Application of Gadolinium-Doped Zinc Oxide Quantum Dots for Magnetic Resonance and Fluorescence Imaging

Abstract

Although the fluorescence imaging (FI) technique has high sensitivity, its penetration capability is very limited. In contrast, magnetic resonance imaging (MRI) has deep tissue penetration but low sensitivity. Thus, more available and accurate diagnostic information can be anticipated after combination of FI with MRI. However, currently existent methods for the fabrication of MRI-FI nanoprobes are complex, and the resultant MRI-FI nanoprobes have many disadvantages such as high toxicity, large particle size, or low relaxivity and quantum yield. To address these issues, we described in this chapter a straightforward and versatile method to develop MRI-FI dual modality nanoprobes by doping Gd3+ ions in low toxic ZnO quantum dots (QDs). The resultant Gd-doped ZnO QDs are ultrasmall in size and have enhanced fluorescence resulting from the Gd doping. In vitro experiments confirm that Gd-doped ZnO QDs can successfully label the HeLa cells in short time and present no evidence of toxicity or adverse effects on cell growth. Besides, they exert a strong positive contrast effect with a large longitudinal relaxivity much higher than that of Gd-based clinical MRI contrast agent.