Energy Transfer Between i‐Motif DNA Encapsulated Silver Nanoclusters and Fluorescein Amidite Efficiently Visualizes the Redox State of Live Cells

Abstract The redox regulation, maintaining a balance between oxidation and reduction in living cells, is vital for cellular homeostasis, intricate signaling networks, and appropriate responses to physiological and environmental cues. Here, a novel redox sensor, based on DNA‐encapsulated silver nanoclusters (DNA/AgNCs) and well‐defined chemical fluorophores, effectively illustrating cellular redox states in live cells is introduced. Among various i‐motif DNAs, the photophysical property of poly‐cytosines (C 20 )‐encapsulated AgNCs that sense reactive oxygen species (ROS) is adopted. However, the sensitivity of C 20 /AgNCs is insufficient for evaluating ROS levels in live cells. To overcome this drawback, the ROS sensing mechanism of C 20 /AgNCs through gel electrophoresis, mass spectrometry, and small‐angle X‐ray scattering is primarily defined. Then, by tethering fluorescein amidite (FAM) and Cyanine 5 (Cy5) dyes to each end of the C 20 /AgNCs sensor, an Energy Transfer (ET) between AgNCs and FAM is achieved, resulting in intensified green fluorescence upon ROS detection. Taken together, the FAM‐C 20 /AgNCs‐Cy5 redox sensor enables dynamic visualization of intracellular redox states, yielding insights into oxidative stress‐related processes in live cells.