  Reactive oxygen and nitrogen species (ROS and RNS) play important roles in
various physiological processes (e.g., phagocytosis) and pathological
conditions (e.g., cancer). The primary ROS/RNS, viz., hydrogen peroxide,
peroxynitrite ion, nitric oxide, and nitrite ion, can be oxidized at different
electrode potentials and therefore detected and quantified by electroanalytical
techniques. Nanometer-sized electrochemical probes are especially suitable for
measuring ROS/RNS in single cells and cellular organelles. In this article, we
survey recent advances in localized measurements of ROS/RNS inside single cells
and discuss several methodological issues, including optimization of
nanoelectrode geometry, precise positioning of an electrochemical probe inside
a cell, and interpretation of electroanalytical data.
