Systems chemistry explores emergent properties from interacting molecular networks, although extending these systems into biologically relevant environments remains challenging. Here, we report a synthetic molecular network that functions dynamically inside living cells by responding autonomously to oxidative stimuli. The network is built from dithiol precursors that undergo oxidation-driven macrocyclization and co-assemble with an aggregation-induced emission luminogen to form fluorescent nanostructures selectively under oxidative conditions. This process is reversible, allowing repeated cycles of fluorescence modulation. By exploiting intracellular oxidation as a stimulus, the system links systems chemistry with biological complexity and enables real-time monitoring of cellular redox dynamics through fluorescence. The fluctuations in signal directly reflect oxidative levels in living cells, providing a tool for tracking redox states. Our work demonstrates adaptive molecular self-assembly in a biological context and opens opportunities for redox bioimaging, diagnostics, and therapeutics regulated by cellular oxidative environments.