Photothermal antimicrobial nanotherapy and nanodiagnostics with self‐assembling carbon nanotube clusters

Abstract Background and Objectives Unique properties of carbon nanotubes (CNTs) would open new avenues for addressing challenges to realize rapid and sensitive antimicrobial diagnostics and therapy for human pathogens. In this study, new CNTs' capabilities for photothermal (PT) antimicrobial nanotherapy were explored in vitro using Escherichia coli as a model bacterium. Study Design/Materials and Methods Single‐walled carbon nanotubes (SWNTs) and multi‐walled carbon nanotubes (MWNTs) were incubated with E. coli K12 strain. CNTs' locations in bacteria and laser‐induced thermal and accompanied effects around CNTs were estimated with TEM and PT microscopy, respectively. Multi‐pulse lasers at 532 and 1064 nm with 12‐ns pulse duration were used for irradiating sample mixtures at different laser fluences. Cell viability was evaluated using a bacterial viability test kit and epi‐fluorescence microscopy. Results This study revealed CNTs' high binding affinity to bacteria, their capability to self‐assemble as clusters at bacteria surfaces, and their inherent near‐infrared (NIR) laser responsiveness. Cell viability was affected neither by CNTs alone nor by NIR irradiations alone. Notable changes in bacteria viability, caused by local thermal and accompanied bubble‐formation phenomena, were observed starting at laser fluences of 0.1–0.5 J/cm 2 with complete bacteria disintegration at 2–3 J/cm 2 at both wavelengths. Furthermore, ethanol in reaction mixtures significantly (more than one order) enhanced bubble formation phenomena. Conclusion This first application of laser‐activated CNTs as PT contrast antimicrobial agents demonstrated its great potential to cause irreparable damages to disease‐causing pathogens as well as to detect the pathogens at single bacterium level. This unique integration of laser and nanotechnology may also be used for drinking water treatment, food processing, disinfection of medical instrumentation, and purification of grafts and implants. Furthermore, the significant ethanol‐induced enhancement of bubble formation provides another unique possibility to improve the efficiency of selective nanophotothermolysis for treating cancers, wounds, and vascular legions. Lesers Surg. Med. 39:622–634, 2007. © 2007 Wiley‐Liss, Inc.