Electrophoretic deposition of bacterial cells Bram Neirinck a , Lieve Van Mellaert b , Jan Fransaer a , Omer Van der Biest a , Jozef Anné b , Jef Vleugels a, * a Department of Metallurgy and Materials Engineering (MTM), K.U. Leuven, Kasteelpark Arenberg 44, B-3001 Heverlee, Belgium b Department Microbiology and Immunology, K.U. Leuven, Minderbroedersstraat 10 Blok x, B-3000 Leuven, Belgium article info Article history: Received 18 June 2009 Received in revised form 29 July 2009 Accepted 29 July 2009 Available online 3 August 2009 Keywords: Electrophoretic deposition (EPD) Alternating current (AC) Electrolysis Bacteria abstract The possibility to use alternating current electrophoretic deposition (AC-EPD) to deposit living cells in the form of Staphylococcus aureus and Escherichia coli on stainless steel was assessed. The experimental results revealed that these bacteria can be successfully deposited on metallic surfaces from demineral- ized water and sucrose based solutions using asymmetric unbalanced electric fields. Cell viability of the deposited bacteria was influenced by the strain and deposition medium. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Recently it was shown that inorganic materials can be deposited from aqueous suspensions using asymmetric unbalanced alternat- ing fields [1,2]. This method offers the advantage of being able to produce thin coatings from more environmentally friendly aqueous suspensions while avoiding damage caused by the electrochemical decomposition of water. The absence of water electrolysis and other electrochemical reactions opens up the possibility to deposit materials which are more sensitive than inorganic particles to gas bubble formation, pH shifts or electrochemical reaction products formed at the electrodes, the most challenging being living cells. Biotechnological advancements have shown promise in the field of green chemistry and it is predicted that 10–20% of all chemicals will be produced by so called white biotechnology by 2010 [3]. Furthermore biosensors offer the possibility to detect specific pathogens, molecules and elements [3–5]. Their selectivity and low detection threshold ensure that these sensors often sur- pass traditional sensors. For both applications however, the manip- ulation of the biological materials still poses some challenge due to their size and sensitivity to environmental parameters. Traditional bioreactors are constructed as batch systems or con- tinuously stirred tank reactors (CSTR), in which the biomaterial is allowed to convert a feedstock into the desired product. The entire content of the reactor is subsequently removed and the product is separated from the biomatter and purified. In some cases, this means that the used biological component is completely discarded. The discontinuous nature of the process renders it less favorable for large-scale production. In a CSTR, feedstock is continuously supplied to the reactor. Simultaneously, a portion of the liquid in the reactor is removed. This mixture of feedstock and reaction products is subsequently purified. Instead of either systems, a plug flow like reactor with flow through feedstock would be ideal. This can currently be achieved by a succession of mixed reactors [6].A true plug flow reactor however requires that the biologically active entities are immobilized along the flow path, for instance by deposition on a mesh. Building a reactor using several of these meshes would allow easy exchange for regeneration of the active components. For biosensors, the biological components are already immobi- lized on the sensor. This is mostly achieved by submerging the sen- sor in a concentrated suspension of the entity and allowing the biological entities sufficient time to adhere to the surface [4]. The random nature of natural adsorption renders it difficult to control the number of adhering active entities, strongly influencing the sensor sensitivity. This problem has directed research towards alternative routes for cell adhesion on structures. Dielectrophoresis followed by chemical fixation, for instance by cross-linking of a hydrogel, has been a promising route [7–9]. In dielectrophoresis suspended entities locate themselves due to differences in dielec- tric properties at the place were the electric field gradients are the largest. Strong high frequency, often in the MHz range, fields have successfully been employed for handling even the most sensi- tive cells [7–9]. The chemical fixation after dielectrophoresis is nec- essary since the cells are not truly deposited on a surface, but rather locate them between two electrodes. If true deposition is to be achieved, a force needs to be applied that brings the cells directly in contact with the substrate where they can adhere due to van der Waals forces. At the same time, the method must be gentle 1388-2481/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2009.07.033 * Corresponding author. Tel.: +32 16 321244; fax: +32 16 321992. E-mail address: Jozef.vleugels@mtm.kuleuven.be (J. Vleugels). Electrochemistry Communications 11 (2009) 1842–1845 Contents lists available at ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom