Spindler Brian D, Chen Xin V, Graf Katerina I, Bühlmann Philippe, Stein Andreas
Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55454, United States.
Langmuir. 2024 Aug 16. doi: 10.1021/acs.langmuir.4c01726.
For ion-selective electrodes (ISEs) to be employed in wearable and implantable applications, the ion-selective membrane components should be biocompatible, and leaching of components, such as plasticizer or ionophore, out of the sensing membrane should be inhibited. To achieve this, we employed a plasticizer-free silicone as the membrane matrix and synthesized as the ionophore a derivative of the bis-crown ether based potassium ionophore BME-44, incorporating a triethoxysilyl functional group that covalently attaches to condensation-cured silicones during the curing process. Soxhlet extraction of these membranes with dichloromethane shows that up to 96% of the ionophore is attached to the silicone membrane during curing. We found that the covalently attachable BME-44 derivative can inadvertently adsorb onto high surface area carbon solid contacts before attaching to the silicone matrix if the curing of the silicone is performed in the presence of the high surface area carbon, resulting in depletion of ionophore from the membrane and yielding solid-contact ISEs with poor selectivity. In contrast, we observed Nernstian responses to K in plasticizer-free silicone-based K ISMs with either mobile BME-44 or the covalently attachable BME-44 derivative when the membranes were prepared on octane-thiol coated gold electrodes, where ionophore adsorption does not occur to a noticeable extent. As compared with ISMs doped with the mobile BME-44, ISMs prepared with the covalently attachable BME-44 derivative have better selectivity for K vs Na ( values of -3.54 and <- 4.05 for mobile and covalently attachable BME-44, respectively) and lower resistance. This can be explained by a more homogeneous incorporation of the covalently attachable BME-44 derivative into the silicone matrix than is the case for the mobile BME-44.
为了使离子选择电极（ISE）能够应用于可穿戴和植入式设备中，离子选择膜组件应具有生物相容性，并且应抑制诸如增塑剂或离子载体等组件从传感膜中浸出。为了实现这一点，我们采用了不含增塑剂的硅酮作为膜基质，并合成了基于双冠醚的钾离子载体BME-44的衍生物作为离子载体，该衍生物含有一个三乙氧基甲硅烷基官能团，在固化过程中可与缩合固化的硅酮共价连接。用二氯甲烷对这些膜进行索氏提取表明，在固化过程中高达96%的离子载体附着在硅酮膜上。我们发现，如果在高表面积碳存在的情况下进行硅酮的固化，可共价连接的BME-44衍生物会在附着到硅酮基质之前无意中吸附到高表面积碳固体接触上，导致膜中离子载体的消耗，并产生选择性较差的固体接触ISE。相比之下，当在辛烷硫醇涂层金电极上制备膜时，我们观察到不含增塑剂的基于硅酮的钾离子选择性膜（K ISM）对钾有能斯特响应，无论是使用可移动的BME-44还是可共价连接的BME-44衍生物，在这种情况下离子载体的吸附并不明显。与掺杂可移动BME-44的离子选择性膜相比，用可共价连接的BME-44衍生物制备的离子选择性膜对钾与钠具有更好的选择性（可移动和可共价连接的BME-44的选择性值分别为-3.54和<-4.05）且电阻更低。这可以通过可共价连接的BME-44衍生物比可移动的BME-44更均匀地掺入硅酮基质中来解释。
