Fig. 1. (a) UV-vis absorption spectra of 5.0 μM NCNO in the absence and presence of excess NO (15 μM). (b) Fluorescence spectra of 5.0 μM NCNO upon the addition of NO (0–12 μM). (c) Relative fluorescence intensity of 5.0 μM NCNO with varying amounts of NO (0–12 μM). (d) Relative fluorescence intensity of 5.0 μM NCNO incubated with various species (20 μM) for metal ions 1–4 (Ca²⁺, Mg²⁺, Zn²⁺, Fe²⁺), 50 μM reactive oxygen species 5–8 (ClO^–, H₂O₂, ˙OH, O₂ ^–), 1.0 mM biological molecules 9–15 (GSH, Cys, Hcy, AA, DHA, MGO), 50 μM reactive nitrogen species 16–17 (NO₂ ^–, ONOO^–) and 15 μM 18 (NO). Reaction time: 30 min.