Fig. 5. Examples of ROS sensing nano-platforms. (a) (Left): Schematic illustration of the dual-emission probe synthesis procedure and the working principle for ratiometric fluorescence detection of ˙OH; (middle): fluorescence spectra of the ratiometric probe solution upon the exposure to different concentrations of ˙OH at various H₂O₂ concentrations; (right): confocal fluorescence images of HeLa cells after being incubated with the dual-emission probe in the absence and presence of ˙OH. The images were collected at 410–520 nm (blue channel) and 580–680 nm (red channel) upon excitation at 405 nm. Scale bar: 20 μm. Reprinted with permission of Royal Society of Chemistry, from Liu et al., Analyst, 2016, 141, 7, 2296–2302; permission conveyed through Copyright Clearance Center, Inc. (b) (Left): Schematic illustration of the H₂O₂-sensitive on-off H₂O₂-AuNPs; (middle): H₂O₂ responsive fluorescence spectra of H₂O₂ sensitive-AuNPs; (right): in vitro confocal microscopic images of activated RAW264.7 cells incubated with the CNPs and H₂O₂ –AuNPs for 3 hours at pH 7.4. Scale bar: 20 μm. Reprinted from Deepagan et al., Macromol. Res., 2018, 26(7), 577–580. Copyright © 2018, The Polymer Society of Korea and Springer Science Business Media B.V., part of Springer Nature. (c) (Left): Schematic illustration of the fluorescent responding mechanism of dLys-AgNCs to Fenton Reagents; (middle): fluorescence spectra of the ratiometric NPs towards different H₂O₂ concentrations; (right): fluorescence confocal images of PC-3 cells alone (first raw), PC-3 cells treated with dLy-AgNC probe (second raw), PC-3 cells incubated with PMA (third raw) and NAC (forth raw) prior to treatment with dLys-AgNCs. Adopted from ref. Liu et al., Anal. Chem., 2016, 88, 21, 10631–10638. Copyright © 2016 American Chemical Society.