Ammonium fluoride-catalyzed sol‒gel route for curcumin encapsulation: potential application for pH sensor development

Abstract

Curcumin has potential application as a colorimetric sensor and can be used to monitor the freshness of foods; however, some of its physicochemical properties, such as its solubility and stability, limit its use. In the present work, a natural curcumin extract was incorporated into organic‒inorganic hybrid silica matrices produced by the sol-gel method using ammonium fluoride as the main catalyst. Curcumin was encapsulated in the presence of a series of organosilanes (methytriethoxysilane, octyltriethoxysilane, octadecyltrimethoxysilane and 3-(aminopropyltriethoxysilane); this resulted in a set of hybrid silicas that were characterized by a series of complementary analytical techniques. The immobilization of the compounds in a solid matrix could cause a shift in the maximum absorption bands in the ultraviolet‒visible region due to the interactions between the organic molecules and the solid support. When curcumin was incorporated into silica, a small disturbance in the percentage of cyclic siloxane arrangements was observed. Nitrogen porosimetry demonstrated that the pore structures remained similar to those of the respective matrices; however, significant variation was observed in the porosities of these materials, and the specific areas varied between 211.1 m²g⁻¹ and 551.2 m²g⁻¹. The incorporation of curcumin into different silica matrices improved the performance of the sensors for ammonia detection by up to 3.5 times greater than that obtained by the free compound.

Graphical Abstract