C-reactive protein (CRP), a biomarker for cardiovascular disease, has been reported to have a strong affinity to zwitterionic phosphorylcholine (PC) groups in the presence of calcium ions. In addition, PC-immobilized surfaces have been used as a nonfouling coating to prevent nonspecific protein binding. By appropriately using the features of PC-immobilized surfaces, including specific recognition to CRP and nonfouling surface, it is reasonable to create an antibody-free biosensor for the specific capture of CRP. In this study, PC-functionalized 3,4-ethylenedioxythiophene (EDOT) monomers were used to prepare PC-immobilized surfaces. The density of PC groups on the surface can be fine-tuned by changing the composition of the monomer solutions for the electropolymerization. The density of PC group was confirmed by X-ray photoelectron spectroscopy (XPS). The specific interaction of CRP with PC groups was monitored by using a quartz crystal microbalance with dissipation (QCM-D). The amount of protein binding could be estimated by the reduction in frequency readout. Through the QCM-D measurement, we revealed the nonfouling property and the specific CRP capture from our PC-immobilized surfaces. Notably, the dissipation energy also dropped during the binding process between CRP and PC, indicating the release of water molecules from the PC groups during CRP adsorption. We anticipate that surface-bound water molecules are mainly released from areas near the immobilized PC groups. Based on Hofmeister series, we further examined the influence of ions by introducing four different anions including both kosmotrope (order maker) and chaotrope (disorder maker) into the buffer for the CRP binding test. The results showed that the concentration and the type of anions play an important role in CRP binding. The present fundamental study reveals deep insights into the recognition between CRP and surface-immobilized PC groups, which can facilitate the development of CRP sensing platforms.

中文翻译：

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耗散的石英晶体微天平对C反应蛋白和表面固定化磷胆碱识别的关键研究

据报道，C反应蛋白（CRP）是心血管疾病的生物标志物，在钙离子存在下，对两性离子磷酸胆碱（PC）组具有很强的亲和力。另外，已将PC固定的表面用作防污涂层，以防止非特异性蛋白质结合。通过适当使用固定在PC上的表面的特征（包括对CRP和无污垢表面的特异性识别），可以合理地创建无抗体的生物传感器来特异性捕获CRP。在这项研究中，使用PC官能化的3,4-乙二氧基噻吩（EDOT）单体制备PC固定的表面。可以通过改变用于电聚合的单体溶液的组成来微调表面上PC基团的密度。PC组的密度通过X射线光电子能谱法（XPS）确认。通过使用带耗散的石英晶体微量天平（QCM-D）监测CRP与PC组的特定相互作用。蛋白质结合的量可以通过减少频率读数来估计。通过QCM-D测量，我们揭示了PC固定表面的无污垢特性和特定的CRP捕获量。值得注意的是，在CRP和PC之间的结合过程中，耗散能量也下降了，这表明在CRP吸附过程中水分子从PC基团中释放出来。我们预计表面结合的水分子主要从固定的PC组附近区域释放。基于Hofmeister系列，我们通过在CRP结合测试的缓冲液中引入四种不同的阴离子（包括共沸物（定序剂）和离液剂（失序剂））进一步检查了离子的影响。结果表明，阴离子的浓度和类型在CRP结合中起着重要作用。本基础研究揭示了对CRP和表面固定PC组之间识别的深刻见解，这可以促进CRP传感平台的开发。