Dissipative enzymatic catalysis-driven modulation of coordination mode and cation valence in MOFs responsive for dual-modality enzyme assay

A dual-modality enzyme assay combining the fluorescence and colorimetry merits based on nanoscale metal-organic frameworks (nMOFs) was established for the analysis of glutathione S-transferase (GST). In this design, HKUST-1 with CuII metal nodes, was chosen as nMOFs and encapsulated with rhodamine 6 G (Rho 6 G) in one-step reaction to fabricate the functional nMOFs (Rho 6 G@Cu-MOFs). As a proof of concept, as a GST binding substrate, reductive glutathione (GSH) invokes competitive coordination with Cu nodes through sulfur atom as well as the valence transformation, of which the process results in coordination bond leakage and even frame-work collapse, leading to the releasing of internal Rho 6 G dyes for fluorescence-modality analysis. In addition, reductive GSH can interact with Cu nodes in the nMOFs and modulate CuII to CuI, along with a color change for colorimetry analysis. The dual-modality assay shows high analytical performance for GST quantification in a linear range of 0.25-100 nM with a detection limit down to 0.13 nM for fluorescence modality, and a linear range of 1-100 nM with a detection limit of 0.64 nM for colorimetry modality. In addition, the precision of the dual-modality assay shows good agreements with commercial GST activity assay kit.