Biosensors and Bioelectronics 24 (2008) 279–283 Contents lists available at ScienceDirect Biosensors and Bioelectronics journal homepage: www.elsevier.com/locate/bios Fast detection of Salmonella Infantis with carbon nanotube field effect transistors Raquel A. Villamizar a,1 , Alicia Maroto a,∗ , F. Xavier Rius a , Isabel Inza b , Maria J. Figueras b a Department of Analytical and Organic Chemistry, University of Rovira i Virgili, Marcel.l´ ı Domingo s/n, 43007, Tarragona, Spain b Department of Basic Medical Sciences, Faculty of Medicine and Health Sciences, University of Rovira i Virgili, Reus, Spain article info Article history: Received 29 November 2007 Received in revised form 13 March 2008 Accepted 31 March 2008 Available online 12 April 2008 Keywords: Biosensor Field effect transistor Carbon nanotubes Bacteria Salmonella abstract In this paper we report a fast, sensitive and label-free biosensor for the selective determination of Salmonella Infantis. It is based on a field effect transistor (FET) in which a network of single-walled car- bon nantotubes (SWCNTs) acts as the conductor channel. Anti-Salmonella antibodies were adsorbed onto the SWCNTs and subsequently the SWCNTs were protected with Tween 20 to prevent the non-specific binding of other bacteria or proteins. Our FET devices were exposed to increasing concentrations of S. Infantis and were able to detect at least 100cfu/mL in 1h. To evaluate the selectivity of our FET devices, Streptococcus pyogenes and Shigella sonnei were tested as potential competing bacteria for Salmonella. At a concentration of 500 cfu/mL, neither Streptococcus nor Shigella interfered with the detection of Salmonella. Therefore, these devices could be used as useful label-free platforms to detect S. Infantis and, by using the suitable antibody, other bacteria or viruses. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Salmonella enterica subsp. enterica serotype Infantis (S. Infantis) is a rod-shaped bacterium that is found in the bacterial flora of liv- ing reptiles and amphibians. It is also very common in poultry, red meat, raw egg shells, unpasteurized milk and their dairy products. S. Infantis can cause gastroenteritis and can be transmitted through the ingestion of contaminated food or water (Boyle et al., 2007; Plym and Wierup, 2006; Shahada et al., 2006). It is one of the most significant pathogenic microorganisms in food-borne infections in humans due to its multidrug resistance. For this reason, there is a widespread need to protect public health by developing fast and reliable techniques to detect it at low concentrations in food and water. Conventional culturing methods are reliable but very time consuming (i.e. typically requiring 3–7 days) and other methods such as the polymerase chain reaction (PCR) or enzyme-linked immunosorbant assays (ELISA) require between 8 and 48 h. Some biosensors have been developed for the label-free detection of ∗ Corresponding author. Tel.: +34 977 558 491; fax: +34 977 558 446. E-mail address: alicia.maroto@urv.cat (A. Maroto). 1 On leave from the Department of Microbiology, University of Pamplona, Colom- bia. pathogens, although they still have limits of detection (LODs) of about 10 3 cfu/mL (Taylor et al., 2006). Single-walled carbon nanotubes (SWCNTs) have outstanding electrical and mechanical properties. Tans et al. (1998) reported the first field effect transistor (FET)-based on a single SWCNT and Kong et al. (2000) used it to develop the first carbon nanotube field effect transistor (CNTFET) chemical sensor. The functionalization of SWC- NTs gives rise to the development of selective CNTFET biosensors based on the principles of molecular recognition. Star et al. used a CNTFET based on a single SWCNT to detect streptavidin by means of the biotin–streptavidin interaction (Star et al., 2003). Byon et al. detected protein–protein interactions at 1 pM concentration with a highly sensitive FET based on networks of SWCNTs (Byon and Choi, 2006). CNTFETs functionalized with aptamers have been applied to detect either thrombin (So et al., 2005) or immunoglobulin E (Maehashi et al., 2006). So far CNTFETs have not been applied to detect bacteria or higher organisms. Only the interaction between CNTs and bacteria has already been studied. Huang et al. (2004) adsorbed anti-Salmonella antibodies on CNTs and then exposed it to 10 8 cfu/mL of Salmonella typhimurium for 1 h. The bacteria linked to the CNTs were observed with scanning electron microscopy (SEM). Elkin et al. (2005) pre- pared immuno-carbon nanotubes by functionalizing SWCNTs with albumin serum bovine (BSA) and anti-E. coli antibodies. The inter- action between the immuno-SWNTs and E. coli cells was evidenced 0956-5663/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.bios.2008.03.046