Construction of hierarchically porous covalent organic frameworks with enhanced enzyme accessibility for sensitive dopamine detection.

Immobilization of fragile enzymes is vital to expanding its application in the extracellular environment. Covalent organic frameworks (COFs), as a class of emerging porous materials, are promising platforms for enzyme immobilization owing to their high porosity and tunable structure. However, the interior pores of COFs often fail to play their roles because of inaccessibility, resulting in decreased performance of immobilized enzymes. Here, we introduce a facile approach to construct hierarchically macro-mesoporous COF (Hm-COF) via a template-assistant strategy. The mesoporous channels of Hm-COF were used to entrap cytochrome c (Cyt c), and the macropores of Hm-COF were adopted as diffusion channels to enhance the mass transfer of guest molecules. The resulting Hm-COF demonstrated an enhanced uptake capacity of Cyt c compared with mesoporous COF (m-COF). Furthermore, the catalytic activity of Cyt c immobilized in Hm-COF (Cyt c@Hm-COF) was remarkably higher than that of Cyt c immobilized in m-COF (Cyt c@m-COF). Taking advantage of the excellent activity, Cyt c@Hm-COF was employed as the sensor for the sensitive detection of dopamine (DA). This study opens a new avenue for the construction of COFs with hierarchical pores and high-performance immobilized enzymes.