Impact of Iron Incorporation on 2-4 nm Size Silicon Nanoparticles Properties

Iron-containing silicon nanoparticles were synthesized in an attempt to understand the effect of iron on the silicon nanoparticle (SiNP) photoluminescence and singlet-oxygen generation capacity. A wet chemical oxidation procedure of the sodium silicide precursor, obtained from the thermal treatment of a mixture of sodium, silicon, and an iron(III) organic salt under anaerobic conditions, was employed. Surface-oxidized and propylamine-terminated SiNPs were characterized using high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, time-resolved and steady-state photoluminescence, and time-correlated fluorescence anisotropy. On the basis of differences in the morphology, crystal structure, density, and photoluminescence spectrum, two distinct types of SiNPs were identified in a given synthesis batch: iron-free and iron-containing SiNPs. The results show that iron is inhomogeneously incorporated in the SiNPs leading to an efficient photoluminescence quenching. Emission arrives mainly from 2 nm size iron-free SiNPs. The nanoparticles were shown to generate singlet oxygen (1O2) upon 355 nm irradiation, though they were able to quench 1O2. Analysis of cytotoxicity using MTT assay on rat glioma C6 cells showed a strong dependence on the nature of the surface groups, as 100 μg/mL of propylamine-terminated iron-containing SiNPs leads to 85% decrease in cell viability while equal amounts of surface oxidized particles induced a 35% of cell death.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada