Targeted nanoparticles for enhanced X-ray radiation killing of multidrug-resistant bacteria† Yang Luo, ab Mainul Hossain, b Chaoming Wang, b Yong Qiao, b Jincui An, b Liyuan Ma b and Ming Su * b This paper describes a nanoparticle enhanced X-ray irradiation based strategy that can be used to kill multidrug resistant (MDR) bacteria. In the proof-of-concept experiment using MDR Pseudomonas aeruginosa (P. aeruginosa) as an example, polyclonal antibody modified bismuth nanoparticles are introduced into bacterial culture to specifically target P. aeruginosa. After washing off uncombined bismuth nanoparticles, the bacteria are irradiated with X-rays, using a setup that mimics a deeply buried wound in humans. Results show that up to 90% of MDR P. aeruginosa are killed in the presence of 200 mg ml 1 bismuth nanoparticles, whereas only 6% are killed in the absence of bismuth nanoparticles when exposed to 40 kVp X-rays for 10 min. The 200 mg ml 1 bismuth nanoparticles enhance localized X-ray dose by 35 times higher than the control with no nanoparticles. In addition, no significant harmful effects on human cells (HeLa and MG-63 cells) have been observed with 200 mg ml 1 bismuth nanoparticles and 10 min 40 kVp X-ray irradiation exposures, rendering the potential for future clinical use. Since X-rays can easily penetrate human tissues, this bactericidal strategy has the potential to be used in effectively killing deeply buried MDR bacteria in vivo. 1 Introduction Treating multidrug-resistant (MDR) bacterial infection is chal- lenging in a deep wound situation. Due to the concern of increased drug resistance evolved from various antibiotics, physical antimicrobial agents with high efficiency are receiving more attention. Silver nanoparticles can be added into bandages to prevent infection and facilitate wound healing. 1 Gold nanoparticles have been used to enhance photo-thermal based bacterial killing. 2–4 Although these methods can kill bacteria from supercial wounds, they are less effective in eradicating bacteria that are deeply buried underneath the dermis. Recently, silver nanoparticle sandwich nanostructures have been developed as bacteriostatic implant coatings, 5 but the controlled release of silver ions is still challenging. Ionizing radiation including X-rays and gamma rays can easily penetrate most tissues and kill bacteria by inducing irreparable DNA damage. 6 Many Gram-negative bacteria such as Pseudomonas aeruginosa (P. aeruginosa), Escherichia coli (E. coli) and Salmonella species can be effectively killed by X-rays in vitro. More recently, high energy X-ray radiation has also been developed to eliminate bacteria in living oysters without killing the oysters, revealing the possibility of X-ray based bacterial killing in living objects. However, no such X-ray radiation- induced bactericidal strategies have been carried out in vivo due to concerns of high dose irradiation exposure. Nanoparticles of heavy elements (such as gold and bismuth), having a large cross-section for X-ray absorption and photo- electron generation, can be used as radiosensitizers to enhance the radiation dose for bacterial killing. 7–9 Free radicals and photoelectrons that are generated by X-ray irradiation of the nanoparticles contribute to signicant DNA damage in the bacteria. If damaged DNAs are not repaired by enzymes in bacteria, damage can be accumulated, eventually causing bacterial death. The bacterial killing effect is signicantly inuenced by the distance between nanoparticles and bacteria due to a short diffusion length (100 nm) of free radicals under physiological conditions. This is evident from previous studies using unconjugated gold nanoparticles which required a high dose (100 Gy) to kill bacteria. 10 Meanwhile, targeted gold nanoparticles attached to the bacterial cell surface have shown higher antimicrobial activity than non-targeted nanoparticles using a photothermal effect. 11 However, this method is limited by low penetrating power of visible light and cannot be used for treating deeply buried bacteria. This paper describes a novel bactericidal approach to kill MDR bacteria using low dose X-rays and antibody conjugated bismuth nanoparticles that can specically be targeted on bacterial surfaces. Since X-rays are highly penetrating, this method has the potential to kill bacteria inside deep tissues. a Department of Laboratory Medicine, Southwest Hospital, Third Military Medical University, Chongqing 400038, China b NanoScience Technology Center, University of Central Florida, Orlando, Florida 32826, USA. E-mail: ming.su@ucf.edu † Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr33154c Cite this: Nanoscale, 2013, 5, 687 Received 12th October 2012 Accepted 20th November 2012 DOI: 10.1039/c2nr33154c www.rsc.org/nanoscale This journal is ª The Royal Society of Chemistry 2013 Nanoscale, 2013, 5, 687–694 | 687 Nanoscale PAPER Published on 23 November 2012. Downloaded by Northeastern University on 03/02/2015 16:03:07. View Article Online View Journal | View Issue