The development of quantum dot/silica particles for fluorescence imaging and medical diagnostics

This chapter introduces our study on development of core-shell silica particles containing quantum dot (QD) for fluorescence imaging and medical diagnostics and is composed of six sections. The first section is Introduction. The second section describes development of methods for preparing colloid solutions of core-shell particles composed of core of nanoparticles and shell of silica. Two types of methods, both of which are sol-gel methods using raw chemicals such as sodium silicate solution and silicon alkoxide, were successfully performed for silica coating of the nanoparticles. For the method using the silicon alkoxide, an amine-free method, or a method without amine that is usually used as a catalyst for the sol-gel method, could be also developed. The third section describes fabrication of core-shell particles containing QD. QD/silica core-shell particles (QD/SiO₂), multilayered core-shell particles composed of QD, silica (inner silica shell), gadolinium compounds (GdC) and silica (outer silica shell) (QD/SiO₂/GdC/SiO₂), and QD/SiO₂ particles with immobilized Au nanoparticles (QD/SiO₂/Au) were fabricated by using our amine-free method. The fourth section describes an effect of silica shell on photostability of QD. The silica shell was rigid enough to prevent O₂ molecules from reaching surfaces of the QD, which maintained their photostability. In addition, the silica shell produced from silicon alkoxide stabilized their photo-property more effectively. The fifth section describes fluorescence imaging techniques using the core-shell particles containing QD. Various tissues in mouse could be imaged by detecting fluorescence emitted from the QD/SiO₂ particle colloid solutions with an in vivo imaging system (IVIS). The QD/SiO₂/GdC/SiO₂ particle colloid solution simultaneously functioned as a fluorescent marker and high-contrast MRI agent. The colloid solution of QD/SiO₂/Au particles functioned as a contrast agent for dual imaging processes based on fluorescence and X-ray absorption. The last section is on Conclusion.