Study On Regulation Of Optics Properties And Crosslinking Self-assembly Of Silane Ligand-modified Luminescent Gold Nanoparticles

Ultrasmall luminescent gold nanoparticles（AuNPs,d<3 nm）have attracted increasing attention in biomedical fields such as biological fluorescence imaging,disease treatment owing to their adjustable optical properties,facile functionalization of the surface and good biocompatibility.It has become a research hotspot in the field of optical imaging to design and develop AuNPs probes emitting in the Near-infrared II region（NIR-II 1000-1700 nm）with high optical penetration depth and low background scattering in recent years.The optical properties of AuNPs are closely related to their surface chemical properties and aggregation state.In addition,luminescent AuNPs can generate singlet oxygen and are also an important class of nanophotosensitizers.It is of great significance to study the influence and regularity of the surface chemical properties and their aggregation states on the luminescence properties and the ability to generate singlet oxygen of AuNPs.Therefore,in this thesis,the surface chemical properties and assembly structure of AuNPs were studied by developing a novel surface functionalization method,so as to tune the optical properties and the ability to generate singlet oxygen of AuNPs.The research contents and results are as follows:The dual-ligand-modified AuNPs（PEG/MPTMS-AuNPs）emitting at 800 nm were synthesized in the organic phase using the silane ligand 3-（trimethoxysilyl）-1-propanethiol（MPTMS）and hydrophilic ligand polyethylene glycol monomethyl thiol（CH₃O-PEG-SH）.The PEG/MPTMS-AuNPs were transferred into the aqueous phase by rotary evaporation,and then the pH value of the assembly solution was adjusted,so that the silane ligands on the surface of AuNPs exhibited different crosslinking states under different pH value.The effect of pH on the assembly structure was systematically studied.It was shown that the transfer of PEG/MPTMS-AuNPs from the organic phase to the aqueous phase resulted in red-shift of the fluorescence from 800 nm（NIR-I）to 1070 nm（NIR-II）.Under alkaline conditions,most of the silanes on the surface of PEG/MPTMS-AuNPs were in the T₃ crosslinking state,and the AuNPs assemblies was tightly dense aggregation,and the corresponding fluorescence emission wavelength of the assembly was 1075-1085 nm.Under acidic conditions,with the passage of aggregation time,the surface silane of AuNPs evolved from the T₃ crosslinking state to the T₀,T₁,and T₂ crosslinking states,and the assembly structure was disassembled from a tightly dense aggregation to loose aggregation.The corresponding fluorescence emission wavelength of the assembly gradually blue-shifted from the Near-infrared II region to the Near-infrared I region.Thus,the controllable tuning of the optical properties of AuNPs is realized.Based on the effect of pH on the assembly structure of PEG/MPTMS-AuNPs,the regularity of the structure and compact state of the assembly on its ability to generate singlet oxygen was systematically studied.Studies have shown that the ability of AuNPs assembly to generate singlet oxygen was positively related to the looseness of the assembly.That is to say,when the silane crosslinking state on the surface of AuNPs is dominated by T₀,T₁,and T₂,the rates of generating singlet oxygen is faster.In addition,the ability of CH₃O-PEG-SH-modified AuNPs（CH₃O-PEG-AuNPs）to generate singlet oxygen is between the tightly dense assembly and loose assembly.The singlet oxygen properties of the assembly were successfully regulated by using pH-mediated aggregation of the AuNPs assembly.The tightly dense aggregation can passivate the singlet oxygen generation,and the loose aggregation can sensitize the singlet oxygen generation.Therefore,this controllable regulation strategy may provide a new idea for the research and design of efficient AuNPs photosensitizers for photodynamic therapy.