Luminescent porous silicon decorated with iron oxide nanoparticles synthesized by pulsed laser ablation

Abstract

Nanomaterials are playing an increasingly prominent role in recent biomedical applications, particularly due to their promising potential to combine diagnostic and therapeutic functions within a single multifunctional carrier. In this context, intrinsically luminescent silicon nanostructures offer a compelling alternative to conventional fluorophores. Their integration with magnetic nanoparticles could pave the way for the development of a traceable, multimodal platform in the field of nanomedicine. With this objective, we investigated the decoration/infiltration of light-emitting porous silicon (pSi) with iron oxide nanoparticles (FeO_xNPs) synthesized by pulsed laser ablation at two different liquid–gas interfaces: water–air (FeO_xNPs–Air), and water–argon (FeO_xNPs–Ar). This kind of polydispersed NPs are well-suited to filling the wide pore size range of the porous network. Moreover, their intrinsic positive surface charge enables straightforward and direct interaction with negatively charged carboxyl-functionalized porous silicon, without requiring additional surface modifications, chemical agents, or time-consuming intermediate processing steps such as the thermal oxidation or dehydration procedures reported in previous studies. The effectiveness of this simple infiltration/decoration approach—achieved through basic chemical mixing in a standard container—was successfully demonstrated by electron microscopies, Z-potential, optical, and magnetization experiments, which indicate a ferromagnetic behavior of the porous Si FeO_x nanocomposites (pSi + FeO_x NCs). The optical emission properties of the pSi + FeO_x NCs were maintained with respect to the bare ones, although slightly less intense and blue-shifted (about 15 nm), in agreement with the change of radiative lifetime from about 30 μs to 20 μs. Magnetic measurements reveal that pSi + FeO_x NCs obtained using FeO_xNPs synthesized at the air–water interface exhibit a weaker, noisier signal with ∼80 Oe coercivity and lower remanence. Conversely, those produced at the argon–water interface show a stronger magnetic response, with ∼170 Oe coercivity and higher remanence. Notably, the magnetic properties of the Ar-synthesized sample remained stable for months without affecting its intrinsic photoluminescence, offering a stable micro–nano optical and magnetic system for theranostics applications.