Silicon Quantum Dot Supraparticles for Fluorescence Bioimaging

We developed a self-limited self-assembly process to produce red-to-near-infrared luminescent supraparticles made from biocompatible silicon (Si) quantum dots (QDs) for fluorescence bioimaging. A starting material is a methanol solution of boron (B) and phosphorus (P) codoped all-inorganic Si QDs. The Si QDs have a heavily B and P codoped amorphous shell, and the shell induces negative potential on the surface, which prevents agglomeration of QDs in polar solvents. By adding toluene to the methanol solution, controlled agglomeration of Si QDs occurs and spherical supraparticles around 100 nm in diameter with a narrow size distribution are grown. The average diameter of supraparticles was controlled by the growth parameters. We also developed a process to stabilize the supraparticles by coating the surface by polyvinylpyrrolidone (PVP) and then by silica. The photoluminescence spectra of PVP- and silica-coated Si QD supraparticles were very similar to those of Si QDs dispersed in solution.