Department of Chemistry, University of Virginia, Charlottesville, VA 22904, USA.
Molecules. 2022 Jun 11;27(12):3768. doi: 10.3390/molecules27123768.
Advanced carbon microelectrodes, including many carbon-nanotube (CNT)-based electrodes, are being developed for the in vivo detection of neurotransmitters such as dopamine (DA). Our prior simulations of DA and dopamine--quinone (DOQ) on pristine, flat graphene showed rapid surface diffusion for all adsorbed species, but it is not known how CNT surfaces affect dopamine adsorption and surface diffusivity. In this work, we use molecular dynamics simulations to investigate the adsorbed structures and surface diffusion dynamics of DA and DOQ on CNTs of varying curvature and helicity. In addition, we study DA dynamics in a groove between two aligned CNTs to model the spatial constraints at the junctions within CNT assemblies. We find that the adsorbate diffusion on a solvated CNT surface depends upon curvature. However, this effect cannot be attributed to changes in the surface energy roughness because the lateral distributions of the molecular adsorbates are similar across curvatures, diffusivities on zigzag and armchair CNTs are indistinguishable, and the curvature dependence disappears in the absence of solvent. Instead, adsorbate diffusivities correlate with the vertical placement of the adsorbate's moieties, its tilt angle, its orientation along the CNT axis, and the number of waters in its first hydration shell, all of which will influence its effective hydrodynamic radius. Finally, DA diffuses into and remains in the groove between a pair of aligned and solvated CNTs, enhancing diffusivity along the CNT axis. These first studies of surface diffusion on a CNT electrode surface are important for understanding the changes in diffusion dynamics of dopamine on nanostructured carbon electrode surfaces.
先进的碳微电极，包括许多基于碳纳米管 (CNT) 的电极，正在被开发用于在体检测神经递质，如多巴胺 (DA)。我们之前在原始、平坦的石墨烯上对 DA 和多巴胺-醌 (DOQ) 的模拟表明，所有吸附物种都具有快速的表面扩散，但目前尚不清楚 CNT 表面如何影响多巴胺的吸附和表面扩散率。在这项工作中，我们使用分子动力学模拟来研究 CNT 的曲率和螺旋度变化对 DA 和 DOQ 吸附结构和表面扩散动力学的影响。此外，我们还研究了两个对齐 CNT 之间的沟槽中的 DA 动力学，以模拟 CNT 组件内接头处的空间约束。我们发现，在溶剂化的 CNT 表面上，吸附物的扩散取决于曲率。然而，这种影响不能归因于表面能粗糙度的变化，因为分子吸附物的横向分布在曲率之间是相似的，锯齿形和扶手椅 CNT 上的扩散率无法区分，并且在没有溶剂的情况下，曲率依赖性消失。相反，吸附物的扩散率与吸附物的部分垂直位置、倾斜角度、沿 CNT 轴的取向以及其第一层水合壳中的水分子数相关，所有这些都会影响其有效水动力半径。最后，DA 扩散到并保留在一对对齐和溶剂化的 CNT 之间的沟槽中，增强了沿 CNT 轴的扩散率。这些关于 CNT 电极表面上表面扩散的初步研究对于理解多巴胺在纳米结构碳电极表面上扩散动力学的变化非常重要。
