pubs.acs.org/cm Published on Web 06/29/2009 r 2009 American Chemical Society 3042 Chem. Mater. 2009, 21, 3042–3044 DOI:10.1021/cm901293e Self-Polymerization of Dopamine as a Versatile and Robust Technique to Prepare Polymer Capsules Almar Postma, †,‡ Yan Yan, † Yajun Wang, † Alexander N. Zelikin, † Elvira Tjipto, † and Frank Caruso* ,† † Centre for Nanoscience and Nanotechnology, Department of Chemical and Biomolecular Engineering, The University of Melbourne, Victoria 3010, Australia, and ‡ CSIRO Molecular and Health Technologies, Victoria 3168, Australia Received May 11, 2009 Revised Manuscript Received June 23, 2009 The development of versatile and robust strategies for the formation of polymer capsules is expected to under- pin new advances in the generation of engineered parti- cles for applications in therapeutic delivery, catalysis, sensing, and (bio)chemical reactions. A prominent method to form polymer capsules with tailored proper- ties is layer-by-layer (LbL) assembly. 1,2 In this process, template particles are coated with multiple layers through the sequential adsorption of polymers from solution, followed by removal of the template cores. The polymer layers can be assembled by exploiting electrostatic interactions, hydrogen bonding, and cova- lent bonding strategies. 3,4 The deposition of polymer films on particles through a single-step solution-based technique would provide direct benefits in the construc- tion of capsules, minimizing labor, cost, and assembly complexity. Furthermore, the ability to control the thickness of the films using a simple single-step adsorp- tion technique would offer new opportunities in tailor- ing the physicochemical properties of polymer capsules. A promising method to form thin polymer films through a single deposition process with control over film thickness is based on the oxidative self-polymerization of dopamine (2-(3,4-dihydroxyphenyl)ethylamine) onto surfaces (Scheme 1). This approach, originally inspired by the adhesive properties displayed by mussels, was recently introduced and shown to generate a range of polydopa- mine (PDA)-coated planar substrates. 5 Recent studies have shown that this technique can also be used for the formation of PDA films on electrodes for biosensing, 6 PDA-stabilized poly(L-lysine)/hyaluronic acid multi- layered freestanding films, 7a and multifunctional PDA- coated carbon nanotubes. 8 Herein, we report the assembly of PDA thin films by the spontaneous oxidative polymerization of a dopamine solution onto silica (SiO 2 ) particles, followed by removal of the template particles to form robust capsules (Scheme 1). We further show that this PDA assembly process can be applied to SiO 2 particles with a range of sizes and mesoporous structures. We also demonstrate that the PDA capsules exhibit negligible toxicity toward cells, which is of importance for the application of these capsules in biomedical applications. The primary advan- tages of the outlined strategy reside in the single poly- mer film deposition step required for the synthesis of capsules and control over the PDA film thickness by varying the polymerization reaction time. Further- more, the technique is versatile, relatively quick, and Scheme 1. Assembly of a PDA Film onto a Particle and Subse- quent Capsule Formation a a Oxidative polymerization of dopamine showing two of the possible structures formed. The polymerization chemistry has recently been reviewed. 9 *Corresponding author. E-mail: fcaruso@unimelb.edu.au. (1) Caruso, F.; Caruso, R. A.; M :: ohwald, H. Science 1998, 282, 1111– 1114. (2) Donath, E.; Sukhorukov, G. 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Ed. 2009, 48, 3914–3921. Downloaded by CSIRO INFO & TECH SERVICES on July 21, 2009 Published on June 29, 2009 on http://pubs.acs.org | doi: 10.1021/cm901293e