Core‐Shell Nanospheres with Controllable Zinc Ion Release for Time‐Sensitive Steganography

Slow‐release platforms have attracted much attention due to their many applications, such as biomedical implants, plant fertilizers, and drug delivery systems. In this work, a green, cost‐effective, and scalable method is reported to synthesize colloidal hybrid nanospheres capable of releasing zinc ions in a highly controllable manner by encapsulating zinc ammonium citrate colloids with a layer of silica. The release rate of zinc ions from resulting core‐shell nanospheres can be conveniently tuned by changing the shell thickness and cross‐linking degree of the silica layer, the solvent composition, and the surrounding temperature. By integrating the temperature‐sensitive release behavior of the hybrid nanospheres, the color shift associated with the complexation of zinc ions with xylenol orange, and the photothermal conversion property of gold nanoparticles, a novel film capable of recording time‐sensitive color information is designed using direct laser writing and further demonstrated its application in steganography.