From rust to riches: phytochemically assisted synthesis of superparamagnetic Fe3O4 nanoparticles with Au for SERS sensing

Abstract

Iron oxide nanoparticles are a prominent choice among applied nanotechnologies, with multiple iterations being FDA-approved therapeutics available to general consumers. While their applications are numerous, their syntheses occasionally involve reagents toxic to the ecosystem and potential human end-users. However, application of natural products to nanoparticle syntheses allows one to traverse these issues. Additionally, recent advances in hybrid nanoparticles have opened the door for possibilities to combine a noble-metal nanoparticle's plasmonic nature with those containing magnetic properties to create magneto-plasmonic materials. The pursuit of these plasmonic and magnetic nanoparticles arises from the emergent properties from the hybrid particle. For example, is the ability to magnetically concentrate the plasmonic nanoparticles to increase SERS intensity, or the ability to apply them for biological imaging and magnetic hyperthermia treatment without needing to use two separate nanoparticles. Here, we describe the synthesis and characterization of hybrid Au/Fe₃O₄ superparamagnetic nanoparticles combining the plasmonic properties of Au with the magnetic properties of Fe₃O₄ to enable surface-enhanced Raman scattering (SERS). We further demonstrate the ability to functionalize these particles with four bioactive compounds: histidine, glutathione, cysteamine, and tiopronin. Lastly, we show the ability to synthesize these magneto-plasmonic nanoparticles (68 emu g⁻¹ magnetic saturation) using locally sourced plant metabolites from the Cercis canadensis, or Eastern redbud, tree. Our SERS measurements indicate the detection of nanogram quantities of an organothiol in solution, and SERS enhancement factors on the order of 10² and 10³ while maintaining magnetic saturations of approximately 30–45 emu g⁻¹ in the presence of Au.