Zn-doped superparamagnetic iron oxide nanoparticles–LCysteine functionalized@N-doped graphene quantum dots as multifunctional contrast agents for dual-model imaging (MRI & FI)

• Zn-SPIONs-L Cys @N-GQDs nanohybrids were designed for dual-modal MRI and FI. • Nanocomposite shows good magnetic and optical properties for biomedical use. • Biocompatibility studies show 73.47 % cell viability at the optimal concentration. • This hybrid nanostructure is a promising agent for multimodal imaging platforms. Recently, multimodal bioimaging approaches have gained more attention for numerous biological applications. In this regard, the combination of superparamagnetic iron oxide nanoparticles (SPIONs) with quantum dots (QDs) seems promising for enhancing imaging sensitivity and specificity, as well as enabling the multiplexing of Magnetic resonance imaging (MRI) and fluorescence imaging (FI). In this research, Zn-doped SPIONs-LCystein@N-doped graphene QD nanohybrids were designed for dual MRI / FI. LCysteine-functionalized core-shell magnetic nanoparticles were synthesized by the co-precipitation method and conjugated to hydrothermally produced N-GQDs. Nanocomposites’ structural and microstructural properties were characterized utilizing numerous methods. Photoluminescence and UV–visible spectroscopy, vibrating sample magnetometer, and MRI relaxometry were used to evaluate the optical and magnetic properties of the nanocomposite. Finally, the MTT assay determined the nanocomposites’ biocompatibility. The results indicate that the nanocomposite exhibits strong emission at 385, 455, and 510 nm when excited with a 300 nm wavelength and has superparamagnetic properties at room temperature (M s = 35.30 emu/g). The r 2 value of the nanocomposite was 13.1 (mmol/l) −1 .s −1 . Biocompatibility assay indicates that 100 µg/mL is the safest quantity for biomedical in vitro applications (73.47 % viability after 72 h incubation). Thus, the resultant nanocomposite is a promising contrast agent with suitable magnetic and optical properties for multimodal imaging.