**Loading Graphene Quantum Dots into Optical-Magneto Nanoparticles for Real-Time Tracking** *In Vivo*

**Yu Wang 1,2, Nan Xu 1,2, Yongkai He 1,2,3, Jingyun Wang 4, Dan Wang 1,2, Qin Gao 1,2, Siyu Xie 1,2, Yage Li 1,2, Ranran Zhang 3,\* and Qiang Cai 1,2,3,\***


Received: 21 May 2019; Accepted: 3 July 2019; Published: 8 July 2019

**Abstract:** Fluorescence imaging o ffers a new approach to visualize real-time details on a cellular level *in vitro* and *in vivo* without radioactive damage. Poor light stability of organic fluorescent dyes makes long-term imaging di fficult. Due to their outstanding optical properties and unique structural features, graphene quantum dots (GQDs) are promising in the field of imaging for real-time tracking *in vivo*. At present, GQDs are mainly loaded on the surface of nanoparticles. In this study, we developed an e fficient and convenient one-pot method to load GQDs into nanoparticles, leading to longer metabolic processes in blood and increased delivery of GQDs to tumors. Optical-magneto ferroferric oxide@polypyrrole (Fe3O4@PPy) core-shell nanoparticles were chosen for their potential use in cancer therapy. The *in vivo* results demonstrated that by loading GQDs, it was possible to monitor the distribution and metabolism of nanoparticles. This study provided new insights into the application of GQDs in long-term *in vivo* real-time tracking.

**Keywords:** GQDs; real-time tracking; optical-magneto nanoparticles; *in vivo*
