Ultrathin films of a metal-organic framework prepared from 2-methylimidazole, manganese(II) and cobalt(II) with strong oxidase-mimicking activity for colorimetric determination of glutathione and glutathione reductase activity.

Nanosheets (NSs; type ZIF-67) of a metal organic framework (MOF) that was prepared from 2-methylimidazole, manganese(II) and cobalt(II) were obtained by an ultrasonic hydrothermal method. Their Mn(II) doping reached as much as 11.3%. The NSs inherit high porosity, a large specific surface, and a large number of active sites. They display superior oxidase-mimicking activity and can catalyze the oxidation of tetramethylbenzidine (TMB) by molecular oxygen to form blue oxTMB. Glutathione (GSH) can reduce oxTMB, so that less blue oxTMB will be present. A simple and rapid method was established for the colorimetric determination of GSH and of the activity of GSH reductase (GR), best at a wavelength of 652 nm. The response to GSH drops linearly in the 0.1-25 μM concentration range. The activity of GR can be quantified in the 0.1 - 3 mU⋅mL-1 activity range. The respective detection limits are 0.07 μM and 0.18 mU⋅mL-1. Graphical abstract Schematic presentation of colorimetric detection of glutathione and glutathione reductase activity by the oxidase-mimicking activity of Mn-Co nanosheets in a metal organic framework.