Splitting and Aggregation of Carbon Dots: Wavelength-Shifted and Ratiometric Fluorescence Sensing of Peroxynitrite.

Peroxynitrite (ONOO) is a short-term reactive biological oxidant and plays an important role in cellular signal transduction and homeostatic regulation. However, excess ONOO is associated with neurodegenerative and cardiovascular diseases. Therefore, rapid, sensitive, and accurate assays for ONOO detection are essential for exploring its physiological and pathological function. In this work, a wavelength-shifted and ratiometric fluorescent sensing platform for ONOO is constructed by splitting green fluorescent carbon dots (G-CDs) and aggregating orange fluorescent carbon dots (O-CDs). The mixed G-CDs and O-CDs (M-CDs) show a fast and precise response to ONOO in the range of 0-250 μM, with a detection limit of 10 nM. In the linearity range within 3 μM ONOO, an obvious wavelength shift of G-CDs from 495 to 475 nm is observed owing to the oxidation and nitration of ONOO to the surface-state fluorescence of G-CDs, accompanied by the splitting of G-CDs. In the linearity range of 3-250 μM ONOO, the fluorescence of G-CDs remains constant, while the molecular-state fluorescence of O-CDs gradually quenches by the oxidation and nitration of ONOO through the fluorescence static process and induces their aggregation. Additionally, M-CDs show favorable intracellular imaging of endogenous and exogenous ONOO. This study not only presents a new fluorescence wavelength shift mechanism for ONOO sensing but also provides insights into CDs' fluorescence mechanism by exploring their morphology and structure via reacting with reactive oxygen species (ROS).