Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/synmet Optimization of the antibacterial activity of silver nanoparticles-decorated graphene oxide nanocomposites Nguyen Thanh Huong b,d , Nguyen Minh Dat a,c , Doan Ba Thinh a,c , Trinh Ngoc Minh Anh a,c , Do Minh Nguyet a,c , Tran Hoang Quan a,c , Phung Ngoc Bao Long a,c , Hoang Minh Nam a,b,c , Mai Thanh Phong b,c , Nguyen Huu Hieu a,b,c, * a VNU-HCM, Key Laboratory of Chemical Engineering and Petroleum Processing (CEPP), Ho Chi Minh City University of Technology (HCMUT), 268 Ly Thuong Kiet Street, District 10, Ho Chi Minh City, Viet Nam b Faculty of Chemical Engineering, Ho Chi Minh City University of Technology (HCMUT), 268 Ly Thuong Kiet Street, District 10, Ho Chi Minh City, Viet Nam c Vietnam National University Ho Chi Minh City, Linh Trung Ward, Thu Duc District, Ho Chi Minh City, Viet Nam d Ho Chi Minh City Pasteur Institute, Ho Chi Minh City, Viet Nam ARTICLE INFO Keywords: Silver/graphene oxide Antibacterial activity Plackett–Burman Box–Behnken Experimental design ABSTRACT In this study, silver/graphene oxide (Ag/GO) nanocomposites were synthesized using the in situ method. Glucose was selected as an eco-friendly reducing agent for the reduction of Ag + into silver nanoparticles (AgNPs). The characterization of GO and Ag/GO with Fourier transform infrared spectroscopy, transmission electron micro- scopy, X-ray diffraction, Raman spectroscopy, scanning electron microscopye, energy-dispersive X-ray spectro- scopy, and X-ray photoelectron spectroscopy. Results showed that Ag/GO was successfully synthesized. Silver nanoparticles (AgNPs) with an average size of 17.68 ± 4.48 nm were uniformly distributed onto GO sheets. The antibacterial activity of GO, AgNPs, and Ag/GO were tested against Staphylococcus aureus ATCC 25,923 (S. aureus) and Salmonella enterica ATCC 35,664 (S. enterica) bacteria by optical density and plate colony–counting methods. Test results showed that Ag/GO had higher antibacterial activity than its precursors (bare AgNPs and GO) with a bactericidal rate of more than 99.90 %. Thus, Ag/GO was selected for further experimentation. Simultaneous effects of the interaction time, Ag/GO concentration, pH, annealing temperature, and S. aureus density on the antibacterial activity of Ag/GO were also investigated with full factorial experimental design according to Placket–Burman and Box–Behnken designs. After 10 min of interaction time at 37 °C, the optimal values of these factors were determined to be: Ag/GO concentration of 48 μg/mL, pH 5, and S. aureus density 5.3 × 10 6 CFU/mL, corresponding to an antibacterial capacity of 99.95 % towards S. aureus. The presented experiment confirmed Ag/GO to be able of eliminating about 99.99 % of S. aureus. All results of the present study affirmed the potential applications of Ag/GO as an antibacterial agent in the medical field. 1. Introduction Due to the emergence of antibiotic-resistant strains of bacteria, focus has been drawn to research on novel antibacterial materials and their synthesis processes. Silver element is currently the most potential antibacterial agents. Silver nanoparticles (AgNPs), in particular, stand out with its extreme cytotoxicity against a broad spectrum of micro- organisms compared to its metal or salt forms [1]. The Ag + released by AgNPs interacts with the bacterial membrane and penetrates the cells by destabilizing them, followed by denaturing protein, damaging the DNA, and inhibiting the bacterial propagation. Silver cations also proved to cripple the respiratory enzymes by binding to the sulfhydryl group (–SH), which reduces the oxygen absorption and metabolization activity of the bacteria, causing cell death [2]. Based on the anti- bacterial mechanism of AgNPs, two primary drawbacks arise: firstly, that the susceptibility to aggregation due to high surface energy causes a critical decrease in antibacterial efficiency. It was cited that with bigger particle sizes, the specific interface area between the nano- particles and bacteria declines, leading to less effective binding and cell penetration. Secondly, the toxicity of AgNPs poses a threat to marine creatures dwelling in water bodies [3,4]. Graphene oxide (GO) is a single layer of C atoms bonded in a unique https://doi.org/10.1016/j.synthmet.2020.116492 Received 22 April 2020; Received in revised form 25 June 2020; Accepted 25 June 2020 ⁎ Corresponding author at: VNU-HCM, Key Laboratory of Chemical Engineering and Petroleum Processing (CEPP), Ho Chi Minh City University of Technology (HCMUT), 268 Ly Thuong Kiet Street, District 10, Ho Chi Minh City, Viet Nam. E-mail address: nhhieubk@hcmut.edu.vn (N.H. Hieu). Synthetic Metals 268 (2020) 116492 0379-6779/ © 2020 Elsevier B.V. All rights reserved. T