Self-assembled Nanomaterials For Rapid Detection Of Pathogenic Bacteria And Antibacterial Treatment

The frequent occurrence of food safety incidents caused by various pollutants has aroused the attention of consumers and has seriously threatened our health and daily life.Among them,bacterial diseases caused by pathogens are one of the most influential,widespread and common diseases in the world,which poses a huge threat to human health.Although traditional detection methods have low cost and high reliability,they can no longer meet the requirements of rapid and sensitive detection of pathogenic bacteria in practical application.Antibiotic therapy is currently the most common treatment for pathogenic bacteria infections.However,after long-term abusing of antibiotics,the emergence of drug-resistant bacteria poses a new and more challenging threat to current anti-infective therapy.The speed of research and exploration of new antibiotics are far slower than the increasing speed of bacterial resistance.In addition,the bacterial biofilms formed on the surface of implantable devices or infected organs after bacteria colonization in the body further increase the difficulty of antibiotic treatment and seriously threaten human health.In order to cope with the challenges from the detection and treatment of pathogenic bacteria,a series of modern detection techniques based on optical detection and electrochemical detection methods have been established.In addition,with the rapid development of nanomaterials and enzyme-free nucleic acid amplification technology,the specificity and sensitivity of these modern detection techniques have been significantly improved.Nanomaterials show great potential in the treatment of pathogen infections,especially in drug delivery,imaging and targeted therapy.Therefore,based on the above research background,the following works have been carried out around the non-enzyme amplification detection method of pathogenic bacteria and antibacterial nanocomposite particles:（1）Nucleic acid aptamers can specifically bind to targets and can be used as recognition elements for rapid detection and targeted therapy of pathogenic bacteria.In this chapter,flagellar aptamers of Pseudomonas aeruginosa were screened and evaluated.A large amount of recombinant protein Fli C was obtained by expressing the p ET-28a-fli C recombinant plasmid in E.coli BL21（DE3）cells.It was further separated and purified by a nickel affinity chromatography column,and Fli C protein with a purity higher than 90%was used for ligand index enhancement system evolution technology screening.After high-throughput sequencing of PCR products,the top 20 sequences with the highest enrichment degree were analyzed for homology and family analysis,and the three most representative nucleic acid aptamers were selected to determine their affinity and specificity.Among them,PA-1 has the best affinity and specificity,which provides a good recognition element for subsequent rapid detection and targeted therapy based on aptamers.（2）Enzyme-free nucleic acid amplification technology not only can be used as a signal amplification technology to improve detection sensitivity,but also can be designed as a separate detection method of pathogenic bacteria.In this chapter,a signal amplification strategy based on hybridization chain reaction（HCR）is designed for rapid detection of Staphylococcus aureus（S.aureus）.Two DNA hairpins HP1 and HP2coexist in solution at metastable state.When 16S r RNA of the bacteria is added,it can initiate cascade HCR,resulting in a long double-stranded DNA structure similar to that of alternating copolymers.This detection method is mainly divided into two parts,one the triggering of the HCR,another is the synergy of the two fluorescent dyes.The HCR sequence used in the experiment was modified with FAM fluorophore.Additionally,fluorescent dye SYBR Green I whose excitation wavelength and emission wavelength are very close to that of FAM,is used to greatly enhance fluorescence.When synchronous fluorescence spectra are used,the fluorescence peaks of FAM and SYBR Green I completely overlap,and the fluorescence signal of the system is significantly enhanced,which can achieve highly sensitive quantitative detection of S.aureus 16S r RNA.Under the optimum conditions,the detection limit of this method is 50 p M for 16S r RNA,and 4×10² CFU·m L^-1 for S.aureus.（3）Here,a rapid colorimetric method for the detection of Escherichia coli K88 was established based on nanoprobe and G-quadruplex.The method consists of two modules:（1）biometric element:aptamer;（2）transducer:capture probe DNA（5′terminal modified Au NPs）.When target bacteria shown in the environment,the aptamer can form a stable double strand with the capture probe DNA,preventing the G-quadruplex from binding to the capture probe DNA.When target bacterium appearing,because the aptamer has a stronger affinity with the target bacteria,the capture probe DNA exposes the binding site to the G-quadruplex,and under the action of the G-quadruplex structure,it leads to the aggregation and color change of Au NPs.The detection period is 60 min,which can directly judge the existence of target bacteria.With the assistance of UV-vis spectrophotometer,the target bacteria can be quantitatively detected by measuring the absorbance of Au NPs solution at 524 nm.Under the optimum conditions,the detection limit of this method is 1.35×10²CFU·m L^-1.It has wide applicability and can be used to detect a variety of pathogenic bacteria by replacing different aptamers.（4）Drug-resistant bacteria have become a serious threat due to excessive use of antibiotics.Among the many treatment strategies,photothermal therapy has become a feasible alternative strategy to antibacterial therapy.In this chapter,we designed a dual stimulus-responsive antibacterial nanocomposite particles（Pd-Cu/AMO@ZIF-8）based on zeolite imidazole skeleton-8（ZIF-8）,which combined photothermal therapy and efficient antibiotic delivery,and achieved effective treatment of bacterial infections of mouse skin.This treatment has a significant therapeutic effect on planktonic G⁺/G^-bacteria as well as biofilms.Further studies have shown that Pd-Cu/AMO@ZIF-8nanoparticles have good biocompatibility,low toxicity to host organs and tissues,reduce the concentration of antibiotics needed to effectively control bacteria and have good biocompatibility.This multi-mode treatment provides an effective strategy for the clinical treatment of pathogenic bacteria.