Development Of Near-Infrared Persistent Luminescence Photothermal Nanomaterials/Nanozyme For Targeted Bacterial Imaging And Responsive Bacterial Killing

Infectious diseases caused by pathogenic bacteria seriously threaten human health.Antibiotics,as the most direct and effective antibacterial drug,are widely used to cure bacterial infectious diseases.However,with the over use of antibiotics,drug-resistant bacteria have been appeared with increasing types and numbers.In view of the bacterial resistance dilemma that antibiotics are difficult to deal with effectively,it is of great significance to develop new efficient and safe strategies that can replace antibiotics.Nanomaterials have become one of the most promising strategies to overcome microbial resistance.However,the performance of a single type of nanomaterial is limited,and it is difficult to achieve precise targeted bactericidal treatment and provide effective real-time imaging monitoring.Persistent luminescence nanoparticle（PLNP）has the characteristic of continuous emitting even after the excitation light stops to achieve continuous luminescence imaging without autofluorescence background.Near-infrared luminescent PLNP is ideal contrast agent suitable for background-free imaging and long-term in vivo tracking due to their strong tissue penetration,ultra-long afterglow and repeatable excitation by red LED lights.This dissertation aims to synthesize multifunctional near-infrared emitting PLNP based nanoplatforms for bacterial targeted imaging and responsive bactericidal therapy.The main results and innovations are as follows:Photothermal nanomaterials usually lack the functions for bacterial targeting and imaging tracking,resulting in uncontrollable distribution and lethal temperatures for normal cells in vivo.To solve this problem,a pH switchable nanoplatform（PLNP@PANI-GCS）for persistent luminescence imaging guided precise PTT was developed.Near-infrared emitting PLNP(Zn_1.2Ga_1.6Ge_0.2O₄:Cr³⁺)was used as the luminescent center to offer activatable persistent luminescence by 650 nm red LED.Polyaniline（PANI）shell was introduced as photothermal reagent via in-situ oxidative polymerization to obtain responsive enhanced photothermal performance in the acidic environment.Then,glycol chitosan（GCS）was further modified as charge-reversal smart targeting agent not only to improve the biocompatibility of nanomaterials,but also to reverse the surface negative charges to positive charges in the acidic environment,getting selective binding ability of bacteria at infection site.The resulting nanocomposite achieved charge reversal and enhanced photothermal effect in acidic microenvironment（pH 6.5）(The temperature of PLNP@PANI-GCS solution at the concentration of 1 mg mL^-1can rapidly rise to 61.0°C under 8 minutes of 808 nm laser irradiation),ensuring the selective retention imaging and responsive bacterial killing in bacterial infection site.The nanoplatform achieved selective long-persistence imaging of bacterial infection in methicillin-resistant staphylococcus aureus（MRSA）infected mouse model,ensuring precise irradiation of 808 nm laser and efficient PTT（The infected site was rapidly heated to 52.2°C under 5 min 808 nm laser irradiation）,while avoiding nonspecific targeting and photothermal damage to normal tissue cells.The PLNP@PANI-GCS achieved a precise photothermal therapy with bacterial targeted background-free luminescence imaging guided responsive enhanced photothermal efficiency,avoiding the nonspecific damage to normal tissue cells and bacterial resistance production in treatment.It is of great significance for the development of new nano-sterilization system and further in vivo applications of nanomaterials.To expand the application of nanomaterials in more bacterial infections,and realize efficient bacterial killing under extreme physiological conditions in vivo,a pH-responsive long persistence luminescent nanozyme（MSPLNP-Au-CB）was prepared as general nanomaterial in gastric acid environment and common bacterial infection environment.The nanozyme contained the near-infrared PLNP(Zn_1.2Ga_1.6Ge_0.2O₄:Cr³⁺)core as the luminescent center and the mesoporous silicon shell layer as the support to immobilize and protect in-situ reduced gold nanoparticles（AuNP）.The obtained MSPLNP-AuNP can improve the stability of AuNP in gastric acid environment,and maintain the pH-responsive oxidase and peroxidase like activities of AuNP.Then,chitosan benzene-boronic acid（CB）with bacterial targeting ability was synthesized,and further modified on MSPLNP-AuNP to ensure specific bacterial targeting ability.MSPLNP-Au-CB achieved targeted long-persistent luminescence imaging and pH responsive killing of Helicobacter pylori（H.pylori）and common bacteria at low doses(30μg mL^-1)in simulated environment.The effective targeted imaging and efficient bacterial killing of MSPLNP-Au-CB in gastric acid environment and common bacterial infection environment provides the possibility for the in vivo bacterial infection treatment.To monitor targeted imaging and cure bacterial infection in vivo,the therapeutic performance of MSPLNP-Au-CB nanozyme on H.pylori and MRSA in vivo infection was further investigated.The nanozyme effectively targeted the H.pylori-infected stomach and MRSA-infected abscess areas in vivo,and enabled long-term in vivo luminescence imaging for3～4 day,with excellent bactericidal treatment of H.pylori and MRSA within 6 days and 10days,respectively.Cytotoxicity experiments and intestinal flora diversity analysis demonstrated the good biocompatibility of MSPLNP-Au-CB.The specific targeting and responsive bactericidal nanozyme not only achieved good therapeutic effect on bacterial infection,but also avoided bacterial resistance caused by antibiotic treatment and overcame the toxic side effects to normal tissue cells and intestinal commensal bacteria.Such multifunctional responsive therapeutic agent is promising for the therapy of drug-resistant bacterial infection,especially bacterial infection in extreme environment.