Dopamine-Modulated Highly Oxygen-Vacancy Ce Metal-Organic Frameworks Boost Phosphatase-Catalyzed Chemiluminescence

Owing to target recognition hindrance, common metal-organic frameworks (MOFs) as nanocarriers lead to the dramatically decreased catalytic activity (by 90%) of immobilized enzymes. Herein, a dopamine-modulated enclosure strategy was proposed to successfully immobilize alkaline phosphatase (ALP) on phosphatase-like Ce-2-methylimidazole (2-MIm) MOFs for the formation of a Ce-2-MIm@ALP@polydopamine (PDA) biocomposite. Although the activity proportion (1.22%) of Ce-2-MIm to Ce-2-MIm@ALP@PDA was negligible, Ce-2-MIm MOFs facilitated 2.5-fold higher catalytic activity of immobilized ALP than free ALP. Note that shortened Ce-Ce bonds and increased Ce-OH groups were verified by X-ray absorption spectroscopy for the increased active Ce sites on the Ce-2-MIm support. Thereby, the phosphatase-like Ce-2-MIm possessed enhanced substrate affinity (K_m = 86.79 μM) 16.5 times superior to ordinary Ce-based nanozymes (K_m = 1428.57 μM). The experimental data and density functional theory calculations demonstrated that the flexible scaffold coating of PDA endowed Ce-2-MIm with improved oxygen vacancies for the preferable binding affinity and hydrolysis activity. The marked affinity effect of the Ce-2-MIm-based support imparted the dominant improvement of catalytic activity to fixed enzymes in the enzyme immobilization. For the proof-of-concept application on chemiluminescence (CL) catalysis, the prepared Ce-2-MIm@ALP@PDA is successfully employed for the detection of carbendazol (CAB), with a low detection limit of 56 pg/mL. This work highlights the merits of nanozymes as an efficient affinity-type support for enzyme assemblies, which exhibits great potential for considerable activity exaltation of enzymes even in an immobilization manner.