Afterglow Nanoparticles For Infection Imaging And Persistent Photodynamic Destruction Of Bacteria

The bacterial infection is one of the major causes of high morbidity and mortality worldwide.Bacterial diagnosis and treatment probes are capable of imaging lesions and administering specific therapies that can efficiently cure bacterial infections and reduce side effects.Nanoprobes that combine diagnosis and treatment have therefore gained widespread attention in the field of biomedicine.Antibiotics,as the most widely used antibacterial tool,are currently limited due to the short blood half-life,toxic side effect,and drug resistance.Photodynamic therapy(PDT)is commonly used due to its advantages such as non-drug resistance,low toxicity,controllability,and limited invasiveness.However,PDT also has problems such as the short-life of reactive oxygen species(ROS)and the phototoxicity to normal tissues.Fluorescence imaging is mostly used for bacterial detection due to its high sensitivity,low cost,and high operability.Traditional fluorescent probes,however,have limitations such as low signal-to-noise ratios and poor image quality,which limit their further applications.The in-situ growth of persistent luminescence nanoparticles on mesoporous silica nanoparticles(MSN) was used to prepare m PL nanoccomposites.Dichlorosilicon phthalocyanine(Si-Pc)was then covalently grafted onto m PL to form m PL@Pc,follwoed by reaction with succinic anhydride to modify part of the carboxyl group on the surface of m PL@Pc(m PL@Pc/COOH).Finally,Cy7 was applied to m PL@Pc/COOH through the electrostatic interaction to obtain m PL@Pc-Cy nanoparticles.Under normal physiological conditions(pH 7.4),m PL@Pc/COOH was negatively charged and could electrostatically absorb Cy7.At this time,the F?ster resonance energy transfer(FRET)effect between m PL and Cy7 would qunech the persistent luminescence of m PL and exhibit no PDT.In the mildly acidic condition(pH 5.5)of bacterial infection,m PL@Pc/COOH was subject to a charge reversal and positively charged,and Cy7 could be desorbed from the nanoparticles to terminate the FRET effect.m PL was used as an internal light source for persistent luminescence imaging and PDT at this time.Through analyzing the fluorescence and photodynamic properties under different pH,m PL@Pc-Cy nanoparticles could turn red and generate singlet oxygen(¹O₂)in pH 5.5 buffers.In vitro antibacterial testings in buffers and culture media showed that m PL@Pc-Cy could respond to pH and exhibited antibacterial effect in acid cinditions.The antibacterial rate in both pH 5.5 and culture media was beyond99.5%.The in vitro fluorescence imaging capability of m PL@Pc-Cy was investigated by incubation with bacterial suspensions,indicating stronger fluorescence as the number of bacteria increased.In the S.aureus-infected skin wounds of mice,m PL@Pc-Cy nanoparticles changed into red in response to the weakly acidic environment of bacterial infection.Besides,the m PL@Pc-Cy treatment accelerated the wound healing and the wounds of the mice were almost completely healed.The main organs of the treated mice had no obvious histological abnormalities.These results dmnstrated the potential of m PL@Pc-Cy nanoparticles for precise diagnosis and efficient destructon of bacterial infecitons.