Singlet oxygen generating nanolayer coatings on NiTi alloy for photodynamic application

Photodynamic Therapy (PDT) is a promising approach for killing microorganism and especially for the inactivation of antibiotic-resistant strains. The photodynamic process rapidly generates reactive oxygen species (ROS) as for instance peroxides, hydroxyl radicals, superoxide ions, and singlet oxygen. Among them, the singlet oxygen is considered to be a major causative agent of cellular damage in photodynamic process. Due to advantage of the cytotoxic effect of PDT on bacteria, the PDT method has been one of the most appropriate tools to prevent the microbes which result in biofilm formation. This work describes a method of singlet oxygen generating nanolayer coating on NiTi alloy which shows a good biocompatibility. The 5,10,15-triphenyl-20-(4-carboxyphenyl)-porphyrin] platinum (PtCP) functional nanolayer coatings were prepared in two steps. In the first step, Al coating was prepared on biomedical NiTi alloy substrate by DC magnetron sputtering, and then this coated substrate alloy was immersed into hot water to form Al₂O₃ coatings. In the second step, a photosensitizer (PS) with carboxyl group was chemically attached to the hydroxyl-terminated Al₂O₃ coatings by a direct esterification method. The microstructure and the elemental and phase composition of the coating were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), and X-ray diffraction (XRD). Results from this study show that the PtCP functional nanolayer coating is composed of many perpendicular nanosheet structures. These very thin nanosheet structures with the thickness of a few nanometers mainly show amorphous phase. The singlet oxygen generation efficiency of the PS being chemically bonded on these nanosheets was detected by an indirect chemical method by using the decomposition of 1,3-diphenyl-isobenzofuran (DPBF).