Versatile metal-organic frameworks as a catalyst and an indicator of nitric oxide

The imaging of nitric oxide (NO) and its donors is crucial to explore NO-related physiological and pathological processes. In this work, we demonstrate the use of Cu-based metal-organic frameworks (Cu-MOFs) as nanoprobes for NO detection and as a catalyst for the generation of NO from the biologically occurring substrate, S-nitrosothiols (RSNOs). The paramagnetic Cu2+ in the MOFs could quench the luminescence of triphenylamine; Cu-MOFs only exhibited weak emission at 450 nm. Upon the addition of NO, the paramagnetic Cu2+ was reduced to diamagnetic Cu+, and thus the luminescence was recovered directly. Cu-MOFs exhibited high selectivity for other species in the reaction system, including NO2-, H2O2, AA, NO3- and O-1(2). More significantly, the Cu+ can react with s-nitrosoglutathione (GSNO), s-nitrosocysteine (CysNO), and s-nitrosocysteamine (CysamNO) to generate NO and then oxidize to Cu2+-MOFs with quenched luminescence, respectively, and thus the catalysis is inhibited, noted as a self-controlled process. The Cu-MOFs catalyst was confirmed by powder X-ray diffraction to remain structurally intact in aqueous environments. The Cu-MOFs have been successfully employed in the biological imaging of NO in living cells. The bifunctional MOFs could offer a novel platform for the real-time monitoring of NO species, provide potential for exploiting NO in cancer therapy and improve the methodologies to elucidate the NO-related biological processes.

Automated summary

In this study, Cu-MOFs were used as nanoprobes for NO detection and as catalysts for NO generation. Cu-MOFs exhibited high selectivity and self-control ability, making them suitable for real-time monitoring of NO species and potential application in cancer therapy.