Carbon nanotube based hybrid nanostructures as photothermal antimicrobial nanomaterials

Antimicrobial resistance (AMR) is estimated to account for nearly 10 million deaths annually by 2050 according to recent high-profile reports. In this respect, AMR is a serious public health concern that requires urgent actions for combating antibioticresistant bacteria. Rapid progress in nanotechnology has opened new horizons for the development of innovative therapies leading to the physical destruction of bacteria as an alternative to biochemical treatments. Photothermal treatment based on nanomaterials is a remarkable solution to kill antibiotic-resistant bacteria through light induced elevated heat generation. However, their heat generation capacity is restricted to inherent light absorption properties of these nanoparticles. In this thesis, we presented two novel methods to prepare effective carbon nanotube (CNT) based photothermal agents by hybridizing with arrays of fluorophores and three-way-junctions DNA nanostructures. These hybridization methods provided an enhancement in the light absorption and heat generation capacity of CNTs and prepared nanohybrids showed remarkable photothermal activity on bacteria. Chapter 2 describes a method to decorate the surface of multi walled carbon nanotubes (MWNTs) with an array of NIR absorbing fluorophores (3,3’-Diethylthiatricarbocyanine, DTTC) acting as a light harvesting antenna under NIR laser irradiation leading to high temperature elevation as a result of the photothermal conversion. Continuous NIR laser irradiation of MWNT/DTTC nanohybrids for 15 minutes resulted in a local temperature of 92°C and a 77% killing efficiency on P. aeruginosa cells in the dispersion. In order to evaluate the photothermal activity of nanohybrids on surfaces as antimicrobial and antibiofilm coatings, MWNT/DTTC nanohybrids were incorporated into waterborne polyurethane (PU) matrix. MWNT/DTTC-PU nanocomposite generated higher temperatures reaching 120°C after only 3 minutes of laser irradiation. After multiple laser irradiation cycles, the light-activated heat generation by MWNT/DTTC-PU nanocomposite was not affected and proved their reusability potential in terms of the photothermal conversion. The antimicrobial activity of MWNT/DTTC-PU nanocomposite on surface attached P. aeruginosa cells was examined using confocal laser scanning microscopy. In Chapter 3, we introduced a novel approach to improve the light absorption capacity of single walled carbon nanotubes (SWNTs) through the arrangement of three individual SWNTs into desired nanostructures with the guidance of DNA self-assembly. The specially designed DNA three-way junction (3WJ) was comprised of three Watson-Crick paired helices with non-complementary single stranded tails designed to wrap around the SWNTs surface. DNA-3WJ nanostructures acted as a dispersion agent for SWNTs and also as a rigid template for the self-assembly of SWNTs into a controlled branched nanostructure through noncovalent binding interaction at an angle of approximately 120° to each other. Hybrids of CNTs and DNA-3WJ nanostructures enabled the fluorescent labeling of SWNTs for biological and sensing applications as well. DNA-3WJ/SWNT nanohybrids presented enhanced NIR absorption and enhanced photothermal conversion with respect to individual SWNTs at the same concentration. This improvement provided a valuable approach for utilization of CNT based nanomaterials as photothermal agents with stronger photothermal activity. Chapter 4 describes the preparation and characterization of broadband light-harvesting nanohybrids as solar photothermal agents by a self-assembly of visible light absorbing fluorophores on the CNTs surface as a continuation of Chapter 2. For this purpose, the surface of CNTs were decorated with multiple fluorophores which possess strong light absorption capacity in UV, Vis and NIR regions of the spectrum. Prepared CNT/Fluorophores nanohybrids were exposed to artificial solar light obtained by the solar simulator to investigate their photothermal conversion efficiency.