A carbon dot based theranostic platform for dual-modal imaging and free radical scavenging

Magnetofluorescent carbon dots (Cdots) doped with both P 3+ and Mn 2+ (abbreviated as PMn@Cdots) have been synthesized in an aqueous solution via a microwave-assisted pyrolysis method. In this system, a P 3+ dopant was introduced to enhance the emission efficiency of the Cdots, while the presence of a Mn 2+ dopant granted magnetic resonance imaging (MRI) capability. To the best of our knowledge, the present work is the first attempt to regulate red-emission and free radical scavenging of PMn@Cdots to serve as a dual-modal imaging nanoprobe and an antioxidant agent. Unlike most red-emitting Cdots, the as-prepared PMn@Cdots can be readily purified from unreacted precursors through antisolvent precipitation instead of by time-consuming purification methods. The whole synthetic procedure is rapid, facile, efficiently reproducible, and scalable. More importantly, further conjugation of the PMn@Cdots with hyaluronic acid (termed PMn@Cdots/HA) gives them good in vivo and in vitro biocompatibility as well as the capability to selectively target CD44-overexpressing cancer cells, as investigated by flow cytometry, fluorescence, and MRI. Meanwhile, PMn@Cdots exhibit antioxidant activity against multiple DPPH, hydroxyl, and superoxide radicals, which is comparable to that for ascorbic acid. Favorably, PMn@Cdots/HA showed a dose-dependent cytoprotective capability against H 2 O 2 -induced oxidative stress in B16F1, HeLa, and HEL cells. Therefore, the Cdot based theranostic platform can simultaneously function as a potential therapeutic candidate and as a dual-modal probe for enabling accurate diagnosis in future clinical applications. Red emitting carbon dots with phosphorus and manganese dopants were explored for synergistic in vitro fluorescence/MR imaging and cytoprotective effects.