Synergistic role of carbon quantum dots in the activity and stability of Candida rugosa lipase encapsulated within metal–organic frameworks (ZIF-8)

Abstract

Carbon quantum dots (CQDs) are particularly attractive in biosensing, bioimaging and drug delivery applications due to their luminescent properties, water dispersibility and favorable biocompatibility. In the study, by combining CQDs derived from edible mushroom Agaricus bisporus and zeolitic imidazolate frameworks (ZIFs) crystals, a new support material was prepared for encapsulation of Candida rugosa lipase. The study aimed to shed light on the activity, thermal and storage stability, and reusability of physically adsorbed or in-situ encapsulated enzyme. The enzyme loading efficiency of the in-situ encapsulation method was 3.11-fold higher (371 mg g−1). Also, catalytic activities were 119.8 U/g (CQDs@ZIF- 8@CRLenc) and 34.2 U/g (CQDs@ZIF-8@CRLads). The CQDs@ZIF-8@CRLenc with the biocatalytic activity was 3.5-folds higher than that of the CQDs@ZIF-8@CRLads. In the in-situ encapsulation, the CQDs and the enzyme were physically entrapped within three-dimensional structures of ZIF-8 that were constructed from tetrahedral zinc ions bridged by imidazolate. The structural, morphological, and spectrophotometric analyses were performed using TEM, SEM-EDX, FT-IR, XRD, UV–vis, fluorescence, and confocal microscopy. The effects of pH (4.0–9.0) and temperature (30–60 °C) on the enzymatic activity were studied and optimized. The coexistence of the CQDs and ZIF-8 crystals remarkably enhanced the activity, reusability, thermal resistance, and storage stability of the enzyme encapsulated within ZIF-8 crystals (the relative enzyme activity; after 6 re-uses: 73%, 2-hour-incubation at 60 °C: 70%, 5-week-storage at 4 °C: 70%). The CQDs from A. bisporus entrapped within ZIF-8 can synergistically enhance the catalytic performance and thermal/storage stability of immobilized C. rugosa lipase.