Highly Efficient Preparation,Size Control And Biomedical Applications Of Organic Functional Molecules@ZIF-8 Composite Nanoparticles

Zeolitic imidazolate framework-8(ZIF-8),one type of porous materials,is constructed from zinc ions and 2-methylimidazole via coordination reaction.Besides the advantages of large surface area,high porosity,good thermal stability and easy surface modification,ZIF-8 nanoparticles also have the distinct characteristics of acid sensitivity,good biocompatibility and low cytotoxicity.Based on these numerous advantages,ZIF-8 nanoparticles show a promising application in biomedicine.In recent years,with the development of molecular imaging and its related technology,the near infrared fluorescence imaging technique has captured growing attention in the field of tumor diagnosis.In addition,the chemotherapy as an important traditional treatment and the emerging photothermal therapy methods are both the research hot areas in the field of cancer therapy.Based on the above-mentioned description,the construction of multifunctional ZIF-8 composites via loading near-infrared fluorescent dyes and anticancer drugs into the pores of the ZIF-8 structure,are of great significance for early diagnosis,efficient treatment and curative effect monitoring of tumor.However,it is rarely reported to construct the integrated ZIF-8 nanocarriers encapsulated with near-infrared fluorescent dyes and anticancer drugs for tumor theranostic.For the purpose of long-term blood circulation and targeted therapy in biomedical applications,the nanocarriers are generally required to be size controllable and highly uniform.Nevertheless,the traditional synthesis methods of ZIF-8 nanoparticle exist some limitations,for example,the size of as-prepared particle is relatively large in the aqueous phase while the organic phase method prolongs the synthesis time and is not easy to load water-soluble functional molecules into the particles.In order to overcome the disadvantages of the traditional methods,meanwhile combine the high efficiency of aqueous phase and size-uniformity of organic phase,For the first time,an organic solvent-assisted one-step approach was proposed to prepare ZIF-8 nanoparticles with uniform particle size in dimethyl sulfoxide/water mixed solvent system.Furthermore,a variety of organic functional molecules with different properties,including hydrophobic near-infrared fluorescent dye Cyanine5.5(Cy5.5),hydrophilic chemotherapeutic drug doxorubicin(DOX)and photothermal agent indocyanine green(ICG),are loaded into the ZIF-8 structure to efficiently construct multi-functional ZIF-8 composites for tumor diagnostics,and the research of application in biomedical field is subsequently performed.The main conclusions are as follows:In dimethyl sulfoxide/water(DMSO/H₂O)mixed solvent,ZIF-8 nanoparticles with uniform size and regular morphology were synthesized by adjusting the reaction parameters,including the percentage of mixed solvent,the molar ratio of reactant,the growing time and surface modification with amino-dextran.The influences of reaction parameters to morphology and diameters of ZIF-8 nanoparticles were further investigated.The optimum parameters are shown as follows: the volume fraction of DMSO was 35%,the molar ratio of zinc to 2-methylimidazole was 1:36 and the growing time was 1 h.The XRD curves showed that the synthesized nanoparticles have ZIF-8lattice structure;the FTIR spectrum proved the modification of amino-dextran on the surface of ZIF-8 nanoparticles;the nitrogen isothermal adsorption-desorption results confirmed the porous nature and high surface area of ZIF-8 nanoparticles.Furthermore,the dimethyl sulfoxide/water mixed solvent system can be utilized for ZIF-8 in-situ growth on the surface of poly-lysine/magnetic particle composite nanospheres.All the results showed that the dimethyl sulfoxide/water mixed solvent system can be used not only to synthesize ZIF-8 nanoparticles with regular morphology and uniform particle size,but also for the in-situ growth of ZIF-8 shell structure on the surface of organic/inorganic composite nanospheres.Based on the mixed solvent system of dimethyl sulfoxide/water,hydrophobic nearinfrared fluorescent dye Cy5.5,hydrophilic chemotherapeutic drug DOX and photothermal agent ICG were respectively loaded into the ZIF-8 structure to construct functional ZIF-8 composites with uniform size and regular morphology.The morphology characteristics,structural properties and drug loading of the composite nanoparticles prepared by the one-step method proposed in this paper and the two-step method reported in the literature were studied,respectively.The results indicated the advantages of the one-step method in the preparation efficiency and drug-loading efficiency of the composite nanoparticles.Furthermore,a variety of functional molecules were simultaneously encapsulated into the ZIF-8 structure by one-step method to construct multifunctional ZIF-8 composite nanoparticles: Cy5.5&DOX@ZIF-8 composite nanoparticles for tumor near-infrared fluorescence imaging/chemotherapy and Cy5.5&ICG@ZIF-8 composite nanoparticles for tumor near-infrared fluorescence imaging/ photothermal therapy.The fluorescent dye Cy5.5 endowed the composite nanoparticles with near-infrared fluorescence imaging performance.The loading of drug DOX endowed the composite nanoparticles with ability of tumor chemotherapy,and the DOX releasing rate increased with the decrease of environmental p H value due to the acid sensitivity of the ZIF-8 structure.Especially,the DOX releasing rate of Cy5.5&DOX@ZIF-8 composite nanoparticles was as high as about 90% in the environment of p H=4.8,so that the composites can be applied to drug controlled release manipulated by acid environment.The photothermal agent ICG endowed the composite nanoparticles with photothermal conversion property.The results showed that the photothermal property was effectively protected by ZIF-8 crystal structure and the photothermal effect of the composite nanoparticles was positively correlated with the concentration of ICG.Significantly,the photothermal conversion efficiency of Cy5.5&ICG@ZIF-8 reach 27.9%,which met the requirements of tumor photothermal therapy.The low cytotoxicity and high biocompatibility of the synthesized composite nanoparticles were confirmed at the cellular level.The A549 human lung adenocarcinoma cell line was selected for cytotoxicity research using CCK-8 assay and calcein-AM/PI staining.The results showed that the cytotoxicities of pure ZIF-8nanoparticles and Cy5.5@ZIF-8 composites were extremely low in the concentration range of 0⁴00 ?g/m L.while the composite nanoparticles encapsulated with chemotherapeutic drug DOX showed obvious cytotoxicity which was associated with the DOX concentration.The cell viabilities were only 10%¹5% at the concentration of 400?g/m L,indicating that the DOX-loaded composite nanoparticles exerted a significant impact on killing tumor cells.Moreover,the cell viabilities of ICG-loaded composite nanoparticles without near-infrared irradiation were as high as 80⁹0%,while the cell survival rate decreased sharply to 8¹0% after near-infrared irradiation,indicating that the ICG-loaded composite nanoparticles had a significant photothermal therapeutic effect on tumor cells.The flow cytometry and laser confocal microscopy characterization further confirmed that A549 tumor cells could endocytose the ZIF-8 composite nanoparticles encapsulated with Cy5.5,DOX and ICG,which also elucidated the root of the above-mentioned results.The application of multifunctional composite nanoparticles in the diagnosis and treatment of malignant tumors was confirmed at animal level.The in vivo imaging studies show that both Cy5.5&DOX@ZIF-8 and Cy5.5&ICG@ZIF-8 composite nanoparticles can be used for near-infrared fluorescence imaging in A549-bearing nude mice.The composite nanoparticles can be effectively accumulated in tumor site,so that the tumor visualization was realized by near-infrared fluorescence imaging and the fluorescent intensity reached a peak in about 8 hours.Furthermore,the fluorescent intensities of various organs in nude mice indicated that the tumor site showed the strongest fluorescence,which further confirmed the tumor targeting of composite nanoparticles.Moreover,A549-bearing nude mice were injected intravenously with DOX@ZIF-8 and Cy5.5&DOX@ZIF-8 for chemotherapy research,respectively.The results of tumor volume and weight showed that the composite nanoparticles obviously inhibited the growth of tumor cells owing to their effective accumulation in tumor site,and the tumor volume and weight were significantly lower than those in PBS blank group and free DOX group.On the other hand,A549-bearing nude mice were injected intravenously with ICG@ZIF-8 and Cy5.5&ICG@ZIF-8 for photothermal imaging and therapy.As a result,the ICG@ZIF-8 composite nanoparticles enriched at the tumor showed a significant photothermal conversion effect.The tumor volume and weight study showed that ICG@ZIF-8 had an effective photothermal therapy on A549 tumor cells under nearinfrared laser irradiation.Therefore,the Cy5.5&ICG@ZIF-8 composite nanoparticles could achieve the integration of near-infrared fluorescence imaging and photothermal therapy for tumor theranostic.