Synthesis And Imaging Applications Of Fluorescent Probes In Response To Bacterial Cell Membranes

Bacterial infections have become a public health problem of global concern due to their high clinical morbidity and mortality.Bacterial cell membrane plays an important role in maintaining the morphology of bacteria and mediating the exchange of substances inside and outside the cell.The development of fluorescent probes based on bacterial cell membrane imaging is of great significance in diagnosing bacterial infections,tracking bacterial viability,and evaluating the antibacterial properties of drugs.The ZTRS compound based on1,8-naphthimide is an environmentally sensitive probe molecule.Zinc ions can inhibit the photo-induced electron transfer(PET)effect in the molecule and enhance its fluorescence.This thesis uses the environmental sensitivity of ZTRS to expand on its structure,introduces long carbon chains of different lengths that can be inserted into bacterial cell membranes,and develops a number of fluorescent probes that respond to bacterial cell membranes,which are used in no-wash imaging of bacteria.The second chapter of the thesis introduced the 18-carbon lipid chain based on the ZTRS structure to construct ZTRS-BP,which can selectively identify the cell membrane of gram-positive bacteria and perform no-wash imaging for real-time tracking of the survival status of positive bacteria.The probe aggregates in an aqueous solution and exhibits aggregation-induced fluorescence quenching.Gram-positive bacteria are able to untie the aggregates and produce enhanced fluorescence in the cell membrane.Since there is no response to Gram-negative bacteria,ZTRS-BP can achieve selective imaging of Gram-positive bacteria.The ZTRS-BP-Zn(II)complex chelated with zinc ions further enhances the fluorescent signal on the bacterial surface by inhibiting the effect of PET.We used ZTRS-BP-Zn(II)to perform differential imaging of Gram-positive live bacteria and dead bacteria,so as to monitor the viability of vancomycin-treated B.cereus in real time.Furthermore,in Chapter 3 of the paper,the length of the hydrophobic carbon chain attached to the probe was changed to synthesize ZTRS-C8 and ZTRS-C12 compounds,with DMNAP as the control molecule.These molecules all aggregate in aqueous solution and quench their fluorescence,and have a certain bacterial cell membrane responsiveness.Among them,ZTRS-C8-Zn(II)shows stronger no-washing characteristics.In addition to responding to Gram-positive bacteria,ZTRS-C8-Zn(II)and ZTRS-C12-Zn(II)can also differentially image different Gram-negative bacteria.Through the study of the mechanism of the probe and the bacteria,it is found that the probe is inserted into the bacterial cell membrane to produce fluorescence mainly through hydrophobic interaction.At the same time,ZTRS-C8-Zn(II)can pass through the damaged cell membrane and combine with bacterial DNA to produce enhanced fluorescence.Therefore,we use a single compound to indicate the survival status of bacteria,and effectively screen the drugs acting on bacterial membranes.