Interconversions between RNS Revealed by Transient Voltammetry with Porphyrin‐Modified Carbon Nanopipettes in Single Living Cells

Abstract Reactive nitrogen species (RNS) play crucial roles in cellular signaling, but their quantification is very challenging due to low‐abundant nature and complex conversions with other reactive molecules in the cells. The well‐established amperometry methods have been widely used to measure the RNS inside the living cells, while the nanometer‐sized tip is limited by the steady‐state studies. In this paper, conductive nanopipettes (CNPs) with porphyrin complexes are functionalized, which allow direct transient voltammetry tests to differentiate and quantify the RNS based on the peak potential and current. It is shown that the oxidation of NO ₂ ^‒ can produce a nitrogen dioxide (NO ₂ ) intermediate, and a CEC (chemical‐electrochemical‐chemical) mechanism is proposed. Moreover, this platform with transient voltammetry enables real‐time quantification of cellular RNS and reveals the dynamic interconversions within RNS, providing valuable insights into their roles in cellular processes.