Institute of Analytical and Bioanalytical Chemistry, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm, Germany.
MG Optical Solutions GmbH, Industriestraße 23, 86919 Utting am Ammersee, Germany.
Anal Chem. 2020 Jun 16;92(12):8404-8413. doi: 10.1021/acs.analchem.0c00995. Epub 2020 May 19.
Polydopamine (PDA) has high potential in biorelevant applications as a versatile thin film material, e.g., as adhesive coating for cell immobilization or for sensing applications due to the plethora of functional groups. In this study we present the modification of conductive colloidal atomic force-scanning electrochemical microscopy (AFM-SECM) probes with electrochemically deposited PDA resulting in functional probes for quantitative electrochemical adhesion studies. Surface functionality of PDA can be altered by oxidation or reduction of functional groups applying an appropriate potential to the PDA-modified AFM-SECM probe, thereby enabling adhesion measurements under potential control. This facilitates probing specific interactions of surface groups present in PDA with various surfaces of different wettabilities. The versatility of such switchable AFM-SECM probes is demonstrated for electrochemical force spectroscopic studies at model samples such as plasma-treated gold substrates, hydrophobic or hydrophilic self-assembled monolayers, and for adhesion measurements of bacteria in dependence of altered surface charges of the colloidal probe. The maximum obtained adhesion force of a positively polarized PDA-modified AFM-SECM probe was 6.2 ± 2.2 nN, and it was about 50% less (i.e., 2.6 ± 1.1 nN) for a negatively polarized probe at a hydrophilic OH-terminated gold surface. control of the active surface groups enabled investigations on the influence of surface charges on adhesion. Furthermore, plateaus of constant force were observed, which are a characteristic of polymer structures. Finally, electrochemical force measurements with switchable probes were used for the first time during adhesion studies of bacterial cells (i.e., ). Positively biased PDA-coated colloidal probes revealed adhesion forces of 6.0 ± 1.1 nN, whereas significantly reduced adhesion forces 1.1 ± 0.7 nN were observed for negatively biased PDA-modified colloidal probes.
聚多巴胺（PDA）作为一种多功能的薄膜材料，在生物相关应用中具有很大的潜力，例如，作为细胞固定化的粘附涂层，或由于其丰富的官能团，用于传感应用。在这项研究中，我们介绍了通过电化学沉积 PDA 对导电胶体原子力扫描电化学显微镜（AFM-SECM）探针进行修饰，从而得到用于定量电化学粘附研究的功能探针。通过向 PDA 修饰的 AFM-SECM 探针施加适当的电位，可以改变 PDA 的表面官能团，从而实现电位控制下的粘附测量。这使得能够探测 PDA 中存在的表面基团与不同润湿性的各种表面之间的特定相互作用。通过在模型样品（例如等离子体处理的金基底、疏水性或亲水性自组装单层）上进行电化学力谱研究，以及在胶体探针的表面电荷发生变化的情况下对细菌的粘附测量，证明了这种可切换的 AFM-SECM 探针的多功能性。在亲水的 OH 终止金表面上，正极化的 PDA 修饰的 AFM-SECM 探针的最大粘附力为 6.2 ± 2.2 nN，而负极化的探针的粘附力约为其一半（即 2.6 ± 1.1 nN）。通过控制活性表面基团，可以研究表面电荷对粘附的影响。此外，还观察到恒定力的平台，这是聚合物结构的一个特征。最后，首次在细菌细胞的粘附研究中使用可切换探针进行电化学力测量（即 ）。带正电的 PDA 涂层胶体探针显示出 6.0 ± 1.1 nN 的粘附力，而带负电的 PDA 修饰胶体探针的粘附力显著降低至 1.1 ± 0.7 nN。
