Fig. 5
From: Strategies for using nanoprobes to perceive and treat cancer activity: a review
a Schematic of the imaging of the tumor microenvironment using ultra pH-sensitive (UPS) nanoprobes. The UPS nanoprobes stay ‘OFF’ at pH 7.4 during blood circulation. After reaching the tumor, the UPS nanoprobes are turned ‘ON’ by the acidic extracellular pHe (6.5–6.8) in the tumor milieu or in endocytic organelles (pHi 5.0–6.0) in the tumorous endothelial cells after receptor-mediated endocytosis. b Structural composition of the two types of nanoprobe, UPSe and UPSi, with pH transitions at pH 6.9 and pH 6.2, respectively. c Normalized fluorescence intensity as a function of pH for UPSe and UPSi nanoprobes. At high pH (e.g., 7.4), both probes stay silent. At pH below the transition levels (i.e., pH 6.9 and 6.2), the nanoprobes can be activated as a result of micelle dissociation. d Fluorescent images of UPSe–Cy5.5 nanoprobe solution in different pH buffers (λex/ λem = 675/710 nm). e Transmission electron micrographs of UPSe nanoprobes at pH 7.4 and pH 6.7 (polymer concentration = 1 mg/ml; scale bars = 100 nm). Reproduced with permission from ref. 46; Copyright 2014 Macmillan Publishers