Untemplated Resveratrol-Mediated Polydopamine Nanocapsule Formation

Nanocapsules can be designed for applications including drug delivery, catalysis, and biological imaging. The mussel-inspired material polydopamine is a promising shell layer for nanocapsules because of its free radical scavenging capacity, ability to react with a broad range of functional molecules, lack of toxicity, and biodegradability. Previous reports of polydopamine nanocapsule formation have relied on a templating approach. Herein, we report a template-free approach to polydopamine nanocapsule formation in the presence of resveratrol, a naturally occurring anti-inflammatory and antioxidant compound found in red wine and grapes. Synthesis of nanocapsules occurs spontaneously in an ethanolic resveratrol/dopamine·HCl solution at pH 8.5. UV-vis absorbance spectroscopy and X-ray photoelectron spectroscopy indicate that resveratrol is incorporated into the nanocapsules. We also observed the formation of a soluble fluorescent dopamine-resveratrol adduct during synthesis, which was identified by high-performance liquid chromatography, UV-vis spectroscopy, and electrospray ionization mass spectrometry. Using transmission electron microscopy and dynamic light scattering, we studied the influence of solvent composition, dopamine concentration, and resveratrol/dopamine ratio on the nanocapsule diameter and shell thickness. The resulting nanocapsules have excellent free radical scavenging activity as measured by a 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay. Our work provides a convenient pathway by which resveratrol, and possibly other hydrophobic bioactive compounds, may be encapsulated within polydopamine nanocapsules.