Abstract
Porous silicon (pSi) microparticles obtained by porosification of crystalline silicon wafers have unique optical properties that, together with biodegradability, biocompatibility and absence of immunogenicity, are fundamental characteristics to candidate them as tracers in optical imaging techniques and as drug carriers. In this work, we focus on the possibility to track down the pSi microparticles also by MRI (magnetic resonance imaging), thus realizing a comprehensive tool for theranostic applications, i.e., the combination of therapy and diagnostics. We have developed and tested an easy, quick and low-cost protocol to infiltrate the COOH-functionalized pSi microparticles pores (tens of nanometers about) with magnetic nanospheres (SPIONs—Super Paramagnetic Iron Oxide Nanoparticles, about 5–7 nm) and allow an electrostatic interaction. The structural properties and the elemental composition were investigated by electron microscopy techniques coupled to elemental analysis to demonstrate the effective attachment of the SPIONs along the pores’ surface of the pSi microparticles. The magnetic properties were investigated under an external magnetic field to determine the relaxivity properties of the material and resulting in an alteration of the relaxivity of water due to the SPIONs presence, clearly demonstrating the effectiveness of the easy functionalization protocol proposed.
Highlights
Porous silicon is a sponge-like material photoluminescent at room temperature. [1] Its distinctive properties make this material a promising tool for theranostics, i.e., the union of therapy and diagnostics. [2] it is biocompatible: [3] it degrades into silicic acids that kidneys are able to secrete, and it is neither toxic for the cells nor activator of the immune system
Porous silicon is produced from crystalline silicon by a cheap and simple fabrication process, i.e., electrochemical etching in acid solution, resulting in pSi microparticles with photoluminescence (PL) in the orange-red portion of the visible spectrum [10,11] due to the quantum confinement effect
[12] The electrochemical etching produces pores on the silicon wafer surface, whose dimensions are adjustable with the etching parameters: in our optimized procedure, the pores are around 20–30 nm. [13] A hydrosilylation procedure is sufficient to stabilize the pSi microparticles for years in ethanol
Summary
Porous silicon (pSi) is a sponge-like material photoluminescent at room temperature. [1] Its distinctive properties make this material a promising tool for theranostics, i.e., the union of therapy and diagnostics. [2] it is biocompatible: [3] it degrades into silicic acids that kidneys are able to secrete, and it is neither toxic for the cells nor activator of the immune system. The magnetic pSi microparticles are drug loaded and delivered under the guidance of a magnetic field In the latter, the magnetite NPs were anchored on the mesoporous silica nanoparticles by a boronate esters linker, to produce a pH-responsive tool for targeted delivery to low pH tissues. The structural and magnetic results of this experimental work clearly show that, by means of an easy (just chemical mixing in a simple bucket), fast (only few minutes) and cheap (very inexpensive reagents: less than 80 euro-cents per mg) chemical protocol, based on the use of cyclohexane diamine (a small molecule that bears two positively charged groups) without the need of any oxidation steps, it is possible to get luminescent pSi microparticles infiltrated with SPIONs, which could be loaded in large quantity and electrostatically attached to the surface of the functionalized pSi pores. In our approach, the photoluminescence of the functionalized pSi infiltrate with SPIONs is completely maintained
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