 1S2, Canada a r t i c l e i n f o Article history: Received 16 December 2011 Received in revised form 13 February 2012 Accepted 3 March 2012 Available online 10 March 2012 Keywords: Bacteriophages Long period fiber grating Spectral interrogation Pathogen Covalent binding a b s t r a c t In this paper we report a stable, label-free, bacteriophage-based detection of Escherichia coli (E. coli) using ultra sensitive long-period fiber gratings (LPFGs). Bacteriophage T4 was covalently immobilized on optical fiber surface and the E. coli binding was investigated using the highly accurate spectral interrogation mechanism. In contrast to the widely used surface plasmon resonance (SPR) based sensors, no moving part or metal deposition is required in our sensor, making the present sensor extremely accurate, very compact and cost effective. We demonstrated that our detection mechanism is capable of reliable detection of E. coli concentrations as low as 10 3 cfu/ml with an experimental accuracy greater than 99%. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Pathogenic Escherichia coli (E. coli) is one of the most danger- ous agents of food-borne disease. Consumption of contaminated food or water can be deadly, especially for children and the elderly. Although E. coli infection is most common in developing countries, many recent outbreaks in Europe and Northern America have been attributed to a strain of E. coli which has been identified among the most common causes of diseases related to food safety (WHO, 2008, http://www.cdc.gov/ecoli/2011/ecolio104/). Accurate routine test- ing is crucial for outbreak prevention. Nevertheless, currently available tests require time-consuming amplification of samples. The standard detection process of E. coli bacteria takes about 24 h to obtain results from culturing methods. Although more recent detection techniques such as PCR, ELISA and IMS offer a more rapid detection, analysis time of several hours is still required. For the specific and rapid detection of such pathogens, bio- recognition elements such as antibodies (Rijal et al., 2005; Arora et al., 2011), nucleic acids (DNA/RNA) (Baeumner et al., 2003; Dorst et al., 2010) and bacteriophages (Balasubramanian et al., 2007; Shabani et al., 2008) have widely been used for the specific cap- turing of the target bacteria. Their binding can be detected by fluorescence labeling methods (Pan et al., 2005; Tombelli et al., 2005) or by label-free methods (Zourob et al., 2005; Nanduri et al., ∗ Corresponding author. E-mail addresses: tripathi.sm1@gmail.com (S.M. Tripathi), Zourob@emt.inrs.ca (M. Zourob). 2007; Smietana et al., 2011). Each of these recognition elements has its own advantages and disadvantages. For example, recogni- tion based on nucleic acid, though offering high specificity, suffers from the inability to discriminate between viable and non-viable cells (Dorst et al., 2010). For antibody-based recognition elements, the drawbacks are high price, stability and cross-binding to other bacteria which may result in false positives (Balasubramanian et al., 2007). Bacteriophage, on the other hand, offers a superior alterna- tive to other recognition elements in terms of their high specificity, fast binding, easy/low-cost production and stability. Furthermore, the bacteriophage has a unique feature to discriminate between the viable and non-viable cells. In principle the bacteriophage binds to both viable and non-viable bacteria as long as the surface receptor (lipopolysaccharides, teichoic acids, proteins) is intact and rec- ognized by the bacteria. To see whether the bacteria are viable, the experiment can be extended past the latent period (the time from infection to bacterial lysis by the bacteriophage progeny). The signal should change since the intact bacteria are now broken (lysed). In the fluorescent-label method, the recognition elements are labeled with specific dyes, making this procedure complex, time- consuming and the potential alteration of the properties of the analyte (Balasubramanian et al., 2007). Label-free methods, on the other hand, are based on changes occurring at the sensor surface, on changes in the analyte refractive index (ARI) or on changes in the thickness of the bio-film – all changes that could modify the optical properties of a sensor. This method is not only very fast but also allows real-time monitoring of the biomolecular interactions occurring while the process of detection takes place. 0956-5663/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.bios.2012.03.006