N-doped carbon nanosheets with antibacterial activity: mechanistic insight† Amlan Chakraborty,‡ a Pranav Patni,‡ a Deepa Suhag,‡ a Gajender Saini, b Anirudha Singh, c Sandip Chakrabarti * d and Monalisa Mukherjee * a The rising incidence of drug resistant diseases has led to an increasing need for developing novel and efficient antimicrobial products that can counter these infections. We report for the first time, the exceptional antibacterial activity of N-doped carbon nanosheets (CNS). The antibacterial activity and mechanism of action of CNS was examined for gram negative E. coli. Based on the cell viability tests, nucleic acid quantitation, time and concentration dependent antibacterial activity tests and SEM and TEM micrographs, performed under similar concentration and incubation conditions, the CNS dispersion shows the highest antibacterial activity, sequentially followed by GO, rGO and CCM, with a loss of cell viability by 92.1  1.7%. We envision that the physical stress and piercing action caused by sharp “knife- edges” as well as the presence of heteroatoms in CNS result in the rupturing of the bacterial cell wall, eventually causing cell death. The high I D /I G ratio (0.99) of CNS is closely related to the formation of structural and edge plane defects, especially in the case of N-doped carbonaceous materials, which is one of the key factors in enhancing the antibacterial activity of the material. Introduction In recent years, the rising number of drug resistant microor- ganisms has led to an increasing need to develop effective antimicrobial products that can combat these strains. Several carbon materials, such as carbon nanotubes (CNT), 1–10 carbon nanobers (CNF), 11,12 carbon nanoparticles (CNP), 13–17 graphene oxide (GO), 18,19 and reduced graphene oxide (rGO), 20,21 have found their use in water treatment, 22 microuidics, 23 chemical and biological sensors, 24,25 separation membranes, 26 energy storage, 27 improved accessibility of reactants to the active sites, 28 and hydrogel 29 along with various other applications. Moreover, carbon materials have also been extensively employed for antibacterial applications. Among them, GO and rGO have been established to have notable antibacterial activity. 30 The antibacterial activity of GO and rGO is attributed to the sharp edge planes present in GO sheets which create membrane stress. This leads to physical damage of the bacterial cell membrane resulting in the loss of membrane integrity and RNA leakage. 31,32 However, according to some groups, cells trapped within the sheets maintain their structural integrity but are unable to proliferate in the media, thereby inhibiting cellular growth. 33 Furthermore, another mechanism by which GO acts on the bacteria and kills them is by inducing oxidative stress which occurs due to the release of reactive oxygen species. 30 Dispersed graphene based materials are known to display strong antibacterial activity. 30 Several other factors inuence the antibacterial activity of carbon materials, which includes the interaction between carbon materials and bacterial cells, such as incubation time, 34 concentration, 35 medium, 36 and light sources. 37 Carbon nanosheets (CNS), which comprise multi-layered graphene lms are a new class of carbon material and possess high surface to volume ratio, sharp edge plane defects and lightness with higher efficacy compared to graphene. 38–40 This is because CNS is made up of fewer graphite layers. 41,42 Conventional antibiotics function by inhibiting the forma- tion of cell wall, nucleic acid synthesis and proteins. 43–45 However, to the best of our knowledge, the antibacterial activity of CNS has not yet been explored. N-doping could also enhance the biocompatibility of carbon nanomaterials. The presence of amino groups may be the reason for better biocompatibility of the N-doped carbon materials when compared to undoped carbon materials. 46 Further, applications of CNS as an a Biomimetic and Nanostructured Materials Research Laboratory, Amity Institute of Biotechnology, Amity University Uttar Pradesh, Sector-125, Noida, India. E-mail: mmukherjee@amity.edu b Advance Instrumentation Research Facility, Jawaharlal Nehru University, New Delhi, India c Faculty of Translational Tissue Engineering Center & Dept. of Urology, Johns Hopkins School of Medicine, Baltimore, Maryland Area, USA d Amity Institute of Nanotechnology, Amity University Uttar Pradesh, Sector-125, Noida, India. E-mail: schakrabarti@amity.edu † Electronic supplementary information (ESI) available: ESI 1: Carbon, hydrogen, nitrogen and oxygen percentages from CNS and CCM. ESI 2: XRD pattern of CNS and CCM. See DOI: 10.1039/c4ra17049k ‡ These authors contributed equally to this work. Cite this: RSC Adv. , 2015, 5, 23591 Received 25th December 2014 Accepted 24th February 2015 DOI: 10.1039/c4ra17049k www.rsc.org/advances This journal is © The Royal Society of Chemistry 2015 RSC Adv. , 2015, 5, 23591–23598 | 23591 RSC Advances PAPER