藉由AFM及QCM-D深度分析具電活性軟物質之表面與介面現象：官能化導電高分子及水凝膠

Abstract

在生物工程領域中，生物傳感器性能的要求很高，尤其是用於體內偵測中電化學傳感器的靈敏度和可靠性。 作為在水相環境中使用的電極材料或軟物質，探索液態與固態介面處的相互作用及現象至關重要。這些材料擁有的電化學控制及傳感能力替進階應用開啟了一扇窗。本文全面研究了具電活性軟物質的表面性質和介面現象，包含了官能化的聚(3,4-乙烯二氧基噻吩) (PEDOT)薄膜，以及兩性離子高分子的吸附行為。 導電高分子(CPs)作為生物工程中的電極材料引起了相當大的關注，與傳統無機材料相比，導電高分子更具有機械柔軟性，更類似於神經和腦等生物組織。為了獲得更好的性能並拓展生物電子應用，具有抗沾黏特性的表面改質成為一種防止蛋白質的非特定性吸附且提高生物相容性的簡便方法。在本文的第一部分，使用原子力顯微鏡(AFM)研究了乙二醇(EG)官能化的PEDOT (PEDOT-EG)的表面特性，包含了表面粗糙度、親水性黏附性。我們比較了具有三種不同EG長度：三乙二醇、四乙二醇、六乙二醇，和兩種末端基團：羥基(-OH)和甲基(-OCH3)，共六種PEDOT-EG表面。在脂多醣-Aβ42（LPS-Aβ42）結合研究中，我們比較了不同官能化的PEDOTs表面親疏水性。透過石英晶體微天平附加耗散偵測(QCM-D)，對LPS-Aβ42結合行為的量測突顯了Aβ42依時間的吸附量變化，暗示了Aβ42結構內部的轉變。這些發現加深了我們對PEDOT功能、LPS-Aβ42相互作用和Aβ42結構動力學的理解，這些對於阿茲海默症的發病機制至關重要。原子力顯微鏡對表面特性的分析也進一步觀察了另一種軟物質：表面具有奈米相分離結構的水凝膠。透過PeakForce QNM模式和force-volume的方法映射試片表面，呈現了表面奈米尺度的力學性質。 第二部分探討了兩性離子高分子在帶電表面上的吸附行為。我們透過外部施加的電位來關注兩性離子中局部偶極矩與帶電表面之間的相互作用。電化學石英晶體微天平附加耗散偵測(EQCM-D)測量從帶負電到帶正電的導電玻璃塗層。儘管兩性離子高分子具有電中性結構，我們發現其在帶電表面上仍然顯示出吸引或排斥的相互作用。除了影響兩性離子高分子的吸附量和吸附速率外，外部施加的電位也會對吸附薄膜的黏彈性質有影響。為了評估所施加表面電位的影響範圍，我們藉由在水溶液中添加100 mM LiClO4的鹽類進一步研究離子強度的影響。與聚(2-甲基磷酸膽鹼) (PMPC)和聚(3-[[2-(甲基丙烯醯氧)乙基]二甲基銨]丙酸酯) (PCBMA)相比，聚([2-(甲基丙烯醯氧)乙基]二甲基-(3-磺丙基)氫氧化銨) (PSBMA)藉由高分子鏈構型的動態變化在加鹽環境中大幅減少而表現出對離子強度的顯著依賴性。 在第三部分中，我們展示了兩性離子高分子刷在PEDOT表面的改質。透過電聚合製備含起始劑的PEDOT薄膜，然後藉由表面起始原子轉移自由基聚合(SI-ATRP)反應製備高分子刷接枝薄膜。對於控制高分子刷的構型和水合狀態而言，離子強度和外部施加電位至關重要。我們定量研究和比較了不同鹽濃度和表面電位下的PMPC和PSBMA高分子刷。AFM分析了高分子刷的表面形態，force-volume方法則可以分析兩種高分子刷的楊氏係數。EQCM-D檢查了高分子刷的水合狀態和蛋白質吸附行為。能量耗散和頻率變化讀數則能對應在不同離子強度下薄膜表面的離子吸附。結果表明PMPC刷具有更大的離子強度獨立性，這意味著PMPC刷的構型不受離子濃度影響。此外，我們還藉由非特異性和特異性吸附行為分析了帶電聚(EDOT-PC)電極與PEDOT薄膜上PMPC刷受到表面電位的影響程度差異。我們得出結論是PMPC刷表現出獨特的行為，其幾乎不受離子濃度的影響。由於在氯化鈉水溶液中，電極表面對外部環境的影響會受到有限的德拜長度抑制，因此表面電位在高分子刷修飾的電極表面影響較小。這項工作深入瞭解了利用兩性離子高分子刷進行表面改質的表面其機械性能與其可控的抗沾黏能力之間的關係。

In the bioengineering field, the performance of biosensors is highly required, especially for in vivo electrochemical sensing in terms of sensitivity and reliability. As electrode materials or soft matters are operated in the aqueous environment, exploring the interactions or the phenomenon at the liquid/solid interface is crucial. Electrochemical controlling and sensing of these materials pave the way for versatile advanced applications. In this dissertation, we comprehensively investigated surface properties and interfacial phenomenon of electroactive soft matters, including the functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) films, and the adsorption behaviors of zwitterionic polymers. Conducting polymers (CPs) have attracted considerable attention as electrode materials in bioengineering mainly because of their mechanical softness compared to conventional inorganic materials, similar to those of biological tissues such as nerve and brain tissues. To achieve better performance and broaden bioelectronics applications, surface modification with antifouling properties represents a facile approach to preventing unwanted nonspecific protein adsorption and improving biocompatibility. In the first section of this dissertation, surface properties including surface roughness, hydrophilicity, and adhesion of ethylene glycol (EG)-functionalized PEDOT (PEDOT-EG) were investigated using atomic force microscopy (AFM). Six kinds of PEDOT-EG, with three different EG lengths (tri-EG, tetra-EG, and hexa-EG) and two types of end groups, hydroxyl (-OH) and methoxy (-OCH3), were compared. In the lipopolysaccharides-Aβ42 (LPS-Aβ42) binding study, diverse functionalized PEDOTs were compared for their wettability characteristics. Using quartz crystal microbalance with dissipation (QCM-D), an investigation into LPS-Aβ42 binding highlighted time-dependent fluctuations in Aβ42 binding, suggesting structural transitions within the Aβ42 assemblies. These findings deepen our comprehension of PEDOT functionality, LPS-Aβ42 interactions, and Aβ42 assembly dynamics, which is critical to the pathogenesis of Alzheimer’s disease (AD). The analysis of surface properties done by AFM was further introduced to another soft matter, hydrogels of a nano-phase-separated structure on the surface. Nanomechanical properties of the surfaces were presented by mapping the surface in PeakForce quantitative nanomechanical mapping (PeakForce QNM) and force-volume methods. In the second section, the adsorption behaviors of zwitterionic polymers on electrified surfaces were explored. We focus on the interaction between the local dipole moments in the zwitterionic moieties and the charged surfaces by applying external surface potentials. Electrochemical QCM-D (EQCM-D) measurements was conducted on negatively to positively charged ITO-coated surfaces. We found the zwitterionic polymers still display attractive or repulsive interaction on the charged surfaces, despite their electrically neutral structures. In addition to the adsorbed amount and adsorption rates of zwitterionic polymers, external surface potentials also have an impact on the viscoelastic properties of the adsorbed thin films. To evaluate the influenced range of the applied surface potentials, the effect of ionic strength was further investigated by adding 100 mM LiClO4 in the aqueous solutions. Compared to poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and (poly(carboxybetaine methacrylate) (PCBMA), poly(sulfobetaine methacrylate) (PSBMA) exhibited a pronounced dependency on the ionic strength by observing the diminishing dynamic change of the chain conformations. In the third section, the surface modification of zwitterionic polymer brushes on PEDOT surface was demonstrated. Initiator-containing poly(3,4-ethylenedioxythiophene) films (poly(EDOT-Br)) were prepared by electropolymerization, and surface-initiated atom-transfer radical polymerization (SI-ATRP) was then carried out to fabricate polymer-brush-grafted films. Ionic strength and applied potentials are crucial in controlling polymer brushes’ conformation and hydration states. We quantitatively investigated and compared PMPC and PSBMA brushes at different salt concentrations and surface potentials. Polymer brushes were carefully characterized for their surface morphologies using an AFM. The force-volume method enabled the analysis of Young’s modulus of the two polymer brushes. Hydration states and protein binding behaviors of polymer brushes were examined using EQCM-D. The energy dissipation and frequency changes corresponded to the ion adsorption on the film surface under different ionic strengths. The results indicate that PMPC brushes have greater ionic strength independency, implying the conformation of the unchanged PMPC brushes. Moreover, we illustrated how the surface potential influences nonspecific and specific binding behavior on PMPC brushes on PEDOT films compared with electrified poly(phosphorylcholine-functionalized EDOT) (poly(EDOT-PC)) electrodes. We concluded that PMPC brushes exhibit unique behaviors that are barely affected by ion concentration. And brushes’ modification results in less influence by surface potential due to the finite Debye length influencing the electrode surface to the outer environment in a NaCl aqueous solution. This work provides an insight into the relation between mechanical properties and its controllable antifouling capabilities for surface modification of zwitterionic polymer brushes.