Microenvironment-Triggered Self-Assembled Theranositc Probe Based On Ultra-Small Luminescence Nanoparticles For Precision Imaging-Guided Sterilization

Bacterial infection has always been a major threat to human life and health.The invention of antibiotics led to a rapid decline in the mortality rate from bacterial infections in a short period of time.However,due to the improper use of antibiotics,the emergence of a large number of drug-resistant bacteria has led to an increasing trend in the mortality rate of bacterial infection.Bacteria rely on the reversible reaction between protein adhesins and nucleophilic ligands on the host surface to achieve attachment,liberation and immune escape on the host surface.If the reversible reaction can be effectively interrupted,the colonization or spread of bacteria can be blocked and the effect of effective inhibition of bacteria can be accomplished.Therefore,adhesin is expected to become a novel bacterial targeting site.Persistent luminescent nanoparticles（PLNPs）have unique optical properties,which make them promising in persistent luminescent imaging and therapeutic applications with high signal-to-noise ratio,autofluorescence-free and no in-situ excitation.How to intelligently adjust the size of PLNPs based nanoprobes to effectively overcome the problems of endothelial reticulum system deposition and slow metabolism of large PLNPs,and to avoid the disadvantages of less aggregation and short residence time of ultra-small PLNPs in the lesion site,so as to achieve the demand of lesion site-specific imaging guided treatment is still a great challenge.In this study,we constructed an ultra-small PLNPs theranostic probe that can self-assemble under the trigger of bacterial microenvironment.The probe not only retained the characteristics of ultra-small PLNPs that circulate and metabolize rapidly,but it also aggregated at high density at the site of bacterial infection to increase the surface tension on the bacterial membrane and destroy the bacterial membrane for accurate imaging and effective sterilization.The main results are as follows:（1）A bacterial microenvironment targeted self-assembly imaging and antibacterial theranostic probe（PLNP-Mal/OPSS）based on ultra-small PLNPs was constructed.The ultra-small Zn Ga₂O₄:Cr_0.004（PLNP-OA）with diameter of 5-8 nm was firstly synthesized by acetylacetone-based solvothermal method.The as-designed PLNP-Mal/OPSS with maleimide（Mal）and dithiopridine（OPSS）functional groups was then obtained by ligand exchange.PLNP-Mal/OPSS had strong phosphorescent emission at 700 nm and lasting persistent luminescence excited by both 254 nm UV lamp and 650 nm LED light,ensuring the subsequent autofluorescence-free imaging available.PLNP-Mal/OPSS can self-assembled into clusters in the simulated bacterial microenvironment（glutathione overexpression）,which established the foundation for bacterial microenvironment-triggered self-assembly imaging and antibacterial.（2）Bacterial microenvironment-triggered self-assembly imaging and antibacterial were realized.PLNP-Mal/OPSS can self-assemble on the surfaces of Escherichia coli and Staphylococcus aureus and lead to bacterial clustering.This was mainly due to the Michael addition reaction between the Mal on the surface of PLNP-Mal/OPSS and the Cys-S residues in the bacterial surface adhesins.At the same time,OPSS was reduced to-SH by glutathione,inducing PLNP-Mal/OPSS to self-assemble on the surface of bacteria and cause bacterial agglomeration.PLNP-Mal/OPSS showed excellent killing effect on Escherichia coli,and the antibacterial efficiency was almost 100%after 1 h incubation.In addition,PLNP-Mal/OPSS also showed good biocompatibility.Even at doses up to 1000μg m L^-1,the cell viability was still above 85%and the hemolysis below 2%.In vivo imaging showed that PLNP-Mal/OPSS could specifically target to bacterial infection sites and retain for a long time.Combined with metabolic experiments,it had been proven that PLNP-Mal/OPSS had a rapid circulating metabolic ability（which can be basically metabolized completely after 12 d of administration）and was primarily excreted through the feces.In addition,PLNP-Mal/OPSS had a good therapeutic effect on bacterial infected mice without causing obvious toxic and side effects.This study provides a new strategy for intelligent imaging-guided sterilization and expands the application of persistent luminescence nanomaterials at the in vivo level.