Latex-templated Synthesis Of Silica Hybrid Nanoparticles With Porous Shell Used For Drug Delivery And Catalysis

The controlled synthesis and applications of core-shell SiO₂@polymer hybrid nanoparticles（NPs）have gained extensive attention due to their tunable chemical and physical properties and excellent biocompatibility.Template-directed synthetic approaches are commonly employed to construct the core-shell SiO₂@polymer hybrid NPs.Templating methods offer a number of advantages.The size and morphology of hybrid silica NPs can be easily tunable by selecting different templates and adjusting the reaction parameters,which guarantee the complete compound between silica and the organic components.Further,calcination or chemical dissolution is neccessry to remove the polymer core,and the obtained hollow SiO₂ structures promise great encapsulation of fluorescent molecules and active agents in the core domain for imading,catalysis and delivery,with higher loading-capacity than a porous silica solid nanoparticles.Here poly（methacryloyloxyethyl trimethyl ammonium chloride）（pDMC）was selected to incorpate to the surfaces of polystyrene（pSt）latex templates.The pDMC chains were anchored around the surfaces of pSt cores to provide:（1）good dispersion property derived from pDMC hydrophic nature;（2）staticelectronic interaction between pDMC and negatively-charged silanolate promotes the in situ deposition of silica.The core-shell pSt-co-pDMC@SiO₂ hybrid nanoparticles had been facilely synthesized via latex templating in aqueous media at room temperature,which avoided the usage of elevated temperature or extreme pH,or involved chemicals.And non-templated silica was obtained.The combined determination of scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and danymic light scattering（DLS）confirmed that the distinct core-shell structure of pSt-co-pDMC@SiO₂ hybrid NPs had been formed,and the diameter of hybrid nanoparticles increased significantly compared with latex templates.The silica deposition mainly took place at surfaces of latex templates to form raspberry-like silica shell.And the shell thickness and morphology of pSt-co-pDMC@SiO₂ hybrid NPs could be turned by adjusting the reaction parameters,such as DMC concentration,TMOS amount and reaction time.With the increase of DMC concentration,the surfaces of pSt-co-pDMC@SiO₂ hybrid NPs became rough and irregular,the typical ball-like morphology changed to strawberry-like.The thickness of pSt-co-pDMC@SiO₂ hybrid NPs increased by increasing TMOS concentration,however,the colloidal dispersibility of silica hybrid nanoparticles became worse and small aggregations had been obseved.Prolonging reaction time led to the increase of thickness of silica shell.Calcination treatment of the as-synthesized SiO₂ hybrid NPs led to the removal of the scarified polymer core to obtain the hollow silica NPs（HSiO₂s）with porous shell.Nitrogen adsorption desorption plots showed that the average pore diameter of the porous silica shell was around 3.68nm.The interior cavity of HSiO₂s particles could be served as resevior to encapsulate catalyst,drug and other active molecules.Aspirin had been adopted as the loading drug into the cavity of HSiO₂s to investigate their in vitro drug-release behavior under different pH conditions.The drug release profile of HSiO₂@Asprin nanocapsules at 37℃ revealed that HSiO₂s equipped sustained release function and acid environment stimulated the HSiO₂@Asprin nanocapsules to fastly release drugs,which was important for minimized pre-mature release.The surfaces of SiO₂ NPs can be easily modified and functionalized due to the abundent silicon hydroxyl groups.HSiO₂s were firstly reacted with ATPES to generate the SiO₂-NH₂ NPs.The reducing role of the-NH₂ groups were confirmed by the direct reaction of HAuCl₄ to achieve separated gold NPs with diameter of 5 nm on the silica surfaces.The catalytic properties of the SiO₂@Au nano-composites were evaluated in the reduction reaction of 2-nitroaniline,showing the higher reaction rate constant of about 7.06×10-3 s-1 than that of pure Au NPs sol.And no significant decrease of conversion was observed after four-times experiments cyclation.It is believed that the constructing process of the SiO₂@Au nano-composites features many implications for creating other functional nano-composites.