Preparation And Applications Of Phosphoryl Pillarenes-Modified Upconversion Nanoparticles

Based on the inorganic nanoparticles functionalized by supramolecular macrocycles,various types of organic-inorganic hybrid nanomaterials,possessing the advantages of high efficiency,desirable controllability and integrated functionalities have been constructed and attracting more and more attention in the fields of material science,life science and industry,especially in the research of biomedicine and therapy.Supramolecular macrocycles exhibit excellent host-guest properties,while inorganic nanoparticles possess unique magnetic,thermal or optical properties.Therefore,supramolecular macrocycle modified inorganic nanoparticles have been endowed with more fascinating characteristics and their applications have been greatly expanded.At present,the reported composite nanoparticles including phosphatepillarenes modified Fe₃O₄ nanoparticles,carboxylatepillarenes stabilized Au nanoparticles,carboxylatepillarenes functionalized CuS nanoparticles and so on,have played important roles in cancer treatment,biological imaging,pesticide detection and other applications.However,very few researches have been reported on the introduction of pillarenes into upconversion nanomaterials based on rare earth metals.Thus,we constructed a new pH-responsive drug delivery system（DDS）based on phosphoryl-functionalized pillar[5]arenes modified upconversion nanoparticles（UCNPs）for controlled cargo release and cell imaging for the first time.The main research contents are summarized as follows:（1）To obtain nanoparticles that are colloidally stable,we synthesized two kinds of pillarenes（2C-PP5/4C-PP5）with different lengths of alkyl groups containing five phosphoryl groups on each rim of the cavity with good water dispersity and thendecorated them,respectively,onto the surfaces ofβ-NaYF₄:Yb/Er nanoparticles（OA-UCNPs）via a ligand-exchange method to afford the PP5-stabilized UCNPs,namely,2C-PP5-UCNPs and 4C-PP5-UCNPs.Considering the similar properties of2C-PP5-UCNPs and 4C-PP5-UCNPs,we selected 4C-PP5-UCNPs for the subsequent experiments,which were comparatively easier to prepare.The asprepared4C-PP5-UCNPs possessed an average particle size of 31.4±4.2 nm with good water dispersity.After ligand exchange,4C-PP5-UCNPs showed almost the same peak patterns of PXRD as OA-UCNPs and the FT-IR spectra did not exhibit any carboxylate anion peaks originating from the octadecyl of oleic acid,but instead clearly showed peaks corresponding to the phosphoryl coordination instead.Moreover,with the increase of the pH value,4C-PP5-UCNPs gradually became dispersible in aqueous media and emitted bright green light under near infrared light（NIR）irradiation.The successful preparation of the monomer 1,4-（phosphonic acid）butoxybenzene（M3）stabilized UCNPs（M3-UCNPs）further demonstrated that phosphoryl plays a crucial role in the ligand exchange process.（2）As a proof-of-concept,rhodamine B（RhB）and 5-aminosalicylic（5-ASA）in its acid hydrochloride salt form were employed as model compounds to be loaded into the nanomaterials via host-guest interactions and electrostatic forces,leading to the formationofapH-responsivecontrolledreleasenanosystem,i.e.,4C-PP5-UCNPs@RhB and 4C-PP5-UCNPs@5-ASA.The fluorescence titrations were performed at 298 K in PBS（pH 5.0 and 7.4）to quantitatively measure the binding of RhB and 5-ASA with 4C-PP5 and the K_a values at pH 7.4 were smaller than the K_a values at pH 5.0.We simulated the different pH environments of the gastrointestinal tract to study the release process of RhB cargo,which include pH 1.9（stomach）,5.0（small intestine）and 7.4（colon）,respectively.The amount of RhB released from 4C-PP5-UCNPs@RhB reached 72%within 90 min at pH 7.4,while less than 17%and 2%within the same length of time at pH 5.0 and 1.9,respectively.（3）Macrophages and human L02 hepatocytes（L02 cells）were chosen to explore the biocompatibility of 4C-PP5-UCNPs.Compared with the control group,the cell viabilities of 4C-PP5-UCNPs groups were more than 85%on both macrophages and L02 cells even at a high concentration of 125μg/mL,indicating that 4C-PP5-UCNPs have good biocompatibility.Next,the results of upconversion luminescence（UCL）cell imaging investigation of 4C-PP5-UCNPs,4C-PP5-UCNPs@RhB and4C-PP5-UCNPs@5-ASA showed that all these three kinds of nanoparticles can be taken up to the cytoplasm and emit bright green fluorescence under the excitation of a980 nm laser.As we expected,4C-PP5-UCNPs were proven to be a promising candidate for high-contrast intracellular fluorescence imaging.