The modularity of RX1 also suits it for flexible adaptation to TrxR1-triggered release of a range of cargos, far beyond the fluorogenic RX1 probe for cell culture. The use of a traceless solubiliser sidechain to ensure reliable and cargo-independent solubility is explicitly intended to favour just such adaptation. The design is suited for translation to any molecular cargo with unmaskable activity: of which the fluorogenic, indigogenic, or bioluminogenic probe possibilities in the section "Probe Design", and the accompanying drugreleasing prodrug possibilities, are just a small selection. Particularly given the strong pharmaceutical interest in TrxR-targeted and redoxactivated drugs in the inflammation, immunity, and cancer therapy fields, 10 it will be exciting to test whether redox-responsive prodrug designs based around RX1-like selenenylsulfides can harness pathologically dysregulated TrxR1 activity to target drugs to diseased tissues. We also anticipate that improved RX1 analogues can be rationally designed to retain its specificity while installing enhanced reaction kinetics, alternative cargo delivery scope, and maximising its still-untested resistance to in vivo metabolism-based cargo release mechanisms, which will further promote its utility in biological and therapeutic applications. We thus expect that the RX1 system will impact both redox biology quantification/mapping studies, as well as translational research and therapy of locally-redox-dysregulated pathologies such as cancer, inflammation and auto-immune disorders.