Hydrophilic Luminescent Silicon Nanoparticles in Steric Colloidal Solutions: Their Size, Agglomeration, and Toxicity

Abstract

Luminescent silicon nanoparticles are promising for intracellular biological research as luminescent probe for in vitro and in vivo studies. We prepared nanoclusters of hydrophilic highly porous silicon having the size around 100 nm, composed of nanocrystals ∼2.5 nm in size, by electrochemical etching. Colloidal suspensions of the nanoparticles in steric organics (bovine serum albumin (BSA), glutamic acid, dextran, and glycine) were prepared to attempt to stabilize the nanoparticles and prevent their further agglomeration. The zeta potential differs from sample to sample – BSA and glycine solutions have zeta potential between −30 and −40 mV indicating good stability of nanoparticles in the solutions, while the zeta potentials of water (−24 mV), dextran (−10 mV), and glutamic acid (−14 mV) are showing that nanoparticles tend to agglomerate. Strong orange luminescence of nanoparticles is situated between 600 and 700 nm and remains stable in all used organic colloidal solutions. Performed study of in vitro toxicity revealed that sterically stabilized silicon nanoparticles are cytotoxic only at the highest used concentration (500 μg ml−1) of the silicon nanoparticles in water and BSA. Only in the case of glycine a significant decrease of the cell viability was observed already at a lower concentration of 250 μg ml−1 and is caused probably by glycine itself.