Heat-initiated detection for reduced glutathione with ¹⁹F NMR probes based on modified gold nanoparticles

For detecting reduced glutathione (GSH) with a ¹⁹F NMR spectroscopy with time-specificity, we developed the probes based on gold nanoparticles modified with the fluorinated groups via the thermally-cleavable linkers. Before the heating treatment with the probe, the maleimide moiety as a binding site with GSH in the probe is inactivated by cycloaddition of furan. At this silent state, the magnitude of ¹⁹F NMR signals from the fluorinated groups was suppressed. By heating for the activation of the probe, the maleimide moiety was produced via retro Diels-Alder reaction, and ¹⁹F NMR signals were observed. From this moment, GSH started the reaction with the probe via Michael addition to the maleimide moiety, leading to the observation of the new peak in ¹⁹F NMR spectra. Finally, the amounts of GSH were determined from the increase of the magnitude of ¹⁹F NMR signals.