Nanoelectrodes, renowned for their small size, rapid mass transport, fast response, and high spatiotemporal resolution, have been recognized as a powerful tool in biosensing, especially for single-cell analysis. However, the nanoelectrode itself has no selectivity and cannot respond to nonelectroactive substances, limiting its wide application to some extent. Herein, we propose a simple and efficient electrochemical conjugation strategy to develop an electrochemical aptamer-coupled (E-AC) sensor for detecting adenosine triphosphate (ATP) in single living cells. Through simple electrochemical conjugation, ferrocene-labeled aptamers could be stably and efficiently coupled onto the surface of carbon fiber electrodes within 5 min. The small size (ca. 400 nm) and biocompatibility of the functionalized nanoelectrodes enabled the E-AC sensors to noninvasively and continuously monitor ATP content in single HeLa cells over 20 min, as well as the cellular ATP fluctuations under glucose starvation. Furthermore, the E-AC sensors exhibit superior specificity, sensitivity, and universality in the application of analysis of ATP in single living Hela cells and MCF-7 cells. They were also versatile for sensing other nonelectroactive targets through modification of the corresponding electroactive marker-labeled aptamers, showing great potential in cell-related physiological processes and drug screening.