Twin Nanopipettes for Real-Time Electrochemical Monitoring of Cytoplasmic Microviscosity at a Single-Cell Level

Cytoplasmic microviscosity (CPMV) plays essential roles in governing the diffusion-mediated cellular processes and has been recognized as a reliable indicator of the cellular response of many diseases and malfunctions. Current CPMV studies are exclusively established by probe-assisted optical methods, which nevertheless necessitate the complicated synthesis and delivery of optical probes into cells and thus the issues of biocompatibility and bio-orthogonality. Using twin nanopipettes integrated with a patch-clamp system, a practical electrochemical single-cell measurement is presented, which is capable of real-time and long-term CPMV detection without cell disruption. Specifically, upon the operation of the twin nanopipettes, the cellular CPMV status, which is correlated to cytoplasmic ionic mobility, could be sensibly transduced via the ionic current passing through the nanosystem. The average CPMV value of HeLa cells was detected as ca. 86 cP. Notably, the correlation between chemotherapy and CPMV alterations makes this approach possible for the real-time and long-term assessment of the evolution of external stimuli, as exemplified by the two natural products taxol and colchicine. Integrated with the patch-clamp setup, this study features the first use of twin nanopipettes for electrochemical CPMV monitoring of single living cells, and it is expected to inspire more interest in the exploitation of dual- and multiple nanopipettes for advanced single-cell analysis.