We report that surface properties can easily be manipulated by organic reaction and surface-initiated polymerization of functional monomers. The studies reported herein have a great potential in the applications including nanodevices, sensors, biofunctional surfaces, and nanotechnology.
Using surface-initiated polymerization of several monomers having functional organic moieties through atom transfer radical polymerization (ATRP), we coated well-defined polymer layers on the surfaces of gold and carbon nanotubes. It is a well-known method to use polymers to tailor surface properties, but the conventional ‘grafting-to’ approach have several serious disadvantages for applications in nanotechnology, such as difficulty in controlling thickness and packing density. In this paper, we established a method for tailoring surface properties by growing functional polymer layers from the surfaces of gold and carbon nanotubes by grafting-from approach.
It is very important to control surface properties of carbon nanotube, because carbon nanotube is not soluble in common solvents. Therefore, changing surface properties using polymers or organic molecules can be a solution to make carbon nanotubes available in nanotechnology application, such as the implementation of nanodevices using carbon nanotubes.
In the first part of this paper, we reported tailoring surface properties of carbon nanotubes using polymers grown by surface-initiated polymerization. This method gives us many advantages, such as good dispersion of carbon nanotubes in polymer matrix and capability to control polymer growth in nanoscale precision. First, we used PMMA to test the reliability of procedure, and showed that surface properties were changed by the polymer layer. In addition, we coated carbon nanotubes with polymers carrying sugar moiety, showing possibility that carbon nanotubes modified with sugar are applicable as a biospecific layer, because sugar moieties spectifically interact with lectin, which is a sugar-binding protein.
In the second part of this paper, we used NTA(nitrilotriacetic acid)molecule to tailor the surface of carbon nanotubes to specifically interact with histidine tagged proteins. The coupling of carbon nanotubes with NTA-$NH_2$ was done by EDC-NHS coupling in water, and then Ni(Ⅱ) ion was coordinated with carbon nanotubes through the nitrilotriacetic group. Since Ni(Ⅱ)-NAT complex specifically interacts with histidine-tagged proteins, NTA-modified nanotube binds with histidine-tagged protein specifically. By tailoring the surface of carbon nanotubes to have a specific affinity toward his-tagged proteins, we showed possibility that nanotube would be applicable in biomacromolecule sensors.
In the third part of paper, we showed the modification of gold surfaces by forming self-assembled monolayers of ATRP initiator and then growing polymer brushes by surface-initiated polymerization from the initiator monolayer. Using polymers to modify surfaces gives more advantages than using self-assembled monolayers, especially in durability. Using ATRP, we could proceed reactions under mild ambient conditions, also controlled the thickness of polymer layer precisely. First, we used MMA as a model study, and then several monomers carrying sugar moieties. Polymer layer having sugar moiety has a spectific affinity toward several lectins, showing possibility of application in biomolecule sensors. To show that this procedure is suitable to fabricate model layers for investigating interactions between lectin and sugar moieties, we grew polymer brushes containing sugar moiety from SPR gold chip by above-mentioned procedure. The grown polymer layer showed small roughness and uniform thickness, qualified as a model surface for SPR analysis.
본 연구에서는 탄소나노튜브와 금 표면에 유기반응과 표면개시고분자화반응을 통해 여러가지 기능성을 가지는 고분자 층을 도입하여 탄소나노튜브와 금의 표면을 개질하는 방법을 제시하였다.
나노튜브를 산화 및 절단한 후, 표면에 생긴 카르복실기를 이용하여 아미드 결합을 통해 표면에 표면개시고분자화반응에 필요한 원자전이래디컬고분자화반응 개시제를 도입할 수 있었다. 이 개시제를 이용하여 나노튜브의 표면으로부터 표면개시고분자화반응을 통해 나노튜브의 표면에 PMMA (Poly(methyl methacrylate))를 도입할 수 있었으며, 이 방법으로 나노튜브의 표면이 개질됨을 확인하였다. 또한, 당구조가 있는 단량체를 합성하고 이를 이용하여 나노튜브의 표면에 당을 도입함으로서, 랙틴과 같은 당결합 단백질과 선택적 상호작용을 할 수 있게 표면을 개질하였다.
또한, 히스티딘 사슬과 선택적으로 결합하는 생기능성 유기물질인 NTA (나이트릴로트라이아세트산)을 나노튜브 표면에 도입한 후, 이를 이용하여 히스티딘으로 표시된 단백질이 선택적으로 나노튜브와 상호작용 하는것을 확인하였다.
또한 본 연구에서는 금 표면 위에 원자전이래디컬고분자화반응 개시제의 단분자막을 형성하고 이를 이용해서 표면개시고분자화반응을 수행함으로서 금 표면을 고분자로 개잘하는 과정에 대해 서술하였다. 이 과정을 통해서 생긴 고분자막의 두께를 반응시간을 조절함으로서 쉽게 조절할 수 있으며, 또한 단량체의 합성시 원하는 구조를 도입하고 이를 이용하여 고분자반응을 수행함으로써 금 표면에 원하는 유기구조를 쉽게 도입할 수 있음을 보였다. 우선 모델 연구로서 메타아크릴레이트를 이용, PMMA 고분자층의 두께를 정밀하게 조절하여 금 표면에 도입하고, 표면이 고분자의 성질을 보임을 적외선 스펙트럼과 접촉각 측정을 통해 확인하였다. 또한, 나노튜브와 마찬가지로 당구조를 가지는 단량체를 이용해서 표면개시 고분자화반응을 수행함으로서 금 표면을 당으로 쉽게 개질할 수 있음을 보였다. 또한 랙틴과 같은 단백질과 당과의 선택적 상호작용을 연구할 수 있음을 보이기 위해 이 방법을 통해 SPR(surface plasmon resonance)에 사용되는 gold chip의 표면을 당으로 개질하였다. 이렇게 생성된 고분자층은 두께가 얇고 균일하여서 SPR에 응용할 수 있음을 확인하였다.
