Atomically Dispersed Manganese on Graphene Nanosheets as Biocompatible Nanozyme for Glutathione Detection in Liver Tissue Lysate Using Microfluidic Paper-based Analytical Devices

Recently, single atom catalysts (SACs) featuring M-Nx (M = metal) active sites on carbon support have drawn considerable attention due to their promising enzyme-like catalytic properties. However, typical synthesis methods of SACs often involve energy-intensive carbonization processes. Herein, we report a facile one-pot, low-temperature, wet impregnation method to fully utilize M-N4 sites of manganese phthalocyanine (MnPc) by decorating molecular MnPc over the sheets of graphene nanoplatelets (GNP). The synthesized MnPc@GNP exhibits remarkable peroxidase-mimic catalytic activity toward the oxidation of chromogenic 3,3',5,5'-tetramethylbenzidine (TMB) substrate owing to the efficient utilization of atomically dispersed Mn and the high surface-to-volume ratio of the porous catalyst. A nanozyme-based colorimetric sensing probe is developed to detect important biomarker glutathione (GSH) within only 5 min in solution phase based on the ability of GSH to effectively inhibit the TMB oxidation. The high sensitivity and selectivity of the developed colorimetric assay enable us to quantitatively determine GSH concentration in different biological fluids. This work, for the first time, reports a rapid MnPc@GNP nanozyme-based colorimetric assay in the solid substrate by fabricating microfluidic paper-based analytical devices (μPADs). GSH is successfully detected on the fabricated μPADs coated with only 6.0 μg of nanozyme containing 1.6 nmol of Mn in the linear range of 0.5-10 μM with a limit of detection of 1.23 μM. This work also demonstrates the quantitative detection of GSH in mice liver tissue lysate using μPADs, which paves the way to develop μPADs for point-of-care testing.

Synthesis, Characterization, and Catalytic Studies of Mn(III)-Schiff Base-Dicyanamide Complexes: Checking the Rhombicity Effect in Peroxidase Studies

The condensation of 3-methoxy-2-hydroxybenzaldehyde and the diamines 1,2-diphenylendiamine, 1,2-diamine-2-methylpropane and 1,3-propanediamine yielded the dianionic tetradentate Schiff base ligands N,N′-bis(2-hydroxy-4-methoxybenzylidene)-1,2-diphenylendiimine (H2L1), N,N′-bis(2-hydroxy-4-methoxybenzylidene)-1,2-diamino-2-methylpropane (H2L2) and N,N′-bis(2-hydroxy-4-methoxybenzylidene)-1,3-diaminopropane (H2L3) respectively. The organic compounds H2L1 and H2L2 have been characterized by elemental analysis, IR, 1H and 13C NMR spectroscopies and mass spectrometry electrospray (ES). The crystal structure of H2L2 in solid state, solved by X-ray crystallography, is highly conditioned in the solid state by two N-H•••N intramolecular interactions. The synthesis of three new manganese(III) complexes 1–3, incorporating these ligands, H2L1–H2L3, and dicyanamide (DCA), is reported. The complexes 1–3 have been physicochemically characterized by elemental analysis, IR and paramagnetic 1H NMR spectroscopy, ESI mass spectrometry, magnetic moment at room temperature and conductivity measurements. Complex 1 has been crystallographically characterized. The X-ray structure shows the self-assembly of the Mn(III)-Schiff base-DCA complex through µ-aquo bridges between neighbouring axial water molecules and also by π-π stacking interactions, establishing a dimeric structure. The manganese complexes were also tested as peroxidase mimics for the H2O2-mediated reaction with the water-soluble trap ABTS, showing complexes 1-2 relevant peroxidase activity in contrast with 3. The rhombicity around the metal ion can explain this catalytic behaviour.