Cu²⁺ and nitro co-functionalized UiO-66 nanozyme powered dual-mode detection and cellular imaging of H₂S

Hydrogen sulfide (H₂S) serves as a critical gasotransmitter that participates in diverse physiological and pathological processes. Developing dual-mode sensing approaches with high specifity, increased accuracy and portable testing for monitoring H₂S level is highly demanded. Herein, a novel Cu²⁺ and nitro co-functionalized nanozyme (Cu@UiO-66-NO₂) has been constructed for colorimetric/ratiometric fluorescence dual-mode sensing H₂S. The Cu²⁺ modification endows the inert UiO-66-NO₂ with oxidase-like activity to dissociate O₂ into •OH and ¹O₂ radicals, that oxidize the substrate o-phenylenediamine (OPD), whereas the nitro group in the skeleton serves as reactive site for H₂S. When H₂S is present, the fluorescence of Cu@UiO-66-NO₂ boosts at 435 nm owing to the reduction of NO₂ into NH₂ but its oxidase-like activity is inhibited, weakening the OPD oxidation. Accordingly, both the colorimetric (λ = 416 nm) and fluorescence (λ_em = 570 nm) signal originated from oxidized OPD decrease remarkably. The absorbance at 416 nm and fluorescence intensity ratio F₄₃₅/F₅₇₀ display good linear responses toward H₂S between 1-20 μM and 2-100 μM, respectively. Moreover, H₂S induces an obvious color transition from yellow to blue under UV light. A smartphone-integrated sensing platform was further established for visual and portable monitoring H₂S. The MTT assay demonstrates the excellent biocompatibility of this nanoprobe and confocal laser scanning microscopy studies imply its efficiency for imaging endogenous and exogenous H₂S in living cells.