Department of Chemistry, Grand Valley State University, 1 Campus Drive, 348 Padnos Hall, Allendale, Michigan 49401, United States.
Anal Chem. 2020 Sep 15;92(18):12663-12669. doi: 10.1021/acs.analchem.0c02889. Epub 2020 Aug 31.
The collision events of single bacteria at Pt disk ultramicroelectrodes (UMEs) were characterized using electrochemistry with correlated microscopy. A finite element model was developed which applied coupled simulations of concentration and solution velocity to elucidate the influence of electroosmotic flow on transport of bacteria near the electrode. The model established that, in stochastic collision experiments with steady-state oxidation at disk UMEs in low ionic strength solutions, electroosmotic flow occurring at the glass insulation of the electrode produces significant convection in the vicinity of the electrode disk (velocities >50 μm/s). For , the particle velocity due to convection driven by electroosmotic flow exceeded that of electrophoresis at locations radial to the electrode disk, leading to transport away from the electrode. Correlated microscopy of collision experiments of using a 5 μm radius Pt disk UME in 2 mM ferrocenemethanol (FcM) with either 0.035 or 0.1 mM KCl confirmed that experienced transport by convection due to electroosmotic flow. Velocities of extracted from correlated microscopy movies collected at the two KCl concentrations agreed with the finite elements model. Current-time (-) curves recorded during the collision experiments showed transients that occurred when colliding reduced transport of FcM to the electrode. The current transients had step shapes when collided and adsorbed and spike shapes when they collided and then moved away from the electrode. By comparing the microscopy to simulations, we concluded that the driving mechanism for the spike-shaped transients was convection due to electroosmotic flow. Moreover, these findings suggest that electroosmotic flow is significant for particle transport in stochastic collision experiments in solutions of low ionic strength, regardless of the analyte.
使用电化学结合相关显微镜技术，研究了单个细菌在 Pt 盘超微电极（UME）上的碰撞事件。建立了一个有限元模型，该模型应用浓度和溶液速度的耦合模拟来阐明电渗流对电极附近细菌传输的影响。该模型表明，在低离子强度溶液中，在盘状 UME 上进行稳态氧化的随机碰撞实验中，发生在电极玻璃绝缘处的电渗流会在电极盘附近产生显著的对流（速度>50 μm/s）。对于，由于电渗流驱动的对流引起的颗粒速度超过了电极盘径向位置的电泳速度，导致了向电极的传输。在 2 mM 二茂铁甲醇（FcM）中使用 5 μm 半径 Pt 盘 UME 进行的 相关显微镜碰撞实验，在 0.035 或 0.1 mM KCl 下，证实了 由于电渗流而发生的对流传输。从在两种 KCl 浓度下收集的相关显微镜电影中提取的速度与有限元模型一致。在碰撞实验过程中记录的电流-时间 (-) 曲线显示了当碰撞时还原的 FcM 向电极传输时发生的瞬变。当 碰撞并吸附时，电流瞬变具有阶跃形状，而当它们碰撞并远离电极时，电流瞬变具有尖峰形状。通过将显微镜与模拟进行比较，我们得出结论，尖峰状瞬变的驱动机制是电渗流引起的对流。此外，这些发现表明，电渗流对于低离子强度溶液中随机碰撞实验中的颗粒传输非常重要，而与分析物无关。
