Optical Regulation And Bioimaging Of Amphiphilic Block Copolymers Functionalized Luminescent Gold Nanoparticles In The Second Near-Infrared Window

Ultrasmall luminescent gold nanoparticles(Au NPs,d<3 nm)have good biocompatibility,stability and adjustable optical properties,showing great potential in the field of biological imaging and biomedicine.In order to overcome the difficulty of regulating the optical properties of Au NPs in the second near-infrared window(NIR-II,1000-1700 nm)and the biological behavior in vivo,in this paper,amphiphilic block copolymers(ABCs)functionalized Au NPs are synthesized and the effect of hydrophobic interaction on the optical properties of Au NPs are also systematically investigated.The NIR-II imaging of Au NPs in ulcerative colitis(UC)-bearing mice are then evaluated to explore the relationship between surface physicochemical properties of Au NPs and biological interactions.In order to enhance the body clearance of assemblies of Au NPs(Au NAs),we synthesize Au Cu alloy nanoassemblies(Au Cu NAs)with the highly reactive Cu,and systematically investigate the biotransformation mechanism of the Au Cu NAs in vivo,which provide a new strategy for regulating the in vivo biotransformation of Au NAs.In order to solve the problems of shorter emission wavelength(<1100 nm)and low quantum yields(QYs)of water-soluble NIR-II Au NPs.We develop a facile strategy to redshift the emission and enhance the QYs of luminescent Au NPs with controllable hydrophobic interactions by using ABCs in unimers or micelles as templates and hydrophobic molecule 3-mercaptopropanoate(EMP)as ligand.The uniform clusters of NIR-II Au NPs(c-Au NPs)are formed in situ inside the hydrophobic cores of ABC micelles with strong interparticle hydrophobic interactions,which enhance the emission at 1080 nm(QY,1.6%).In contrast,the rigid NIR-II Au NPs(r-Au NPs)generated with ABC unimers attached on the surface exhibit strong intraparticle hydrophobic interactions and redshifted emission at 1280 nm(QY,0.25%).The results of lifetime indicate that r-Au NPs with fast emission delay(68 ns)and c-Au NPs with slow emission delay(200 ns)belong to metal-core emission and ligand-to-metal charge transfer,respectively.These findings provide new strategies for the design of redshifted luminescent Au NPs,and open new possibilities to further expand the biological applications of Au NPs with different hydrophobic interactions.In order to explore the biological interactions of ABCs functionalized NIR-II Au NPs,the diagnostic ability of the ABCs functionalized Au NPs with different surface hydrophilicity for UC is studied.At room temperature,the r-Au NPs are monodisperse and gradually self-assembly into large nanostructure,while the morphology of c-Au NPs remain stable,the optical properties and core size of the Au core are also unchanged.Contact Angle analysis show that surface hydrophilicity of r-Au NPs(θ=53.8~o)is weaker than c-Au NPs(θ=40.9~o),which result in different biological interactions of them.In metabolic experiments,after intragastrical administration,the r-Au NPs exhibit clearance percentages of 58%and 82%at 12 and 24 h in the UC-bearing mice,much lower than those of the c-Au NPs(74%and 90%,respectively),indicating that r-Au NPs show stronger affinity toward injured intestinal mucosa.In NIR-II fluorescence imaging,after intragastric administration,the fluorescence signal of r-Au NPs and c-Au NPs in healthy mice decrease significantly after 6 h.However,the fluorescence signals in the UC-bearing mice show a much slower decay after 6 h and can be clearly observed even after 12 h,and the r-Au NPs show an intensity retention of 38%,higher than those of the c-Au NPs(18%),indicating that the r-Au NPs with F127 unimers show better sensitivity in UC imaging.Furthermore,the ex vivo fluorescent images confirm that both Au NPs arrive at the colon at comparable times(<6 h)after intragastrical administration but show a longer retention time in the inflammatory colon.Unlike the c-Au NPs inside the micelles,the r-Au NPs exhibit a stronger interaction with the injured mucus layer,with reduced thickness and increased mucosal permeability during inflammation.These findings provide a new pathway for the diagnosis of UC,a new strategy for regulating the surface properties of Au NPs with enhanced biological interactions,which are helpful for the development of biological applications of luminescent Au NPs.In order to enhance the body clearance of ABCs functionalized Au NAs in the blood circulation,we synthesized Au Cu NAs with the highly reactive Cu.The results of X-ray photoelectron spectroscopy and thermogravimetric analysis show that the content of metal(I)and the ratio of ABCs unimers to ligand on the surface of nanoparticles are regulated by Cu-doping,which lead to the alteration of interaction models between nanoparticles from the bridging effect in Au NAs to the van der Waals interaction and depletion effect in Au Cu NAs,thus resulting in the morphology of the NAs change from the triangular shape of Au NAs to the short chain shape of Au Cu NAs.For in vivo imaging,the retention rates of fluorescence intensity of Au NAs and Au Cu NAs in mouse liver regions are 42.7%and 8%,respectively,at 7d p.i...Tissue slice imaging experiments reveal that Au NAs are segregated by Kuffer cells,while Au Cu NAs are distributed in the liver sinusoid and hepatocytes,which contain abundant glutathione(GSH).In vitro experiments demonstrate that Au Cu NAs show a stronger affinity toward GSH,and the hydrated particle size(～6 nm)obtained after co-incubation with GSH is much smaller than the～28 nm of incubated Au NAs,thus resulting in different clearance kinetics in imaging experiments.In vivo metabolic studies show that the renal clearance of Au Cu NAs is significantly enhanced and Cu content-dependent compared with Au NAs at 48 h after injection.Thus,resulting in the high enrichment of Au NAs in the liver(70.6%ID/g,ID at injection dose),and the alloy NAs with high Cu-doping content(42%and 65.2%)show significantly reduced liver accumulation(16.7%ID/g and 3.9%ID/g,respectively),enhanced blood circulation time and bioavailability.These results suggest that high content of Cu is beneficial to enhance renal clearance of NAs,which is attributed to GSH-mediated biotransformation.These results provide a new strategy for the regulation of body clearance of Au NAs,will further promote the clinical transformation of AuNAs.