HSA functionalized Gd2O3:Eu3+ nanoparticles as an MRI contrast agent and a potential luminescent probe for Fe3+, Cr3+, and Cu2+ detection in water

Abstract

Polyvinylpyrrolidone (PVP) capped rod-shaped europium (Eu³⁺) doped gadolinium oxide (Gd₂O₃) nanoparticles (PVP@Gd₂O₃:Eu³⁺ NPs) were synthesized by a wet chemical method at 90 °C. NPs were characterised by X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), fluorescence spectroscopy and inductively coupled plasma optical emission spectrometry (ICP-OES). The PVP@Gd₂O₃:Eu³⁺ NP surface was then functionalized with human serum albumin (HSA) to form HSA@PVP@Gd₂O₃:Eu³⁺ NPs. Both PVP@Gd₂O₃:Eu³⁺NPs and HSA@PVP@Gd₂O₃:Eu³⁺ NPs showed strong host sensitized fluorescence in water. The surface functionalization with HSA enhanced the stability of the NPs in both aqueous and biological media. The NPs dispersed in water were highly sensitive towards Fe³⁺, Cr³⁺ and Cu²⁺ ion detection, among various transition and heavy metal ions. The HSA@PVP@Gd₂O₃:Eu³⁺ NPs exhibited almost five times lower detection limit for Fe³⁺, Cr³⁺ and Cu²⁺ ions compared to PVP@Gd₂O₃:Eu³⁺ NPs. PVP@Gd₂O₃:Eu³⁺ NPs were highly selective for a water sample containing >0.667 ppm Fe³⁺, Cu²⁺, and Cr³⁺ ions, while the HSA@PVP@Gd₂O₃:Eu³⁺ NPs at <0.667 ppm were highly selective towards Fe³⁺ ion sensing. The PVP@Gd₂O₃:Eu³⁺ and HSA@PVP@Gd₂O₃:Eu³⁺ NPs were employed as contrast agents in MRI with improved longitudinal relaxivity (r₁) values of 6.96 and 6.15 mM⁻¹ s⁻¹, respectively. These values are higher than that of the commercial contrast agent Magnevists. The Gd₂O₃:Eu³⁺ NPs were capped with PVP and coated with HSA for surface functionalization as a useful MRI contrast agent and for transition metal ion detection.