| When the frequency of incident light matches the inherent oscillation frequency of free electrons in metal nanoparticles(NPs),metal NPs are bound to enhance the absorption of incident light,and localized surface plasmon resonance(LSPR)phenomenon also occurs.Metal NPs that can produce LSPR phenomenon are called plasmonic metal nanomaterials(mainly including Au,Ag,and Cu),they exhibit excellent surface–enhanced Raman scattering(SERS)and photothermal conversion properties,showing broad application prospects in SERS bioanalysis and photothermal antibacterial therapy.SERS bioanalytical applications involve the interaction of enhancement substrate with complex biological systeme,thus enhancement substrate is one of the key factors to ensure the sensitivity and reproducibility of bioanalysis.Conventional plasmonic metal–based substrates have poor stability under certain specific conditions(such as high–concentration salt solutions,strong acid environments,and long–term laser irradiation),their applications in SERS bioanalysis are therefore limited.Photothermal antibacterial therapy uses photothermal reagents to absorb light energy and further convert it into heat energy,and the generated high temperature is further used for bacterial treatment.Conventional plasmonic metal–based photothermal reagents may aggregate or leak metal ions under high temperature and physiological conditions,resulting in reduced treatment efficiency and even cause unnecessary biosafety issues.Therefore,we urgently need to propose a feasible strategy to realize the preparation of plasmonic metal nanomaterials with superior and stable SERS and photothermal conversion performance.This thesis is devoted to confining plasmonic metal nanomaterials in the nanospace of thickness–tunable graphene shells by chemical vapor deposition(CVD)method,and four kinds of plasmonic metal graphitic nanocapsules with different LSPR properties and superior stability have prepared via rationally modulating the composition,size and morphology of the metal core,their applications in SERS bioanalysis and photothermal antibacterial therapy are finally systematically explored.The details are as follows:1.Preparation of ultrastable graphene–isolated Au Ag nanocapsules(GIAAN)and their SERS detection and imaging applications(Chapter 2)Ag nanocrystals have large optical absorption cross–sections,but are easily oxidized,which limits their SERS bioanalytical applications.The encapsulation of graphene can effectively protect the stability of Ag nanocrystals,but the weak catalytic activity makes it difficult to achieve direct and efficient growth of graphene on their surface by CVD method.This chapter makes full use of the excellent catalytic activity of Au nanocrystal to achieve the growth of graphene on Ag surface,and GIAAN with superior stability and SERS performance is prepared via modulating the ratio of Au and Ag precursors as well as the CVD growth conditions.First,quantitative SERS analysis of trace antibacterial agents in the homogeneous system is realized by surface modification of GIAAN with amphiphilic polyethylene glycol molecules;multimodal Raman imaging of breast cancer cell line MCF–7 is also realized by using the inherent Raman scattering characteristic peaks of GIAAN as signal labels.Secondly,the simultaneous SERS monitoring of water–and lipid–soluble drug model molecules is achieved based on the unique interfacial self–assembly properties of unmodified GIAAN(u GIAAN).The multifunctional GIAAN prepared in this work offers a good nanoplatform for sensitive SERS analysis,and is even expected to provide new ideas for in vivo drug delivery,dynamic monitoring and therapy.2.Graphene–isolated Au nanocapsules(GIAN)platform for SERS monitoring of graphene interfacial charge transfer modulation(Chapter 3)In graphene–based biosensing platforms,different degrees of charge transfer widely exist between graphene and substances,and different degrees of charge transfer may affect the application performance.Therefore,developing a r ational strategy to realize the monitoring of charge transfer changes can provide important reference for the construction and improvement of graphene–based biosensing platforms.Charge transfer is the most important component of the chemical enhancement mechanism of SERS spectroscopy technique,and changes in the degree of charge transfer are often accompanied by changes in SERS spectra,SERS technique is therefore expected to realize the monitoring of graphene interfacial charge transfer modulation.Plasmonic metal graphitic nanocapsules have both an excellent graphene interface and a SERS–active metal core,providing a good nanoplatform for studying the monitoring of graphene interfacial charge transfer changes.In this chapter,the GIAN prepared by CVD method is exploited as the nanoplatform,experiments and theoretical calculations prove that halide ions can enhance the degree of charge transfer between graphene andπ–conjugated small molecules,and the SERS signal ofπ–conjugated small molecules is significantly enhanced(>10 times).M oreover,further studies show that halide ions enhancing the charge transfer between graphene andπ–conjugated small molecules are universal phenomenon.In addition to halide ions,we find some other anions with strong electron–withdrawing ability also have similar performance for enhanced charge transfer accompanied by enhanced SERS signal.This work provides a new strategy for studying the changes of graphene interfacial charge transfer,which is expected to point a new direction for the construction of next–generation graphene–based biosensing platforms.3.Preparation of anisotropic Au nanorod graphitic nanocapsule s(Au NR@G)and their near infrared-I photothermal antibacterial therapy applications(Chapter 4)Near infrared(NIR)light-mediated photothermal antibacterial therapy strategy uses photothermal reagents to absorb light energy and convert it into heat energ y,and then bacterial treatment is achieved through the generated high temperature,which possesses numerous merits like minimized damage,good controllability and high tissue penetration property.Plasmonic metal nanomaterials with tunable LSPR properties are widely used as photothermal reagents,but they often exhibit poor stability in physiological and high temperature environments,which may lead to low photothermal antibacterial efficiency and potential biotoxicity.Therefore,it is of great significance to prepare photothermal reagents with superior and stable NIR light absorption properties by a simple and feasible method.In this chapter,the photothermal reagent of anisotropic Au NR@G is prepared by confinement CVD method,which exhibits excellent and stable NIR–I light absorption properties.We further prepare Au NR@G-doped polyvinyl alcohol/chitosan hydrogel(abbreviated as AG-PCH)for efficient photothermal antibacterial therapy,and the photothermal antibacterial mechanism is also systematically studied.In addition,the AG-PCH has superior physiological environment and photothermal stability stability,thus it is able to effectively avoid unnecessary biosafety problems caused by photothermal reagents entering the blood circulation during the photothermal antibacterial therapy process.The proposed AG-PCH based photothermal antibacterial therapy strategy in this work can effectively avoid the risk of bacterial resistance,and has important guidance for bacterial therapy in vivo.4.Preparation of cavity-structured graphene–isolated Au Ag nanocapsules(cGIAAN)and their NIR-II photothermal antibacterial therapy applications(Chapter 5)Compared with NIR-I(700–900 nm)lasers,NIR-II(1000–1700 nm)lasers have deeper tissue penetration,less energy dissipation,and higher skin tolerance thresholds(maximum allowable exposure of 1064 nm laser is 1 W/cm~2)and lower biotoxicity.Hence,it is of great significance to prepare plasmonic metal-based photothermal reagents with superior and stable NIR-II light absorption properties.In this chapter,the photothermal reagent of cGIAAN with superior and stable NIR–II light absorption property is prepared by modulating the flow and supply time of carbon source during the CVD growth process.We further prepare the cGIAAN-doped oxidized hyaluronic acid–graft–aniline tetramer/O–carboxymethyl chitosan hydrogel(abbreviated as cGIAAN-OT/OCSH)as wound dressing,efficient photothermal antibacterial therapy both in vitro and in the bacterial-infected full thickness skin defect model in mice is achieved under the irradiation of safe power laser(1 W/cm~2 1064 nm).In addition,the proposed cGIAAN-OT/OCSH based photothermal antibacterial therapy strategy has good biosafety,which neither causes significant negative effects on the major organs of mice nor irreversible damage to the wound skin.This work provides new ideas for safe and reliable photothermal antibacterial therapy,and is even expected to be applied to clinical bacterial therapy. |
