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Xiangya School of Pharmaceutical Sciences, Central South University
Keywords: polydopamine, nanomaterial surfaces and interfaces, metal-ion coordination, DNA
Dopamine (DA) is a neurotransmitter that can undergo oxidative self-polymerization under certain conditions to form polydopamine (PDA), as shown in Figure 1. As early as 2007, the Messersmith group reported that PDA could form a shell on almost any solid material surface [1]. Since then, PDA shells have been widely used in fields such as cellular internalization, soft lithography, biocompatible surface modification, nanomaterial detoxification, nanomaterial functionalization, interface science, sensing and catalysis [2, 3].
Figure 1: A schematic of DA self-polymerization into PDA and a local view of PDA coating a nanoparticle.
Like the adhesive proteins secreted by mussels to anchor themselves, PDA, which contains many catechol structures, has exceptionally strong adhesion. PDA uses this adhesion to coat nanoparticles, forming a “nanocoat” that gives the particles PDA's properties. Catechol structures give the nanoparticles a negative charge, and strong electrostatic repulsion makes PDA-coated nanoparticles highly stable. Catechol groups also act as strong ligands for multivalent metal ions, including iron, zinc, copper, cerium and gadolinium ions. Thus, through metal-ion coordination, PDA can indirectly bind other molecules, such as drugs [4] and DNA [5].
PDA contains reactive double bonds that can undergo chemical reactions with several groups, such as amino groups (-NH2) and thiol groups (-SH) [6]. Molecules containing thiol groups can therefore be attached to the PDA shell, further functionalizing the nanoparticles. In addition, large amounts of thiol-containing compounds can cause PDA shells to degrade. For example, after PDA-coated nanoparticles enter cells, intracellular glutathione can degrade their shells.
Structural fragments of PDA form conjugated systems rich in π-electron clouds. These can form π–π interactions with other molecules containing π systems, thereby binding small molecules [7]. For example, PDA-coated nanoparticles have a high loading capacity for the chemotherapy drug doxorubicin.
The PDA-shell-based “nanocoat” therefore has broad potential applications in biomedicine and nanomaterials.
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References:[1] Lee, H., et al., Mussel-Inspired Surface Chemistry for Multifunctional Coatings. Science, 2007. 318(5849): p. 426-430.
[2] Hong, S., et al., Non-Covalent Self-Assembly and Covalent Polymerization Co-Contribute to Polydopamine Formation. Advanced Functional Materials, 2012. 22(22): p. 4711-4717.
[3] Liu, Y., K. Ai, and L. Lu, Polydopamine and its derivative materials: synthesis and promising applications in energy, environmental, and biomedical fields. Chemical Reviews, 2014. 114(9): p. 5057-5115.
[4] Zheng, X., et al., Polydopamine Coatings in Confined Nanopore Space: Toward Improved Retention and Release of Hydrophilic Cargo. Journal of Physical Chemistry C, 2016. 119(43): p. 24512–24521.
[5] Meng, Y., et al., Bioorthogonal DNA Adsorption on Polydopamine Nanoparticles Mediated by Metal Coordination for Highly Robust Sensing in Serum and Living Cells. ACS Nano, 2018, DOI: 10.1021/acsnano.8b03019.
[6] Cho, H.J., et al., Effective Immobilization of BMP-2 Mediated by Polydopamine Coating on Biodegradable Nanofibers for Enhanced in Vivo Bone Formation. Acs Applied Materials & Interfaces, 2015. 6(14): p. 11225-11235.
[7] Zheng, X., et al., Silica-assisted incorporation of polydopamine into the framework of porous nanocarriers by a facile one-pot synthesis. Journal of Materials Chemistry B, 2016. 4(14): p. 2435-2443.
