Agglomeration of Luminescent Porous Silicon Nanoparticles in Colloidal Solutions.

Kateřina Herynková,Miroslav Šlechta,Anna Fučíková,Petra Šimáková,Ondřej Cibulka

doi:10.1186/s11671-016-1593-4

Abstract

We have prepared colloidal solutions of clusters composed from porous silicon nanoparticles in methanol, water and phosphate-buffered saline (PBS). Even if the size of the nanoclusters is between 60 and 500 nm, due to their highly porous “cauliflower”-like structure, the porous silicon nanoparticles are composed of interconnected nanocrystals having around 2.5 nm in size and showing strong visible luminescence in the orange-red spectral region (centred at 600–700 nm). Hydrophilic behaviour and good solubility of the nanoclusters in water and water-based solutions were obtained by adding hydrogen peroxide into the etching solution during preparation and 16 min long after-bath in hydrogen peroxide. By simple filtration of the solutions with syringe filters, we have extracted smaller nanoclusters with sizes of approx. 60–70 nm; however, these nanoclusters in water and PBS solution (pH neutral) are prone to agglomeration, as was confirmed by zeta potential measurements. When the samples were left at ambient conditions for several weeks, the typical nanocluster size increased to approx. 330–400 nm and then remained stable. However, both freshly filtered and aged samples (with agglomerated porous silicon nanoparticles) of porous silicon in water and PBS solutions can be further used for biological studies or as luminescent markers in living cells.

Highlights

Nanocrystalline silicon has been studied for the 20 years due its potential use in silicon nanophotonics or for enhancing solar energy conversion [1] and in biological and medical applications
Silicon nanoparticles extracted from highly porous silicon (Si-ncs) showing visible room-temperature luminescence have been suggested to be used, e.g. as fluorescent labels, biological sensors, photoresponsive systems for regulated drug delivery or scaffold for various tissues [2–5]
We report on colloidal solutions of Si-ncs in methanol, water and phosphate-buffered saline (PBS)

Summary

Introduction

Nanocrystalline silicon has been studied for the 20 years due its potential use in silicon nanophotonics or for enhancing solar energy conversion [1] and in biological and medical applications. For biological in vivo studies, perhaps even for the use of silicon nanoparticles for controlled drug delivery, suitable samples are colloidal solutions in water-based (non-toxic) or isotonic solvents such as phosphate-buffered saline (PBS); alcohol solutions in methanol or ethanol must be strongly diluted because of their toxicity for living cells. The Si-ncs have to be hydrophilic ( soluble in water) and stable in time, without any agglomeration tendency. Methanol was used for comparison and easy solubility of the Si-ncs in it; an intentional solvent was PBS because it is a non-toxic and isotonic buffer solution commonly used in biological research and medicine. Hydrophilic oxidized Si-ncs tend to agglomerate due to their physical properties, such as zeta potential, but it is relatively a long process, it takes its course in the time interval of several weeks

Methods

Results

Conclusion