Stabilization of silicon nanoparticles in colloidal solutions

Silicon nanoparticles, apart from their potential use in optoelectronics or photovoltaics, are very promising also for biological applications. Typical requirements for such nanoparticles used in biological research differ from that for optoelectronics - the aim is to prepare aqueous or isotonic (such as phosphate buffered saline - PBS) colloidal solutions of stable, uniform and strongly luminescing nanoparticles, with sizes suitable for the process of cell endocytosis, ideally in the range of tens to hundreds of nanometers. We have prepared colloidal solutions of luminescing porous silicon nanoparticles (size around 100 nm) obtained by electrochemical etching of silicon wafers. Adding hydrogen peroxide to the etching bath results in oxidized nanoparticle surface and hydrophilic behavior. However, the as-prepared samples agglomerate – the dynamic light scattering revealed the increase of the agglomerates size from 60 nm in fresh samples to 400 nm in one-month-old samples. The tendency to agglomerate was confirmed by zeta-potential measurements. The first attempt to steric stabilization by bovine serum albumin, glycine, glutamic acid and dextran is presented, where the increased stability was observed in the glycine- terminated samples. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)