Development Of Persistent Luminescence-based Responsive Theranostic Probe For Imaging-guided Synergistic Sterilization

Bacterial infection is a serious threat to social development and human health.Fortunately,the successful development of antibiotics has effectively controlled bacterial infectious diseases.However,the abuse of antibiotics has led to the emergence of drug-resistant bacteria,causing a huge economic burden to the society.Photodynamic therapy（PDT）is a promising emerging treatment for bacterial infection,but most photosensitizers are usually in"always on"activated state and lack of bacterial targeting,which is easy to cause non-specific damage to normal tissues.Besides,oxygen（O₂）depletion and limited penetration of light severely limit the efficiency and clinical application of photodynamic therapy.Chemodynamic therapy（CDT）is an emerging therapy that relies on endogenous hydrogen peroxide（H₂O₂）to fight bacterial infection.The combination of PDT and CDT is expected to address limitations such as O₂depletion and limited penetration depth of light,and achieve a synergistic effect of“1+1>2”.However,most traditional CDT systems rely on metal oxides,which not only have relatively low catalytic activity,but also cause long-term toxicity to organisms due to their non-biodegradability.The aim of this thesis is to construct a bacterial microenvironment-responsive theranostic nanoprobe for dual-channel smart imaging guided on-demand self-regulated PDT/CDT synergistic sterilization and wound healing.The main research results are as follows:A bacterial microenvironment-responsive phosphorescence/fluorescence dual-channel imaging guided on-demand self-regulated PDT/CDT synergistic theranostic nanoprobe was developed.Acid-degradable Zn₂Ge O₄:Mn persistent luminescence nanoparticles（PLNP）were prepared as the matrix,acid-responsive phosphorescent imaging unit and acid/H₂O₂dual-stimuli mediated CDT agent.p H-responsive near-infrared fluorescence/photodynamic-in-one probe（PS）was designed as acid-activatable fluorescence imaging unit and PDT agent.Meanwhile,piperazine-functionalized polyethylene glycol was employed as a bridge and charge-reversed intelligent target unit to build the intelligent theranostic nanoprobe（PLNP-PS）.PLNP-PS exhibits strong green phosphorescence under simulated normal physiological conditions（p H 7.4）,while the gradual degradation of PLNP matrix results in the disappearance of green phosphorescence of PLNP-PS under simulated bacterial acidic microenvironment（p H6.0）.Meanwhile,Mn²⁺was released from PLNP matrix and CDT performance was activated by H₂O₂ overexpressed in bacterial infection microenvironment.At the same time,the dissociated PS changed from the basic form to the acid form,and the self-quenching effect disappeared,resulting in the near-infrared fluorescence recovery and activation of photodynamic properties.In addition,the zeta potential of PLNP-PS changes from-13.9±0.9m V to 2.4±0.3 m V during this process,which provides the possibility of charge-reversed intelligent targeting.The as-prepared PLNP-PS lays a foundation for the follow-up dual-imaging-guided on-demand self-regulated PDT/CDT synergistic sterilization.The mechanism of phosphorescence/fluorescence dual-channel bacterial targeting imaging and efficient synergistic sterilization of PLNP-PS theranostic nanoprobe was elucidated.Confocal laser scanning microscope images results showed that PLNP-PS had bacteria-targeting and bacteria-specific dual-channel imaging properties.With the extension of culture time,the green phosphorescence signal gradually weakened,while the red fluorescence signal gradually increased.In vitro bactericidal experiment results showed that PLNP-PS had a strong bactericidal effect(the bactericidal rate was nearly 100%when the concentration was0.4 mg m L^-1)under the microenvironment of weak acid and H₂O₂ and 808 nm excitation light irradiation(0.6 W cm^-2,10 min).While the bactericidal rate of PLNP control group under the same concentration was 73.46%and 54.81%towards Escherichia coli and Staphylococcus aureus,respectively.Reactive oxygen species and singlet oxygen indicator（DCFH-DA and SOSG）staining results further confirmed that the bactericidal effect of PLNP-PS is related to the production of hydroxyl radical and singlet oxygen,suggesting that PLNP-PS intelligent theranostic nanoprobe hold a great promising for dual-channel imaging guided PDT/CDT synergistic treatment for bacterial infection.Bacterial microenvironment-responsive dual-channel smart imaging guided on-demand self-regulated PDT/CDT synergistic sterilization and wound healing was realized.When PLNP-PS concentration was up to 1.0 mg m L^-1,the cell survival rate was still higher than 85%,indicating that PLNP-PS had good biocompatibility.PLNP-PS hydrogel was developed subsequently and used for the bacteria infected wounds healing.The results showed that the hydrogel had good synergistic bactericidal performance and promote the wound healing ability without obvious side effects.PLNP-PS hydrogel shows great application prospect in new wound dressings.