Rough Surface Enhanced Interfacial Synthesis of Core‐Shell Magnetic Fluorescent Microspheres for Enhanced Latent Fingerprint Visualization

Abstract Developing latent fingerprints is extremely significant for personal identification and criminal investigation. Sub‐micrometer core‐shell structured magnetic fluorescent composite which combines the merits of noncontact magnetic responsiveness and strong fluorescence emission is highly desired for the visualization of latent fingerprint on various substrates with high resolutions. However, it remains a great challenge to synthesize uniform magnetic fluorescent composites with well‐defined structure and functionalities due to the uncontrollable heterogeneous growth. Herein, a urea‐assisted rough interface precipitation method is proposed to controllably synthesize uniform core‐shell structured magnetic fluorescent composite microspheres (Fe₃O₄@mesoSiO₂@Y₂O₃:Eu³⁺). The composite microspheres with magnetic core and mesoporous silica shell (Fe₃O₄@mesoSiO₂) possess huge guest‐host interface, numerous nucleation sites, and rough surface morphology, facilitating the efficient adsorption of Y³⁺/Eu³⁺ ions, and further controllable interface deposition of metal (Y, Eu) hydroxides induced by slow release of OH⁻ and CO₃²⁻ anions via the in‐solution decomposition of urea. After subsequent thermal annealing, the obtained Fe₃O₄@mesoSiO₂@Y₂O₃:Eu³⁺ microspheres possess high magnetization for convenient magnetic manipulation, strong fluorescence intensity and negligible quenching effect, enabling a superior performance in latent fingerprint visualization with high contrast and resolution on various substrates.