Fabrication of quantum dot/silica core–shell particles immobilizing Au nanoparticles and their dual imaging functions

The present work proposes preparation methods for quantum dot/silica (QD/SiO₂) core–shell particles that immobilize Au nanoparticles (QD/SiO₂/Au). A colloid solution of QD/SiO₂ core–shell particles with an average size of 47.0 ± 6.1 nm was prepared by a sol–gel reaction of tetraethyl orthosilicate in the presence of the QDs with an average size of 10.3 ± 2.1 nm. A colloid solution of Au nanoparticles with an average size of 17.9 ± 1.3 nm was prepared by reducing Au³⁺ ions with sodium citrate in water at 80 °C. Introduction of amino groups to QD/SiO₂ particle surfaces was performed using (3-aminopropyl)-triethoxysilane (QD/SiO₂-NH₂). The QD/SiO₂/Au particles were fabricated by mixing the Au particle colloid solution and the QD/SiO₂-NH₂ particle colloid solution. Values of radiant efficiency and computed tomography for the QD/SiO₂/Au particle colloid solution were 2.23 × 10⁷ (p/s/cm²/sr)/(μW/cm²) at a QD concentration of 8 × 10⁻⁷ M and 1180 ± 314 Hounsfield units and an Au concentration of 5.4 × 10⁻² M. The QD/SiO₂/Au particle colloid solution was injected into a mouse chest wall. Fluorescence emitted from the colloid solution could be detected on the skin covering the chest wall. The colloid solution could also be X-ray-imaged in the chest wall. Consequently, the QD/SiO₂/Au particle colloid solution was found to have dual functions, i.e., fluorescence emission and X-ray absorption in vivo, which makes the colloid solution suitable to function as a contrast agent for dual imaging processes.