Contents lists available at ScienceDirect Photodiagnosis and Photodynamic Therapy journal homepage: www.elsevier.com/locate/pdpdt The effect of indocyanine green loaded on a novel nano-graphene oxide for high performance of photodynamic therapy against Enterococcus faecalis Tayebeh Akbari a , Maryam Pourhajibagher b , Farzaneh Hosseini a , Nasim Chiniforush c , Elham Gholibegloo d,e , Mehdi Khoobi e,f , Sima Shahabi c,g , Abbas Bahador c,h, ⁎ a Department of Microbiology, Islamic Azad University, North Tehran Branch, Tehran, Iran b Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran c Laser Research Center of Dentistry (LRCD), Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran d Department of Chemistry, Faculty of Sciences, University of Zanjan, Zanjan, Iran e Nanobiomaterials Group, Pharmaceutical Sciences Research Center, Tehran University of Medical Sciences, Tehran, Iran f Department of Pharmaceutical Biomaterials and Medical Biomaterials Research Center, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran g Research Center for Science and Technology in Medicine, Tehran University of Medical Sciences, Tehran, Iran h Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran ARTICLE INFO Keywords: Biofilm Enterococcus faecalis Indocyanine green Nano-graphene oxide Photodynamic therapy ABSTRACT Background: Recently developed photodynamic therapy (PDT) has gained attention for achieving effective root canal disinfection. Using an optimized nontoxic photosensitizer (PS), such as indocyanine green (ICG), is an imperative part of this technique. Therefore, the objective of the current study was to improve ICG photo- dynamic properties through incorporation of ICG into nano-graphene oxide (NGO) in order to produce NGO-ICG as a new PS and also to assess the antimicrobial effects of NGO-ICG against Enterococcus faecalis after photo- dynamic therapy. Materials and methods: NGO-ICG was synthesized based on oxidation of graphite flakes and direct loading of ICG onto NGO. NGO-ICG formation was confirmed using the Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), and UV–vis spectrometry. The antimicrobial and anti-biofilm potential of NGO-ICG-PDT against E. faecalis was assessed via colony forming unit and crystal violet assays, respectively. Results: FT-IR, SEM and UV–vis spectrometry confirmed successful synthesis of NGO-ICG containing 200 μg/mL of ICG. NGO-ICG-PDT at an energy density of 31.2 J/cm 2 showed a significant reduction (2.81 log) in the count of E. faecalis (P < 0.05). NGO-ICG-PDT significantly reduced the biofilm formation ability of E. faecalis up to 99.4% (P < 0.05). The overall antimicrobial and anti-biofilm potential of NGO-ICG-PDT was higher than PDT based on ICG (1000 μg/mL) (47% and 21%, respectively). Conclusion: Because NGO-ICG-PDT showed a significant reduction in the number and biofilm formation ability of E. faecalis at low ICG concentrations (200 μg/mL), it could be a new approach to adjuvant treatment of endodontic infections. 1. Introduction One part of endodontic infection treatment is the management of microorganisms and their by-products, which targets the microorgan- isms residing inside the infected root canal system [1]. The complexity of the root canal system and increased bacterial resistance make it practically impossible to completely remove microorganisms from in- fected root canals through instrumentation, irrigation, and intracanal medicaments [1–3]. Enterococcus faecalis, a facultative anaerobic Gram-positive coccus, is one of the most predominant bacteria isolated from root canals after endodontic failure [4]. Reports show that E. faecalis is resistant to common antimicrobial irrigants such as sodium hypochlorite, calcium hydroxide, and chlorhexidine due to biofilm formation [5]. Evidence shows that bacteria in biofilm matrices are more resistant (up to 1000 times more resistant) to antimicrobial agents when compared to their planktonic counterparts [6]. Moreover, some chemical disinfectant treatments have also been discontinued due to their side effects of tissue damage or accidental injury caused by leakage [3]. Therefore, it is es- sential to develop effective root canal disinfection methods to improve the outcomes of endodontic infection treatment [7,8]. Successful endodontic infection treatment requires an effective http://dx.doi.org/10.1016/j.pdpdt.2017.08.017 Received 21 June 2017; Received in revised form 13 August 2017; Accepted 15 August 2017 ⁎ Corresponding author at: Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Keshavarz Blvd, 100 Poursina Ave., Tehran, Iran. E-mail addresses: abahador@sina.tums.ac.ir, ab.bahador@gmail.com (A. Bahador). Photodiagnosis and Photodynamic Therapy 20 (2017) 148–153 Available online 01 September 2017 1572-1000/ © 2017 Elsevier B.V. All rights reserved. MARK