One-step hydrothermal synthesis of ultrabright water-soluble silicon nanoparticles for folate-receptor-mediated bioimaging

Fluorescent silicon nanoparticles (SiNPs) exhibiting excellent photostability and colloidal stability and favorable biocompatibility are emerging as novel fluorescent nanoprobes for biological and biomedical imaging. However, studies on the synthesis of highly bright SiNPs and their specific targeted biolabeling are still limited. Herein, we report a facile one-pot hydrothermal approach for the synthesis of ultrabright SiNPs, in which N-[3-(trimethoxysilyl)propyl]ethylenediamine (DAMO) molecules and trisodium citrate acted as silicon precursor and reducing agents, respectively. Remarkably, the prepared SiNPs were small (~ 3.5 nm diameter) and showed ultrahigh photoluminescence quantum yield of 85.2% and long-term stability (in pH range of 4–13 and almost saturated NaCl solution, and at 80 °C). The low cytotoxicity of the resultant SiNPs facilitated conjugation with biomolecules such as folic acid (FA) for bioimaging. The FA-conjugated SiNPs specifically bound receptor-positive HepG2 cells over receptor-negative A549 cells, indicating the potential of these SiNPs as robust bioprobe both in vitro and in vivo.