Impedimetric detection of pathogenic bacteria with bacteriophages using gold nanorod deposited graphite electrodes† Farzaneh Moghtader, ab Gulsah Congur, c Hadi M. Zareie, de Arzum Erdem * c and Erhan Piskin * ab Electrochemical impedance spectroscopy (EIS) is applied for the detection of bacteria using bacteriophages as a bioprobe together with gold nanorods (GNRs). Escherichia coli – E. coli K12 was used as a model target bacteria and also for the propagation of its specific T4-phages. Gold nanorods (GNRs) were synthesized via a two-step protocol and characterized using different techniques. EIS measurements were conducted in an electrochemical cell consisting of a three electrode system. Single-use pencil graphite electrodes (PGE) were modified by the physical adsorption of GNRs to increase their interfacial conductivity and therefore sensitivity for impedimetric measurements. Therefore, interfacial charge-transfer resistance values (R ct ) sharply decreased after GNRs deposition. Phages were adsorbed on these electrodes via a simple incubation protocol at room temperature, which resulted in an increase in R ct values, which was concluded to be as a result of nonconductive phage layers. These phage-carrying GNRs–PGEs were used for impedimetric detection of the target bacteria, E. coli. Significant increases at the R ct values were observed which were attributed to the insulation effects of the adsorbed bacterial layers. This increase was even more when the bacterial concentrations were higher. In the case of the non-target bacteria Staphylococcus aureus (S. aureus), conductivity noticeable decreases (due to nonspecific adsorption). However, in the case of E. coli, the R ct value increase is time dependent and reaches maximum in about 25–30 min, then decreases gradually as a result of bacterial lysis due to phage invasion on the electrode surfaces. In contrast, there were no time dependent changes with the non-target bacteria S. aureus (no infection and no lytic activity). It is concluded that the target bacteria could be detected using this very simple and inexpensive detection protocol with a minimum detection limit of 10 3 CFU mL 1 in approximately 100 mL bacterial suspension. Introduction According to the WHO (World Health Organization), more than 2.2 million deaths occur annually due to food and water-borne diseases, which are mostly caused by pathogenic bacteria, including Escherichia coli, Salmonella, Staphylococcus, and many others, even in developed countries. The infectious dose of these pathogens can be very low (around 10 bacteria). The emergence of drug-resistant strains makes this problem very severe. The scenario that we see today is only modern daily life incidences. Highly pathogenic bacteria can also be used as biological warfare agents, and not only are they very common, but they can be easily distributed via food and water, and unfortunately living creatures, such as human and animals, as a result of the very intense mobility traffic worldwide. Moni- toring food and water quality has therefore been argued as the most important priority towards national and international health and safety issues, with global emphasis on the rapid and early detection of pathogen contamination, especially in food and water. The current pathogen detection methods include: (i) microbiological techniques (conventional culturing); (ii) nucleic-acid based (e.g. PCR and DNA hybridization using oligonucleotides as bio-recognition elements or bio-probes) 1–4 and (iii) immunological (e.g., ELISA using specic antibodies as bio-probes). 5 Microbiological techniques are the oldest, but are still considered the most accurate approach. In this technique, a Hacettepe University, Faculty of Engineering, Chemical Engineering Department, Graduate School of Science and Engineering – Nanotechnology and Nanomedicine Division, 06800, Ankara, Turkey b Biyomedtek/NanoBMT, 06800, Ankara, Turkey. E-mail: erhanpiskin@biyomedtek. com c Ege University, Faculty of Pharmacy, Analytical Chemistry Department, 35100, ˙ Izmir, Turkey. E-mail: arzum.erdem@ege.edu.tr; arzume@hotmail.com d ˙ Izmir Institute of Technology, Department of Material Science and Engineering, 35430, Urla, ˙ Izmir, Turkey e University of Technology, School of Physics and Advanced Materials, Microstructural Analysis Unit, Sydney, Ultimo NSW 2007, Australia † Electronic supplementary information (ESI) available. See DOI: 10.1039/c6ra18884b Cite this: RSC Adv. , 2016, 6, 97832 Received 25th July 2016 Accepted 28th September 2016 DOI: 10.1039/c6ra18884b www.rsc.org/advances 97832 | RSC Adv., 2016, 6, 97832–97839 This journal is © The Royal Society of Chemistry 2016 RSC Advances PAPER Published on 29 September 2016. Downloaded by Izmir Yuksek Teknoloji on 16/06/2017 09:21:55. View Article Online View Journal | View Issue