Synthesis And Properties Of Curcumin/Silica Composite Particles

Curcumin(cur)has widespread applications in food and drug,fluorescence imaging,ion detection,photodynamic therapy and other fields because of its various biological activities and unique optical properties.Curcumin has low bioavailability due to its good solubility in organic solvents,but low solubility in water.Curcumin can be deprotonated under strong alkaline conditions,which can improve its solubility in water,but the stability of deprotonated curcumin is poor,which is insufficient to meet the needs of practical application.Incorporating curcumin into colloidal particles with good dispersion in water can improve its dispersibility in water and effectively improve its stability.Silica particles are an ideal type of carrier for curcumin due to their good biocompatibility and chemical/colloidal stability.Using ammonia to catalyze the hydrolysis and condensation of tetraethylorthosilicate(TEOS)in an ethanol/water mixture,known as the Stober method,is currently one of the most commonly used methods for preparing silica particles.In this reaction system,curcumin is difficult to be incorporated into silica particles due to electrostatic repulsion between the negatively charged silica particles and curcumin.To solve this problem,we introduced the surfactant hexadecyltrimethylammonium bromide(CTAB),which can interact with curcumin and silica simultaneously.We systematically studied the effect of ammonia and CTAB on the deprotonated and dissolution or dispersion process of curcumin,and the growth of silica particles in the ethanol/water mixture.It is expected to realize the high loading efficient and effective protection of curcumin by silica particles,which can provide the experimental basis for the development and utilization of curcumin.Firstly,we conducted a systematic study on the deprotonation and dissolution/dispersion process of curcumin with different concentrations of ammonia and CTAB in ethanol/water mixture.It was found that with the increase of ammonia concentration,curcumin gradually undergoes deprotonation,and its dissolution/dispersion ability is adequate,but its stability decreased significantly.The addition of CTAB can promote the deprotonation process of curcumin to a certain extent,and inhibit its protonation process to a certain extent.When the concentration of CTAB in the solution is higher than its critical micelle concentration(CMC),curcumin can be dispersed into the hydrophobic area of micelles,which can improve its dispersibility and stability.Adding TEOS to a curcumin ethanol/water mixture containing appropriate concentrations of ammonia and CTAB can realize in-situ growth of silica particles,thus curcumin can be incorporated into silica particles with the assist of CTAB.It was found that with the increase of CTAB concentration in the solution,the morphology of the particles gradually evolved from spherical to ellipsoidal,and the loading efficiency of curcumin increased first and then decreased.Under the optimized reaction conditions,the loading efficiency of curcumin in silica particles can be as high as 93%.After being incorporated into silica particles,the stability and luminous efficiency of curcumin have been significantly improved.Compared with CTAB micelle-loaded curcumin,curcumin loaded in the silica particles is more sensitive to copper ions.CTAB micelles were firstly into silica particles,and then the particles were added into curcumin solution to further regulate the incorporation of curcumin.By changing the concentration of CTAB,we can obtain silica particles in which CTAB micelles exist in two different forms: quasi-crystalline phase and amorphous phase.It is found that both two kinds of silica particles with different microenvironments can achieve efficient and rapid incorporation of curcumin and improve its stability.Compared with curcumin in the amorphous microenvironment,curcumin in the quasi crystalline microenvironment is more sensitive to copper ions.The above-mentioned two kinds of silica particles with different microenvironments can also achieve high loading efficiency of different dyes.The silica particles incorporated with curcumin and fluorescein can exhibit multicolor emission based on the excited state resonance energy transfer between curcumin and fluorescein.This kind of multicolor particle can monitor environmental pH and copper ion concentration through fluorescence intensity and emission color,which provides a foundation for the application of curcumin in high-throughput visual detection.