A DNA-based ratiometric reporter of disulfide reduction and is an intracellular thiol-disulfide exchange reporter. It can target the endosome and lysosome in-vitro in HeLa cells and C. elegans. It is relevant to several diseases such as pathogenic infections. This figure (Dan et al., Nat. Nanotechnol., 2019) demonstrates spatiotemporal detection of thiol-disulfide exchange reaction in the endolysosomal compartment of C. elegans coelmocytes.