de Coene Yovan, Jooken Stijn, Deschaume Olivier, Van Steenbergen Valérie, Vanden Berghe Pieter, Van den Haute Chris, Baekelandt Veerle, Callewaert Geert, Van Cleuvenbergen Stijn, Verbiest Thierry, Bartic Carmen, Clays Koen
Laboratory of Molecular Imaging and Photonics, Department of Chemistry, KU Leuven, Celestijnenlaan 200D, Leuven, 3001, Belgium.
Laboratory of Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, Leuven, 3001, Belgium.
Small. 2022 May;18(18):e2200205. doi: 10.1002/smll.202200205. Epub 2022 Mar 30.
Optical interrogation of cellular electrical activity has proven itself essential for understanding cellular function and communication in complex networks. Voltage-sensitive dyes are important tools for assessing excitability but these highly lipophilic sensors may affect cellular function. Label-free techniques offer a major advantage as they eliminate the need for these external probes. In this work, it is shown that endogenous second-harmonic generation (SHG) from live cells is highly sensitive to changes in transmembrane potential (TMP). Simultaneous electrophysiological control of a living human embryonic kidney (HEK293T) cell, through a whole-cell voltage-clamp reveals a linear relation between the SHG intensity and membrane voltage. The results suggest that due to the high ionic strengths and fast optical response of biofluids, membrane hydration is not the main contributor to the observed field sensitivity. A conceptual framework is further provided that indicates that the SHG voltage sensitivity reflects the electric field within the biological asymmetric lipid bilayer owing to a nonzero tensor. Changing the TMP without surface modifications such as electrolyte screening offers high optical sensitivity to membrane voltage (≈40% per 100 mV), indicating the power of SHG for label-free read-out. These results hold promise for the design of a non-invasive label-free read-out tool for electrogenic cells.
对细胞电活动进行光学检测已证明，对于理解复杂网络中的细胞功能和通信至关重要。电压敏感染料是评估细胞兴奋性的重要工具，但这些高度亲脂性的传感器可能会影响细胞功能。无标记技术具有一个主要优势，即它们无需这些外部探针。在这项工作中，研究表明活细胞内源性二次谐波产生（SHG）对跨膜电位（TMP）的变化高度敏感。通过全细胞电压钳对活的人胚胎肾（HEK293T）细胞进行同步电生理控制，结果显示SHG强度与膜电压之间存在线性关系。结果表明，由于生物流体的高离子强度和快速光学响应，膜水合作用并非观察到的场敏感性的主要贡献因素。进一步提供了一个概念框架，表明SHG电压敏感性反映了由于非零张量而在生物不对称脂质双层内的电场。在不进行诸如电解质筛选等表面修饰的情况下改变TMP，对膜电压具有高光学敏感性（每100 mV约40%），这表明SHG用于无标记读出的能力。这些结果为设计用于电生细胞的非侵入性无标记读出工具带来了希望。
