Size Control Synthesis of Melanin-Like Polydopamine Nanoparticles by Tuning Radicals

As synthetic mimics of naturally occurring melanins, polydopamine nanoparticles (PDA NPs) have been investigated extensively as efficient antioxidant and photothermal therapeutics. Unlike the widely adopted PDA coatings, the fabrication approaches for the convenient and critical control of NP size are still limited and new methods are highly desirable. Herein, we report the first effort to control the size of the formed PDA NPs via adding either strong free radical scavengers (i.e. edaravone) or stable free radicals (i.e. PTIO˙) during the polymerization. The results revealed that the former method could mostly inhibit the NP growth while the latter one mainly facilitated the seed formation process, both resulting in a decrease of NP size. We also found that the photothermal effect and free radical scavenging activity of PDA NPs are influenced by NP size which can be facilely tuned by free-radical mediated synthetic strategies. We believe that this work not only aids in the understanding of the fundamentals of dopamine polymerization but also provides a new methodology for fabricating PDA-based synthetic melanins with critically controlled NP properties.