Metal−organic frameworks (MOFs) with uniform porosity and large surface areas can function as carriers of immobilized enzymes. However, drawbacks including long response times or enzyme leakage have hindered their applicability. In this study, a boronic acid-functionalized hierarchically porous MIL-88B (HP-MIL-88B-BA) was prepared as an efficient immobilization matrix for glucose oxidase (GOx). HP-MIL-88B-BA features a hierarchical, porous structure with sufficient recognition sites that facilitate GOx immobilization and prevent enzyme leakage. This hierarchical porosity increased the substrate mass transfer efficiency, thereby reducing the response time. Moreover, HP-MIL-88B-BA can be used as a horseradish peroxidase mimic. In this manner, an integrated nanozyme was constructed for the rapid one-step detection of glucose. GOx@HP-MIL-88B-BA exhibited a rapid response to glucose (10 min) and displayed a good linear relationship from 2 to 100 μM with a detection limit of 0.98 μM. This novel methodology provides a straightforward, rapid, and efficient strategy for integrated nanozyme synthesis for biosensing purposes.
Pore size and functionalization are
two critical factors for covalent
organic frameworks (COFs) as effective adsorbents. However, due to
the low crystallinity of COFs, it is a grand challenge to accomplish
pore diameter adjustment and functionalization at the same time. In
this work, we developed a simple and ingenious strategy, cutting off
linkage, to synchronously construct hierarchical porosity and modify
thiol groups in COFs under mild conditions. The hybrid COFs containing
disulfide bonds were designed and synthesized, and then the disulfide
bonds were cleaved by glutathione, resulting in the formation of thiol
groups as well as the increase in pore size caused by skeleton defects.
The pore diameter of thiol-functionalized hierarchical porous COFs
(denoted as HP-TpEDA-SH) was concentrated at 2.6 and 3.5 nm. Thanks
to the electrostatic attraction of thiol groups to cationic dyes and
the higher number of available adsorption sites, the maximum extraction
amounts of methylene blue (MB), malachite green (MG), and crystal
violet (CV) by HP-TpEDA-SH were 2.6, 2.1, and 3.3 times those of microporous
COFs under optimal extraction conditions, respectively. The proposed
analytical method (solid-phase extraction-high-performance liquid
chromatography/ultraviolet (SPE-HPLC/UV)) with HP-TpEDA-SH as the
adsorbent showed low detection limits of 1.3, 0.13, and 0.12 μg·L–1 for MB, MG, and CV, respectively. The recoveries
of three spiked water samples ranged from 81.5 to 113.8%, with relative
standard deviations (RSDs) less than 9.7%. This work not only opened
a new avenue for the preparation of functionalized hierarchical porous
COFs but also established an effective method for detecting trace
cationic dyes in fishery water.
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