“…In addition to hypoxia, increased viscosity is an important characteristic of cancer cells. 18,19 Several research groups have developed fluorescent probes based on the cascade response of viscosity and other biomarkers including glutathione (GSH), 20 H 2 O 2 , 21 H 2 S, 22 and ONOO − 23 with exciting results. However, no such fluorescent probes for NTR have been reported.…”