Fig. 4: Chemical structures of chosen NO sensors and example for NO sensing from endothelial cells.

a General scheme for the transformation of phenylene diamine-functionalized fluorophore to a triazole-functionalized analogue. The grey colour represents a fluorophore that emits poorly because it is quenched by PET, while the blue colour represents a fluorophore that has recovered a strong emission. b Molecular formulae of a selection of organic nitric oxide sensors based on the phenylenediamine motif^119,189,190. c General sensing method for NO by metal-based fluorescent probes. d Molecular formulae of selected examples of transition metal-based NO sensors^191,196. e Selected nitric oxide sensors useful for sensing endothelial dysfunction. f Detection of NO produced by endothelial cells in vitro using Lippard’s molecular probe 17. (i) NO detection in porcine aortic endothelial cells (PAECs); Left: 45 min incubation of 17 (20 µM). Right: 45 min incubation of 17 (20 µM) and H₂O₂ (150 µM). Top: bright-field images of cells. Bottom: fluorescence images of cells. Scale bar is 50 µm. (ii) Detection of NO with 17 in Human Coronary Artery Endothelial Cells (HCAECs), with or without NO-inhibitor (L-NAME). Shown are the fluorescence images after 45 min co-incubation of the probe 17 (2 µM) with H₂O₂ (150 µM), L-NAME (100 µM), and/or Acetylcholine (ACh) (10 µM) according to scheme. Scale bar is 75 µm (Reprinted with permission from ref. ¹⁴⁶).