Enzymatic Micromotors As A Mobile Photosensitizer Platform For Highly Efficient On-Chip Targeted Antibacteria Photodynamic Therapy

Photodynamic therapy (PDT) functions when the light-excited photosensitizers transfer energy to oxygen molecules (O-3(2)) to produce cytotoxic singlet oxygen (O-1(2)) that can effectively kill cells or bacteria. However, the PDT efficacy is often reduced by the limited availability of O-3(2) surrounding the photosensitizer and extremely short diffusion range of the photoactivated O-1(2). Herein, an enzymatic micromotor based on hollow mesoporous SiO2 (mSiO(2)) microspheres is constructed as a mobile and highly efficient photosensitizer platform. Carboxylated magnetic nanoparticles are connected with both hollow spheres and 5,10,15,20-tetrakis(4-aminophenyl)porphyrin molecules through covalen linkage between amino and carboxylic groups within a one-step reaction. Due to the intrinsic asymmetry of the mSiO(2) spheres, the micromotors can be propelled by ionic diffusiophoresis induced by the enzymatic decomposition of urea. Via numerical simulation, the self-propulsion mechanism is clarified and the movement direction is identified. By virtue of active self-propulsion, the current system can overcome the long-standing shortcomings of PDT and significantly enhance the PDT efficacy by improving the accessibility of the photosensitizer to O-3(2) and enlarging the diffusing range of O-1(2). Therefore, by proposing a new solution to the bottleneck problems of PDT, this work provides insightful perspectives to the biomedical application of multifunctional micro/nanomotors.