PH Reversibly Switchable Nanocapsule For Bacteria Targeting Imaging-guided Precision Photodynamic Sterilization

Bacterial infection,especially drug-resistant bacterial infection,has attracted more and more public attention.The abuse of antibiotics has led to severe drug resistance of bacteria,making the treatment of bacterial infection difficult.Photodynamic antimicrobial therapy is a new method of sterilization.However,the absorption wavelength of the existing photosensitizers is mostly limited to the UV-visible region,and the tissue penetration is poor.In addition,most existing photosensitizers are in"always on"mode?always activated?and lacks bacterial specificity,which inevitably causes non-specific damage to normal tissues.This thesis focuses on the development of smart nanocapsule diagnostic probes to achieve specific imaging of bacterial infection and precise photodynamic therapy to overcome the deficiencies of existing photodynamic sterilization systems.The main results are as follows:A novel pH reversibly activated photosensitizer was designed and synthesized for subsequent construction of intelligent microcapsule diagnosis and treatment system.The photosensitizer?Acy-S-S-Py?was synthesized by using pH-responsive asymmetric cyanine?Acy?as the parent molecule to covalently connect pyridine?-S-S-Py?.The-S-S-Py group is the pharmacophore of allicin,which helps to improve the bactericidal effect.The pK_a and the pH sensitive range of Acy-S-S-Py were determined to be 5.8 and 4.6-7.4,respectively,by the fluorescence titration,matching well with the bacterial infection acidic microenvironment.The developed Acy-S-S-Py emits near-infrared fluorescence in the simulated acidic microenvironment of bacterial infection and produces singlet oxygen under the irradiation of808 nm,but it does not have the above functions under normal physiological condition.This property of Acy s-S-Py provides an opportunity for the treatment of deep tissue infection without non-specific injuries.Nanocapsule?DPD@Acy-S-S-Py?was prepared by self-assembly of amphiphilic distearylphosphatidyl ethanolamine?DSPE?and 2,3-dimethylmaleic anhydride?DMMA?functional PEG?DSPE-PEG-DMMA?and Acy-S-S-Py.The synthesized nanocapsule was spherical,with a particle size of 40.0±3.2 nm,a hydration particle size of 116.3±3.3 nm,and a polydispersity index?PDI?value of 0.152,showing good dimensional stability.Compared with the free Acy-S-S-Py,the DPD@Acy-S-S-Py nanocapsule retains its pH reversible activation property and the ability to produce singlet oxygen,while its biocompatibility and anti-photobleaching property are also improved.The Zeta potential of the nanocapsule was-12.7±1.0 mV under normal physiological conditions,but 6.0±0.3 mV under pH 6.0,which successfully realized charge inversion and provided the possibility for subsequent bacteria targeting imaging-guided precision photodynamic sterilization.pH reversibly switchable nanocapsule achieved imaging-guided photodynamic sterilizatin.The photodynamic sterilizatin effect of DPD@Acy-S-S-Py nanocapsule was evaluated by in vitro antibacterial experiments.Under acidic condition?pH 6.0?and 808 nm(0.6 W cm^-2)laser irradiation for 10 min,DPD@Acy-S-S-Py(Acy-S-S-Py,5.0×10^-6 mol L^-1)had a bactericidal efficiency of nearly 100%for Escherichia coli?10⁸ CFU?and Staphylococcus aureus?10⁹ CFU?,but no bactericidal effect on both Escherichia coli and Staphylococcus aureus under normal physiological conditions.In vivo experiments revealed that DPD@Acy-S-S-Py not only enabled targeted imaging of bacterial infection without autofluorescence interference,but also gave rapid therapy effect for bacterial infection.