Ultra-thin layer coating on bulk- and nanomaterials: Catecholic ligand coating assisted by small amine molecule.

Abstract

Mussel is one of the spotlighted models for surface chemistry to various scientific fields because of their special properties that strongly bind to diverse materials in harsh condition and maintain their adherent force in water. This adhesion is performed by their byssus threads. The one mussel can express a lot of byssus to adhere. The adherent mechanism is related with catechol group highly expressed in mussel foot protein (Mefp) expressed in byssus structure. This Mefp are polyphenolic proteins has highly express catechol group. Mefp-3,5 are most important proteins to adhere and different Mefp structure has different function each other. The catechol and amine group are important to adhere mechanism but it is not clear until now. Recently studies show polydopamine coating has cohesive and adhesive properties using dopamine. Dopamine containing catechol and amine group in one single molecule. It is biomimetic structure like Mefp-3,5 structure. The polydopamine coating show same properties like mussel adhesion. It is adoptable for many kinds of materials by simple dipping method. But is show surface independent manner. The coating thickness increased as incubation time was increased and the coated surface is sticky, so it is necessary further surface modification to protect coated surface. This sticky property may adhesive property from free catechol group on coated surface. We hypothesized only adhesive property can drive by separating catechol and amine group from one single molecule dopamine because of the crosslinking is occurred by luekodopamine structure. Here we show amine group assisted catechol ligand ultra-thin layer coating on various bulk- and nanomaterials. It show metal dependent coating with high stability and low non-specific binding on their coated surface with large scale by simple preparation steps. The simple dip coating method shows less than 2 nm thickness on bulk and nanomaterials. This small amine molecule is called as coating reagent for convenience. The further functionalize of surface also performed using by different kinds of coating reagent. The coated surface show coating reagent dependent property and only short length coating reagents are available to obtain densely coated and large surface area. We adopt this new technique to nanomaterials. In nanotechnology, the surface chemistry is important in specially bio-application area. We successfully obtain catechol ligand coated many kinds of nanomaterials and design Mefp like oligomer (MLO) to obtain enough stability for bio-application. For bio-application the stability, low non-specific binding and low toxicity are necessary. Iron oxide is expected as next generation contrast agent. We success to coating iron oxide by MLO it has high stability, low non-specific binding and low toxicity. Also preparation steps are easy and available at large scale. We use MLO coated iron oxide as blood pool contrast agent and enhance MR performance because of their thin layer thickness and high stability in in vivo. This catechol ligand coating was performed in bulk- and nano-sized various materials and we further analysis of coating mechanism. We find secondary amine from coated sapphire wafer by XPS analysis and molecular weight matched with sum of tert-butylcatechol(TBC) and 2-(2-Aminoethoxy)ethanol(AEE) by TOF-SIMS. The amine group stabilize catechol group by like Michael addition. It is confirmed by FT-IR shows tetra-substituted benzene ring structure and aromatic amine. 3 nm core sized Al2O3 nanoparticle was coated by TBC and AEE for 13C solid state NMR. The result show secondary carbon from AEE, we can know the amine group of AEE attack benzene ring structure of TBC and make less than 2 nm carbon shell on nanoparticle surface. We suggest new model of catechol drive adhesive force from conformational change of benzene ring of catechol group by amine group it will enhance understanding adherent mechanism of mussel foot protein and these thin layer coating can applicable on various materials will be widen the width of many research fields.