Dual-responsive multilayer beads with zero leakage and controlled release triggered by near-infrared light

Abstract

Multilayer beads made from biomacromolecules are useful for encapsulating, protecting, and delivering active ingredients such as drugs, dyes, and proteins. However, their encapsulated cargos are allowed to diffuse slowly out into the surrounding solvent during storage. This study describes a “smart” multilayer bead that can achieve zero leakage for encapsulated materials during storage and controlled release after triggered by near-infrared (NIR) light. The innermost layer of the multilayer bead containing Fe3O4 magnetic nanoparticles is prepared based on the thermal-responsive sol-gel transition of agar, which offers magnetic responsiveness to the bead. The middle layer of the bead embedding gold nanorods (Au NRs) is produced by the ionic crosslinking between alginate and terbium ions. Moreover, encapsulated materials (drugs, dyes, and agrochemicals) are loaded in the middle layer. The outermost layer of the bead, a paraffin-wax shell, is formed at 75 ℃ through the phase transition of paraffin wax. Because of the protection of the paraffin-wax shell, the encapsulated materials present zero leakage when the multilayer bead is placed in aqueous solutions for at least six weeks. Under the irradiation of 808 nm NIR light for 1 min, the multilayer bead is heated up to 50 ℃ by the photothermal effect of Au NRs in the middle layer, which triggers the melting of the paraffin-wax shell. Then, the controlled release of the encapsulated materials can be achieved by the rest of the bead. Furthermore, the bead can be recycled after the release due to its magnetic responsiveness. Consequently, the multilayer bead is a novel, green and economical candidate for diverse applications, especially for the encapsulation and controlled release of hydrophilic materials in bio-related applications.