Fig. 5. One-pot oxidase/MOF nanozyme cascade reactions enabled by microenvironmental pH modulation.

a Schematic illustration of pH mismatch between oxidases and peroxidase-mimicking nanozymes, which can be overcome through microenvironmental pH modulation. b Schematic illustration of a one-pot cascade reaction catalysed by an oxidase coupled with a peroxidase-mimicking nanozyme, which can be fulfilled through microenvironmental pH modulation. c Relative activity of D-amino acid oxidase (DAAO) at pHs 4.0 and 7.4. d Time evolution of absorbance at 652 nm (A_{652 nm}) for monitoring one-pot cascade reactions catalysed by DAAO coupled with PCN-222-Fe NPs at pHs 4.0 and 7.4, or PCN-222-Fe@PAA NPs at pH 7.4. e Schematic illustration of L-amino acid and D-amino acid, which can be recognised through DAAO/MOF nanozyme cascade reaction. f Time evolution of A_{652 nm} for chirality recognition of alanine through DAAO/PCN-222-Fe@PAA cascade reaction. g Optical density at 652 nm (OD_{652 nm}) for chirality recognition of four natural amino acids including alanine, valine, proline, and isoleucine using a microplate reader through DAAO/PCN-222-Fe@PAA cascade reaction. h Fluorescence intensity at 585 nm (I_{585 nm}) for chirality recognition of natural amino acids as mentioned in (g). λ_ex = 560 nm. i I_{585 nm} for chirality recognition of four non-natural amino acids. Data in (c, g, h, and i) are expressed as mean values ± SEM, n = 3.