Abstract
Polydopamine (PDA) deposition, obtained from the oxidation of dopamine and other catecholamines, is a universal way to coat all known materials with a conformal coating which can subsequently be functionalized at will. The structural analogies between polydopamine and eumelanin, the black-brown pigment of the skin, were incited to produce stable polydopamine nanoparticles in solution, instead of amorphous precipitates obtained from the oxidation of dopamine. Herein, we demonstrate that size-controlled and colloidally stable PDA-based nanoparticles can be obtained in acidic conditions, where spontaneous auto-oxidation of dopamine is suppressed, using sodium periodate as the oxidant and a protein, like alkaline phosphatase (ALP), as a templating agent. The size of the PDA@ALP nanoparticles depends on the dopamine/enzyme ratio and the obtained particles display enzymatic activity of alkaline phosphatase, with an activity extending up to two weeks after particle synthesis. The PDA@ALP nanoparticles can be engineered in polyelectrolyte multilayered films to potentially design model biosensors.
Highlights
Inspired by the adhesion of mussels [1] to the surface of wood, or stones in a wet environment, dopamine [2] and other catecholamines [3,4] were proven to be interesting molecules to coat the surface of all known materials, with a conformal coating having an adjustable thickness from a few nm to more than 100 nm
Alloxidation the particles prepared in the presence area/volume of the of dopamine is performed in. These findings strongly suggest that the strong oxidant does not affect the enzymatic activity of the enzyme itself, and this is reflected by the fact that the PDA@alkaline phosphatase (ALP) particles keep the enzymatic activity expected for ALP after oxidative synthesis in the presence of NaIO4 and subsequent dialysis against Tris buffer at pH 8.5
Those of nanoparticles keep the 4enzymatic activityofofalkaline the usedphosphatase enzyme, andallows seem to at production pH 8.5. Those nanoparticles keep the enzymatic activity of the used enzyme, and seem to be of stable nanoparticles of controlled size in a much shorter time than by auto-oxidation enriched in enzyme on their corona with respect to their core
Summary
Inspired by the adhesion of mussels [1] to the surface of wood, or stones in a wet environment, dopamine [2] and other catecholamines [3,4] were proven to be interesting molecules to coat the surface of all known materials, with a conformal coating having an adjustable thickness from a few nm to more than 100 nm. The oxidation of dopamine and its subsequent self-assembly/polymerization [5,6] is at the origin of the deposition of those “polydopamine” (PDA) films on various substrates. In the presence of Tris buffer at pH 8.5, the film thickness saturates at 40–45 nm after about 16 h of auto-oxidation in the presence of dopamine at 2 mg·mL−1 [2]. A major drawback of PDA and related films is the slow deposition kinetics. This problem was addressed and partially solved by depositing PDA by means of spray deposition [8], or using stronger oxidants than the oxygen dissolved in water [9,10,11]
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