Gold nanoclusters decorated with magnetic iron oxide nanoparticles for potential multimodal optical/magnetic resonance imaging

Abstract

Efficient nanoprobes for fluorescent and magnetic resonance multimodal imaging (MRI/FI) are in high demand in bioimaging. Herein, a nanoprobe with fluorescent gold nanoclusters (NCs) and magnetic iron oxide composite materials (Fe₃O₄@AuNCs) was prepared for dual bioimaging. The AuNCs were synthesized using the glutathione (GSH) template. The hydrophobic Fe₃O₄ magnetic nanoparticles (MNPs) were capped with cetyltrimethyl ammonium bromide (CTAB) to obtain hydrophilic Fe₃O₄ MNPs. Subsequently, the Fe₃O₄@AuNCs were prepared by the adsorption of Fe₃O₄–CTAB on the GSH–AuNCs through electrostatic attraction. The resultant Fe₃O₄@AuNCs, having an average size of 13.5 nm, can be readily dispersed in water, which displayed a strong red fluorescence (λ_Em = 650 nm) with a quantum yield of 4.3%. Confocal laser scanning microscopy studies proved that the Fe₃O₄@AuNCs have good photostability and low cytotoxicity to 293T cells. The magnetic properties of Fe₃O₄@AuNCs showed that this material was a T₂-based contrast agent for MRI with a transverse relaxivity r₂ of 20.4 mM⁻¹ S⁻¹. Furthermore, the signal intensity of the T₂-weighted MRI decreased with an increase in the concentration. The dual optical and magnetic properties of the synthesized Fe₃O₄@AuNCs were applicable to dual fluorescence and MR-based imaging.