Heavy metal-free ¹⁹F NMR probes for quantitative measurements of glutathione reductase activity using silica nanoparticles as a signal quencher

For the quantitative assessment of the glutathione reductase (GR) activity with a ¹⁹F NMR spectroscopy, we developed the heavy metal-free probes based on silica nanoparticles modified with water-soluble perfluorinated dendrimers via the disulfide linkers. Before enzymatic reaction, the molecular rotation of the perfluorinated dendrimers is highly restricted, and the magnitude of ¹⁹F NMR signals from the perfluorinated dendrimers can be suppressed. By the reductive cleavage of the disulfide linkers with the reduced glutathione-mediated enzymatic reaction of GR, perfluorinated dendrimers can be released from the surfaces of the nanoparticles. Consequently, the ¹⁹F NMR signals of perfluorinated dendrimers were recovered. The enzymatic activity of GR was determined from the increase of the magnitude of ¹⁹F NMR signals. Finally, to demonstrate the feasibility of the probe in the presence of miscellaneous molecules under bio-mimetic conditions, the comparison study was executed with the cancer cell lysate. The value determined from our method showed a good agreement with that from the conventional method.