Site-Selective Functionalization of Polydopamine Films via Aryl Azide-Based Photochemical Reaction
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Communication www.springer.com/13233 pISSN 1598-5032 eISSN 2092-7673
Site-Selective Functionalization of Polydopamine Films via Aryl Azide-Based Photochemical Reaction Jaehoon Jeong Eunseok Kim Wonwoo Jeong Hyeongeun Kang Daewha Hong*
Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 46241, Korea
Received September 23, 2019 / Revised December 27, 2019 / Accepted January 9, 2020
Abstract: Although the post functionalization of versatile polydopamine (pD) films enables the expression of functional groups of interest on target substrates, their immobilization generally lacks site-selectivity within a surface platform. In this paper, we report a site-selective conjugation method to functionalize pD films based on the combination of simple photolithographic techniques. The essence of the chemical functionalization strategy was the use of the aryl azide group, whose photolysis induces the generation of reactive nitrene groups that functionalize hydrocarbon networks of pD films. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) analyses indicated that the pD film was functionalized primarily with aryl azide groups under UV irradiation and the introduction of a photomask enabled the pattern generation of the initiator that was tethered with the aryl azide group. A subsequent surface-initiated polymerization on their substrates produced a patterned polymer brush, expressing their own functionality on the surface platform. Keywords: polydopamine, aryl azide, photoreaction, site-selective functionalization, polymer brush.
The development of polydopamine (pD)-based surface coatings has attracted extensive interest for a variety of applications, including biosensors, energy storage, tissue regeneration, and anti-bacterial surfaces.1 The wide applicability of pD coatings can be attributed primarily to their simple coating process on virtually all type of surfaces regardless of their size, shape, and chemical composition.2 Dopamine, a mimic building block of mussel adhesive proteins undergoes oxidative polymerization under mild alkaline condition (aqueous, pH 8.5), and can be used to coat pD film on various surfaces, including electrodes, biochips, membranes, and even living cell surfaces.3-5 Along with the substrateindependent coating capability of pD films, their post-functionalization via surface organic reaction with external moieties further improves their out-layer properties artificially. The most common approach involves performing Michael addition and/ or Schiff base formation between quinone groups of the pD film and external nucleophiles, such as thiol and amine groups.6 Alternatively, residual amine groups of the pD film were utilized to attempt acylation or aza-Michael reaction with acyl chloride or α,β-unsaturated carbonyl functional groups, respectively.7,8 By taking advantage of this surface chemistry, a variety of functional materials, including antifouling oligomer, ATRP initiator, cell growth factor,
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