Nano Suspension of Porous Silicon in Water: Two Methods of Material Preparation and Modification by Surfactants

Abstract

Luminescent silicon nanocrystals (Si-nc) are promising material for biomedical purposes. However, as-prepared Si-nc are H-terminated and not miscible with biological (aqueous) liquids. We used physical and chemical adsorption of undecylenic acid to make porous silicon (porSi, material containing Si-nc assemblies) miscible with water solutions. PorSi powders prepared by two different methods, electrochemical anodization and stain etching were modified and suspended in water. Luminescent properties of aqueous suspensions have been then monitored for long time. The many- fold buildup of initial luminescence intensity during the first 3-6 days has been observed for electrochemically prepared porSi material. This phenomenon was explained as disaggregating of the primary micelles formed from surfactant- covered porSi particles into smaller ones. Contrary to this, the stain etched porSi powder exhibited a continuous decrease of the luminescence intensity with time and, moreover, was much less luminescent. Thus, electrochemically prepared porSi is found more appropriate for photosensitizing biomedical applications.