Antimicrobial supported nanoparticles: Gold versus silver for the cases of Escherichia coli and Salmonella typhi Roberto Guerra a , Enrique Lima b,⇑ , Ariel Guzmán c a Universidad Autónoma Metropolitana, Iztapalapa, Av. San Rafael Atlixco No. 186, Col. Vicentina, CP 09340 México D.F., Mexico b Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Circuito exterior s/n, Cd. Universitaria, Del. Coyoacán, CP 04510 México D.F., Mexico c Instituto Politécnico Nacional – ESIQIE, Av. IPN UPALM Edif. 7, Zacatenco, 07738 México D.F., Mexico article info Article history: Received 3 October 2012 Received in revised form 6 November 2012 Accepted 26 November 2012 Available online 2 December 2012 Keywords: Escherichia coli Salmonella Silicalite Silver Gold abstract Silver and gold nanoparticles were dispersed on TS-1 silicalite with a low titanium content. These mate- rials were evaluated as biocides for Escherichia coli and Salmonella typhi. In the presence of TS-1, free of silver or gold, both bacteria use the silicalite’s surface to reproduce rapidly. Ag- and Au-TS-1 were shown to be efficient for eliminating both E. coli and S. typhi present in a nutritive media. The efficiency of mate- rials was related to their textural properties. In general, E. coli was eliminated faster than S. typhi. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction Antimicrobial agents are required to inhibit the reproduction of pathogens in several media therefore numerous antimicrobial agents have been proposed. Their efficiencies are determined by several physicochemical factors [1–3]. Many of them, however, are toxic, which makes them undesirable for applications in sensi- tive media such as drinking water, foods or textiles. In this sense, silver is a non-toxic, non-tolerant disinfectant that can significantly reduce many bacterial infections [4]. In fact, silver has been com- monly used to treat or avoid infections since long time [5–7]. Com- monly, silver is used in the form of ions, Ag + , but this form is unwelcome for some specific applications, for instance where Ag + could incorporate to materials by exchange cations. This com- monly occurs with non-supported silver species and for example the application in textiles is not desirable in this form. Thus, re- cently it was proposed that silver nanoparticles supported on zeo- lites could be lethal for bacteria [8]. Zeolitic supports, however, differ greatly regarding their physicochemical properties, which in turn tune the properties of the metal being supported [9–11]. Silver-supported particles have shown to be efficient inhibiting the growth of pathogens but it is also true that silver-resistant bac- teria are more and more frequently reported [12,13]. The relation- ship between resistance and eventual bioaccumulation of silver is not clear still [14,15]. In this sense, new materials, few explored as bactericide could be an alternative for silver materials. Actually, gold complexes with sulfur have been applied in some arthritis treatments [16] and since few years gold nanoparticles have been efficacy used as catalysts in a wide variety of reactions [17,18]. We have started this work in order to explore silicalite-sup- ported silver and gold as bactericide for Escherichia coli and Salmo- nella. This support was selected because it has been shown to be very desirable to stabilized small gold particles [19] and the amount of ions stabilized by exchange ionic does not occur. 2. Experimental procedure 2.1. Support’s synthesis The TS-1 sample was prepared by a hydrothermal synthesis. Tetraethyl orthosilicate (TEOS) and tetrabutyl orthotitanate (TBOT) were used as source of silicon and titanium, respectively. Briefly, to one solution tetrapropylammonium hydroxide (TPAOH, 25 wt.%) were added a mixture of TEOS and TBOT (ratio Si/Ti equal to 50) under vigorous stirring. The reagent mixture was stirred for 12 h at room temperature, and then hydrothermally treated at 453 K for 90 h. The obtained solids were dried at 383 K for 24 h, and then calcined in air at 823 K for 5.0 h. The TS-1 sample contained Ti 2 wt.%, as determined by inductively coupled plasma-atomic emis- sion spectroscopy (ICP-AES). 1387-1811/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.micromeso.2012.11.036 ⇑ Corresponding author. Tel.: +52 55 5622 4640; fax: +52 55 5616 1371. E-mail address: lima@iim.unam.mx (E. Lima). Microporous and Mesoporous Materials 170 (2013) 62–66 Contents lists available at SciVerse ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso