Chemistry Department, Virginia Commonwealth University, Richmond, VA, 23294, USA.
Chemistry Department, Khulna University of Engineering and Technology, Bangladesh.
Analyst. 2024 May 28;149(11):3214-3223. doi: 10.1039/d4an00134f.
We recorded current-time (-) profiles for oxidizing ferrocyanide (FCN) while spherical yeast cells of radius ( ≈ 2 μm) collided with disk ultramicroelectrodes (UMEs) of increasing radius ( ≈ 12-45 μm). Collision signals appear as minority steps and majority blips of decreased current overlayed on the - baseline when cells block ferrocyanide flux (). We assigned steps to adsorption events and blips to bouncing collisions or contactless passages. Yeast cells exhibit impact signals of long duration (Δ ≈ 15-40 s) likely due to sedimentation. We assume cells travel a threshold distance () to generate collision signals of duration Δ. Thus, represents a distance from the UME surface, at which cell perturbations on blend in with the UME noise level. To determine , we simulated the UME current, while placing the cell at increasing distal points from the UME surface until matching the bare UME current. -Values at 90°, 45°, and 0° from the UME edge and normal to the center were determined to map out T-regions in different experimental conditions. We estimated average collision velocities using the formula /Δ, and mimicked cells entering and leaving T-regions at the same angle. Despite such oversimplification, our analysis yields average velocities compatible with rigorous transport models and matches experimental current steps and blips. We propose that single-cells encode collision dynamics into - signals only when cells move inside the sensitive T-region, because outside, perturbations of fall within the noise level set by and / (experimentally established). If true, this notion will enable selecting conditions to maximize sensitivity in stochastic blocking electrochemistry. We also exploited the long Δ recorded here for yeast cells, which was undetectable for the fast microbeads used in early pioneering work. Because Δ depends on transport, it provides another analytical parameter besides current for characterizing slow-moving cells like yeast.
我们记录了氧化亚铁氰化物（FCN）的电流-时间 (-) 曲线，同时半径约为 2μm 的球形酵母细胞与半径不断增加（约 12-45μm）的盘状超微电极（UME）发生碰撞。当细胞阻断亚铁氰化物通量时，碰撞信号表现为电流减少的少数阶跃和多数突发（）。我们将阶跃分配给吸附事件，将突发分配给反弹碰撞或非接触通过。酵母细胞表现出持续时间较长的冲击信号（Δ≈15-40s），可能是由于沉降所致。我们假设细胞在达到碰撞信号持续时间 Δ之前会行进一段阈值距离 ()。因此，代表距离 UME 表面的距离，在此距离处，细胞对的扰动与 UME 噪声水平混合。为了确定，我们模拟了 UME 的电流，同时将细胞放置在距离 UME 表面越来越远的位置，直到与裸露的 UME 电流匹配。通过从 UME 边缘以 90°、45°和 0°的角度和垂直于中心的位置确定值，以绘制不同实验条件下 T-区域的图谱。我们使用公式 /Δ 来估计平均碰撞速度，并模拟细胞以相同角度进入和离开 T-区域。尽管这种简化很粗糙，但我们的分析结果与严格的传输模型得出的平均速度相匹配，并与实验电流阶跃和突发相匹配。我们提出，只有当细胞在敏感的 T-区域内移动时，单细胞才会将碰撞动力学编码到 - 信号中，因为在该区域之外，的扰动落入由和 /（实验确定）设定的噪声水平内。如果这是真的，那么这个概念将能够选择条件以最大化随机阻塞电化学的灵敏度。我们还利用了这里记录的酵母细胞的长 Δ，这对于早期开创性工作中使用的快速微球是无法检测到的。因为 Δ 取决于传输，所以它提供了除电流之外的另一个分析参数，用于表征像酵母这样的缓慢运动的细胞。
