One-Step Synthesis of Antibacterial Coatings by Plasma Electrolytic Oxidation of Aluminum Janaina S. Santos,* Andressa Rodrigues, Anna P. Simon, Carlise H. Ferreira, Vidiany A. Q. Santos, Mariana S. Sikora, Nilson C. Cruz, Giovanni P. Mambrini, and Francisco Trivinho-Strixino Aluminum oxide films containing small quantities of silver are produced by plasma electrolytic oxidation of aluminum (97%) in different electrolytes aiming the synthesis of bactericidal coatings over aluminum for food packaging applications. Sodium citrate, citric acid, and sodium silicate, containing Ag nanoparticles (Ag-NPs) or Ag þ ions (AgNO 3 ) are tested as electrolyte. The galvanostatic anodization curves are used as diagnostic to evaluate the production of Ag-alumina coatings in a one-step procedure. Citric acid and silicate media provide more stability and reproducibility in coatings production; however, only coatings produced in silicate solution exhibit antimicrobial effect against Bacillus subtilis bacteria. The oxide films are characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). An irregular porous structure and a silver content of 0.1–1.9 wt.% in the oxide coatings are observed. Plasma electrolytic oxidation (PEO) is an anodization performed under high electric field (10 6 10 8 Vcm 1 ) used to produce oxide coatings on metals improving their mechanical resistance and corrosion protection. [1,2] This short-time synthesis method can be performed in temperatures close to the room temperature and it allows to obtain ceramic coatings strongly adhered to the surface of metallic objects with different geometric shapes. [2] In this study, aluminum oxide (Al 2 O 3 , alumina) coatings containing silver were produced in one step using PEO technique and a low-cost aluminum (97%) as substrate. The alumina layer was formed in the anode due to aluminum oxidation and the silver species from the electrolyte solution were incorporated into the alumina coatings during the process. Silver presents antimicrobial properties and low level of toxicity for humans, [3] being useful for implants, surgical materials, and food packaging materials. Silver/alumina composites for bactericidal applications are usually obtained by deposition of Ag film or Ag nanoparticles (Ag-NPs) over alumina substrates. The alumina is commonly synthetized via chemical routes, [4] magne- tron sputtering, [5] or conventional anodiza- tion, [6] whereas the silver can be deposited in a second step by magnetron sputtering, [5,7] chemical reduction, [7,8] and impregnation methods. [9–11] In addition, the antimicrobial tests are generally performed against pathological agents, as Escherichia coli. [5–10] However, in food packaging materials, it is interesting to carry out inhibition tests using spoilaging microorganisms and thermore- sistant spore producers, [12–15] as Bacillus subtilis. [12,15] These organisms present high resistance and can persist in food packaging materials, decreasing the food shelf-life and safety for humans. [12,14] Different from these conventional methods, PEO process requires a significantly reduced synthesis time, since all procedures for fabrication of the material can be performed in one step. [16] Under PEO conditions, the system reaches potential values above dielectric breakdown of the oxide and the incorporation of electrolyte species into the oxide film can increase due to localized destruction/rebuilding processes of oxide caused by electrical discharges, Joule heating effect, and oxygen evolution. [17–20] These processes affect the morphology, composition, and structure of the anodic oxide, although they can be controlled by anodization regime, electrolyte composition, anodization time, and temperature. [18,21] Herein it is described an exploratory analysis of anodizing conditions for synthesis of Al 2 O 3 films containing silver over aluminum substrates. The oxide growth was monitored by anodization curves. The effect of electrolyte composition on morphological properties and silver content of alumina coatings was evaluated in sodium citrate, citric acid, and sodium silicate containing Ag-NPs or Ag þ as additives. Antimicrobial tests were performed using B. subtilis bacteria, as model of sporulated bacterium, [12] which is used in the food industry as package cleaning indicator. [15,22] Dr. J. S. Santos, A. Rodrigues, Prof. Dr. G. P. Mambrini, Prof. Dr. F. Trivinho-Strixino Department of Physics, Chemistry and Mathematics Federal University of S~ ao Carlos (UFSCar) Via Jo~ ao Leme dos Santos Km 110, 18052-780 Sorocaba, Brazil E-mail: jsstos@ufscar.br A. P. Simon, C. H. Ferreira, Dr. V. A. Q. Santos, Prof. Dr. M. S. Sikora Department of Chemistry Federal University of Technology  Paraná (UTFPR) Via do Conhecimento Km 1, 85503-390 Pato Branco, Brazil Prof. Dr. N. C. Cruz Laboratory of Technological Plasmas Sao Paulo State University (UNESP) Av. Tr^ es de MarS co, 511, 18087-180 Sorocaba, Brazil DOI: 10.1002/adem.201900119 www.aem-journal.com COMMUNICATION Adv. Eng. Mater. 2019, 1900119 © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1900119 (1 of 6)