Carboxyl functionalization of ultrasmall luminescent silicon nanoparticles through thermal hydrosilylation

Functionalization of ultrasmall semiconductor nanoparticles to develop new luminescent probes that are optically bright, stable in aqueous environments, and sized comparably to small organic fluorophores would be of considerable utility for myriad applications in biology. Here, we report one of the first examples of thermal hydrosilylation between a bi-functional alkene and ultrasmall (∼1 nm) H-passivated silicon nanoparticles (Si-np-H) to prepare strongly luminescent, water stable, carboxyl functionalized nanoparticles (Si-np-COOH). Nuclear magnetic resonance, infrared absorption spectroscopy (FTIR), size exclusion chromatography (SEC), and photoluminescence spectroscopy are used to characterize the Si-np dispersions. Based on the SEC and FTIR data, a reaction scheme is proposed to account for side products formed through a free radical cross-linking mechanism. The Si-np-COOH may find use in applications such as biomolecular labeling and biological imaging.