Functional nucleic acid engineered double‐barreled nanopores for measuring sodium to potassium ratio at single‐cell level oleh Xiao‐Mei Shi, Fang‐Qing Liu, Bing Wang, Si‐Yuan Yu, Yi‐Tong Xu, Wei‐Wei Zhao, Dechen Jiang, Hong‐Yuan Chen, Jing‐Juan Xu